Carbon dioxide accumulation, walking performance, and metabolic cost in the NASA launch and entry suit

Background: In the event of an emergency on landing, Space Shuttle crewmemb ers while wearing the Launch and Entry Suit (LES) must stand, move to the h atch, exit the spacecraft with the helmet visor closed breathing 100% O-2,O - and walk or run unassisted to a distance of 380 m upwind from the vehicle . The purpose of this study was to characterize the inspired CO2 and metabo lic requirements during a simulated unaided egress from the Space Shuttle i n healthy subjects wearing the LES. Methods: As a simulation of a Shuttle l anding with an unaided egress, 12 male subjects completed a 6-min seated pr e-breathe with 100% O-2 followed by a 2-min stand and 5-min walking at 1.56 m . s(-1) (5.6 km . h(-1), 3.5 mph) with the helmet visor closed. During w alks with four different G-suit pressures (0.0, 0.5, 1.0, 1.5 psi; 3.4, 6.9 , 10.3 kPa), inspired CO2 and walking time were measured. After a 10-min se ated recovery, subjects repeated the 5-min walk with the same G-suit pressu re and the helmet visor open for the measurement of metabolic rate ((V) ove r dot O-2). Results: When G-suit inflation levels were 1.0 or 1.5 psi, only one-third of our subjects were able to complete the 5-min visor-closed wal k after a 6-min pre-breathe. Inspired CO2 levels measured at the mouth were routinely greater than 4% (30 mmHg) during walking. The metabolic cost at the 1.5 psi G-suit inflation was over 135% of the metabolic cost at 0.0 psi inflation. Conclusion: During unaided egress, G-suit inflation pressures o f 1.0 and 1.5 psi resulted in elevated CO2 in the LES helmet and increased metabolic cost of walking, both of which may impact unaided egress performa nce. Neither the LES, the LES helmet, nor the G-suit were designed for ambu lation. Data from this investigation suggests that adapting fight equipment for uses other than those for which it was originally designed can result in unforeseen problems.