Indices of Increased Decompression Stress Following Long-Term Bed Rest

Area of Science:

• Space exploration physiology
• Hyperbaric medicine
• Decompression sickness research

Background:

• Human extravehicular activity (EVA) is critical for space exploration but carries the risk of decompression sickness (DCS).
• Head-down bed rest (HDBR) is an Earth-based model simulating microgravity's physiological effects.
• Venous gas emboli (VGE) formation is a key indicator of decompression stress.

Purpose of the Study:

• To investigate the impact of various resting and exercise regimens on VGE formation post-hyperbaric exposure within an HDBR model.
• To assess the influence of prolonged HDBR on decompression sensitivity.

Main Methods:

• Eight healthy males underwent a 35-day 6° HDBR regimen.
• Five hyperbaric exposures (HE) were conducted before, during, and after HDBR, including resting, knee-bend exercise, and supine cycling interventions.
• Post-HE, precordial Doppler measurements evaluated VGE, graded using the Kisman Masurel scale (KISS).

Main Results:

• Hyperbaric exposure during the end of HDBR resulted in significantly higher VGE grades and KISS scores compared to supine controls (p < 0.01).
• Pre-dive knee-bend exercise showed a protective effect, reducing bubble production.
• Prolonged bed rest prior to HE appeared to promote post-decompression VGE formation.

Conclusions:

• The HDBR model suggests that prolonged recumbency may increase susceptibility to VGE formation, contrasting with the absence of DCS during actual EVA.
• Further research is needed to determine if this discrepancy is due to differences in decompression stress (hypo- vs. hyperbaric) or the HDBR model's limitations in simulating microgravity's effects on decompression sensitivity.