cardiovascular physiology g... · 2011-07-05 · contents the following presentation will address...
TRANSCRIPT
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Kostadin Kichukov, Genadi KaninskiDepartment Cardiology and Angiology
Tokuda Hospital – Sofia
Head: Ass. Prof. Ivo Petrov, MD, PhD
Cardiovascular Physiology
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Contents
The following presentation will address the following key elements in cardiovascular physiology:
– Electrophysiology of the heart
– Principles of cardiac mechanics
– Factors influencing cardiac performance
– Cardiac coronary reserve and its regulation
– Unbalances of cardiac output
– Specific conditions
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Electrophysiology
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SA node action potential
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Cardiomyocite action potential
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Sequence of Excitation
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Sequence of Excitation
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Cardiac Mechanics
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Cardiac CycleSystole:1. Isovolumic contraction2. Ejection
Diastole:3. Relaxation
• Early Isovolumetric4. Filling
• Early, rapid• Late, diastasis
Key definitions and values:• (EDV) in the ventricle about
120mL• SV at rest is about 80mL
(47mL/m2 body surface)• Mean ejection fraction
(SV/EDV) at rest is about 0.67.• (ESV) is about 40mL
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Work diagram of the heart (left ventricle)
•The work diagram of the heart can be constructed by plotting the changes in ventricular pressure over volume during one complete cardiac cycle
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The good old Frank-Starling Law
• The heart autonomously responds to changes inventricular volume load or aortic pressure loadby adjusting the stroke volume (SV) inaccordance with the myocardial preload (restingtension). The Frank-Starling Mechanism (FSM)also functions to maintain an equal SV in bothventricles to prevent congestion in thepulmonary or systemic circulation
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Frank-Starling Law of the Heart
Preload, or degree of stretch, of cardiac muscle cellsbefore they contract is the critical factor controllingstroke volume; EDV leads to stretch of myocardium.– preload stretch of muscle force of contraction SV– Unlike skeletal fibers, cardiac fibers contract MORE FORCEFULLY when
stretched thus ejecting MORE BLOOD ( SV)
– If SV is increased, then ESV is decreased!!
Slow heartbeat and exercise increase venous return (VR)to the heart, increasing SV– VR changes in response to blood volume, skeletal muscle
activity, alterations in cardiac output
– VR EDV and in VR in EDV
– Any in EDV in SV
Blood loss and extremely rapid heartbeat decrease SV
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Preload change
• When the volume load(preload) increases, thestart of isovolumiccontraction shifts to theright along the passive P–Vcurve (1, from point A topoint A1). This increasesend-diastolic volume (EDV),stroke volume (SV), cardiacwork and end-systolicvolume (ESV) (A).
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Afterload change
• When the aortic pressure load(afterload) increases, the aorticvalve will not open until thepressure in the left ventricle hasrisen accordingly (A2, point Dt).Thus, the SV in the shorttransitional phase (SVt) willdecrease, and ESV will rise (ESVt).Consequently, the start of theisovolumic contraction shifts to theright along the passive P–V curve(A2, point A2). SV will thennormalize (SV2) despite theincreased aortic pressure (D2),resulting in a relatively largeincrease in ESV (ESV2).
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Effects of pretension (preload), heart rate and sympathetic stimuli on myocardial force
and contraction velocity
While changes in the preload only affect the force of contraction (1), changes incontractility also affect the velocity of contraction (2). The steepest increase inisovolumic pressure per unit time (maximum dP/dt) is therefore used as a measureof contractility in clinical practice. dP/dt is increased E and NE and decreased bybradycardia (B2) or heart failure.
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Cardiac Output (CO) and Cardiac Reserve
CO is the amount of blood pumped by each ventricle in one minute
CO is the product of heart rate (HR) and stroke volume (SV)
CO = HR x SV
(ml/min) = (beats/min) x ml/beat
HR is the number of heart beats per minute
SV is the amount of blood pumped out by a ventricle with each beat
Cardiac reserve is the difference between resting and maximal CO
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Factors Affecting Cardiac Output
Figure 20.20
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Unbalanced Ventricular Output
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Coronary blood flow
2/3 of coronary blood supply is provided through heart diastole;
Oxygen extraction in myocardium is at its maximal rate even at rest. SatO2 at the coronary sinus is 25 – 35%
Increased oxygen needs could only be supported by increased coronary blood flow
Coronary blood flow at rest – 1.0 +/- 0.2 ml/g myocardium tissue/min
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Coronary reserve
The ability of the coronary arteries to increasethe blood flow reaching the myocardium inresponse to increased oxygen demand is calledcoronary reserve.
