Short-Term Cardiovascular Response to Short-Radius Centrifugation With and Without Ergometer Exercise

Abstract

Artificial gravity (AG) has often been proposed as an integrated multi-system countermeasure to physiological deconditioning associated with extended exposure to reduced gravity levels, particularly if combined with exercise. Twelve subjects underwent short-radius centrifugation along with bicycle ergometry to quantify the short-term cardiovascular response to AG and exercise across three AG levels (0 G or no rotation, 1 G, and 1.4 G; referenced to the subject’s feet and measured in the centripetal direction) and three exercise intensities (25, 50, and 100 W). Continuous cardiovascular measurements were collected during the centrifugation sessions using a non-invasive monitoring system. The cardiovascular responses were more prominent at higher levels of AG and exercise intensity. In particular, cardiac output, stroke volume, pulse pressure, and heart rate significantly increased with both AG level (in most of exercise group combinations, showing averaged increments across exercise conditions of 1.4 L/min/g, 7.6 mL/g, 5.22 mmHg/g, and 2.0 bpm/g, respectively), and workload intensity (averaged increments across AG conditions of 0.09 L/min/W, 0.17 mL/W, 0.22 mmHg/W, and 0.74 bpm/W respectively). These results suggest that the addition of AG to exercise can provide a greater cardiovascular benefit than exercise alone. Hierarchical regression models were fitted to the experimental data to determine dose-response curves of all cardiovascular variables as a function of AG-level and exercise intensity during short-radius centrifugation. These results can inform future studies, decisions, and trade-offs toward potential implementation of AG as a space countermeasure.

Cardiopulmonary Responses to Sub-Maximal Ergometer Exercise in a Hypo-Gravity Analog Using Head-Down Tilt and Head-Up Tilt

“…Only statistically significant coefficients were included in the regressions, and further interaction terms (not shown) were not significant. Similar to previous gravitational dose-response curves under orthostatic stress generated by short-radius centrifugation (Diaz-Artiles et al, 2018), results show that AG level contributes to changes in all variables, either directly ( β 1 and β 2 ) or through the interaction term (β 5 ). Figure 6 shows that generally HR and V T increase with AG, especially between Moon and Earth condition, while VO 2 , VCO 2 , V E , and R f decrease with gravity level.…”

“…Previous ground-based investigations on cardiopulmonary responses to ergometer exercise in altered-gravity have focused primarily on studying hypergravity conditions (>1 g), especially through the use of small radius centrifuges equipped with cycle ergometers (Bonjour et al, 2010, 2011; Diaz Artiles, 2015; Diaz et al, 2015b; Diaz Artiles et al, 2016; Diaz-Artiles et al, 2018). When hypogravity conditions (<1 g) have been investigated, most studies have been limited to small experiments in actual microgravity conditions during spaceflight that resulted in very few data points, typically less than four subjects, and they only compared 0 to 1 g conditions (Girardis et al, 1999; Trappe et al, 2006; Bonjour et al, 2011).…”

Gravity Threshold and Dose Response Relationships: Health Benefits Using a Short Arm Human Centrifuge

“…We should also highlight here the wide-range, dose response curves constructed from healthy individuals. These add to the knowledge obtained so far from previous studies where selective g levels of 1.0 and 2.0g were studied only without exercise (Goswami et al, 2015;Masatli et al, 2018;Verma et al, 2018), or dose response curves were generated by regression models since selective Gz of 1 G, and 1.4 G at the feet were used combined with different intensity exercise levels (Diaz-Artiles et al, 2018). To fill in this gap and better understand the relationship between gravitational dose and physiological response (Clément, 2017), dose response curves were constructed based on all intermediate stages tested from 0.5 to 2g in both men and women combined with mild intensity exercise well controlled by HR and HRV.…”

Cardiorespiratory and Neuromuscular Demand of Daily Centrifugation: Results From the 60-Day AGBRESA Bed Rest Study

“…Exercise during centrifugation in a supine position has even been associated with lower oxygen uptake compared to the same exercise in an upright position without centrifugation, presumably because the whole body is supported during centrifugation, eliminating the need for constant postural adjustments ( Piotrowski et al, 2018 ). Studies comparing exercise in a recumbent position with and without centrifugation found small increases in cardiovascular response with higher artificial gravity levels ( Diaz-Artiles et al, 2018 ), whereas passive centrifugation has been associated with reduced cardiac output, reduced pulmonary perfusion capacity and thus reduced oxygen transport ( Pendergast et al, 2012 ). In contrast to the low oxygen demand observed during centrifugation, exercise countermeasures that have been tested in bed rest studies with similar duration had much higher cardiorespiratory demands.…”