Estimation of Stroke Volume in the Dog by a Pulse Contour Method

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Abstract
A method for estimating the stroke volume (SV) from the systolic area of a single-channel record of the central aortic pressure has been tested in 12 anesthetized open-chest dogs. The formula used was SV = K·Psa·(1 + Ts/Td), where Psa is the area under the systolic part of the curve above end-diastolic pressure, Ts and Td are the durations of systole and diastole, respectively, and K is an arbitrary constant derived from measurement of an initial SV by electromagnetic flowmeter in each dog and used thereafter without change, in that dog. In the 12 dogs, 541 simultaneous determinations of SV by the pressure contour and electromagnetic flowmeter methods were compared under normal and altered circulatory conditions employing 12 different interventions. The total range of SV was 2.4 to 28.1 ml, of heart rate 35 to 207/min, and of mean arterial pressure 24 to 166 mm Hg. The overall correlation coefficient (r) was 0.928 with a regression line y = 1.04x + 0.21 ml (SE) of estimate, ±17.4%. Except for three sympathomimetic drugs, the r values for all other interventions ranged from 0.93 to 0.99. These observations compare favorably with those of previously reported pulse contour methods. The windkessel origin of the formula is noted, and a new derivation from a modification of the "water-hammer" equation is given.

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