• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content
Physiologic and pathophysiologic function of the heart
 

Physiologic and pathophysiologic function of the heart

on

  • 1,284 views

FULL WEB Interactive version

FULL WEB Interactive version
http://www.scribd.com/doc/182401977/Physiologic-and-Pathophysiologic-Function-of-the-Heart-Cardiac-Cycle-Graphs-Curves-Loops-and-CO-Calculations

Statistics

Views

Total Views
1,284
Views on SlideShare
1,278
Embed Views
6

Actions

Likes
2
Downloads
0
Comments
0

1 Embed 6

http://www.imhotepvirtualmedsch.com 6

Accessibility

Upload Details

Uploaded via as Adobe PDF

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

    Physiologic and pathophysiologic function of the heart Physiologic and pathophysiologic function of the heart Presentation Transcript

    • Physiologic and Pathophysiologic Function of the Heart Prepared and presented by Marc Imhotep Cray, M.D. Basic Medical Sciences and Clinical Knowledge (CK) Teacher From: USMLE Step 1 CV Review Tools Cloud Folder
    • CV Physiology Concepts Schematic From IVMS Function of the Heart illustrations and Equations Notes Online reference resource to the presentation that follows: Cardiovascular Physiology Concepts Richard E. Klabunde, PhD Click for enlarged view
    • TOPICS DISCUSSION OUTLINE The physiologic function of the heart can be represented in several ways:  Cardiac output as measured using the Fick principle  Cardiac Cycle (Wiggers diagram)  Pressure– Volume Loops: pressure–volume loops provide a tool for analyzing the cardiac cycle, particularly ventricular function  Frank– Starling curves: Effects of Cardiac Output, Total Peripheral Resistance, Contractility, Preload, and Afterload as represented on the Frank– Starling curve  Common Valvular Abnormalities 3
    • Cardiac Output Measurement  Cardiac output =volume of blood pumped by each ventricle per minute. (N5L/min)  Cardiac output (QT) is regulated by autonomic nerves and hormones through changes in heart rate (HR) or stroke volume (SV)  In adults, cardiac output is usually expressed in liters per minute: QT = (SV × HR)/1000 QT = Cardiac output (L/min) SV = Stroke volume (mL/min) HR = Heart rate (beats/min)  Cardiac output can also be measured clinically in the cardiac catheterization laboratory, using a thermodilution method  A cold saline solution of known temperature and volume is injected into the right atrium.  The reduction in blood temperature measured downstream in the pulmonary artery is a function of cardiac output. Example If resting SV is 70 mL and HR is 70 beats/min, then QT = (70 mL × 70 beats/min)/1000 = 4.9L/min 4
    • Cardiac Output Measurement THE FICK PRINCIPLE (1)  A traditional physiologic method for calculating cardiac output applies the Fick principle, which derives blood flow from variables related to O2 consumption Example A person consumes 250 mL of O2 per  Cardiac output can be calculated by min. Arterial O2 content is 20 mL of O2 per dL applying the Fick concept to the entire of blood, and the O2 content of body, relating total body O2 consumption mixed venous blood is 15 mL of O2 per dL of to the difference in O2 content between blood: blood in the systemic arteries and the QT = 250 (mL/min) ÷ (20 mL/dL − 15 mL/dL) = mixed venous blood sampled from the 50 dL/min pulmonary artery or the right ventricle QT = 50 dL / min = 5 L / min QT = VO2 /(CaO2 − CvO2) QT = Cardiac output VO2 = O2 consumption CaO2 = Arterial O2 content CvO2 = Mixed venous O2 content 5
    • THE FICK PRINCIPLE (2) The Fick principle for measuring cardiac output is expressed by the following equation: ■ The equation is solved as follows: 1. O2 consumption for the whole body is measured. 2. Pulmonary vein [O2] is measured in a peripheral artery. 3. Pulmonary artery [O2] is measured in systemic mixed venous blood For example, a 70-kg man has a resting O2 consumption of 250 mL/min, a peripheral arterial O2 content of 0.20 mL O2/mL of blood, a mixed venous O2 content of 0.15 mL O2/mL of blood, and a heart rate of 72 beats/min. What is his cardiac output? What is his stroke volume? 6
