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Winning isnt everything--but wanting to win is ---Vince Lombardi (The greatest football coach of all time)                ...
The pumping action starts with the simultaneouscontraction of the two atria. This contraction serves to givean added push ...
homeostasis. For example oxygen is picked up by blood as       Table 1. Typical values of properties of human blood [4].it...
Ionic Composition of Body Fluids                  Concentration Units are in mEq/L                    Cations             ...
Table 4. Summary of composition of intravenous fluid [6].                                                                 ...
is not anemic. It usually takes less than 10 minutes for the    Artificial blood has many applications. It has uses inbloo...
Heparin is an anticoagulant. It is a protein with a molecularweight ranging from 6,000 to 40,000 Da. Heparin has aunique f...
sectional area, that is determined by the diameter of the                 VELOCITY AND TURBULENCE IN BLOODvessel. Thus a r...
dynes / cm 2. At 70 % of the stroke volume will have 2.99 x106 ergs of energy in the increased blood pressure. Inaddition,...
results, even though are only reasonable to order ofmagnitude, are of negligible orderSimilarly, Reynolds number is only u...
of certain diseases or medical conditions. For example,                                                              resea...
SOME PATIENTS WHO HAVE HAD HEART             TRANSPLANT [34]William Schroeder (53) was the second Jarvik-7 recipientand li...
abdominal wall. It monitors and controls the pumpingspeed of the heart. The external component is the batterypack that can...
support in patients with potentially reversible heart failure.The BVS-5000 underwent preclinical studies at the TexasHeart...
as 40 percent and decreasing the left ventricular strokework and myocardial oxygen requirements. In this manner,the balloo...
A local anesthetic is given over the artery at the top of theballoon that sits in the aorta and is hooked up to a largecon...
Figure 27. Peristaltic pump and the roller [26].         Figure 28. Inherently controllable blood pump developed          ...
percent, with a slightly higher proportion of patients post-    2. Hemorrhage occurs in about one third of patientscardiot...
BIOFLUID DYNAMICS OF THE ARTIFICIAL HEART
BIOFLUID DYNAMICS OF THE ARTIFICIAL HEART
BIOFLUID DYNAMICS OF THE ARTIFICIAL HEART
BIOFLUID DYNAMICS OF THE ARTIFICIAL HEART
BIOFLUID DYNAMICS OF THE ARTIFICIAL HEART
BIOFLUID DYNAMICS OF THE ARTIFICIAL HEART
BIOFLUID DYNAMICS OF THE ARTIFICIAL HEART
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BIOFLUID DYNAMICS OF THE ARTIFICIAL HEART

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Transcript of "BIOFLUID DYNAMICS OF THE ARTIFICIAL HEART"

  1. 1. Winning isnt everything--but wanting to win is ---Vince Lombardi (The greatest football coach of all time) BIOFLUID DYNAMICS OF THE ARTIFICIAL HEART1 <Sachin Gursahani>sgurs001@fiu.edu, <Eric Ponce>eponce@crdus.jnj.com, <Mahesh Nagaraju >mnaga001@fiu.edu and <Sujit Tatke>statk001@fiu.edu.2Abstract -The heart pumps blood to the human body. The use of artificial organs has been a mainstay in clinicalArtificial hearts are implanted in patients suffering approaches to treat chronic illnesses for several decades.from severe heart diseases. For the artificial heart The use of the artificial kidney (dialyzer), artificial heart,system, we need to consider body fluids such as: Blood, cardiac pacemaker, artificial hips and knees, cochlearintracellular fluids, extra cellular fluids, intravenous implants, and intraocular lenses offers treatment for afluids and artificial (synthetic) blood. The use of variety of debilitating illnesses. Numerous recent advancesanticoagulants (Heparin or Coumarin) is necessary in in the design and development of these systems have leadthe implantation of an artificial organ. These act as to breakthroughs in the successful treatment of (what wouldblood thinners and prevent thromboembolism. otherwise be) fatal illnesses. It is, therefore necessary toCardiovascular biomaterials are used to developartificial heart valves, mechanical heart valves, 1. Understand and apply basic terminology, theory,pacemakers, vascular grafts, oxygenerators and cardiac principles and knowledge of artificial heart, and itsassist systems (medical devices) like total artificial functions.hearts, intra-aortic balloon pumps etc. Some of the 2. Identify the important issues, emerging technology,biomaterials used in medicine are metals, polymers and clinical imperatives in the field of artificial heart.ceramics and hydrogels. Biopumps can be peristaltic 3. Evaluate design criteria for artificial heart.type, syringe type, or centrifugal type. Severe heart 4. Understand the issues associated with thediseases can be treated by using the cell transfer development and clinical trials for artificial heart andtechnique developed by Bioheart Inc.. The heart valves.Computational Fluid Dynamics (CFD) is employed to 5. Understand the interaction betweendesign a product and calculate fluid flow behavior. mechanical/electrical approaches to artificial heartUtilizing CFD as a tool for analyzing preexisting designs and biological/cellular techniques.scenarios is advantageous because if offers insight, 6. Understand the issues associated with theforesight, as well as efficiency for product design. development and selection of appropriate biomaterials used for artificial heart.Key Words -Artificial heart, Blood, Blood substitutes, 7. Develop an understanding of new therapeuticIntracellular fluids, extra cellular fluids, approaches to chronic illnesses.Anticoagulants. Total Artificial Heart, AbioCor, Intraaortic balloon pump. Biomaterials, Bioheart, Myoblasts, Cardiovascular replacements encompass the followingCardiac assist devices, Biopumps. areas of study: INTRODUCTION 1. Heart Assist Devices. 2. Heart Replacement Systems.The heart is amongst the most important organs in the 3. Vascular Replacement Systems.human body. It is a complex muscular pump that maintains 4. Tissue Engineered Systems (Bioheart )oxygen and blood circulation through the lungs and the 5. Cellular Repair and Replacement Systems.rest. of the body. The heart pumps about 7200 liters of 6. Heart Valve Replacement and Repair.blood in a single day and thus has a heavy workload. Its 7. Cardiac Transplants.failure sometimes necessitates the implantation artificialheart in the patient. DESCRIPTION OF THE SYSTEM The heart has four chambers: right and left atria and right___________________ and left ventricles (Figure 1). The two atria act as collectingThe numbers in parenthesis refer to bibliographical reservoirs for blood returning to the heart while the tworeferences with cited pages. ventricles act as pumps to eject the blood to the body. The1 heart has 4 valves. See Appendix I for the description of This review article was prepared for the Congress on the phases of “Cardiac cycle” and the description for ECG.Biofluid Dynamics of Human Body Systems. BiomedicalEngineering Institute, Florida International University, Deoxygenated blood returns to the heart via the superior10555 West Flagler Street, Miami-Fl-33174, organized on and inferior vena cava, enters the right atrium, passes intoApril 17, 2003. For details contact <Dr. Megh R. Goyal> the right ventricle, and from here it is ejected to them_goyal@ece.uprm.edu or <Dr. Richard T. pulmonary artery. Oxygenated blood returning from theSchoephoerster> Schoepho@fiu.edu lungs enters the left atrium via the pulmonary veins, passes2 into the left ventricle, and is then ejected to the aorta. The contributors appear in the alphabetical order.2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-1
