Respiratory modulation of cardiovascular rhythms before and after short-duration human spaceflight
Astronauts commonly return from space with altered short-term cardiovascular dynamics and blunted baroreflex sensitivity. Although many studies have addressed this issue, post-flight effects on the dynamic circulatory control remain incompletely understood. It is not clear how long the cardiovascular system needs to recover from spaceflight as most post-flight investigations only extended between a few days and 2 weeks. Methods:
In this study, we examined the effect of short-duration spaceflight (1–2 weeks) on respiratory-mediated cardiovascular rhythms in five cosmonauts. Two paced-breathing protocols at 6 and 12 breaths min−1 were performed in the standing and supine positions before spaceflight, and after 1 and 25 days upon return. Dynamic baroreflex function was evaluated by transfer function analysis between systolic pressure and the RR intervals. Results:
Post-flight orthostatic blood pressure control was preserved in all cosmonauts. In the standing position after spaceflight there was an increase in heart rate (HR) of approx. 20 beats min−1 or more. Averaged for all five cosmonauts, respiratory sinus dysrhythmia and transfer gain reduced to 40% the day after landing, and had returned to pre-flight levels after 25 days. Low-frequency gain decreased from 6.6 (3.4) [mean (SD)] pre-flight to 3.9 (1.6) post-flight and returned to 5.7 (1.3) ms mmHg−1 after 25 days upon return to Earth. Unlike alterations in the modulation of HR, blood pressure dynamics were not significantly different between pre- and post-flight sessions. Conclusion:
Our results indicate that short-duration spaceflight reduces respiratory modulation of HR and decreases cardiac baroreflex gain without affecting post-flight arterial blood pressure dynamics. Altered respiratory modulation of human autonomic rhythms does not persist until 25 days upon return to Earth.