Modelflow estimates of cardiac output compared with Doppler ultrasound during acute changes in vascular resistance in women

We compared Modelflow (MF) estimates of cardiac stroke volume (SV) from the finger pressure-pulse waveform (Finometer (R)) 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 mu g 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 SVMF yielded lower estimates than SVDU during infusion of 0.01 mu g kg-1 min-1 isoprenaline (SVMF 92.7 +/- 15.5 versus SVDU 104.3 +/- 22.9 ml, P = 0.03) and SHG (SVMF 78.8 +/- 12.0 versus SVDU 106.1 +/- 28.5 ml, P < 0.01), while larger estimates were recorded with SVMF during -45 mmHg LBNP (SVMF 52.6 +/- 10.7 versus SVDU 46.2 +/- 14.5 ml, P = 0.04) and HUT (SVMF 59.3 +/- 13.6 versus SVDU 45.2 +/- 11.3 ml, P < 0.01). Linear regression analysis revealed a relationship (r2 = 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.