Effects of prolonged bed rest on the total peripheral resistance baroreflex

Orthostatic intolerance following prolonged exposure to microgravity continues to be a primary concern of the human space program. Reduced autonomic tone has been demonstrated to contribute to this phenomenon, and the heart rate baroreflex, in particular, has been repeatedly shown to be impaired. However, only the works of Yelle et al. (1996, 2002) have attempted to address the role of the total peripheral resistance (TPR) baroreflex, a potentially more significant contributor to blood pressure regulation. We applied a previously developed method for estimating the static gains of both the arterial and cardiopulmonary TPR baroreflexes to data obtained before and after 16 day bed rest. Reductions in the estimated static gains of the arterial (statistically significant) and cardiopulmonary TPR baroreflex were found after bed rest. This study supports the works of Yelle et al., which imply that the TPR baroreflex is reduced after spaceflight.