Key result
Pulse contour analysis failed to track the 46% increase in cardiac output during spaceflight measured by the rebreathing method (5.91 vs 7.00 l/min inflight; P<0.001 for interaction).
Why the study?
Does pulse contour analysis accurately track changes in cardiac output compared to rebreathing during human spaceflight in healthy male astronauts?
Observational (n=9)
Does pulse contour analysis accurately track changes in cardiac output compared to rebreathing during human spaceflight in healthy male astronauts?
Pulse contour analysis fails to accurately track the increase in cardiac output measured by rebreathing during human spaceflight, likely due to changes in vascular compliance.
Modelflow underestimates Q̇ changes in microgravity; leaves open validation of noninvasive monitoring for spaceflight.
Pulse contour analysis of the noninvasive finger arterial pressure waveform provides a convenient means to estimate cardiac output (Q̇). The method has been compared with standard methods under a range of conditions but never before during spaceflight. We compared pulse contour analysis with the Modelflow algorithm to estimates of Q̇ obtained by rebreathing during preflight baseline testing and during the final month of long-duration spaceflight in nine healthy male astronauts. By Modelflow analysis, stroke volume was greater in supine baseline than seated baseline or inflight. Heart rate was reduced in supine baseline so that there were no differences in Q̇ by Modelflow estimate between the supine (7.02 ± 1.31 l/min, means ± SD), seated (6.60 ± 1.95 l/min), or inflight (5.91 ± 1.15 l/min) conditions. In contrast, rebreathing estimates of Q̇ increased from seated baseline (4.76 ± 0.67 l/min) to inflight (7.00 ± 1.39 l/min, significant interaction effect of method and spaceflight, P < 0.001). Pulse contour analysis utilizes a three-element Windkessel model that incorporates parameters dependent on aortic pressure-area relationships that are assumed to represent the entire circulation. We propose that a large increase in vascular compliance in the splanchnic circulation invalidates the model under conditions of spaceflight. Future spaceflight research measuring cardiac function needs to consider this important limitation for assessing absolute values of Q̇ and stroke volume. NEW & NOTEWORTHY Noninvasive assessment of cardiac function during human spaceflight is an important tool to monitor astronaut health. This study demonstrated that pulse contour analysis of finger arterial blood pressure to estimate cardiac output failed to track the 46% increase measured by a rebreathing method. These results strongly suggest that alternative methods not dependent on pulse contour analysis are required to track cardiac function in spaceflight.
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Hughson et al. (2017) conducted an observational in Healthy astronauts during spaceflight (n=9). Pulse contour analysis (Modelflow algorithm) vs. Rebreathing method was evaluated on Cardiac output (Q̇) during spaceflight (p=<0.001). Pulse contour analysis failed to track the 46% increase in cardiac output during spaceflight measured by the rebreathing method (5.91 vs 7.00 l/min inflight; P<0.001 for interaction).
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