CARDIOVASCULAR PHYSIOLOGY

Moderator: Dr Shaila S. Kamath

Presenter :Samiksha Khanooja

Cardiac cycle

JVP

Myocardial action potential

Coronary circulation

OVERVIEW:

Modern concept of circulation & heart as generator of

circulation was advanced by Harvey in 1628.

Field of cardiac physiology has developed to include

• physiology of heart as pump

• cellular & molecular biology of cardiomyocyte, &

• regulation of cardiac function by neural & humoral

factors

INTRODUCTION

Basic anatomy of heart consists of 2 atria & 2 ventricles - provide 2 separate circulations in series.

Pulmonary circulation, low-resistance & high-capacitance vascular bed, receives output from right side heart, chief function - bidirectional gas exchange.

Systemic circulation, high resistance, receives output from left side heart & provides output for systemic circulation, delivers O2, nutrients & removes CO2 & metabolites from tissue beds.

Cont..

CARDIAC CYCLE Sequence of electrical & mechanical events during

course of single heart beat.

1. Electrical events represented by ECG

2. Mechanical events represented by left atrial & left

ventricular pressure pulses correlated in time with

aortic flow & ventricular volume

PHYSIOLOGY OF INTACT HEART

Electrical events of pacemaker & specialized

conduction system are represented by ECG at body

surface & is result of differences in electrical potential

generated by heart at sites of surface recording.

ELECTRICAL EVENTS AND THE ECG

P wave action potential initiated at SA node is

propagated to both atria by specialized conduction

tissue, it leads to atrial systole (contraction) & P wave

of ECG

P-R interval.. PR interval can be used to measure

delay between atrial & ventricular contraction at

level of AV node

Cont..

From distal His bundle, electrical impulse propagated through left & right bundle branches finally to Purkinje system fibers

Electrical signals are transmitted from Purkinje system to individual ventricular cardiomyocytes.

Cont..

Spread of depolarization to ventricular myocardium

is manifested as QRS complex on ECG.

Depolarization is followed by ventricular

repolarization and appearance of T wave on ECG.

Cont..

LATE DIASTOLE

Mitral & tricuspid valves - open, aortic & pulmonary

valves -closed

Blood flows into heart throughout diastole

Rate of filling declines as ventricles become

distended, —especially when heart rate is low—

cusps of AV valves drift toward closed position

Pressure in ventricles remains low

MECHANICAL EVENTS

Atrial Systole

It pumps additional blood into ventricles, but about

70% of ventricular filling occurs passively during

diastole Contraction of atrial muscle that surrounds the

orifices of SVC,IVC & pulmonary veins narrows

their orifices; however, there is some regurgitation

of blood into veins during atrial systole

Cont..

Ventricular Systole

Mitral & tricuspid valves close

Intraventricular pressure rises sharply as myocardium presses on blood in ventricle .

Cont..

This isovolumetric (isovolumic, isometric) ventricular contraction lasts about 0.05 s, until pressures in left & right ventricles exceed pressures in aorta (80 mm Hg ) & pulmonary artery (10 mm Hg) & aortic & pulmonary valves open

AV valves bulge into atria, causing a sharp rise in atrial pressure

Cont..

When aortic pulmonary valves open, phase of ventricular ejection begins

Rapid at first, slowing down as systole progresses.

Intraventricular pressure rises to a maximum ,then declines before ventricular systole ends

Peak left ventricular pressure is about 120 mm Hg, & peak right ventricular pressure is 25 mm Hg or less

Cont..

Late in systole, the aortic pressure actually exceeds

the ventricular, but for a short period momentum

keeps the blood moving forward

The AV valves are pulled down by the contractions of

the ventricular muscle, and atrial pressure drops

Cont..

Amount of blood ejected by each ventricle per stroke at rest is 70–90 mL.

End-diastolic ventricular volume is about 130 mL. Thus, about 50 mL of blood remains in each

ventricle at end of systole (end-systolic ventricular volume), the ejection fraction, percent of EDVV-that is ejected with each stroke, is about 65%.

Ejection fraction is a valuable index of ventricular function.

Cont..

Early Diastole Once ventricular muscle is fully contracted,already

falling ventricular pressures drop more rapidly This is the period of protodiastole ,lasts about 0.04sec,

ends when aortic & pulmonary valves close

After the valves close, pressure continues to drop rapidly during isovolumetric ventricular relaxation

Cont..