  2. 2. The pumping action starts with the simultaneouscontraction of the two atria. This contraction serves to givean added push to get the blood into the ventricles at the endof the slow-filling portion of the pumping cycle called"diastole." Shortly after that, the ventricles contract,marking the beginning of "systole." The aortic andpulmonary valves open and blood is forcibly ejected fromthe arteries, while the mitral and tricuspid valves close toprevent backflow (Figure 2).At the same time, the atria start to fill with blood again.After a while, the ventricles relax, the aortic and pulmonaryvalves close, and the mitral and tricuspid valves open andthe ventricles start to fill with blood again, marking the endof systole and the beginning of diastole. Though equalvolumes are ejected from the right and the left heart, yet theleft ventricle generates a much higher pressure than doesthe right ventricle.The four valves of the heart are essential to the heartspumping action. They allow blood to flow in one directiondepending upon the pressure gradients and thus prevent a Figure 1. Internal structure of the human heart [1].backflow of blood. Figure 2 shows the location of fourheart valves.Any damage to heart valves poses a significant health riskfor that individual. The valves can be damaged due to avariety of reasons: Rheumatic heart disease, valveinfection, and calcification/ stiffness caused by long-termwear and tear.These diseases can cause two major problems: 1. Stenosiswherein the valve does not open fully and this results inhigher-pressure gradients. 2. The insufficiency wherein thevalve does not close and this causes a backflow of blood.In such cases, the heart becomes less efficient at pumpingblood. Over time the increased load and strain mayeventually cause the heart to fail and lead to death. Thephysician treating the disease has several options:Providing medications in order to improve the heartspumping is a viable alternative. If the defect is serious thenrepairing the valve is an option. If the damage is such that itcannot be surgically repaired then only option is to replacethe valve by an artificial valve for extending the lives ofsuch patients; however, there remains a consistent shortage Figure 2. Anatomy of the human heart [2].of available donor hearts for transplantation. This spawnedresearch into the development of artificial hearts. PROPERTIES, FUNCTIONS AND COMPOSITION OF BIOFLUIDSThe Jarvik-7, named for its designer Dr. Robert Jarvik,functions like the natural heart. In 1982, surgeons at the Blood is a medium in which dissolved gases, nutrients,University of Utah implanted the device in a patient named hormones and electrolytes are transported. It removes theDr.Barney Clark., a dentist. He survived with the Jarvik-7 waste products of metabolism like urea and ammonia ions.for 112 days. The longest survivor was William Schroeder, It provides protection against the toxins and pathogenswho was supported by the Jarvik-7 for 620 days. The (White Blood Corpuscles and antibodies). It also plays anJarvik-7 was also called the Symbion total artificial heart important role in the stabilization of pH and temperature of(TAH). Today, it is called the Cardio West total TAH. our body. Finally, blood has the property of clotting thatVarious models of artificial heart were subsequently prevents the loss of blood from the body [14,15].developed such as Jarvik 2000, Akutsu TAH, Liotta TAH,and AbioCor TAH. Blood along with the heart and the blood vessels comprises the circulatory system of the body that helps in maintaining2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-2
  3. 3. homeostasis. For example oxygen is picked up by blood as Table 1. Typical values of properties of human blood [4].it passes through the lungs. This flows through successivelynarrower blood vessels: from arteries to arterioles and Physical Value Commentsfinally to the capillaries, where the oxygen rich blood Property Range (Average)delivers its oxygen to the cells. Figures 3 and 4 show how pH 7.38-7.40 (7.31) Arterial bloodthe rheology of blood is affected due to bypass surgery and Venous blooddue to dilution of plasma by 50%, respectively. Table 1 Relative 3.00 Invitershows typical values of properties of human blood. viscosity (2.18-3.59) determination Refractive 17.4 --- index (16.2-18.5) Specific gravity 1.058 Copper (1.052-1.064) Sulpahte method used Specific Heat, 0.92 -- g-cal Surface tension, 55.5-61.2 --- dynes/cm Colloid osmotic 344 (310-376) Arterial blood pressure, 337 (300-373) Venous blood mm H2O Average 5000-6000 Varies with Volume of height, weight blood in the and age body, mL Production rate 5000 mL/min Blood is composed of about 46-63 % plasma that contains suspended cells. Plasma is the fluid component of the blood and is composed of 92% water, 7% proteins and 1 %Figure 3. Changes in the Rheology of blood as a result of plasma solutes. Proteins include albumins; globulins,cardiopulmonary bypass surgery [3]. fibrinogen and hormones while the plasma solutes are composed of electrolytes, organic nutrients and organic wastes. The remaining 37-54 % are the formed elements. Solid components in blood are specialized cells, such as: 1. Red blood cells (RBC) also called erythrocytes: RBC account for 99% of the formed elements. The male person has 4.5-6.3 RBC per cubic micro liter compared to 4.2-5.5 for a female. 2. White blood cells (WBC) also called leukocytes: The WBC provide defense against toxins and pathogens. This is a called nonspecific protection. They also provide specific defenses e.g. Defense against a specific antigen. There are 6000-9000 WBC per cubic micro liter in both males and females. 3. The platelets are basically cell fragments from an earlier cell. They initiate and control the clotting process. They clump physically to form a platelet plug causing a reduction in the site of injury and slow the blood loss. There are about 150,000 to 500,000 platelets per cubic micro liter. All body fluids can be generally separated into two fluid compartments: the fluid found inside of cells (intracellularFigure 4. Rheology of the blood due to 50% dilution of the fluid) and the fluid found outside of cell (extracellularoriginal plasma [3]. fluid) as shown in figure 5 and table 2. Intracellular fluid makes up about 63% of all the fluid in our bodies while the remaining is the extra cellular fluid.2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-3
  4. 4. Ionic Composition of Body Fluids Concentration Units are in mEq/L Cations Anions 140 110 More protein Extracellular 24 And more cations Fluid Na+ Cl HCO3 in plasma than Ca2+ Interstitial fluid Mg2+ Protein-- Intracellular K+ Fluid 140 Phosphate and Organic Anions Figure 5. Ionic composition of body fluids [10].Table 2. Dissolved materials and their distribution [7]. Dissolved Intra cellular Extra cellular materials fluid fluid compartment compartment Sodium Low high Potassium High low Calcium Very low higher Magnesium High low Chlorides Low high Figure 6. Composition of body fluid. Bicarbonates Low high Phosphates High low Thirdly electrolytes help in maintaining the nor mal acid- Sulphates No real difference ---- base balance required for normal cellular activities. In normal human pH is between 7.35 and 7.45 and it is critical that this range is maintained. The amount of water and theThe dissolved material in these fluids includes ions and concentration of electrolytes are important to bodilyorganic materials like sugars, amino acids, and proteins. functions.The functions of each of the dissolved materials are asfollows. Sodium and Potassium creates much of the When the body is “in fluid balance” it means that theosmotic pressure of extra cellular fluid and intracellular various body compartments (cells, tissues, organs) containfluid respectively. They are essential for electrical activity. the required amount of fluids to carry out normal bodily functions. The regulation of the body fluids is achievedCalcium is found in tissues and fluids and plays a role in through: Osmosis, Diffusion, and Filtration and by theblood clotting. Magnesium is essential for action of the Na-K pump.AdenineTriPhosphate production and activity of neuronsand muscle cells. Chloride is the most abundant anion in Figure 7 shows the composition of body fluids for a 70 kgextra cellular fluid regulates osmotic pressure. Sulfate is person. Table 3 shows the values of extra cellular and intrapart of some amino acids and proteins in the form of sulfur. cellular body water for a human.The electrolytes serve 3 functions. Firstly the electrolytes INTRAVENOUS FLUIDSare needed for normal metabolism. Secondly, electrolytesare needed for proper fluid movement between semi- Intravenous fluids can supply fluid volume andpermeable compartments (from cell to cell, from tissue to electrolytes. These fluids are usually provided fortissue, and from organ to organ). Fluids move through the expanding intravascular volume: To correct an underlyingprocess of osmosis from one compartment to another imbalance in fluids or electrolytes; To compensate for anwithin fractions of a second. The concentrations and nature ongoing problem that is affecting either fluid orof the solutes in the fluids determines the fluid balance. electrolytes.2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-4