    • Cardiac Output Measurement During the early stages of exercise, CO is maintained by↑ HR and ↑ SV During the late stages of exercise, CO is maintained by↑HR only (SV plateaus) If HR is too high, diastolic filling is incomplete and CO↓(e.g., ventricular tachycardia) Source: Tao Le T and Bhushan V, Cardiovascular, In First Aid for the USMLE Step 1 2013:553 7
    • Cardiac cycle(1) The seven phases of the cardiac cycle are (1) atrial systole; (2) Isovolumetric contraction; (3) rapid ejection; (4) reduced ejection; (5), isovolumetric relaxation; (6) rapid filling; and (7) reduced filling. Source: Klabunde, RE, Ventricular Pressure-Volume Relationship 8
    • Cardiac cycle (2) Expressed as pressure-volume loop Source: Tao Le T and Bhushan V, Cardiovascular, IN First Aid for the USMLE Step 1 2013:556 Phases-left ventricle: 1) Isovolumetric contraction - period between mitral valve closure and aortic valve opening; period of highest 02 consumption 2) Systolic ejection - period between aortic valve opening and closing 3) Isovolumetric relaxation - period between aortic valve closing and mitral valve opening 4) Rapid filling- period just after mitral valve opening 5) Reduced filling- period just before mitral valve closure 9
    • Steps in the Cardiac cycle (3) 1 2 (isovolumetric contraction) On excitation, the ventricle contracts and ventricular pressure increases. The mitral valve closes when left ventricular pressure is greater than left atrial pressure. Because all valves are closed, no blood can be ejected from the ventricle (isovolumetric). 2 3 (ventricular ejection) The aortic valve opens at point 2 when pressure in the left ventricle exceeds pressure in the aorta. Blood is ejected into the aorta, and ventricular volume decreases. The volume that is ejected in this phase is the stroke volume. Thus, stroke volume can be measured graphically by the width of the pressure– volume loop. The volume remaining in the left ventricle at point 3 is ESV. 10
    • Steps in the Cardiac Cycle (4) 3 4 (isovolumetric relaxation) At point 3, the ventricle relaxes. When ventricular pressure decreases to less than aortic pressure, the aortic valve closes. Because all of the valves are closed again, ventricular volume is constant during this phase. 4 1 (ventricular filling) Once left ventricular pressure decreases to less than left atrial pressure, the mitral (AV) valve opens and filling of the ventricle begins. During this phase, ventricular volume increases to about 140 mL (the end-diastolic volume). 11
    • Cardiac output variables Stroke Volume is affected by Contractility, Afterload, and Preload ↑ SV when ↑ preload,↓ afterload , or ↑ contractility Contractility (and SV) ↑ with : • Catecholamines (↑ activity of Ca2+ pump in sarcoplasmic reticulum) • ↑ intracellular Ca2+ • ↓extracellular Na+ (↓ activity of Na+/Ca2+ exchanger) • Digitalis ( blocks Na+-K+ pump→ ↑ intracellular Na+ → ↓ Na+/Ca2+ exchanger activity → ↑ intracellular Ca2+) Contractility (and SV) ↓with: • β1-blockade (↓ cAMP) • Heart failure (systolic dysfunction) • Acidosis • Hypoxia /hypercapnea (↓ PO2 / ↓ PCO2) • Non-dihydropyridine Ca2+ Channel blockers 12
    • Preload and afterload Preload =ventricular EDV Afterload = mean arterial pressure (proportional to peripheral resistance) Venodilators (e.g., nitroglycerin) ↓ Preload. Vasodilators (e.g., hydralazine) ↓ Afterload (arterial) Preload ↑ with : • Exercise (slightly) • ↑ blood volume (e.g., overtransfusion) • Excitement (↑ sympathetic activity) 13
    • Ventricular pressure-volume loop (1) Source: Klabunde, RE, Ventricular Pressure-Volume Relationship Generated by plotting ventricular pressure against ventricular volume at many different corresponding points during a single cardiac cycle 14
    • Ventricular pressure-volume loop (2) Source: Klabunde, RE, Ventricular Pressure-Volume Relationship EDPVR, end-diastolic pressure-volume relationship; ESPVR, end-systolic pressure-volume relationship; SV, stroke volume (EDV - ESV) 15
    • Left ventricular pressure and volume (3)  Correlation between changes in left ventricular pressure (upper panel ) and left ventricular volume (lower panel ) during a single cardiac cycle  Landmark events of valve opening and closure and the point where peak systolic blood pressure occurs are noted at points A–E Kibble JD and Halsey CR, CV Physiology, In Medical Physiology The Big Picture ; McGraw-Hill 2009:144-57 16
