Simulated shuttle egress: role of helmet visor position during approach and landing.

Background: We previously reported that carbon dioxide (CO2) rapidly accumulates in the helmet of the NASA Launch and Entry Suit (LES) during a simulated egress from the Space Shuttle following 6 min of visor-closed seated rest to simulate approach and landing. The purpose of this study was to determine if CO2 accumulation and walking time in the LES would be improved by helmet visor-open rather than visor-closed seated rest prior to the performance of the simulated egress.

Methods: Wearing the LES, 12 male subjects performed 4 laboratory egress simulations consisting of 6-min seated rest, 2-min stand, and 5-min walk at 1.56 m x s(-1) (3.5 mph). During seated rest, subjects sat either with the visor open, breathing room air until the visor was closed on standing, or with the visor closed for the duration of the simulation. For all visor-closed operations 100%, O2 was supplied. The G-suit was either deflated (0.0 psi) or inflated to 1.5 psi. Inspired CO2 and walking time were measured. Data were analyzed at the end of seated rest, standing, and after 5 min of walking at 0.0 psi or after 2 min of walking at 1.5 psi (>90% of data available).

Results: Walk time was not different following visor-open (0.0 psi: 5.0 +/- 0.0; 1.5 psi: 3.4 +/- 0.3 min) or visor-closed (0.0 psi: 4.8 +/- 0.2; 1.5 psi: 3.5 +/- 0.4 min) seated rest at either G-suit pressure. Inspired CO2 levels were not different between the two conditions during walking at 5 min at 0.0 psi (p = 0.50; Open: 4.39 +/- 0.14; Closed: 4.48 +/- 0.18%) or at 2 min at 1.5 psi (p = 0.53; Open: 3.59 +/- 0.12; Closed: 3.65 + 0.21%).

Conclusions: Visor position during seated rest immediately preceding the egress walk had no effect on inspired CO2 or walking time.