Download - Cvs physio
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