Habituation of phasic total respiratory resistance responses.

We examined the effects of repetitious stimulation on phasic respiratory resistance responses of 30 healthy adult males. Individuals were told either that they would inhale a substance which would cause bronchoconstriction or that they would inhale a substance which would cause no breathing changes. All subjects completed four inhalation trials. During each trial a lamp was turned on to indicate the presence of the inhalant; in reality, the subjects inhaled no substances. Respiratory resistance and functional residual capacity were measured just before and during the time the lamp was on. Regardless of the type of instruction, the response to the inhalation task was predominantly an increase in respiratory resistance. During Trials 1, 2, and 3, the number of subjects who increased respiratory resistance was greater than the number of subjects who decreased respiratory resistance. The number of subjects who increased respiratory resistance was not different from the number of subjects who decreased respiratory resistance during Trial 4. Changes in functional residual capacity did not affect changes in respiratory resistance; functional residual capacity changed neither within nor between trials. Given a progressive decrease in the number of subjects who increased their respiratory resistance on successive trials, the results were consistent with a response habituation model.