Cardiac Output

1. Cardiac Output Prof. K. Sivapalan Cardiac output

2. Cardiac output. • Stroke volume:- volume of blood pumped in one beat. • SV = End diastolic volume – End systolic volume. • Ejection fraction = stroke volume / end diastolic volume x 100 = 65 %. • Heart rate :- number of heart beats per minute. • Cardiac output is the volume of blood pumped by each ventricle in one minute. • CO is equal for both ventricles but stroke volume could vary between ventricles. Cardiac output

3. Measurement of cardiac output. • Cut aorta and collect blood • not accurate, not possible. • Dilution method. • Indocyanine green-dye • Cold water. • Inject dye or cold water into vein and monitor the concentration in arterial blood. The dye enters right heart, pulmonary circulation, left heart and into peripheral circulation. • The concentration increases rapidly and declines because of washing out from cardiac chambers, and starts rising again as it returns for the second time. • Extrapolate the decline to calculate average concentration [assuming all blood is collected] • Flow in measured time = amount injected divided by average concentration [or temperature]. • Fick principle: • Output = O2 consumed [mL/min] divided by difference between arterial and venous blood [mL/min]. • Echocardiogram Cardiac output

4. Cardiac index. • Cardiac index = cardiac output per minute per square meter body surface. • 3.2 L / min / M2. • Useful to compare individuals. Cardiac output

5. Factors affecting C.O. Cardiac output depends on, • Venous return [Frank Starling law]. • Benefit for transplant patients. • Heart rate [ventricular filling]. • Catecholamines [force of contraction]. Within physiological range, cardiac out put isnot affected by peripheral resistance. Cardiac output

6. Cardiac metabolism. • Oxygen consumption [metabolism] of • myocardium (stopped)- 2 ml / 100 g / min. • skeletal muscle 0.2 ml / 100 g / min. • Beating heart at rest- 9 ml / 100 g / min. • Energy requirement depends on, • Heart rate • Intra myocardial tension • Contractile state of myocardium • Intra myocardial tension [wall] generates intra cardiac pressure according to the law of Laplace. Cardiac output

7. Intra mural pressure and wall tension. Cardiac output

8. Contractile state of myocardium. • Sympathetic and parasympathetic impulses. • Circulating catecholamines.. • Hypoxia, hypercapnoea, acidosis. • Loss of myocardium. • Drugs- depressants and stimulants. • Intrinsic depression. Cardiac output

9. Cardiac work. • In heart, P = TW/r • [P- pressure, T-tension, W- thickness, r- radius.] • When pressure is same and radius increased, tension also increased. – disadvantage in cardiac dilatation. • But increase in thickness is beneficial. • Mechanical work per beat: =QR + MV2 / 2G [G = 9.8 g.m.] (Q-Stroke volume, R- Mean arterial pressure, M- mass of blood pumped, V- mean velocity in aorta. • R in systemic circulation is 7 times more than in pulmonary circulation. • Increase in pressure work [after load] causes higher increase in oxygen consumption than with volume work [preload]. Cardiac output