Cardiac Output Prof K Sivapalan 2013 Cardiac output

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Cardiac Output Prof. K. Sivapalan 2013 Cardiac output 1

Cardiac Output Prof. K. Sivapalan 2013 Cardiac output 1

Cardiac output. • Stroke volume: - volume of blood pumped in one beat. •

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 2

Measurement of cardiac output. • Cut aorta and collect blood – not accurate, not

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 = O 2 consumed [m. L/min] divided by difference between arterial and venous blood [m. L/min]. • Echocardiogram 2013 Cardiac output 3

Cardiac index. • Cardiac index = cardiac output per minute per square meter body

Cardiac index. • Cardiac index = cardiac output per minute per square meter body surface. • 3. 2 L / min / M 2. • Useful to compare individuals. 2013 Cardiac output 4

Factors affecting C. O. Cardiac output depends on, Ø Venous return [Frank Starling law].

Factors affecting C. O. Cardiac output depends on, Ø Venous return [Frank Starling law]. ØBenefit for transplant patients. Ø Heart rate [ventricular filling]. Ø Catecholamines [force of contraction]. Within physiological range, cardiac out put is not affected by peripheral resistance. 2013 Cardiac output 5

Cardiac metabolism. • Oxygen consumption [metabolism] of – myocardium (stopped)- 2 ml / 100

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 6

Intra mural pressure and wall tension. 2013 Cardiac output 7

Intra mural pressure and wall tension. 2013 Cardiac output 7

Contractile state of myocardium. • Sympathetic and parasympathetic impulses. • Circulating catecholamines. . •

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 8

Cardiac work. • In heart, P = TW/r – [P- pressure, T-tension, W- thickness,

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 / 2 G [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 9