1. 2013 Cardiac output 1 Cardiac Output Prof. K. Sivapalan

2. 2013 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.

3. 2013 Cardiac output 3 Cardiac index. Cardiac index = cardiac output per minute per square meter body surface. 3.2 L / min / M 2. Useful to compare individuals.

4. 2013 Cardiac output 4 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 is not affected by peripheral resistance.

5. 2013 Cardiac output 5 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.

6. 2013 Cardiac output 6 Intra mural pressure and wall tension.

7. 2013 Cardiac output 7 Contractile state of myocardium. Sympathetic and parasympathetic impulses. Circulating catecholamines.. Hypoxia, hypercapnoea, acidosis. Loss of myocardium. Drugs- depressants and stimulants. Intrinsic depression.

8. 2013 Cardiac output 8 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 + MV 2 / 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].