  5. 5. Table 4. Summary of composition of intravenous fluid [6]. Fluid Na+ K+ Ca++ Cl- Other pH Crystalloids Bicarbonate 1000 - - - HCO3 8 8.4% 1000 Dextrose 30 - - 30 Dextrose 4.0 4%/saline 40g 0.18% Dextrose 5% - - - - Dextrose 4.0 50g Hartmanns 131 5 2 111 Lactate 6.5 29g Saline 154 - - 154 - 5.0 (0.9%) Colloids Albumin <160 <2 - 136 Albumin 7.4 4.5% 40-50g Gelofusine 154 <0.4 <0.4 125 Gelatin 7.4 40g Haemaccel 145 5 6.25 145 Gelatin 7.4 35gFigure 7. Composition of the body fluids for a 70 kg Hetastarch 154 - - 154 Starch 5.5person [5]. (HES or 60g Hespan)Table 3. Values of extra cellular and intra cellular body Pentastarch 154 - - 154 Starch 5.0water for a human [4]. 100g Subject Parameter Value in ml/kg Figure 8 shows the components that are used for transfer of body weight and delivery of IV fluids. Table 4 gives a summary of Newborn Extra cellular 353 composition of IV fluids. 2-9 months body water 267 Adult 158 Conventional crystalloids are fluids that contain a Newborn Intracellular body NA combination of water and electrolytes. They are divided 2-9 months water NA into "balanced" salt solutions (e.g.: Ringers lactate) and Adult 413 hypotonic solutions. Either their electrolyte composition approximates that of plasma, or they have a total calculated osmolality that is similar to that of plasma. Common used colloids include albumin, hydroxyethyl starch (HES, also known as hetastarch: Hespan) and dextran. Colloid molecules are sufficiently large that they normally do not cross capillary membranes in significant numbers. ARTIFICIAL BLOOD Blood Transfusion A unit of blood is 450 milliliters (1 pint) and is mixed with chemicals (CPD) to prevent clotting. Each year, approximately 12 million to 14 million units of blood are donated in the United States. A health history is taken to ensure that the donor has not been exposed to diseases that can be transmitted by blood, and to determine if donatingFigure 8. Stedim components for transfer and delivery of blood is safe for that persons own health. The donor’sIV fluids [11]. temperature, pulse, blood pressure and weight are obtained. A few drops of blood are obtained to make sure the donor2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-5
  6. 6. is not anemic. It usually takes less than 10 minutes for the Artificial blood has many applications. It has uses inblood to be removed once the needle has been placed. trauma, site of accidents, angioplasty and in heart surgery.Sterile, single-use equipment is used so there is no danger Development of artificial blood products is a subject ofof infection to the donor [13]. ongoing research in many countries especially in Canada, Asia and Europe.Blood supply cells with oxygen, thus keeping them alive. Aloss of only 30% of blood volume in a patient, can lead toirreversible shock if not treated rapidly. There are manypractical difficulties involved in blood transfusions. Itrequires many volunteers. A number of other factors havedriven the need for a viable substitute for human blood—This includes the need to eliminate transfusion-relatedtransmission of infectious disease; reduce the need for crossmatching and related costs; and increase shelf life andstability at ambient temperatures. The aim is to find a fluidthat has the ability to carry oxygen, i.e., oxygen has todissolve well in the fluid.Patients requiring blood replacement need a short-termreplenishment of the oxygen-carrying capacity ofhemoglobin. This continues until the body can synthesizereplacement of RBC. The hemoglobin requiresrefrigeration. Also it has a relatively short shelf life, andmust be carefully matched for correct blood type and otherfactors. This trifold problem has intensified efforts todevelop hemoglobin alternative. It should have a capacity Figure 8. Comparision of the size of RBC and artificialto be stored for a long period of time at room temperature blood particles [8].and transfused to restore the oxygen-carrying function ofhemoglobin without the need for type matching. There is a The total market for artificial blood worldwide is estimatedproblem in delivering free hemoglobin. This is because on the order of tens of billions of dollars. Thus it can act ashemoglobin, when separated from the red blood cells a life saving instrument in emergency situations.divides into halves, which lose the capacity to oxygenatethe tissue. To overcome this problem a cross-binding ANTICOAGULANTSreagent is required It should prevent the hemoglobinmolecules from splitting after removal from the red blood Often, implantation of an artificial organ necessitates thecells. Attempts to develop blood substitutes have followed use of anticoagulants such as Heparin or Coumarin. Ana number of different strategies. One involves extracting anticoagulant is a drug that helps prevent the clottingand chemically processing hemoglobin from donated (coagulation) of a blood. Patients fitted with artificial hearthuman blood. This method does not require blood typing. valves or who have atrial fibrillation are at a risk forHowever it is still dependent on the availability of donated forming blood clots. They are administered anticoagulants.blood. Anticoagulants are different from antiplatelet agents.Another approach is to develop genetically engineered Antiplatelet agents are drugs that interfere with the abilityhemoglobin molecule. It should be capable of releasing of blood to clot. Theyre used to prevent blood clots fromenough oxygen Synthetic Blood International (SYBD: forming that can lead to heart attack or stroke. AntiplateletKettering, OH) has developed a blood substitute based on agents work by preventing the platelets in the blood fromperflurocarbons. Blood gases such as oxygen and carbon clumping. Examples of antiplatelet include: aspirin,dioxide are highly soluble in perflurocarbons. SYBDs dipyridamole etc.Oxycyte is intended to provide an effective means oftransporting oxygen to tissues and carbon dioxide to thelungs. Compared with hemoglobin, Oxycyte has beenfound to be capable of carrying at least five times moreoxygen. Additionally, perflurocarbons are considered to bemore effective than hemoglobin for delivering oxygen atthe tissue level. Also, the perflurocarbons micro dropletsthat carry the oxygen are 1/70th the size of the red cells.They can therefore reach many areas of the body thathuman RBC cannot. The product is inert and can be fullysterilized. It can be stored at room temperature and does notrequire typing and cross matching prior to use. Figure 9. Residues of Heparin [9].2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-6
  7. 7. Heparin is an anticoagulant. It is a protein with a molecularweight ranging from 6,000 to 40,000 Da. Heparin has aunique five-residue sequence as shown in Figure 9. It formsa high-affinity complex with antithrombin. This increasesthe rate of inhibition of two principle procoagulantproteases: factor Xa and thrombin. The normally slow rateof inhibition of both these enzymes (~ 103 - 104 M-1s-1) byantithrombin alone is increased about 1,000-fold byheparin. The rapid inactivation of both the active forms ofproteases prevents the subsequent conversion of fibrinogento fibrin that is crucial for clot formation (Figure 10). Theaction of Heparin is immediate and it is non-toxic. It ismost often used in acute conditions and is administeredparenterally.Heparin is generally given to postoperative patients and tothose with acute infarctions requiring immediateanticoagulant action. In contrast, Coumarin is a principallyoral anticoagulant. They exert their effects only after alatent period of 12 to 4 hours and the effects last for 1.5 to5 days. Anticoagulants, citric acid, is used in vitro. BIOMATERIALSBiomaterials science is an interdisciplinary endeavorcharacterized by medical needs, basic research, ethicalconsiderations, and federal regulations [16,1-2]. Some ofthe classes of biomaterials used in medicine are ceramics,natural materials, composites and fabrics. Here we will Figure 10. Effect of Heparin on the inactivation of Factorpresent biomaterials specific to cardiac applications that Xa and Thrombin [9].have made rapid advances in the past 30 years.Biomaterials are required for the development of Table 5. Typical applications of common biomaterialsmechanical heart valves, pacemakers, vascular grafts, [17,14.3].oxygenerators, and heart assist systems such as: totalartificial hearts, intra-aortic balloon pump etc. Biomaterial Application Hydrogels Catheter coatingsMechanical heart valves are most commonly made from Elastomer Intra aortic balloon pumpsilicone elastomer, cobalt chrome based alloys, titanium Artificial heart bladdersand prolytic carbon. The prosthetic valves are made from Plastics Housings for extramaterials of biological origin and are classified homografts corporeal devicesor xenografts depending upon whether they are obtained Bioresorables Sutures, catheterfrom human species or non-human species (pig, cow) componentsrespectively. Biologically derived Heart valves, vascular grafts materialsStents are typically made from inert materials like nickel Metals and alloys Guide wires, biologic hearttitanium, polyethylene tetraphthlate, polyurethane and valve stentsvarious acrylate compositions. Pacemakers typically use a Biodegradable Hemodialysis membranes,lithium-iodine battery, while the electrodes are made of macromolecules scaffolds for tissueplatinum, stainless steel, or cobalt alloys. The Intra Aortic engineeringBalloon Pumps use a polyurethane balloon and helium or Bioactive coatings Thromboresistancecarbon dioxide is the gases that are used to inflate it [16,283-296]. Table 5 shows typical applications of common FLUID MECHANICSbiomaterials. The continuity equation for the velocity of the blood:Future cardiovascular research in particular will focus on v=Q/A /1/the development of cardiac materials that will eventuallyintegrate with its biological environment. Such a device Where: v = Mean velocity.will release molecules similar to the organ it replaces, Q = Volume flow rate.encourage entry and organization of the tissue cells within A = Cross-sectional area.its structure and become completely or partially replaced bythe host cells. For aorta, if Q = 100 ml/s and A = 3 cm2, then v = 100/3 = 33.3 cm/s. Velocity is inversely proportional to the cross2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-7