Isovolumetric relaxation ends when ventricular pressure falls below atrial pressure & AV valves open, permitting ventricles to fill

Filling -rapid at first, then slows as next cardiac contraction approaches

Atrial pressure continues to rise after the end of ventricular systole until AV valves open, then drops and slowly rises again until next atrial systole

Cont..

Length of Systole & Diastole

Cardiac muscle has unique property of contracting & repolarizing faster when heart rate is high

Duration of systole decreases from 0.27 s at a heart rate of 65 to 0.16 s, diastole from 0.62sec to 0.14 sec at a rate of 200 beats/min

THUS, duration of systole is much more fixed than diastole, & when heart rate is increased, diastole is shortened to much greater degree

Cont..

This fact has important physiologic and clinical implications

It is during diastole that heart muscle rests, and coronary blood flow to the subendocardial portions of the left ventricle and most of the ventricular filling occurs

Cont..

At heart rates up to about 180, filling is adequate as long as there is ample venous return, and cardiac output per minute is increased by an increase in rate

At very high heart rates, filling may be compromised such that cardiac output per minute falls and symptoms of heart failure develop

Cont..

JVP is a vertical height from sternal angle to zone of transition of distended & collapsed IJV’s

Patient reclining at 45 degree,it is normally 4-5cm It is an indicator of right mean atrial pressure. It is the reflection of phasic pressure changes in right

atrium Consists of three positive waves (a,c,v) and two

negative troughs(x,y)

JUGULAR VENOUS PRESSURE(JVP)

JVP wave forms

a wave depicts atrial contraction(atrial systole)

c wave depicts bulging of tricuspid valve into the atria (isovolumetric contraction)

x descent shows atrial relaxation(ventricular systole)

v wave venous filling,(isovolumetric relaxation)

y descent indicates atrial emptying(ventricular filling)

Cont..

The types of action potential in the heart can be separated into two categories:

fast-response action potentials, which are found in the His-Purkinje system and atrial or ventricular cardiomyocytes,

and Slow response action potentials, which are found in the

pacemaker cells in the SA and AV nodes

MYOCARDIAL ACTION POTENTIAL

Fast response action potential

Phase 0 – Depolarization ( Na influx) Phase 1 -Transient repolarization(activation of

transient outward K+ current) Phase 2 -Plateau phase(net influx of Ca2+ through L-

type calcium channels efflux of K+ through K+ channels

Phase 3 -Repolarization(when efflux of K+ from 3 outward K+ currents exceeds the influx of Ca2+)

Phase 4 -Diastole(little ionic changes)

Cont..

Action potentials in SA & AV nodes are largely due

to Ca+, with little contribution by Na influx

So there is no sharp rapid depolarization spike before

plateau,as in other parts of conduction system

When compared with fast-response action potential,

phase 0 is much less steep, phase 1 is absent, phase

2 is indistinct from phase 3

Slow Response Action Potential

Cont..

ANATOMY RCA and LCA RCA - rt atrium, most of rt ventricle & inferior wall

of left ventricle In 85% cases,RCA gives rise to posterior descending

artery(superior posterior IVS & inferior wall)-Rt Dominant Circulation

CORONARY CIRCULATION

LCA –left atrium, most of interventricular septum, left ventricle

Bifurcates into left anterior descending(septum &anterior wall) and circumflex artery(lateral wall)

SA node-RCA(60%), LAD(40%) AV node-RCA(85%),circumflex(15%) Bundle of His-PDA,LAD

Cont..

Difference between aortic & ventricular pressure CPP= arterial diastolic pressure – LVEDP Decrease in aortic pressure ,increase in VEDP

reduces CPP Increase in heart rate also decrease CPP(because of

reduction in diastolic time) Endocardium-most vulnerable to ischemia

Determinants of Coronory Perfusion

Parallels myocardial metabolic demand Approx 250ml/min at rest Myocardium regulates its own blood flow between

perfusion pressures 50 &120mm Hg Changes in blood flow mainly due to coronary

arterial tone Hypoxia cause vasodilation(directly or by adenosine

release) Sympathetic stimulation increases myocardial blood

flow

Control of Coronary Blood Flow

Most important determinant of myocardial blood flow

Myocardium extracts 65% of oxygen in arterial blood, compared with 25% in other tissues

Coronary sinus saturation -30% Myocardium cannot compensate for blood flow

reductions by extracting more O2 from Hb Increase in demand must be met by increase in CBF

Myocardial Oxygen Balance