Physiological response to “pressure-demand” respirator wear

Thirty-seven male and female volunteers, twenty-two normal and fifteen moderately impaired with respect to lung function were submaximally exercised with and without a “pressure-demand” type air-line respirator. The respirator was equipped with an inspiratory reststance of 85 mmH₂0 at 85 L/ min air flow and expiratory resistance of 25 mmH₂0 at 85 L/ min air flow over and above the inhalation and exhalation “pressure-demand” resistance of 25 mmH₂0. Comparisons between normals and moderately impaired at submaximal workloads of 35%, 50%, and 80% of maximal capacity (VO₂max) exhibited no difference in response, even though the impaired subjects were utilizing a greater percentage of their pulmonary reserves at 80% VO_2max. However, the pressure swings across the facepiece were 22-25 cmH₂0 at 80% VO_{2 max} as a result of inordinately high impaired pressures and may have been the primary cause that 50% of both groups of subjects were unable to complete the 80% VO_2max workload. Also, it was noted that the greater the ventilatory demand imposed by the high workloads the more like a “demand” type respirator the “pressure-demand” system became, regardless of an individual's lung function. Hence, it was concluded that the ventilatory stresses of high workloads emphasized the inadequacy of current pressure-demand designs and placed significant psychophysiological stress on the wearer. Further to the current work a need for determining the relationship between MVV.25 and VO_2maxwith and without respirator wear was identified.