  8. 8. sectional area, that is determined by the diameter of the VELOCITY AND TURBULENCE IN BLOODvessel. Thus a reduction in the vessel diameter causes an VESSELSincrease in blood velocity. This might happen in “AorticStenosis”. The pressure difference (∆P) is the difference between the maximum and residual ventricular pressures. Assuming aThe velocity and pressure are related to each other. The maximum normal systolic pressure of 120 mmHg and adynamic pressure increases with increase in linear velocity. residual pressure of 9 mmHg, the pressure difference in theTotal pressure is a sum of hydraulic pressure and dynamic ventricle is 111 mmHg, or 1.5 x 105 dynes / cm2. Thepressure. This implies that the static pressure reduces with stroke volume V (the amount of blood expelled into theincreasing velocity. From the physiological point of view, aorta during ventricular contraction) is about 80 cm 3. Thisif the velocity goes really low due to “Aortic Stenosis” then means that the heart does about 1.18 x 10 7 ergs of workthe static pressure will reduce and can suck blood back during a ventricular contraction. Only about 70% of thatfrom those arteries. This means that there is less or no work is done before the blood velocity reaches itsblood to the heart and this causes a heart pain. Hagen- maximum. So the amount of energy available to movePoiseuille’s Law is as follows: blood at its maximum velocity is 0.83 x 10 7 ergs. R = ∆ P/Q = 8 µ L / ∆ r4 /2/ Q α 1/L. Q α r4 Q α 1/µWhere: Q is the flow rate. L is the vessel length. r is the vessel radius. µ is the viscosity. R is a hydraulic resistance.Poiseuilles Law applies for steady, laminar and Newtonianfluid. Though the blood flow is not a steady flow yet it canbe considered so, since the arterial system acts as ahydraulic filter to smooth out much of the pulsing. Thusflow becomes a steady flow.Blood flow is usually laminar, however it gets turbulent Figure 11. Velocity of blood in arteries, capillaries,since pressure is proportional to the square of the flow. venules and veins [20].Blood is a non-Newtonian fluid, however blood can beconsidered Newtonian for shear rates greater than 50 perseconds.During ventricular contraction, work done by the heart isgiven by: W = ∆P * Q /3/Where: W = Work. P = Pressure. Q = Flow rate.Not all of that energy goes into moving the blood. Some ofit is stored as: potential energy, elastic energy, and asfrictional losses.W = K + U blood pressure + U aortal walls + E dissipation /4/Where: K = Kinetic energy of the blood. Figure 12: Graphical representation of blood flow through U = Potential energy of the blood. a blood vessel [19]. E = Energy of dissipation. The pressure energy of the blood increases as the blood pressure increases from its diastolic to its systolic levels. Assuming a normal diastolic pressure of 80 mmHg, the pressure difference in the blood is 40 mmHg, or 5.3 x 10 42003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-8
  9. 9. dynes / cm 2. At 70 % of the stroke volume will have 2.99 x106 ergs of energy in the increased blood pressure. Inaddition, potential energy is stored in the arterial walls asthey expand. Assuming the Hookean behavior with a springconstant of k = 1.25 x 10 6 dynes / cm and a variation inradius of 0.2 cm in the aorta, we will have 2.5 x 10 4 ergs ofelastic energy.Poiseuille’s equation is used to calculate the pressure lossalong the aorta and then the energy loss due to dissipationis computed using the stroke volume. Assume a flow rateof 96 cm 3 /s. The average radius of the aorta is 1.25 cm,and its length is approximately 30 cm. Therefore, thepressure drop along the aorta will be 120.2 dynes / cm 2. Itimplies that energy lost in dissipation is 9.6 x 10 3 ergs.This being a negligible amount, dissipation loss in the aortacan be ignored for the purpose of computing aortal Figure 13: Plot of velocity of blood vs. radius of the vesselvelocity. Hence velocity can be computed by the following [20].equation: Using the above computations, we find ta = 0.7 K = W - U blood pressure /5/ milliseconds. The eddy length scale, which tells us the size of an eddy, that can form in that time is:Or (1/2) ρ (0.7 V) v 2 = 8.29 x 10 6 - 2.99 x 10 6 ergs l a = (µ 3 ∆t V / ρ 2 K) ¼ /8/Where: ρ (0.7 V) is the mass of the blood moved during The eddy length scale for the above results was found 5.2 xthe heartbeat. This gives us a velocity of v = 425 cm / s. 10 - 3 cm. This indicates that small eddies are being formedDuring pulsatile flow, the velocity rises sharply and drops and dissipated in very short lengths of time.again to zero within the first quarter of the heartbeat, in anormal patient. Fluid flow in a pipe crosses the threshold In normal patients, the velocity reaches its peak and falls infrom laminar to turbulent flow when "Reynolds’s Number" approximately 0.2 seconds. If, as seems likely from the(Re) reaches about 2000. Re is a ratio of the inertial forces dependence of t a and l a on energy, the length scales as theto viscous forces. It is defined as: square root of the time, then the expected aortal eddy size is 0.09 cm. The magnitude of this value indicates that normal Re = ρ L v / µ /6/ flow in the aorta is laminar, but on the verge of turbulence.Where: v = Velocity of the fluid. Certain assumptions are made during these computations L = the characteristic "length" of vessel. concerning the energy output of the heart: ρ = Fluid density. µ = Fluid viscosity. This equation is only valid if the ventricular contraction is instantaneous, since the volume is assumed to be constant.The inertial forces tend to keep the fluid flowing, while the A constant volume of blood undergoes a change inviscous forces tend to slow the motion due to contact with pressure, and then is placed instantly into the aorta. Whileadjacent layers of fluid. Its value indicates the relative this is obviously a simplification, it is necessary in order tounimportance of viscosity i.e., low Re corresponds to very avoid more complex mathematical treatment. Heuristicviscous situations. For a value for aortal velocity of 425 cm approach to compensating for this simplification was to say/ sec computed above, Re is 28,000 in the aorta. This value that only 70 % of the work done by the heart is done by theis rather misleading. While Re reaches a value which might time, the blood reaches its maximum velocity.indicate the presence of turbulence in the aorta, it is notclear how long Re remains that large. If it is not that high Next major idealization is treating the walls of the aorta asfor an adequate time to form macroscopic eddies, we would “Hookean springs". While the aortal walls have very highnot expect to detect the turbulence. The eddy advection resilience, there stress versus strain curves are not lineartime is: throughout the range of radii during pulsatile flow. Since the normal radial variation is on the order of plus or minus eight percent, it can be justified in saying that they do not ta = ∆t V / K /7/ deviate too far from Hookean behavior.Where: ∆t = Time duration of a heartbeat. Finally, in using Poiseuilles law and Reynolds’s number, K = Kinetic energy of the blood. equations for pulsatile flow in flexible blood vessels with V = Stroke volume. equations designed for constant flow through straight and rigid tubes are assumed. In the case of Poiseuilles law the2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-9
