Wearable sensors non-intrusively monitor cardiovascular and respiratory adaptation to simulated microgravity

The cardiovascular and respiratory systems adapt during prolonged exposure to microgravity, which often manifests as a reduction in cardiorespiratory fitness. Accordingly, these systems are the target of many exercise countermeasures to prevent physical deconditioning. Conventional assessment of these systems can be time and resource intensive. Instead, the Canadian Space Agency's Bio-Monitor wearable sensor shirt allows for continuous monitoring of cardiovascular and respiratory function, sleep characteristics, and activity levels without interfering with daily tasks. In the present study, we used the commercially available equivalent of the Bio-Monitor, Hexoskin, to measure cardiovascular and respiratory changes over two weeks of six-degree head down tilt bed rest in a group of 22 healthy older adults (11 women, age: 59 ± 3 yrs). Half of the participants were randomized into the intervention group, where they performed a total of 60-minutes daily exercise consisting of aerobic, strength, and high-intensity interval training. Participants wore the Hexoskin smart shirts for 24-hr periods during baseline data collection (BDC), head down bed rest day 1 (HDBR-1), HDBR-6, HDBR-12, and the third day of recovery (R+3). Sensor shirts were also worn during moderate-intensity exercise performed before and after bed rest. During the overnight period (22:00-06:00), mean heart rate increased progressively over the course of the bed rest and recovery for both the exercise and control groups (interaction effect: p = 0.038; BDC-Control: 62 ± 12, R+3-Control: 70 ± 8, BDC-Exercise: 56 ± 7, R+3-Exercise: 62 ± 8 beats/min). Breathing frequency while sleeping was slightly elevated (main effect of time: p < 0.001) at HDBR-1 (14.9 ± 1.7 breaths/min) and HDBR-6 (14.6 ± 1.6 breaths/min) compared to BDC (13.8 ± 1.5 breaths/min), but returned to BDC levels by HDBR-12. As expected, the mean heart rate measured by the smart shirt during moderate-intensity exercise was significantly higher (main effect of time: p < 0.001) post-bed rest (103 ± 10 beats/min) compared to BDC (94 ± 11 beats/min) for the same exercise work rate, but there was not a condition by time interaction (p = 0.244). The percent increase in mean exercising heart rate was associated with the reduction in measured peak oxygen uptake from BDC to day 2 of recovery (r = -0.643, p = 0.003). In conclusion, non-intrusive wearable sensors worn during 24-hr periods were able to detect changes in heart rate, which were indicative of a progressive reduction in cardiorespiratory fitness, and could identify subtle acute changes in breathing pattern induced by head down tilt bed rest. Interestingly, the multi-modal exercise intervention utilized in this study was ineffective at attenuating the bed rest-induced increase in heart rate in this group of older adults. Moving forward, small wearable technology, such as the Hexoskin on Earth and Bio-Monitor in space, appear to be valuable tools for investigating spaceflight-induced adaptions and the effectiveness of deconditioning countermeasures, as well as more broadly for remote tracking of cardiorespiratory health. Supported by Canadian Institutes of Health Research and Canadian Space Agency.