Respiratory Responses during Exercise in Self-contained Breathing Apparatus among Firefighters and Nonfirefighters

Background: Firefighters are required to use self-contained breathing apparatus (SCBA), which impairs ventilatory mechanics. We hypothesized that firefighters have elevated arterial CO₂ when using SCBA. Methods: Firefighters and controls performed a maximal exercise test on a cycle ergometer and two graded exercise tests (GXTs) at 25%, 50%, and 70% of their maximal aerobic power, once with a SCBA facemask and once with protective clothing and full SCBA. Results: Respiratory rate increased more in controls than firefighters. Heart rate increased as a function of oxygen consumption (V._O2 ) more in controls than firefighters. End-tidal CO₂ (ETCO₂) during the GXTs was not affected by work rate in either group for either condition but was higher in firefighters at all work rates in both GXTs. SCBA increased ETCO₂ in controls but not firefighters. Conclusions: The present study showed that when compared to controls, firefighters’ hypoventilate during a maximal test and GXT. The hypoventilation resulted in increased ETCO₂, and presumably increased arterial CO₂, during exertion. It is proposed that firefighters have altered CO₂ sensitivity due to voluntary hypoventilation during training and work. Confirmation of low CO₂ sensitivity and the consequence of this on performance and long-term health remain to be determined.