  10. 10. results, even though are only reasonable to order ofmagnitude, are of negligible orderSimilarly, Reynolds number is only useful in situationswhere the velocity is essentially constant over time. This iswhy one has to examine the eddy time and length scales.Since the velocity changes during pulsatile flow, one mustlook deeper into the conditions required for macroscopicturbulence. COMPUTATIONAL FLUID DYNAMICSThe use of Computational fluid dynamics (CFD) analysisstreamlines the design and manufacture of the TotalArtificial Heart (TAH). For the device design, CFDprovides detailed performance assessment. Therefore,reduces the need for costly experimentation. CFD is acomputational technology to study the dynamics of flow.CFD enables sophisticated analysis to predict fluid flowbehavior as well as heat transfer, mass transfer (e.g.perspiration, dissolution), phase change (e.g. freezing, Figure 14. CFD flow analysis for Artificial Heart: Deboiling), chemical reaction (e.g. combustion), mechanical Bakey VAD [23].movement (e.g. impeller turning), and stress or deformationof a related structure. CFD allows the user to build acomputational model that represents a system or device(e.g. Artificial Heart). Then fluid flow physics is applied tothe device, and the software outputs a prediction of thefluid dynamics [20, 21]. CFD is a versatile tool for theprediction of detailed flow patterns: • Regions of stagnant. • Re-circulating fluid. • Detailed pressure variations. • Shear stresses in the fluid and at boundaries.CFD is a valuable tool for device design and manufacturingprocesses by simulating various physiological flows,including ones that interact with the actual medical devices.Flow modeling provides engineers with the ability toaccurately determine the performance of design concepts,reducing the need for physical testing and building ofprototypes. This allows the engineering team to evaluatemore designs with less cost and more efficiency. Finally, itresults in a substantial improvement in performance. At thesame time, the lower cost and shorter lead-times of Figure 15. CFD low analysis in Artificial Heart: DeBakeydevelopment work provide speed to market and reduced VAD [23].development costs [20, 21]. All of this is done before physical prototyping andThe flexibility of CFD analysis also provides an efficient testing. The foresight one gains from CFD helps tomethod of carrying out sensitivity studies on key design design better and faster.parameters. Such analyses can identify which parameters 3. Efficiency: Better design leads to shorter designare the most significant for device design. Basically, the cycles. Time and money are saved. CFD is a tool forcompelling reasons to use CFD are: compressing the design and development cycle.1. Insight: There are many devices and systems that Computational fluid dynamics for Artificial Heart are very difficult to prototype. Often, CFD analysis shows the parts of the system or phenomena Cardiovascular simulation is a coupled problem. Not only happening within the system that would not otherwise the blood is an inhomogeneous, Anisotropic, non- be visible through any other means. Newtonian fluid, but also the boundaries of the flow, (the2. Foresight: CFD is a tool that predicts what will arteries, veins, heart, etc.) are not rigid, and in many happen under a given set of circumstances. It can instances can have a pronounced effect on the flow. answer many ‘what if?’ questions.2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-10
  11. 11. of certain diseases or medical conditions. For example, researchers at the Thomas Jefferson University modeled blood flow in arteries to predict the growth and rupture risk of cerebral aneurysms. Aneurysm is caused by weakness of the arterial wall resulting in a balloon-shaped bulge in the artery. The arterial wall weakness may be caused by abnormally large flow shear stresses that damage wall cells. Once an aneurysm is formed, the blood flow within it may induce vibrations of the aneurysm wall that will progress and eventually rupture [22]. The simulation of blood flow with CFD provides more information than current diagnostic tools for the flow patterns a prototype (See figures 14 and 15). As CFD analysis is further developed into a practical diagnostic tool, it is expected to dramatically improve the ability of physicians to weigh the results of alternativeFigure 16. CFD flow analysis of bearing design for treatment methods. The exacting demands posed by theDeBakey VAD [23]. human body on the artificial organs require a quantum paradigm shift from conventional methods. This utilizes the latest computer tools from aerospace (e.g. CFD, CAD) for “Rapid Prototyping the design of medical devices”. Some of the active areas of research include: constitutive modeling of blood, computer simulation of transport, advanced flow visualization, blood damage modeling, computerized optimization of shape, methods of control and power generation, and a multidisciplinary design (See figures 16 to 18).Figure 17. CFD flow analysis of bearing design forDeBakey VAD [23]. DEVELOPMENT OF THE ARTIFICIAL HEART The various milestones in the development of artificial hearts are described in table 6. Table 6. Chronological developments of the Artificial Heart. Year Scientist Remarks 1964 Hardy Unable to sustain the cardiac cycle and support circulation 1967 Dr. Christiaan Internal bleeding 24 hours Barnard post surgery 1967 Dr.Adrian Death was due to rejection of Kantrowitz the heart 1968 Dr. Barnard Successful 1980 Dr. Shumway a Incidence of rejection andFigure 18. CFD flow analysis optimization of design for Dr.Lower- infection decreasedDeBakey VAD [23]. cyclosporine was usedTherefore predictions are not possible using rigid wall, or 1982 Dr. DeVries Successfulprescribed-boundary-motion approximations. 1984 Dr. DeVries SuccessfulOn a more fundamental level, the modeling of fluid Dr. Sembtransport in organ systems leads to a better understandingof physical mechanisms that contribute to the development2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-11
  12. 12. SOME PATIENTS WHO HAVE HAD HEART TRANSPLANT [34]William Schroeder (53) was the second Jarvik-7 recipientand lived the longest, 620 days, after the pump wasimplanted on November 25, 1985, at the Humana HeartInstitute in Louisville, KY. He died after a series of strokesimpaired his ability to breathe. He was the first patient tolive outside the hospital with the artificial heartMurray Haydon (59) a retired autoworker, became thethird recipient of the Jarvik-7 on February 17, 1985. Hedied at age 59 after 488 days on the heart. He left thehospital briefly on three occasions, but spent most of histime in the Humana intensive care unit. Haydon died ofkidney failure on June 19, 1986.Leif Stenberg (53) of Sweden, received an artificial heartin his native country on April 7, 1985, and survived 229days until November 21. He was able to leave the hospitaland even eat in restaurants. But he died of a massive stroke. Figure 19. The AbioCor artificial heart system [29].Haskell Karp (47) of Skokie-IL received an artificial heartApril 4, 1969 at St. Lukes Episcopal Hospital in Houston.Dr. Denton Cooley did the procedure. The patient lived 65days with the externally powered heart while awaiting adonor heart, but died 30 hours after receiving thetransplant.Barney Clark (61) was dying of heart failure when hereceived a Jarvik-7 artificial heart in Salt Lake City onDecember 2, 1982. He returned to surgery twice because ofcomplications and suffered seizures and pneumonia beforedying of multi-organ failure on March 23, 1983. "It was astruggle throughout the 112 days," said Don Olsen, one ofthe Utah researchers who led the study. "He looked at it asone in a long series of experiments. He knew eventually hewould die on the device."Jack Burcham (62) received an artificial heart at Humanaon April 14, 1985; he died 10 days later of bleeding Figure 20. AbioCor implantable replacement heart[29].complications ABIO COR™ Implantable Replacement HeartMike Templeton (34) of Humble, received anexperimental HeartMate: a left ventricular assist device, on The AbioCor is the first completely self-contained totalSeptember 3, 1991 at St. Lukes Episcopal Hospital. He artificial heart developed by ABIOMED Inc. and itslived with it for 16 months. Eventually, he was able to visit collaborators, with the support of the National Heart, Lunghis family at home and spend some time out of the hospital. and Blood Institute (figures 19 and 20). It consists of aHe was awaiting a transplant when he died of a stroke on hydraulic pump for transporting hydraulic fluid from sideJanuary 19, 1993. to side and a hydraulic pump rotating at approximately 10000 rpm. Valve opens and closes to let the hydraulicWillebrordus Meuffels (36) received an externally fluid flow from one side of the artificial heart to the otherpowered artificial heart at St. Lukes on July 23, 1981. The side. When the fluid moves to the right, blood gets pumpedheart kept the Dutch tour bus driver alive for 54 hours until to the lungs through an artificial ventricle. When the fluidhe received a heart transplant on July 26. But Meuffels died moves to the left, blood gets pumped to the rest of theon August. 2 with massive infection and organ failure. body.Federal regulators told Cooley that further such use ofartificial hearts would require advance approval. A rechargeable battery is implanted inside the patients abdomen. This gives a patient 30 to 40 minutes to perform certain activities, such as showering, while disconnected from the main battery pack. The internal components include an electronic controller implanted in the patients2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-12
