title: Interactions of the human cardiopulmonary, hormonal and body fluid systems in parabolic flight.
abstract: OBJECTIVE
  Commercial parabolic flights accessible to customers with a wide range of health states will become more prevalent in the near future because of a growing private space flight sector. However, parabolic flights present the passengers' cardiovascular system with a combination of stressors, including a moderately hypobaric hypoxic ambient environment (HH) and repeated gravity transitions (GT). Thus, the aim of this study was to identify unique and combined effects of HH and GT on the human cardiovascular, pulmonary and fluid regulation systems.
  
  
  METHODS
  Cardiac index was determined by inert gas rebreathing (CI(rb)), and continuous non-invasive finger blood pressure (FBP) was repeatedly measured in 18 healthy subjects in the standing position while they were in parabolic flight at 0 and 1.8 G(z). Plasma volume (PV) and fluid regulating blood hormones were determined five times over the flight day. Eleven out of the 18 subjects were subjected to an identical test protocol in a hypobaric chamber in ambient conditions comparable to parabolic flight.
  
  
  RESULTS
  CI(rb) in 0 G(z) decreased significantly during flight (early, 5.139 ± 1.326 L/min; late, 4.150 ± 1.082 L/min) because of a significant decrease in heart rate (HR) (early, 92 ± 15 min(-1); late, 78 ± 12 min(-1)), even though the stroke volume (SV) remained the same. HH produced a small decrease in the PV, both in the hypobaric chamber and in parabolic flight, indicating a dominating HH effect without a significant effect of GT on PV (-52 ± 34 and -115 ± 32 ml, respectively). Pulmonary tissue volume decreased in the HH conditions because of hypoxic pulmonary vasoconstriction (0.694 ± 0.185 and 0.560 ± 0.207 ml) but increased at 0 and 1.8 G(z) in parabolic flight (0.593 ± 0.181 and 0.885 ± 0.458 ml, respectively), indicating that cardiac output and arterial blood pressure rather than HH are the main factors affecting pulmonary vascular regulation in parabolic flight.
  
  
  CONCLUSIONS
  HH and GT each lead to specific responses of the cardiovascular system in parabolic flight. Whereas HH seems to be mainly responsible for the PV decrease in flight, GT overrides the hypoxic pulmonary vasoconstriction induced by HH. This finding indicates the need for careful and individual medical examination and, if necessary, health status improvement for each individual considering a parabolic flight, given the effects of the combination of HH and GT in flight.
authors.affiliation: Department of Anesthesiology and Surgical Intensive Care Medicine, Merheim Medical Center, Hospitals of Cologne, University Witten/Herdecke, Ostmerheimer Strasse 200, 51109, Cologne, Germany, limperu@kliniken-koeln.de.
authors.forename: U
authors.initials: U
authors.lastname: Limper
authors.forename: P
authors.initials: P
authors.lastname: Gauger
authors.forename: P
authors.initials: P
authors.lastname: Beck
authors.forename: F
authors.initials: F
authors.lastname: Krainski
authors.forename: F
authors.initials: F
authors.lastname: May
authors.forename: L E J
authors.initials: LE
authors.lastname: Beck
mesh_terms: D000305:Adrenal Cortex Hormones / Q000097:blood*; D000328:Adult; D001794:Blood Pressure; D002302:Cardiac Output; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology; D008297:Male; D010953:Plasma Volume; D012119:Respiration; D014655:Vascular Resistance; D014893:Weightlessness / Q000009:adverse effects*; D018474:Weightlessness Simulation
chemical_list: D000305:Adrenal Cortex Hormones