We compared Modelflow (MF) estimates of cardiac stroke volume (SV) from the finger pressure-pulse waveform (Finometer) with pulsed Doppler ultrasound (DU) of the ascending aorta during acute changes in total peripheral resistance (TPR) in the supine and head-up-tilt (HUT) postures. Twenty-four women were tested during intravenous infusion of 0.005 or 0.01 microg kg(-1) min(-1) isoprenaline, 10 or 50 ng kg(-1) min(-1) noradrenaline and 0.3 mg sublingual nitroglycerine. Responses to static hand-grip exercise (SHG), graded lower body negative pressure (LBNP, from 20 to 45 mmHg) and 45 deg HUT were evaluated on separate days. Bland-Altman analysis indicated that SV(MF) yielded lower estimates than SV(DU) during infusion of 0.01 microg kg(-1) min(-1) isoprenaline (SV(MF) 92.7 +/- 15.5 versus SV(DU) 104.3 +/- 22.9 ml, P = 0.03) and SHG (SV(MF) 78.8 +/- 12.0 versus SV(DU) 106.1 +/- 28.5 ml, P < 0.01), while larger estimates were recorded with SV(MF) during 45 mmHg LBNP (SV(MF) 52.6 +/- 10.7 versus SV(DU) 46.2 +/- 14.5 ml, P = 0.04) and HUT (SV(MF) 59.3 +/- 13.6 versus SV(DU) 45.2 +/- 11.3 ml, P < 0.01). Linear regression analysis revealed a relationship (r(2) = 0.41, P < 0.01) between the change in TPR from baseline and the between-methods discrepancy in SV measurements. This relationship held up under all of the experimental protocols (regression for fixed effects, P = 0.46). These results revealed a discrepancy in MF estimates of SV, in comparison with those measured by DU, during acute changes in TPR.