Cardiovascular responses to standing and walking in earth and simulated moon and mars gravities

Introduction Human cardiovascular responses to standing and walking in simulated reduced gravity were measured using a treadmill enclosed in a lower‐body positive pressure (LBPP) chamber (AlterG device). Methods Heart rate, HR, continuous blood pressure, BP, (Portapres), segmental fluid shift (THRIM), diastolic function and stroke volume (Biosounds) were recorded on 7 subjects (4 males, 3 females) at supine and while standing and walking under 100% (earth), 40% (mars), and 20% (moon) body weights (BW). Results Subjects standing at 20% and 40% BW had reduced HR (p<0.01), increased systolic BP (p<0.05) and increased thoracic impedance (p<0.001) compared to standing. Reduced BW was associated with increased upper and lower leg impedance (loss of fluid volume, p<0.05). Stroke volume was greatest while supine, at 20%, 40% BW and walking compared to standing (p<0.01). Mitral E to A ratio was reduced for 20%, 40%, and 100% BW compared to supine (p<0.01). The number of blood pressure ramps and baroreflex sequences decreased as body weight was reduced. Conclusion Fluid redistribution in the body and short‐term cardiovascular changes induced by Alter‐G unloading are compatible with those resulting from exposure to microgravity. Supported by KY NASA EPSCoR 52611.