Alterations in Physiological and Perceptual Variables during Exhaustive Endurance Work while Wearing a Pressure-Demand Respirator

Abstract

The purpose of this investigation was to describe the time course of changes in physiological and perceptual variables during exhaustive endurance work with and without an air-supplied, full-facepicce, pressure-demand respirator. Thirty-eight healthy subjects(24 to 51 years of age) volunteered for this study. Treadmill speed was set at 5.5 kph (3.4 mph) and elevation was set at a level calculated to elicit 70% of a previously determined maximal aerobic capacity (V˙O_2max). Subjects continued at this rate to exhaustion. Despite a constant work rate, V˙O₂ and %V˙O_2max increased during exercise and were significantly greater with the respirator (34.4±1.1 mL/kg. min; 84% V˙O_2max) than without the respirator (31.9±1.1 mL/kg. min; 76% V˙O_2max) at the “final” measurement point prior to termination of exercise by each subject. The final values for ventilation volume (V˙_E) also were significantly greater with the respirator(89.2±3.4 L/min) than without (73.4±3.7 L/min). At the conclusion of the endurance walk, dyspnea index (V˙_E/MMV_.25) remained well below maximal values (with=58.6±2%; without=44.6±2%; p<0.001). Also, at the final period, no significant differences occurred in the subjects' perceptual ratings of work of breathing, yet work performance time was significantly reduced (p<0.0001) from 69.1±4.4 min (without) to 55.6±3.8 min (with). A significantly greater swing in peak pressure (maximum pressure measured within the facepiece of respirator), however, from inspired (PP_i) to expired (PP_e) occurred with the respirator (13.42 cmH₂O) than without the respirator (9.25 cmH₂O). The equivalent work intensifies of both endurance walks to exhaustion were noted in similar final physiological values for beart rate(HR), frequency of breathing(f_B), and ratings of perceived exertion (RPE) and breathing (BrSc). At 30 min when an equal number of subjects (n=32) were performing work, RPE and BrSe were increased significantly during respirator wear. This increased perception of work and breathing occurred despite equivalent work loads. Perceptual measures reliably indicated impending fatigue. Therefore, the interaction of added respiratory work over time caused added physiological work that was perceived by the subject and resulted in an earlier termination of work.