Submaximal exercise with self-contained breathing apparatus: the effects of hyperoxia and inspired gas density.

Background: The self-contained breathing apparatus (SCBA) used by firefighters, and other working in dangerous environments, adds an external resistance to expiration, which increases expiratory work during heavy exercise.

Hypothesis: Compressed air is typically used with the SCBA and we hypothesized that changing the inspired oxygen concentration and/or gas density with helium would reduce the external expiratory resistance.

Methods: On separate days, 15 men completed four 30-min bouts of treadmill exercise dressed in protective clothing and breathing the test gases through the SCBA. Four different gas mixtures were assigned in random order: [compressed air (NOX: 21% O2, 79% N2), hyperoxia (HOX: 40% O2, 60% N2), normoxic-helium (HE-OX: 21% O2, 79% He), and helium-hyperoxia (HE-HOX: 40% O2, 60% He)].

Results: Compared with NOX, the two helium mixtures (but not HOX), decreased the external breathing resistance and all three gas mixtures decreased the peak expired mask pressure and the ventilatory mass moved. Both hyperoxic mixtures decreased blood lactate and the rating of perceived exertion was decreased at 30 min with HE-HOX.

Conclusions: These results demonstrate that the helium-based gas mixtures, and to a lesser extent HOX, reduce the expiratory work associated with the SCBA during strenuous exercise.