    • Pressure-volume loop (4)  Left ventricular pressure is plotted as a function of left ventricular volume  Landmark events of valve opening and closure and the point where peak systolic blood pressure occurs are noted at points A–E Kibble JD and Halsey CR, CV Physiology, In Medical Physiology The Big Picture McGraw-Hill 2009:144-57 17
    • Effects of increasing venous return on LV pressure-volume loops Source: Klabunde, RE, Ventricular Pressure-Volume Relationship  This diagram shows the acute response to an increase in venous return.  It assumes no cardiac or systemic compensation and that aortic pressure remains unchanged  Increased venous return increases end-diastolic volume (EDV) but it normally does not change ESV; therefore, stroke volume (SV) is increased. ESPVR, end-systolic pressurevolume relationship. 18
    • Factors that Increase Ventricular Preload Source: Klabunde RE. Cardiovascular Physiology Concepts 2nd Ed. http://www.cvphysiology.com/textbook.htm 19
    • Effects of changes in afterload (PAo) LV pressure-volume loops Source: Klabunde, RE, Ventricular Pressure-Volume Relationship Increased aortic pressure solid red loop) decreases stroke volume (width of loop) and increases end-systolic volume (ESV), whereas decreased aortic pressure (AO dashed red loop) increases stroke volume and decreases end-systolic volume. Preload and inotropy are held constant in this illustration. 20
    • Effects of increasing inotropy on ventricular pressure–volume loops Source: Klabunde, RE, Ventricular Pressure-Volume Relationship Increased inotropy shifts the ESPVR up and to the left, thereby increasing stroke volume and decreasing endsystolic volume (ESV). Decreased inotropy shifts the end-diastolic pressure–volume relationship down and to the right, thereby decreasing stroke volume and increasing endsystolic volume. Preload and aortic pressure are held constant in this illustration. 21
    • Factors that increase inotropy Source: Klabunde RE. Cardiovascular Physiology Concepts 2nd Ed. http://www.cvphysiology.com/textbook.htm 22
    • Effects of changes in preload, afterload, and contractility on the ventricular pressure–volume loop Increased afterload results from an increase in aortic pressure, which leads to a decrease in SV. This decreases the width of the loop. Increased contractility Increased contractility leads to the ventricle developing greater tension during systole and increases the SV. Source: Klabunde, RE, Ventricular Pressure-Volume Relationship Increased preload Increased preload results in an increase in EDV. This increase causes an increase in SV (due to FrankStarling relationship), which is reflected as an increased width of the loop. 23
    • Changes in the ventricular pressure–volume loop “Describe each” Source: Costanz LS. Cardiovascular Physiology IN BRS Physiology 5th ed. LLW, 2012 24
    • Interdependent effects of changes in preload, afterload, and inotropy on left ventricular pressure-volume loops (1) A shows effects of increasing preload (enddiastolic volume) with and without a secondary increase in afterload (aortic pressure) Source: Klabunde, RE, Ventricular Pressure-Volume Relationship 25
    • Interdependent effects of changes in preload, afterload, and inotropy on left ventricular pressure-volume loops (2) B shows the effects of increasing afterload with and without a secondary increase in preload. Source: Klabunde, RE, Ventricular Pressure-Volume Relationship 26
    • Interdependent effects of changes in preload, afterload, and inotropy on left ventricular pressure-volume loops(3) C shows the effects of increasing inotropy with and without secondary changes in preload and afterload. Source: Klabunde, RE, Ventricular Pressure-Volume Relationship 27
    • Starling curve Source: Tao Le T and Bhushan V, Cardiovascular, IN First Aid for the USMLE Step 1 2013:554 Force of contraction is proportional to end diastolic length of cardiac muscle fiber (preload) ↑ contractility with sympathetic stimulation, catecholamines, digoxin ↓contractility with loss of myocardium (MI) , β-blockers, calcium channel blockers EF↓ in systolic heart failure 28
    • Wiggers diagram, a correlation of electrical and mechanical events during the cardiac cycle Kibble JD and Halsey CR, CV Physiology, IN Medical Physiology The Big Picture M-H 2009 A phonocardiogram records heart sounds 29
