Relationship of subjective tolerance of respirator loads to physiologic effects and psychophysical load sensitivity

The degree to which subjective tolerance of respirator loads is related to physiologic effects and to psychophysical load sensitivity was investigated in this study. Fifty-two normal volunteers walked on a treadmill while breathing through a variety of respirator-type resistance and dead-space loads. Visual analog scales measuring perceived time limit of exercise and discomfort were both related to the ventilatory work imposed by the loads. Respiratory timing was related to discomfort but not to time limit. Psychophysical sensitivity to added resistive loads (LSS) was measured by the magnitude estimation method. Persons with higher objectively measured LSS had greater subjective intolerance induced by respirator use than persons of lower LSS. These findings suggest that subjective respirator tolerance is related to a person’s psychophysical characteristics and to the actual physiologic effects. Furthermore, discomfort may be dissociated from actual exercise limitation.