Pulse contour methods to estimate cardiovascular indices in micro- and hypergravity.

Background: The importance of noninvasive health monitoring in space increased as a result of the long-duration missions on the International Space Station (ISS). In order to monitor changes in cardiovascular indices such as cardiac output (CO) and total peripheral resistance (TPR), many methods have been developed using signal processing and mathematical modeling techniques. However, their performance in various gravitational conditions has not been known. Methods: The present study compared 10 methods to estimate CO and TPR by processing peripheral arterial blood pressure signals recorded from 8 subjects in multiple gravity levels (1 G, 0 G, and 1.8 G) during parabolic flights. For reference data sets, CO and TPR were simultaneously obtained by an inert gas rebreathing technique. Root normalized mean square errors and Bland-Altman plots were used to evaluate the estimation methods. Results: The corrected impedance method achieved the lowest estimation errors (20.0% CO error and 23.5% TPR error) over the three gravity levels. In microgravity, mean arterial pressure was also demonstrated to be an indicator of CO (24.5% error). Discussion: The corrected impedance method achieved low estimation errors for a wide range of the gravity levels. Gravity-dependent performance was observed in the mean arterial pressure method that achieved low errors in the short-term 0 G.