Various physical characteristics ofsystemic circulation:These either directly or indirectly affects the systemiccirculation and are interrelated to each other .1.Cross sectional area of the vessels.2. Pressure in various portions.3. Resistance provided by various structures.4. Venous return5. Blood flow6. Vascular distensiblity.7. Vascular compliance.
Total crossectional Average velocity of area (cm2) blood flowAorta 4.5 40 cm/secSmall arteries 72 (16times that of 1.4 cm/sec aorta)Arterioles 400 0.5 mm/secCapillaries 4500 (1000 times that 0.3 mm/sec of aortaSmall veins 80 1-2 cm/secInferior vena cava and 18 7-10 cm/secsuperior vena cava
Left atruim 7-8/zeroLeft ventricle 120/zero mmHgAorta and its larger branches 120/70 mmHgArterioles 60 mmHgMetarterioles 40 mmHgCapillaries 25 mmHgVenules and larger veins 10 mmHgVena cava(superior and inferior) 2 mmHg
ARTERIAL PRESSURE: Arterial blood pressure is defined as the lateral pressure exerted by the contained column of blood on the walls of arteries. Generally the term pressure/blood pressure refers to arterial blood pressure.It is further of 4 different types1. Systolic blood pressure2. Diastolic blood pressure3. Pulse pressure4. Mean arterial pressure
CENTRAL FACTORS PERIPHERAL FACTORS(Factors pertained to heart) (Factors pertaining to blood vessels)1. Cardiac output 1. Peripheral resistance2. Heart rate 2. Blood volume 3. Venous return 4. Elasticity of blood vessels 5. Velocity of blood flow 6. Diameter of blood vessels 7. Viscosity of blood
COMPONENT DEFINATION CHARACTERISTIC NORMAL FEACTURES VALUE (mmHg)1. SYSTOLIC It is the maximum -undergo considerable RangeBLOOD pressure exerted fluctuations 100-140PRESSURE during systole - It indicates force with Average(SBP) which the heart works 120 and degree of pressure which arterial walls have to withstand.2. DIASTOLIC It is the minimum -undergoes much less RangeBLOOD pressure exerted fluctuations 70-90PRESSURE(DB during diastole -it is measure of total AverageP) peripheral resistance. 803. PULSE It is the difference of -it determine the pulse AveragePRESSURE SBP and DBP i.e volume 40(PP) PP=SBP-DBP4. MEAN It is average pressure It is calculated as RangeBLOOD throughout cardiac MBP=DBP+1/3 PP 95-100PRESSURE cycle.(MBP)
Calculated as:Systolic blood pressure-diastolic blood pressure= pulse pressureIt is dependent upon 3 factors Stroke volume (directly proportional) Amount of blood ejected from left ventricle (directly proportional) Compliance of aorta (indirectly proportional)
LOW PULSE PRESSURE:A pulse pressure is considered abnormally low if it is less than 25% of the systolic value.e.g in Heart failure Aortic stenosis Shock HaemrhageHIGH PULSE PRESSURE:A pulse pressure higher than 25%of systolic value is consider high pulse pressure. It is temporary in case of exercise but constant high PP is in Artherosclerosis Chronic aortic regurgitation Heart block Endocarditis
1. Central venous pressure (CVP) 2. Peripheral venous pressure (PVP)Blood from all systemic veins flow It is the pressure in peripheralinto right atrium, therefore right veins. Large veins offeratrium pressure is called central considerable resistance to bloodvenous pressure. Normally it is 1-6 flow because they remainmmHg. compressed at many points by the surrounding tissues. e.g abdominal veins by diff. organs and intra-abdominal pressure, arm veins by first rib and neck vein by atmospheric pressure. It is about 10 mmHg.
Factors affecting venous return Venous pressure Position of the body: From lying to standing – increase of the blood in veins – dilation of veins in the lower part of the body – decrease of venous return Action of “muscular pump” Respiration movement. Gravity
According to OHM’S law: F=ΔP/RWhere F= blood flow ΔP= pressure gradient R= vascular resistance
Pressure gradient i.e p1-p2.Where p1 is pressure at proximal end of vessel & p2 pressure at distal end of vessel. Pressure gradient is directly proportional to blood flow. Viscosity of blood: volume of blood flow is inversely proportional to viscosity of blood. Diameter of blood vessels: volume of blood flow is directly proportional to the diameter of vessel. Resistance to blood flow:Resistence= pressure gradiant/volume of blood flow
When the pressure in blood vessels is increased, this dilates the blood vessels and therefore decreases their resistance.The result is increased blood flow not only because of increased pressure but also because of decreased resistanceThe most distensible by far of all the vessels are the veins. Even slight increases in venous pressure cause the veins to store 0.5 to 1.0 liter of extra blood. Therefore, the veins provide a reservoir function for storing large quantities of extra blood that can be called into use whenever required elsewhere in the circulation.
Anatomically, the walls of the arteries are far stronger than those of the veins. Consequently, the arteries,on average, are about eight times less distensible than the veins. That is,a given increase in pressure causes about eight times as much increase in blood in a vein as in an artery of comparable size.
It is Important to know the total quantity of blood that can be stored in a given portion of the circulation for each millimeter of mercury pressure rise than to know the distensibilities of the individual vessels. This value is called the compliance or capacitance of the respective vascular bed; that is,
Compliance and distensibility are quite different. highly distensible vessel that has a slight volume mayhave far less compliance than a much less distensiblevessel that has a large volume because compliance isequal to distensibility times volume. The compliance of a systemic vein is about 24 timesthat of its corresponding artery because it is about 8times as distensible and it has a volume about 3 timesas great (8 ×3 = 24).