Blood Flow Measurement:The Cardiac Output and Vascular Resistance Grossman’s cardiac catheterization, angiography, and intervention CV R5 許志新醫師 Supervisor: 趙庭興醫師

Cardiac Output The maintenance of blood flow commensurate with the metabolic needs of the body is a fundamental required of human life The quantity of blood delivered to the systemic circulation per unit time is termed the cardiac output

Arteriovenous difference and extraction reverse The extraction of a given nutrient from the circulation is expressed arteriovenous difference. The factor by which arteriovenous can increase at constant flow is termed extraction reverse. The normal extraction reserve for oxygen is 3.

Lower limit of cardiac output Fall in resting cardiac output to below one- third of normal ( CI < 1) is incompatible with life.

Upper limit of cardiac output Largest increase in cardiac output can be achieved by a trained athlete at maximal exercise is 600 % of the resting output.

Factors Influencing Cardiac Output in Normal subjects Body area Age Posture Body temperature Anxiety Environmental heat and humidity

Techniques for Determination of Cardiac output Fick oxygen technique Indicator dilution technique

Fick Oxygen Method Cardiac output = oxygen consumption / arteriovenous oxygen difference

Oxygen Consumption

Oxygen consumption may be measured using the metabolic rate meter. VO 2 =( F R O 2 x V R ) - ( F M O 2 x V M ) V M =V R - V i + V e VO 2 =V M ( F R O 2 - F M O 2 ) + F R O 2 ( V i - V e ) VO 2 = V M (0.209-F M O 2 ) ( V i - V e ) VO 2 = 0.01 V M ( V i - V e )

Arteriovenous Oxygen Difference

Sources of error Improper collection of the mixed venous sample is a common source of error The total error is about 10 % Resting O2 consumption is 125 mL/m 2, or 110 mL/m 2 for older patients

Indicator Dilution Methods Injected indicator ( indocyanine green dye) into proximal vessel or chamber then continued indicator concentration from the injected area to radial or femoral artery.

Thermodilution Method Does not require withdrawl of blood Does not require an artery puncture An inert and inexpensive indicator No recirculation and makes computer analysis simple

Source of Error Unreliable in significant tricuspid regurgitation Baseline temperature of blood in the pulmonary artery fluctuations with respiratory and cardiac cycle Overestimation cardiac output in patients with low cardiac output

Poiseuille’s Law

Estimation of Vascular Resistance in the Clinical Situation Systemic vascular resistance =( mean systemic pressure - mean RA pressure) /Qs Total pulmonary resistance = mean pulmonary pressure / Qp Pulmonary vascular resistance = mean pulmonary pressure - mean LA pressure / Qp SVRI equals SVR multiplied by BSA

Normal Values for vascular Resistance

Clinical Use of Vascular Resistance Low values for measured vascular resistance are commonly seen in patients with severe chronic anemia

Systemic Vascular Resistance Hypotension or reduced cardiac output generally triggers increased systemic vascular resistance, but these influences may be opposed if decreased tissue perfusion with local hypoxia and acidosis

Pulmonary Vascular Resistance Increased by hypoxia, hypercapnia, increased sympathetic tone, polythemia, serotonin, pulmonary emboli, pulmonary edema, lung compression. Decreased by oxygen, adenosine, isoproterenol, alpha antagonists, prostacyclin infusion, high dose of CCB

Pulmonary Vascular Disease in Patients with Congenital Central Shunts PVR/SVR is used as a criterion for operability in dealing with congenital heart disease Normally, this ratio is less than or equal to 0.25 Surgical correction of the congenital defect is considered contraindication when PVR/SVR equals 1.0 or more

Pulmonary Vascular Disease in Patients with Mitral Stenosis Marked elevations in pulmonary vascular resistance may also been seen in mitral stenosis. Most patients experience significant reduction in pulmonary vascular resistance following successful repair.

Assessment of Vasodilator Drugs Low cardiac output with high ventricular filling pressure and systemic vascular resistance, vasodilator might be beneficial. Low cardiac output with high vascular resistance and normal filling pressure, selective lowering of resistance would be desirable. Low cardiac output with normal resistance,combined inotrophic agent and nitrate may be helpful.