Cardiovascular mechanisms are maintained by intermittent artificial gravity exposure during bed rest deconditioning

Abstract

Successful countermeasures to adverse cardiovascular effects of spaceflight have not yet been developed. In this study cardiovascular parameters were measured at rest and in response to 30 minutes of 80° head up tilt (HUT) in two groups of men before, during and after 21 days of 6° head down bed rest (BR). 8 men received a daily, one hour dose (2.5 Gz at the foot decreasing to 1.0 Gz at the heart) of artificial gravity (AG), while 7 underwent no countermeasure. After 21 days of BR, AG‐treated subjects demonstrated greater orthostatic tolerance than control subjects (p = .012). Cardiovascular variables responsible for maintaining tolerance in AG treated subjects included an enhanced ability to increase heart rate (HR) and low frequency spectral power of blood pressure as well as to maintain stroke volume (SV) during tilt. Additionally, AG treated subjects demonstrated a more rapid return to pre‐BR responses to HUT than did control subjects by minimizing tilt‐induced increases of HR (p = .04) and decreases of SV (p = .05). Variables recorded during BR days are being analyzed to develop a model to predict orthostatic tolerance upon returning to gravity. Our data support the hypothesis that AG treatment lessens cardiovascular deconditioning in bed rested men by improving both cardiac and peripheral function and should be pursued as a space flight countermeasure. Supported by The NASA AG‐Bed Rest Project and KY NASA EPSCoR WKU52611.