Interactions of the human cardiopulmonary, hormonal and body fluid systems in parabolic flight

U Limper,P Gauger,F Krainski,F May,L E J Beck,P Beck

doi:10.1007/s00421-014-2856-3

Abstract

PurposeCommercial 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.MethodsCardiac index was determined by inert gas rebreathing (CIrb), 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 Gz. 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.ResultsCIrb in 0 Gz 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 Gz 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.ConclusionHH 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.Electronic supplementary materialThe online version of this article (doi:10.1007/s00421-014-2856-3) contains supplementary material, which is available to authorized users.

Highlights

Parabolic flights performed in slightly modified passenger airplanes operating in the troposphere have been used extensively in past decades for space-related human physiological research
To date, no research has investigated how the body fluid system is influenced by parabolic flights, some evidence suggests that the intravascular volume may increase on the day of a parabolic flight, as stated by Schlegel et al (2001)
Confirmation of the observations of the studies of Iwase et al (1999a) and Beckers et al (2003) who found that cardiovascular responses to the transition into weightlessness in a standing position are different between the early parabolas of a parabolic flight and the later parabolic phases

Summary

Introduction

Parabolic flights performed in slightly modified passenger airplanes operating in the troposphere have been used extensively in past decades for space-related human physiological research. Most of these life science experiments have been conducted on parabolic flights in a KC 135 aircraft in the USA or in an Airbus A300 aircraft in Europe. Extensive previous research was aimed at investigating the cardiovascular system in the context of changing gravity in general and weightlessness in particular (Liu et al 2012; Mukai et al 1991; Petersen et al 2011). To date, no research has investigated how the body fluid system is influenced by parabolic flights, some evidence suggests that the intravascular volume may increase on the day of a parabolic flight, as stated by Schlegel et al (2001)

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