Maximal stress test performance while wearing a self-contained breathing apparatus.

Fifteen adult male volunteers (mean age = 31.0 years; eight non-smokers and seven smokers) carried out a Bruce protocol maximal treadmill stress test under four separate conditions. These four conditions were (1) without Scott Air Pak (SAP) respirator; (2) with SAP respirator apparatus but not wearing face mask; (3) with SAP apparatus, wearing face mask in "demand" breathing mode; and (4) with SAP respirator apparatus, wearing face mask in "pressure-demand" breathing mode. The data indicate that the overriding factor in the approximately 20% decrement in work performance during conditions 2, 3, and 4 was related to the weight of the SAP respirator (15.8 kg), P less than 0.05. Only during condition 3 did eight of 15 subjects report lack of air as one reason for termination. Conditions 3 and 4 resulted in a significant decrease in TFore (2.5 degrees C) and was primarily related to the decreased Tinsp which reached a maximum decrement of 9.7 degrees C. Under all conditions the smokers' work time was significantly less than nonsmokers, P less than 0.05.