Effects of Pressure-Demand Respirator Wear on Physiological and Perceptual Variables during Progressive Exercise to Maximal Levels

Abstract

Current regulations governing the certification of respiratory protective devices are based on data published in the early 1950s. The limited data base of this early work and documented increases in the average height of the population underscore the need for additional information concerning the parameters of certification. In the present study, a protocol using an inclined treadmill (0.5% grade every 12 sec) was used to test a heterogeneous population (n=38). Through submaximal up to and including maximal exercise levels with and without respirator wear, maximal oxygen uptake (V˙O2max) was significantly greater (p<0.01) with the respirator (44.11±1.3 mL/kg·min) than without the respirator (42.18±1.4 mL/kg·min) while maximal ventilation volumes (V˙Emax) were not significantly different (with=118.7±4 L/min; without 119.6±5 L/min). While peak inspired flows (PFI) with the respirator (268±7 L/min) were less than without the respirator (281±9 L/min), p>0.05, the lower peak expired flow (PFE) with the respirator (289±12 L/min) than without the respirator (324±13 L/min), p<0.01, indicated a significant blunting effect of the respiratory flows by the expired resistance during exercise to maximal levels. Peak inspired pressures (PPi) with and without the respirator were not significantly different (p>0.05). The negative values obtained within the facepiece of the respirator (−7.65±0.8 cmH2O), however, indicate that the positive pressure within the facepiece was lost, and respiratory protection may be compromised. Peak expired pressure with the respirator (13.05±0.7 cmH2O) was significantly greater than without the respirator (10.7±0.5 cmH2O) indicating that, despite a lower PFE, greater force was required to overcome the resistances of the respirator on expiration. The dyspnea index, an index of physiological effort; suggests that the subjects were working at a higher percentage of their respiratory reserve with the respirator (p<0.05) than without. Perceptually, subjects also felt that breathing with the respirator was more difficult (p<0.05). The maximum heart rate and the ratings of perceived exertion were not significantly different between the two tests at maximal exercise levels. Maximum oxygen uptake was considered reached when subjects attained a respiratory exchange ratio of at least 1.15, when a heart rate response at or greater than age-predicted maximum was achieved, when ratings of perceived exertion indicated exhaustion, and/or when the measure of V˙O2 had plateaued during the final minute of exercise. The significance of these data lies not within the average values but the extreme ranges that represent the general population needing respiratory protection. Current respirator designs provide respiratory protection for 50% of the population up to exercise intensities of 50% V˙O2max. It is recommended that pressure demand respiratory devices be redesigned to provide adequate protection for up to 99% of the general population up to maximal exercise levels. These new designs should provide respiratory protection for V˙ES up to 199 L/min, PFis to 400 L/min, PFEs to 496 L/min, and pressure swings of 30 cmH2.