title: Respiratory modulation of cardiovascular rhythms before and after short-duration human spaceflight.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Laboratory of Experimental Cardiology, University Hospital Gasthuisberg, Leuven, Belgium. bart.verheyden@med.kuleuven.be
authors.forename: B
authors.initials: B
authors.lastname: Verheyden
authors.forename: F
authors.initials: F
authors.lastname: Beckers
authors.forename: K
authors.initials: K
authors.lastname: Couckuyt
authors.forename: J
authors.initials: J
authors.lastname: Liu
authors.forename: A E
authors.initials: AE
authors.lastname: Aubert
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D018480:Astronauts; D001683:Biological Clocks / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D009991:Oscillometry / Q000379:methods; D015656:Respiratory Mechanics / Q000502:physiology*; D013026:Space Flight; D014893:Weightlessness