Noninvasive assessment of cardiac output from arterial pressure profiles during exercise

Abstract

The stroke volume of the left ventricle (SV) was assessed in nine young men (mean age 22.2, ranging from 20 to 25 years) during cycle ergometer upright exercise at exercise intensities from 60 to 150 W (about 20% to 80% of individual maximal aerobic power). The SV was calculated from noninvasive tracings of the arterial blood pressure, determined from photoplethysmograph records and compared to the SV determined simultaneously by pulsed Doppler echocardiography (PDE). Given the relationship SV = As.Z-1 in which A(s) is the area underneath the systolic pressure profile (in millimetres of mercury and second), and Z (in millimetres of mercury and second per millilitre) is the apparent hydraulic impedance of the circulatory system, a prerequisite for the assessment of SV from the photoplethysmograph tracings is a knowledge of Z. The experimental value of Z (hereafter defined Z*) was calculated by dividing A(s) (from the finger photoplethysmograph) by SV as obtained by PDE. When the whole group of subjects was considered, Z* was not greatly affected by the exercise intensity: it amounted to 0.089 (SD 0.028; n = 36). The Z was also estimated independently of any parameter other than heart rate (HR), mean (MAP) and pulse (PP) arterial blood pressure obtained from the photoplethysmograph. A computerized statistical method allowed us to interpolate the experimental values of Z*, HR, PP and MAP by the equation Zm = a.(b + c.HR + d.PP + e.MAP)-1, thus obtaining the coefficients a to e. The mean percentage error between Zm (calculated from the coefficients obtained and Z* was 21.8 (SD 14.3)%. However, it was observed that, in a given subject, Z* was significantly affected by the exercise intensity. Therefore, to improve the estimate of Z a second algorithm was developed to update the experimental value of Z determined initially at rest (Zin). This updated value (Zcor) of Z was calculated as Zcor = Zin. [(f/(i + g.(HR/HRin) + h.(PP/PPin) + 1.(MAP/MAPin)], where HRin, PPin, MAPin, HR, PP, MAP are the above parameters at rest and during exercise, respectively. Also in this case, the coefficients f to 1 were determined by a computerized statistical method using Z* as the experimental reference. The values of Zcor so obtained allowed us to calculate SV from arterial pulse contour analysis as SVF = As.Z-1cor. The mean percentage error between the SVF obtained and the values simultaneously determined by PDE, was 10.0 (SD 8.7)%. It is concluded that the SV of the left ventricle, and hence cardiac output, can be determined during exercise from photoplethysmograph tracings with reasonable accuracy, provided that an initial estimate of SV at rest is made by means an independent high quality reference method.

Effects of prolonged bed rest on cardiovascular oxygen transport during submaximal exercise in humans

“…For computation of c at the steady state of exercise at 100-W, the algorithm provided by Antonutto et al (1995) was used. This algorithm relies on the calibration of the pulse pressure area made at rest.…”

“…The former was measured continuously by electrocardiography. The latter was measured using the pressure pulse contour method (Antonutto et al 1995). For this purpose, continuous monitoring of the arterial blood pressure pro®le was obtained using a Finapres device (Ohmeda, USA).…”

Beat-to-beat noninvasive stroke volume from arterial pressure and Doppler ultrasound

“…In clinical practice a measure of CO is preferably continuous and non-invasive. Non-invasive continuous tracking of changes in SV by ultrasound (US) and arterial pulse wave analysis (Jansen et al 1990;Antonutto et al 1994Antonutto et al , 1995 have the potential to appreciate the importance of systemic blood flow. A general shortcoming with respect to the validation of beat-to-beat tracking of SV is that it is based on a comparison with conventional measurements of SV such as thermodilution-based estimates or inert gas rebreathing which are obtained as averages over at least some 20 heart beats (Hamilton 1948).…”

Cardiovascular deconditioning in microgravity: some possible countermeasures

“…The most relevant findings are the decreases of the stroke volume (SV, ml), of the ventricular end-diastolic volume and of the estimated left ventricular mass (Henry et al 1977;Charles and Lathers 1991). A substantial fall of SV after Space flight in two subjects participating to the Euromir '94 mission was also observed utilizing together CO 2 -rebreathing (Fahri et al 1976) and pulse contour (Antonutto et al 1994(Antonutto et al , 1995 methods (Antonutto et al, unpublished observation). Indeed, 2 days after reentry to Earth (R+2) from 31 days of Space flight, in one subject SV was reduced by 17%.…”