  13. 13. abdominal wall. It monitors and controls the pumpingspeed of the heart. The external component is the batterypack that can operate for 4 hours. Power to the AbioCor isachieved with a Transcutaneous Energy Transmission(TET) system. The TET system consists of internal andexternal coils that are used to transmit power via magneticforces from an external battery across the skin. The internalcoil receives the power and sends it to the internal batteryand controller device. Because tubes or wires do not piercethe skin, the chances of developing an infection areminimal.AbioCor patient must meet the following criteria: • Have end-stage heart failure. • Have a life expectancy of less than 30 days. • Not eligible for a natural heart transplant. • Have no other viable treatment optionsJarvik-7 Total Artificial HeartThe Jarvik-7 TAH is named for its designer, Dr. Robert Figure 21. Jarvik-7 Total Artificial Heart [30].Jarvik. The Jarvik-7 was designed to function like thenatural heart (Figure 21). Today, it is called the CardioWestTAH and is used in selected centers as a bridge totransplantation.The Jarvik-7 has two pumps, much like the heartsventricles. Each sphere-shaped polyurethane "ventricle"has a disk-shaped mechanism that pushes the blood fromthe inlet valve to the outlet valve. Air is pulsed through theventricular air chambers at rates of 40 to 120 beats perminute. The artificial heart is attached to the natural atriaby cuffs made of Dacron felt. The drive lines out of theventricular air chambers are made of reinforcedpolyurethane tubing. The lines are covered where they exitthe skin with velour-covered Silastic to ensure stability andencourage tissue growth.The air-driven, external power system powers the pumpthrough drive lines that enter the heart through the left sideof the patient. The large console on wheels is as large andas heavy (but not quite as tall) as a standard household Figure 22. Jarvik 2000 [31].refrigerator, and is normally connected to sources ofcompressed air, vacuum, and electricity. The system is weighs 85 grams. The impeller is a neodymium-iron-boronbacked up by a rechargeable battery in case of a power magnet, which is housed inside a welded titanium shell.failure and includes on-board compressed air tanks The impeller is supported by ceramic bearings. A small(modified scuba type) for use during patient transport. cable, which exits the body through the abdominal wall,Controls in the console allow the doctor to control pump delivers power to the impeller. All of the blood-contactingrate, pumping pressure and other essential functions. surfaces are made of highly polished titanium. The normal operating speed ranges from 8,000 to 12,000 rpm that willJarvik 2000 (Figure 22) generate an average pump flow rate of 5 liters per minute. An analog controller controls the pump speed. The pumpJarvik Heart Inc. and the Texas Heart Institute began speed can be manually adjusted from 8000 to 12000 rpm indeveloping the Jarvik 2000 in 1988. About the size of a "C" increments of 1000. The control unit monitors the pumpbattery, the device is a valveless, electrically powered axial function and the remaining power in the batteries. Audibleflow pump that fits directly into the left ventricle and and visual alerts notify the user of any problems.continuously pushes oxygen-rich blood throughout thebody. ABIOMED BVS-5000®The Jarvik 2000 is an axial flow blood pump that uses The ABIOMED BVS-5000 (Figure 23) is used worldwideelectrical power to rotate a vaned impeller—its only for temporary left, right, or biventricular (both ventricles)moving part. The device is 2.5 cm wide x 5.5 cm long, and2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-13
  14. 14. support in patients with potentially reversible heart failure.The BVS-5000 underwent preclinical studies at the TexasHeart Institute (THI) from 1986 to 1988 and wasintroduced for use in patients at THI in 1988. It was thefirst heart assist device approved by the U.S. Food andDrug Administration for the support of post-cardiotomypatients (those who have developed heart failure as a resultof heart surgery). Since that time, hundreds of patients havebeen sustained by the BVS-5000, with durations of supportup to 63 days. In addition to post-cardiotomy support, theBVS-5000 may also be used in the following cases:1. Donor heart dysfunction or donor heart failure after heart transplantation.2. Right-sided heart failure after placement of a left ventricular assist device.3. Acute heart attack.4. Acute heart disorders, such as viral myocarditis.5. Trauma to the heart.6. Disease of the heart muscle (cardiomyopathy).In patients whose hearts have not recovered after temporary Figure 23. Abiomed BVS 5000 [32].support, the BVS-5000 may be used as a bridge to anotherdevice or as a bridge to heart transplantation.This air-driven blood pump is placed outside the body(extra corporeally). A unique feature of this system is itsdual-chamber design, which is similar to the natural heart(see figure 23). This design provides support for either theleft or right ventricle, or both.The pump houses two polyurethane chambers: an atrialchamber that fills with blood through gravitational forceand a ventricular chamber that pumps blood by air-drivenpower. The atrial chamber is vented outside the patient.The ventricular chamber is connected to the power consoleby a 0.25-inch pneumatic (air) line. Two trileaflet valvesseparate the atrial and ventricular chambers. The pump canproduce blood flow up to 5 liters per minute.The BVS-5000 console can support one or two bloodpumps. It is fully automatic and compensates for changesboth in preload and after load. The left and right sides aretriggered independently of each other. A backup battery Figure 24. Intra Aortic Balloon Pump [33].provides 1 hour of support, and an alarm will sound whenonly 10 minutes of power remain. A foot pump can also 1. Failure to wean from cardiopulmonary bypass.serve as a backup power source. By using the console to 2. Cardiogenic shock.limit blood flow, patients can be slowly weaned from 3. Heart failure.support. 4. Acute heart attack. 5. Support during high-risk percutaneous transluminalIntra-Aortic Balloon Pump (IABP) coronary (balloon) angioplasty, rotoblator procedures, and coronary stent placement.Dr. Adrian Kantrowitz introduced the intra-aortic balloonpump (IABP) in the late 1960s to increase coronary The IABP is a polyethylene balloon mounted on a catheter,perfusion. Because it is easy to insert, the IABP is the most which is generally inserted into the aorta through thewidely used form of mechanical circulatory support. At the femoral artery in the leg. The pump is available in a wideTHI, the IABP is now used in more than 450 patients each range of sizes (2.5 ml to 50 ml). The balloon is guided intoyear. Although the IABP (Figure 24) was first used for the descending aorta, approximately 2 cm from the leftsurgical patients, the pump can now be used along with subclavian artery. At the start of diastole, the ballooninterventional cardiology procedures and medical therapy inflates, augmenting coronary perfusion. At the beginning(medications). Indications for its use include: of systole, the balloon deflates. The blood is ejected from the left ventricle, increasing the cardiac output by as much2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-14
