Determinants of pattern of breathing during respirator use.

The relationship between the pattern of breathing in response to respirator-type loads and an individual's psychophysiologic sensitivity to loads (load scaling sensitivity, LSS) was investigated in the study of 11 normal volunteers. LSS was measured by having the subjects numerically rate a series of resistors; Steven's Psychophysical Law was used to evaluate sensitivity as the slope relating log (sensation) to log (stimulus). Peak pressure and actual added resistance were the stimuli. Inspiratory time, peak pressure, duty cycle, and tidal volume were inversely related to independently measured LSS during exercise and with a respiratory-type dead space and inspiratory resistance load. Because the need for changes in respiratory timing is a major adaptation in respirator use, it suggests that workers who are very sensitive to loads may have limited ability to adapt to respirator use.