Subjective tolerance of respirator loads and its relationship to physiological effects.

Subjective and physiological responses to a variety of respiratory loads were measured in a group of 52 normal volunteers during steady, moderate treadmill exercise. Subjective response (SR) was determined with two visual analogue scales developed for this study: EXERT (perceived limitation of exercise duration) and DISC (perceived discomfort). There was a linear relationship between inspiratory resistance and SR. Expiratory and inspiratory resistance loading produced similar subjective effects. Dead space loading, however, produced very little subjective effect on either scale. The study suggests that subjective response can be measured quantitatively and should be considered in respirator design.