Estimation of beat-to-beat changes in stroke volume from arterial pressure: a comparison of two pressure wave analysis techniques during head-up tilttesting in young, healthy men

Objective: The aim of this study was to compare beat-to-beat changes in str oke volume (SV) estimated by two different pressure wave analysis technique s during orthostatic stress testing: pulse contour analysis and Modelflow, ie, simulation of a three-element model of aortic input impedance. Methods: A reduction in SV was introduced in eight healthy young men (mean age, 25; range, 19-32 y) by a 30-minute head-up tilt maneuver. Intrabrachia l and noninvasive finger pressure were monitored simultaneously. Beat-to-be at changes in SV were estimated from intrabrachial pressure by pulse contou r analysis and Modelflow. In addition, the relative differences in Modelflo w SV obtained from intrabrachial pressure and noninvasive finger pressure w ere assessed. Results: Beat-to-beat changes in Modelflow SV from intrabrachial pressure w ere comparable with pulse contour measures. The relative difference between the two methods amounted to 0.1 +/- 1% (mean +/- SEM) and was not dependen t on the duration of tilt. The difference between Modelflow applied to intr abrachial pressure and finger pressure amounted to -2.7 +/- 1.3% (p = 0.04) . This difference was not dependent on the duration of tilt or level of art erial pressure. Conclusions: Based on different mathematical models of the human arterial s ystem, pulse contour and Modelflow compute similar changes in SV from intra brachial pressure during orthostatic stress testing in young healthy men. T he magnitude of the difference in SV derived from intrabrachial and finger pressure may vary among subjects; Modelflow SV from noninvasive finger pres sure tracks fast and brisk changes in SV derived from intrabrachial pressur e.