  15. 15. as 40 percent and decreasing the left ventricular strokework and myocardial oxygen requirements. In this manner,the balloon supports the heart indirectly.The balloon is inflated with helium, an inert gas that iseasily absorbed into the bloodstream in case of rupture.Inflation of the balloon can be triggered according to thepatients electrocardiogram, the blood pressure, apacemaker (if they have one), or by a pre-set internal rate.The balloon pump console drives the IABP. The operatingcontrols are located on a touch pad below the displaymonitor and can be programmed to produce rates as high as140 beats per minute. The on-board battery provides powerfor up to 2 hours.Cardiac Assist Devices Figure 25. Pacemaker and the heart [24].The human heart is a pump that consists of 4 chambers.The ventricles are power pumps and act as the major People with pacemakers can do most normal activities:pumping chambers. The coordinated and efficient pumping Drive a car, bathe, swim, or play non-contact sports.of the heart is possible due to the natural pacemaker. The Pacemakers are protected from electrical interference andSino Atrial Node also called the natural pacemaker controls there are no problems with microwave ovens, televisionsthe rate of heartbeat and the pumping action of the heart. and most electrical tools. Medicines also do not interfereThe electrical signal originates at the SA node. From there, with the functioning of the pacemaker.the pulse travels to the atrioventricualr node (AV node)through the atria. The AV node is located at the junction of A Cardioverter is also called, as an Implantablethe atria and the ventricles. Cardioverter Defibrillator (ICD). It is similar to a pacemaker with some additional functions. The ICDIt serves as a delay line, which ensures that the atrial monitors the heart rhythm and delivers the programmedcontraction is complete before the ventricular filling starts. treatment. In case of ventricular tachycardia that is not tooFrom the AV node the impulse propagates to the “Bundle fast, the ICD can deliver several pacing signals in a row.of His”, which is composed of the left and right bundle When those signals stop, the heart may go back to a normalbranches. These are conducting pathways that spread out rhythm. This is called pacing. If the pacing does not work,into the ventricles. Finally the impulse spreads to the cardioversion can be used wherein a mild shock is sent toPurkinje fibers, which conduct the impulse throughout the the heart to stop the fast heartbeat. If ventricular fibrillationventricles. is detected, a stronger shock is sent. This stronger shock can stop the fast rhythm and help the heartbeat go back toHowever sometimes the natural pacemaker property of the normal. This is called fibrillation. Finally the ICD can alsoSA node may be lost due to damage to the SA node or atria. check when the heart beats too slowly. It can act like aOn other occasions the presence of heart blocks may pacemaker and bring the heart rate up to normal.prevent the signal from traveling its full path. In such acase, it is essential to provide artificial stimulation to the Ventricular Fibrillation is the condition when the heartheart muscles. This is done with the help of a pacemaker. stops pumping blood to the brain and the body. Ventricular Fibrillation occurs without warning and can have fatalA pacemaker is a small electronic device that regulates the consequences. This condition is treated with an externalheart beat by sending electrical signals to the heart. Figure defibrillator. A defibrillator consists of 2 paddles that are25 shows the heart and the pacemaker. It has two parts: A pressed on the outside of the chest and they deliver a shockbattery-powered generator and the wires that connect it to to the patients’ heart. This shock stops the irregularthe heart. The generator is about the size of a silver dollar heartbeat and helps the heart recover its rhythimicity.and has an effective life of seven to 12 years. It isimplanted just beneath the skin below the collarbone. The Left Ventricular Assist Devices (LVAD)leads are threaded into position through veins leading backto the heart. These leads carry electrical signals from the LVAD is a useful class of devices used in patients withpacemaker to the heart. severe heart failure when the heart is no longer capable of pumping blood. The LVAD takes over the hearts pumpingThe most commonly used pacing device is the demand action until an artificial heart is available for implant. Thepacemaker. As the name suggests it provides pulses only LVAD is inserted in the chest cavity. This device simplywhen there is a demand for them. It monitors the pacing moves blood from the left ventricle to the aorta and backactivity of the heart and provides pulses only of the beats through an air driven pump. One such LVAD is the IABP,per minute fall below a minimum value, which can be used in the intensive care unit, cardiac catheterizationdecided beforehand. It is usually set to 60 BPM. laboratory, or the operating room.2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-15
  16. 16. A local anesthetic is given over the artery at the top of theballoon that sits in the aorta and is hooked up to a largeconsole that is continuously maintained by a speciallytrained technician. The console inflates the balloon duringthe time that heart is filling with blood for the next heartbeat. The inflated balloon pumps the blood and thendeflates when the heart is ready with the next heartbeat.Thus, enough blood flow is supplied to the organs of thebody and some of the workload of the heart is reduced.This allows the heart to recover its strength. AthoughLVAD are currently used for short-term use, yet it isproposed that they will eventually replace artificial heartsand be used in permanent long-term implantation [23]. BIOHEARTUnlike most organs in the body, the heart does not grownew cells to replace worn ones. As a result when heart cellsdie during an attack, this portion of the heart becomes deadtissue. The rest of the organ must work harder tocompensate. This begins a cascade reaction towards heartfailure. The best cure is a heart transplant. But the shortageof available organs as well as the dangers involved in thistransplantation process has motivated scientists to searchfor a way to regenerate heart tissue. Bioheart Inc. inFt.Lauderdale- FL is working on a Myoblast technique. Figure 26. Bioheart’s Myoblasts technique [25].Heart muscle cells were also considered, but these can faildue to the lack of oxygen. Hence heart muscle cells are notused for the regeneration. Instead cells from the thighs are This technique is called myogenesis and is a part of studyused since they are more robust and are able to repair of tissue engineering. The technology developed bythemselves. Bioheart Inc. involves cell transplantation, that does not depend upon the availability of hearts for a transplant.A silver-dollar size portion of thigh muscle removed. Thetissue is sent to a Bioheart laboratory, where it is putthrough an 18-step process to select out and multiply BIOPUMPSimmature muscle cells, called myoblasts. Now the cellularcomposition is delivered to the area of the heart muscle that Peristaltic pumpis damages due to infarction. For this a specialized system,Bioheart Myocath catheter system is used. Using this A Peristaltic pump (Figure 27) consists of a tube and acatheter, 10 to 30 pellets, each consisting of some 50 roller system. It is a totally closed system with the tubemillion cells, are injected in and around the damaged area carrying the material to be transported e.g. blood. The tubeof the heart. acts a valve as well as the transport mechanism. A roller compresses the tube in its forward motion. As a result theThe damaged heart muscle is now partially regenerated liquid tends to be pushed forward. These arewith healthy tissue. The implanted myoblast cells completely self-priming, positive-displacement pumps withproliferate in a controlled manner growing in the oxygen no check valves or components in the fluid stream.deprived area. They are inherently resistant to ischemia andthrive only in an oxygen deprived infarct environment. A Since the system is non-contact fluid can be deliveredseries of injections through the infarct area is then without contamination and this is most important forperformed. After about 3-8 weeks, the autologous cells biomedical applications. Because the tubing can bedevelop into functional contractile cells within the damaged sterilized, the Peristaltic pump is the ideal system for sterilemyocardium. The initially scarred area now becomes and other sensitive precision pumping situations.functional myocardial tissue to a significant degree [25]. The peristaltic pumps come in a variety of designs andThe above technology developed by Bioheart is called as sometimes come with 2 rollers. The accuracy of a fill canthe Myocell™ [25]. It is an autologous cell based product be improved by increasing the number of rollers, which inused for the treatment of Myocardial infarction and turn increases the frequency of the pulse and reduces theCongestive Heart Failure. It is currently in the clinical trial impact of a single pulse.stage in US and Europe. Clinical trials began in Europe inMay 2001.2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-16
