Comparison of pulse contour, aortic Doppler ultrasound and bioelectrical impedance estimates of stroke volume during rapid changes in blood pressure

New Findings

What is the central question of this study?

Pulse contour analysis of the finger arterial pressure by Windkessel modeling is commonly used to continuously estimate stroke volume; but, is it valid during dynamic changes in blood pressure?

What is the main finding and its importance?

Second‐by‐second analysis revealed that pulse contour analysis underestimated stroke volume by up to 25% after standing from a squat, and 16% after standing thigh cuff release when compared to aortic Doppler ultrasound estimates. These results reveal that pulse contour analysis of stroke volume should be interpreted with caution during rapid changes in physiological state.

Abstract

Dynamic measurements of stroke volume (SV) and cardiac output (Q̇) provide an index of central hemodynamics during transitional states, such as posture changes and onset of exercise. The most widely used method to assess dynamic fluctuations in SV is the Modelflow method, which uses the arterial blood pressure waveform along with age and sex specific aortic properties to compute beat‐to‐beat estimates of aortic flow. Modelflow has been validated against more direct methods in steady state conditions, but not during dynamic changes in physiological state, such as active orthostatic stress testing. The present study compared the dynamic SV responses from Modelflow (SV_MF), aortic Doppler ultrasound (SV_U/S), and bioelectrical impedance analysis (SV_BIA) during two different orthostatic stress tests, a squat‐to‐stand (S‐S) transition, and standing bilateral thigh cuff release (TCR) in 15 adults (6 females). Second‐by‐second analysis revealed that when compared to estimates of SV by aortic Doppler ultrasound, Modelflow underestimated SV by up to 25% from 3 – 11 seconds after standing from the squat position and by up to 16% from 3 – 7 seconds following TCR (P < 0.05). SV_MF and SV_BIA were similar during the first minute of the S‐S transition but were different 3 seconds after TCR, and at intermittent time points between 34 and 44 seconds (P < 0.05). These findings indicate that the physiological conditions elicited by orthostatic stress testing violate some of the inherent assumptions of Modelflow and challenge models used to interpret bioelectrical impedance responses resulting in an underestimation in SV during rapid changes in physiological state.

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