Noninvasive cardiac output measurement in orthostasis: pulse contour analysis compared with acetylene rebreathing

Academic Medical Center, Department of Physiology, University of Amsterdam, 1105AZ Amsterdam, The Netherlands We tested the reliability of noninvasive cardiac output (CO) measurement in different body positions by pulse contour analysis (CO pc ) by using a transmission line model (K. H. Wesseling, B. De Wit, J. A. P. Weber, and N. T. Smith. Adv. Cardiol. Phys. 5, Suppl. II: 16-52, 1983). Acetylene rebreathing (CO rebr ) was used as a reference method. Twelve subjects (age 21-34 yr) were studied: 1 ) six in whom CO rebr and CO pc were measured in the standing and 6° head-down tilt (HDT) postures and 2 ) six in whom CO was measured in the 30° HDT, supine, 30° head up-tilt (HUT), and 70° HUT postures on a tilt table. The CO rebr -to-CO pc ratio in (near) the supine position during rebreathing was used as the calibration factor for CO pc measurements. Calibrated CO pc (CO cal sup ) consistently overestimated CO in the upright posture. The drop in CO with upright posture was underestimated by ~50%. CO cal sup and CO rebr values did not differ in the 30° HDT position. Changes in the CO rebr -to-CO pc ratio are highly variable among subjects in response to a change in posture. Therefore, CO pc must be recalibrated for each subject in each posture. Finapres; stroke volume; blood pressure; tilt; standing