Cardiac Output Prof. K. Sivapalan 2013 Cardiac output

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. 2013 Cardiac output

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 2013 Cardiac output

Cardiac index. Cardiac index = cardiac output per minute per square meter body surface. 3.2 L / min / M2. Useful to compare individuals. 2013 Cardiac output

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. 2013 Cardiac output

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. 2013 Cardiac output

Intra mural pressure and wall tension. 2013 Cardiac output

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

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]. 2013 Cardiac output