Communicated by Guido Ferretti.
The online version of this article (doi:10.1007/s00421-014-2856-3) contains supplementary material, which is available to authorized users.
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.
Cardiac 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.
CIrb 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.
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.
Online Resource 1.: The video shows the five members of the experiment team inflight on board A300 Zero-G during a single parabola. The pilot’s announcements of the parabolic phases from the cockpit are audible. The experiment rack consists of two identical test units including in duplicate: Innocor rebreathing device; Biopac device for ECG, ICG and accelerometer data collection; Finometer MIDI non-invasive finger blood pressure measurement device; laptop for data storage and a battery of blood sampling tubes. The cooler for blood sample storage is not visible on the video. The experiment design allows the simultaneous accomplishment of multiple measurements in two subjects. The two subjects are connected via face masks to the two Innocor rebreathing devices and via an “umbilical” cord to the Finometer and Biopac units. Two operators fixed to the floor by straps and harnesses are assisting the subjects during the hyper-g phases and especially during free floating passively after the transition into weightlessness. A third operator is leading the subjects through the rebreathing procedure by guiding the subjects’ breathing with hand signs and starting the measurements immediately after the transition to weightlessness. (MPG 263130 kb)
Online Resource 2.: Extended methodological description including additional fundamental literature for the procedures of inert gas rebreathing, intravascular volume determination and biochemical analyses. (DOCX 33 kb)
Online Resource 3.: Cardiovascular results of N = 18 as the mean ± SD of the parabolic flight tests are shown. (DOCX 16 kb)
Online Resource 4.: Pulmonary results of N = 18 as the mean ± SD of the parabolic flight tests are shown. (DOCX 15 kb)
Online Resource 5.: Cardiovascular results as the mean ± SD of the hypobaric chamber tests are shown. N = 11 for both pulmonary and cardiovascular parameters. (DOCX 16 kb)
Online Resource 6.: Plasma volume and biochemical responses in parabolic flight and the hypobaric chamber are given as the mean ± SD; # indicates parabolic flight values as the mean ± SD, which are presenting excluding the responses of the motion-sick subjects 0AP, 0AD and 0AT. The parabolic flight values of these subjects’ parameters are shown individually in Fig. 4. ‡, reninactive responses of subject 0AL in the hypobaric chamber were not included for mean and SD calculations because of an exceptional response. The 0AL-reninactive responses are shown individually in Fig. 4. (DOCX 16 kb)
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- Interactions of the human cardiopulmonary, hormonal and body fluid systems in parabolic flight
L. E. J. Beck
- Springer Berlin Heidelberg