  17. 17. Figure 27. Peristaltic pump and the roller [26]. Figure 28. Inherently controllable blood pump developed by Foster Miller Technologies [27].The pump head is typically made of polypropylene withsilicone coated rollers. The pump heads are driven with The pump is programmable and the program can beprecision stepper motors or DC motors. A micro controller changed even while the pump is in operation. New bar-usually controls the pumps and can this be programmed to code reading feature enables quick drug identification andsuit the application. Usually a digital thumb switch is setting of infusion rates with laser-reading of the drug’s barprovided to set the pump speeds. A 3 digit LED displays code (located on the syringe). This feature of the Harvard Ithe current speed. represents a major milestone in the reduction of medication errors. Other special features of the pump include anMagnetic Bearing Pump advance “Near empty syringe ” warning, LCD display screen, capacity to store up to 3000 drugs along with theirFoster Miller technologies are developing a high efficiency safety limits and infusion ratings. Figure 29 shows theblood pump in association with the Cleveland Clinic syringe pump developed by Harvard 1 medicalfoundation (Figure 28). The pumps are based on the technologies.principle of magnetic levitation. This is a rotary pumpdesigned for 5 liter/min and 100 mm Hg. It uses less than 8 ROLE OF TAH IN TREATMENT OF END STAGEW of input power. The magnetic suspension consists of a HEART FAILUREsingle active magnetic thrust bearing and a permanent-magnet radial bearing. The simple, radial flow impeller has Consistent estimates are that at least 50,000 to 100,000no shroud or discharge stator blades. A secondary impeller patients yearly might benefit from mechanical cardiacprovides a secondary blood flow path to minimize blood assistance, but there has been no consistent estimate as tostagnation. Another design includes a flat motor. Two how many might be in need of a TAH. There is nopermanent-magnet rings, one on the stator and one on the evidence that imminently available technologies willrotor, support the pump in a plane. Three specially tuned dramatically decrease the need for mechanical assistance,electromagnets keep the pump stable in the magnetic field. or TAH in particular. However, as more mechanical support devices have become available, it is still uncertainSyringe Infusion Pump how the correct device should be selected for each patient. The initial impression derived from post-cardiotomyThe Syringe infusion pump provides a uniform flow of experience was that biventricular support would befluid by precisely driving the plunger of a syringe down its required for a majority of patients, reported by somebarrel. It provides accurate and continuous flow centers to exceed 50 percent. More recent experiencerate for precise delivery of I.V. medication in critical indicates a lower need for biventricular support in chronicmedical care. heart failure, which may reflect in part differences in chronic heart failure and acute post-cardiotomy shock, andHarvard 1 has developed a syringe pump that is powered also the benefit of wider use of nitric oxide to reduceby Li-ion battery. The pump is lightweight and convenient pulmonary vascular resistance The current need forto carry around in hospital from bed to bed [5]. biventricular support when mechanical assist devices are used in chronic heart failure is estimated to be 10 to 202003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-17
  18. 18. percent, with a slightly higher proportion of patients post- 2. Hemorrhage occurs in about one third of patientscardiotomy and post-infarction who will be best served by receiving the TAH and remains a significant clinicalreplacement with a TAH. problem. Bleeding is usually observed in the perioperative period or in the early postoperative period. Up to 50 percent of patients with VADs require re-operation for bleeding, although the operative use of the fibrinolytic inhibitor aprotinin may decrease both postoperative blood loss and the need for blood product transfusion. The causes of hemorrhage in TAH recipients are protean and are associated with preoperative coagulopathies due to hepatic dysfunction or poor nutritional status, cardiopulmonary bypass - induced thrombocytopenia or platelet dysfunction, and prolonged antibiotic therapy. This may be accentuated by the necessity of using antithrombotic therapy in some device recipients due to activation of both the coagulation cascade and platelets following exposure to the artificial surfaces of the device together with turbulent blood flow. In general, bleeding may be more of a clinical problem in patients who receive the TAH emergently following failed cardiac surgery with extended CPB or those supported for prolonged periods with extra corporeal membrane oxygenation. Conversely, the risk of bleeding is lower following shorter surgical implantation procedures. Bleeding may also be a significant problem during device explanation due to extensive adhesions.Figure 29. Syringe pump of Harvard 1 medicaltechnologies [28]. Hemorrhage remains a significant cause of death in recipients of both VAD’s and TAH’s. However, even ifDespite the prevalence of biventricular failure in patients hemorrhage is not life threatening, it often necessitateswith chronic heart failure, some, at least in the short term, blood transfusion. The transfused erythrocytes may benow demonstrate resolution of severe heart failure more prone to hemolysis by the device, and the increasedsymptoms with left ventricular support alone. The long- hemolysis can lead to renal failure. The transfusedterm persistence of this improvement is not yet established. granulocytes can also lead to alloimmunization, that mayIt is not known how many patients are considered ineligible be a clinical problem during subsequent heartfor isolated left ventricular support due to predominant transplantation.right ventricular compromise, intrinsic valve disease, smallleft ventricular cavity size, complex congenital anatomy 3. Infection remains a major cause of death and morbidityand other factors. There is also insufficient information in TAH/VAD recipients. Infection is seen in 25 to 48regarding the long-term success of LVAD placement in percent of VAD recipients and approximately 37 percent ofpatients with ongoing ischemia TAH recipients. Infection during VAD implantation has been associated with a decreased probability of survivalLIMITATIONS OF VAD AND TAH when used as a bridge to transplantation.1. Thromboembolism in VAD and TAH recipients is In a recent clinical study of the TAH, infections were mostthought to result from biomaterial surface- induced commonly noted approximately seven days postthrombus formation with systemic embolization. implantation, but infectious complications can be observedConsiderable progress has been made in the development weeks to months after implantation. Most infectiousof materials with improved blood compatibility, but no complications are related to the device and often the use ofmaterials developed to date are completely blood percutaneous drivelines has been implicated. Other device-compatible and surface-induced thrombosis remains a real related infections included abdominal pocket infections;concern. Some devices employ a textured surface, which at colonization of surface-induced thrombi; and directfirst appears counter-intuitive. However, while the bacterial colonization of the device lining materials.roughness of such surfaces encourages fibrin depositionand platelet adhesion, the development of an adherent The principal pathogens associated with device infectionpseudointima so formed may be less prone to embolization have been Staphylococcus aureus, Staphylococcusthan thrombi forming on smooth surfaces. The use of these epidermidis, Coagulase- negative staphylococci,textured surfaces has ranged from 8 to 35%. Also, use of Enterococcus faecalis, Enterococcus faecium, Serratiathese textured surfaces has decreased thromboembolism marcescens, and Candida species. Device recipients alsofrom approximately 20 to 2.7 % (events per patients - may be susceptible to nosocomial infection due to longmonth). hospital stays, prolonged immobilization, and multiple2003 Congress on Biofluid Dynamics of Human Body Systems at Biomedical Engineering – FIU, Miami-FL. B-18

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