    • Summary of normal pressures within the cardiac chambers and great vessels  The higher of the two pressure values (expressed in mm Hg) in the right ventricle (RV), left ventricle (LV), pulmonary artery (PA), and aorta (Ao) represent the normal peak pressures during ejection (systolic pressure) Source: Klabunde RE. Cardiovascular Physiology Concepts 2nd Ed., LLW 2012 http://www.cvphysiology.com/textbook.htm WHEREAS  The lower pressure values represent normal end of diastole pressure (ventricles) or the lowest pressure (diastolic pressure) found in the PA and Ao. Pressures in the right atrium (RA) and left atrium (LA) represent average values during the cardiac cycle 30
    • NORMAL HEART SOUNDS & COMMON VALVULAR ABNORMALITIES A. First (S1) and second (S2) heart sounds. B. Physiologic splitting of S2. S1 is caused by the closure of the atrioventricular valves; S2 is caused by the closure of the semilunar valves. Physiologic splitting mainly results from the delayed closure of the pulmonic valve on inspiration. M1, mitral valve closure; T1, tricuspid valve closure; A2, aortic valve closure; P2, pulmonic valve closure. Kibble JD and Halsey CR, CV Physiology, In Medical Physiology The Big Picture McGraw·Hill 2009:144-57 Also see: Audio-HEART and LUNG Auscultation Sounds mp3s 31
    • Aortic Stenosis Systolic murmur of aortic stenosis A. Paradoxical splitting of the second (S2) heart sound occurs because the aortic valve (A2) closes later than the pulmonic valve (P2) due to prolonged left ventricular systole B. Pressure gradient across the narrowed aortic valve Kibble JD and Halsey CR, CV Physiology, In Medical Physiology The Big Picture; McGraw-Hill 2009:144-57 Paradoxical splitting of S2 occurs when closure of the aortic valve is delayed, causing P2 to occur first, followed by A2. The most notable causes are aortic stenosis (which prolongs left ventricular systole) and left bundle branch block (which delays the onset of left ventricular contraction) 32
    • Aortic Stenosis pressure-volume loop Source: Klabunde, RE, Ventricular Pressure-Volume Relationship In aortic stenosis (red loop in figure)  Left ventricular emptying is impaired because of high outflow resistance caused by a reduction in the valve orifice area when it opens.  This high outflow resistance causes a large pressure gradient to occur across the aortic valve during ejection, such that the peak systolic pressure within the ventricle is greatly increased.  This leads to an increase in ventricular afterload, a decrease in stroke volume, and an increase in end-systolic volume.  Stroke volume (width of pressure-volume loop) decreases because the velocity of fiber shortening is decreased by the increased afterload (see force-velocity relationship).  Because end-systolic volume is elevated, the excess residual volume added to the incoming venous return causes the end-diastolic volume to increase.  This increases preload and activates the Frank-Starling mechanism to increase the force of contraction to help the ventricle overcome, in part, the increased outflow resistance. 33
    • Mitral Insufficiency Systolic murmur of mitral insufficiency A. The early aortic valve (A2) sound indicates the shortened systole due to retrograde blood flow into the left atrium B. The large atrial v wave due to regurgitation of blood from the left ventricle into the left atrium during systole Kibble JD and Halsey CR, CV Physiology, In Medical Physiology The Big Picture; McGraw-Hill 2009:144-57 34
    • Mitral Insufficiency pressure-volume loop Source: Klabunde, RE, Ventricular Pressure-Volume Relationship mitral valve regurgitation (red pressure-volume loop in figure)  As the left ventricle contracts, blood is not only ejected into the aorta but also back up into the left atrium.  This causes left atrial volume and pressure to increase during ventricular systole. During ventricular diastolic filling, the elevated pressure within the left atrium is transmitted to the left ventricle during filling so that left ventricular EDV (and pressure) increases.  This would cause wall stress (afterload) to increase if it were not for the reduced outflow resistance because of mitral regurgitation that tends to decrease afterload during ejection because of reduced pressure development by the ventricle.  The net effect of these changes is that the width of the pressure-volume loop is increased (i.e., SV is increased); however, ejection into the aorta (forward flow) is reduced.  The increased ventricular "stroke volume" (measured as the EDV minus the ESV) in this case includes the volume of blood ejected into the aorta as well as the volume ejected back into the left atrium. 35
