Reliability of the Portable Metabolic Gas Analysis System used on the International Space Station

Abstract

Metabolic gas analysis is utilized for both research and medical operations purposes on the International Space Station (ISS). Data regarding reliability of metabolic gas analysis system used on board the ISS, the Portable Pulmonary Function System (PPFS – Danish Aerospace Corporation, Odense, DK), has not been reported. PURPOSE: To determine the reliability and intra-subject repeatability of metabolic gas analysis data collected by the PPFS. METHODS: Subjects (n=8: 5M, 3F) performed 3 peak cycle tests, consisting of three 5-min stages designed to elicit 25%, 50%, and 75% peak oxygen consumption (VO2peak) followed by stepwise increases of 25 W/min until reaching volitional exhaustion. Metabolic gas analysis was performed using the PPFS during these tests. Intraclass correlation coefficients (ICC), within-subject standard deviations (WS SD), and coefficients of variation (CV %) were calculated. RESULTS: The ICC, WS SD and CV % for peak exercise are contained in the table below. Across all exercise stages, the ICC values for oxygen consumption (VO2), carbon dioxide production (VCO2), and ventilation (VE) ranged from 0.79 to 0.99; however, the ICC for respiratory exchange ratio (RER) indicated poorer agreement between trials (ICC=0.11 to 0.51). The CV values for all dependent variables ranged from 2.6% to 6.6%, which are consistent with reported values obtained using other metabolic gas analysis devices.Table: No title available.CONCLUSIONS: The PPFS appears to yield reliable metabolic gas analysis data. Lower reliability of RER measurements are reported in the literature using other devices and is not likely a function of the PPFS. The PPFS should provide accurate and reliable data for research and monitoring of human adaptation to spaceflight.