Magnitude estimation of inspiratory resistive loads in children with life-threatening asthma.

The perception of inspiratory resistive (R) loads was studied in nonasthmatic children and in children with a history of life-threatening asthma. It was hypothesized that the children with life-threatening asthma would have a reduced sensitivity to added mechanical loads as measured by magnitude estimation of resistive loads (ME). The subjects were screened from the experimenter and seated in a sound-isolated room in a lounge chair facing an oscilloscope, and they respired through a nonbreathing valve with the inspiratory port connected to the loading manifold. The oscilloscope displayed the inspiratory V, and each subject was required to inspire to the same peak V for each breath. The subject's inspiratory background R was measured by the interrupter method. Five magnitudes of R loads and no-load were presented randomly 10 times each for a single inspiration after the illumination of a light cue. The subjects were initially given a training trial breathing to the V target. The loads were presented in two trials. The load was estimated using the modified Borg scale. The slope of the log-log relationship between R load magnitude and the ME is a measure of the sensitivity of the subject to R loads. The slope for children with life-threatening asthma was significantly less than that for asthmatic and nonasthmatic children. There were no significant differences in the slope related to race, sex or age in the nonasthmatic children or in the asthmatic children. The reduced sensitivity to increased R loads suggests that these children are at risk of a life-threatening asthmatic attack in part because of an underestimation or delay in the perception of the increased mechanical load that occurs during an asthmatic attack.