Assessment of cardiac output from noninvasive determination of arterial pressure profile in subjects at rest

The stroke volume of the left ventricle (SV) was calculated from noninvasive recordings of the arterial pressure using a finger photoplethysmograph and compared to the values obtained by pulsed Doppler echocardiography (PDE). A group of 19 healthy men and 12 women [mean ages: 20.8 (SD 1.6) and 22.2 (SD 1.6) years respectively] were studied at rest in the supine position. The ratio of the area below the ejection phase of the arterial pressure wave (A(s)) to SV, as obtained by PDE, yielded a "calibration factor" dimensionally equal to the hydraulic impedance of the system (Zao = A(s).SV-1). The Zao amounted on average to 0.062 (SD 0.018) mmHg.s.cm-3 for the men and to 0.104 (SD 0.024) mmHg.s.cm-3 for the women. The Zao was also estimated from the equation: Zao = a.(d + b.HR + c.PP + e.MAP)-1, where HR was the heart rate, PP the pulse pressure, MAP the mean arterial pressure and the coefficients of the equation were obtained by an iterating statistical package. The value of Zao thus obtained allowed the calculation of SV from measurements derived from the photoplethysmograph only. The mean percentage error between the SV thus obtained and those experimentally determined by PDE amounted to 14.8 and 15.6 for the men and the women, respectively. The error of the estimate was reduced to 12.3 and to 11.1, respectively, if the factor Zao, experimentally obtained from a given heart beat, was subsequently applied to other beats to obtain SV from the A(s) measurement in the same subject.