Coronary blood flow increase with increased HR,contractility and wall stress.
Coronary reserve could reach 3 – 5 times thebasal coronary blood flow mainly due tovasodialtion of resistive vessels (< 300 mcm).
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Balance between demand and supply
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Coronary blood flow in CAD (stenoses of epicardial vessels)
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Coronary blood flow in CAD(stenoses of epicardial vessels and microvascular disease)
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Conditions of special interest
Cardiomyopathies
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Hypertrophic cardiomyopathy
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Hypertrophic cardiomyopathy
• Most common location: subaortic , septal, and ant. wall.
• Asymmetric hypertrophy (septum and ant. wall): 70 %.
• Basal septal hypertrophy: 15- 20 %.• Concentric LVH: 8-10 %.• Apical or lateral wall: < 2 % (25 % in
Japan/Asia): characteristic giant T-wave inversion laterally & spade-like left ventricular cavity: more benign.
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Hypertrophic cardiomyopathy
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Hypertrophic cardiomyopathy
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Hypertrophic cardiomyopathy
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Hypertrophic cardiomyopathy
Dynamic LV outflow tract obstruction
Diastolic dysfunction
Myocardial ischemia
Mitral regurgitation
Arrhythmias
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Restrictive cardiomyopathy
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Restrictive cardiomyopathy
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Restrictive cardiomyopathy
Hallmark: abnormal diastolic function
The characteristic feature of restrictive cardiomyopathy is amarked increased stiffness of the myocardium orendocardium, which causes the ventricular pressure to risedramatically with only small changes in volume, causing anupward shift of the left ventricular pressure/volumerelationship and a dip-and-plateau or square roothemodynamic pattern
Bears some functional resemblance to constrictivepericarditis
importance lies in its differentiation from operableconstrictive pericarditis
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Restrictive cardiomyopathy
Cardiac catheterization - LVEDP often >5 mm Hg greater than RVEDP, but may be identical. RV systolic pressure >50 mm HgRVEDP less than one-third of RV systolic pressure
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Dilated cardiomyopathy
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Dilated cardiomyopathy
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Dilated cardiomyopathy
• Symptoms of heart failure
• pulmonary congestion (left HF)dyspnea (rest, exertional, nocturnal), orthopnea
• systemic congestion (right HF)edema, nausea, abdominal pain, nocturia
• low cardiac outputfatigue and weakness
• hypotension, tachycardia, tachypnea, JVD
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Pericardial Disease
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Pericardial effusion
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Pericardial effusion
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Constrictive pericarditis
Cardiac Catheterization – Gold standard for diagnosis. RVEDPand LVEDP usually equal. With inspiration - Increase in RVsystolic pressure and decrease in LV systolic pressure. Withexpiration, opposite changes
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Valvular Disease
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Aortic stenosis
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Aortic regurgitation
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Mitral stenosis
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Mitral regurgitation
MR causes LV and left atrialvolume overload. The degree ofvolume overload depends on theregurgitant volume. Theregurgitant volume is determinedby the size of the regurgitantorifice area (ROA), the durationof systole and the systolicpressure gradient between theleft ventricle and left atrium.
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Mitral regurgitation
Initially, as the severity of MR increases there is progressiveenlargement of the left atrium and left ventricle tocompensate for the regurgitant volume. LV dilatation occursas a result of remodeling of the extracellular matrix withrearrangement of myocardial fibers, in association with theaddition of new sarcomeres in series and the development ofeccentric LV hypertrophy. In patients with severe, chronic MR,the left atrium is markedly dilated and atrial compliance isincreased. Although there is fibrosis of the atrial wall, leftatrial pressure can be normal or only slightly elevated.
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Thank you for the attention