Finger-to-brachial comparability of 'modelflow' stroke volume improves after pulsewave reconstruction

Abstract

Modelflow is a method that determines stroke volume (SV) from central or peripheral continuous blood pressure signals. Pulsewaves are changed along the arterial tree; distortion occurs as the mean pressure level gradually declines. These changes might jeopardize the determination of SV from a distal measurement site. Techniques have been assessed to reconstruct brachial artery pressures (BAPs) from non-invasive finger blood pressure (FIN) waveforms. In this study, we determined the effect of different forms of brachial reconstruction techniques on the comparability of modelflow SV from FIN and BAP. Supine resting FIN and BAP were measured simultaneously in 57 subjects, covering a wide range of blood pressures and degrees of vascular disease. SV from the two sites were compared before correction and after correction for pulsewave distortion or pressure gradient. The latter was determined by a regression formula and by a return to flow (RTF) method, using the brachial cuff pressure at the moment of reappearance of FIN during cuff deflation. SV from unfiltered FIN exceeded BAP-derived SV by 4.6 (SD 11) ml. This difference was positively related to the subjects' age. Correction for pulsewave distortion increased the average difference to 13 (12) ml (P < 0.05 to the unfiltered condition). Adjustment for the pressure gradient reduced the difference to -2.5 (7) ml (P < 0.01). RTF had no additional effect. We concluded that the FIN-to-BAP comparability can be increased by brachial reconstruction techniques, which correct for the pressure gradient. This can be adequately performed without additional measurements, allowing its application to measurements already taken.