    • Aortic Insufficiency Diastolic murmur of aortic insufficiency. A. Sound intensity of the murmur decreases during diastole as a function of aortic blood pressure. S1 is the first heart sound; A2 indicates timing of the closure of the aortic valve. B. Pathologic runoff of blood from the aorta into the left ventricle decreases aortic diastolic blood pressure and increases left ventricular filling, increasing stroke volume and systolic blood pressure. Kibble JD and Halsey CR, CV Physiology, In Medical Physiology The Big Picture McGraw-Hill 2009:144-57 36
    • Aortic regurgitation pressure-volume loop Source: Klabunde, RE, Ventricular Pressure-Volume Relationship As long as the ventricle is not in failure, end-systolic volume may only be increased a small amount (as shown in figure) due to the increased afterload (ventricular wall stress). If the ventricle goes into systolic failure, then end-systolic volume will increase by a large amount and the peak systolic pressure and stroke volume (net forward flow into aorta) will fall. In aortic valve regurgitation (red loop in figure)  Aortic valve does not close completely at end of systolic ejection. As the ventricle relaxes during diastole, blood flows from the aorta back into the ventricle so the ventricle immediately begins to fill from the aorta.  Once the mitral valve opens, filling occurs from the left atrium; however, blood continues to flow from the aorta into the ventricle throughout diastole because aortic pressure is higher than ventricular pressure during diastole.  This greatly enhances ventricular filling so that enddiastolic volume is increased as shown.  The increased end-diastolic volume (increased preload) activates the Frank-Starling mechanism to increase the force of contraction, ventricular peak (systolic) pressure, and stroke volume (as shown by the increased width of the pressure-volume loop). 37
    • Mitral Stenosis Diastolic murmur of mitral stenosis A. An opening snap (OS) is a unique sound that is characteristic of mitral stenosis. The sound produced by obstructed flow through the mitral valve is described as a presystolic murmur (PSM). Obstructed ventricular filling may delay closure of the mitral valve (M1) relative to closure of the tricuspid valve (T 1). B. Obstruction of the mitral valve causes a sustained increase in left atrial pressure. Kibble JD and Halsey CR, CV Physiology, In Medical Physiology The Big Picture McGraw·Hill 2009:144-57 38
    • Mitral stenosis pressure-volume loop Mitral stenosis (red pressure-volume loop in figure)  Impairs left ventricular filling so that there is a decrease in end-diastolic volume (preload)  This leads to a decrease in stroke volume by the Frank-Starling mechanism and a fall in cardiac output and aortic pressure. Source: Klabunde, RE, Ventricular Pressure-Volume Relationship  This reduction in afterload (particularly aortic diastolic pressure) enables the endsystolic volume to decrease slightly, but not enough to overcome the decline in enddiastolic volume.  Therefore, because end-diastolic volume decreases more than end-systolic volume decreases, the stroke volume (shown as the width of the loop) decreases 39
    • The End, Thank you for your attention!!! Also see companion PowerPoint: Cray MI, RELATIONSHIPS BETWEEN CARDIAC OUTPUT AND VENOUS RETURN Last updated-11-13 References and suggested reading : Costanzo LS, Cardiovascular Physiology. In Physiology: with STUDENT CONSULT Online Access, 5e; Saunders 2013:189-95 Kibble JD and Halsey CR, CV Physiology, In Medical Physiology The Big Picture McGraw·Hill 2009:144-57 Klabunde RE, Ch. 4-Cardiac Function and Ch. 5-Vascular Function. In Cardiovascular Physiology Concepts.2e; LLW 2011:60-120 Tao Le T and Bhushan V, Cardiovascular, In First Aid for the USMLE Step 1 2013; McGraw·Hill 2013:254-59 40