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.

Cardiorespiratory Fitness Is Associated with Gait Changes among Firefighters after a Live Burn Training Evolution

BACKGROUND: Recommendations have been proposed for minimum aerobic fitness among firefighters but it is unclear if those criteria relate to performance on the fireground. Less fit individuals fatigue more quickly than fit individuals when working at comparable intensity and may have gait changes, increasing risk of falls. We evaluated the effect of fatigue during a live burn evolution on gait parameters and functional balance comparing them to aerobic fitness levels. METHODS: A total of 24 firefighters had gait and balance tested before and after a live burn evolution. Data were stratified by aerobic fitness of greater/less than 14 metabolic equivalents (METs). RESULTS: Analysis of gait cycles measurements before and after the live burn evolution revealed that single leg stance, cycle, and swing time decreased (p < 0.05) but there were no differences in the other measures. There were no differences in time to complete the functional balance test, or errors committed before or after a live burn evolution. When firefighters were sorted by fitness level of 14 METs, there were no differences for errors or time before or after the live burn evolution. Balance data were analyzed using a linear regression. Individuals with lower fitness levels required more time to complete the test. CONCLUSION: A 14-MET criterion failed to distinguish gait or balance characteristics in this group. However, less fit firefighters did require more time to complete the balance test (p = 0.003). Aerobic fitness alone does not predict gait changes among firefighters following a live burn evolution but does appear to influence functional balance.

Effects of Low-Dose Aspirin Therapy on Thermoregulation in Firefighters

BACKGROUND: Heart attack is the most common cause of line-of-duty death in the fire service. Daily aspirin therapy is a preventative measure used to reduce the morbidity of heart attacks but may decrease the ability to dissipate heat by reducing skin blood flow. METHODS: In this double-blind, placebo-controlled, crossover study, firefighters were randomized to receive 14 days of therapy (81-mg aspirin or placebo) before performing treadmill exercise in thermal-protective clothing in a hot room [38.8 +/- 2.1degrees C, 24.9 +/- 9.1% relative humidity (RH)]. Three weeks without therapy was provided before crossing to the other arm. Firefighters completed a baseline skin blood-flow assessment via laser Doppler flowmetry; skin was heated to 44degrees C to achieve maximal cutaneous vasodilation. Skin blood flow was measured before and after exercise in a hot room, and at 0 minutes, 10 minutes, 20 minutes, and 30 minutes of recovery under temperature conditions (25.3 +/- 1.2degrees C, 40.3 +/- 13.7% RH). Platelet clotting time was assessed before drug administration, and before and after exercise. RESULTS: Fifteen firefighters completed the study. Aspirin increased clotting time before and after exercise compared with placebo (p = 0.003). There were no differences in absolute skin blood flow between groups (p = 0.35). Following exercise, cutaneous vascular conductance (CVC) was 85 +/- 42% of maximum in the aspirin and 76 +/- 37% in the placebo groups. The percentage of maximal CVC did not differ by treatment before or after recovery. Neither maximal core body temperature nor heart rate responses to exercise differed between trials. CONCLUSION: There were no differences in skin blood flow during uncompensable heat stress following exercise after aspirin or placebo therapy.