PERCEPTION OF CHANGES IN AIR-FLOW RESISTANCE IN OBSTRUCTIVE PULMONARY DISORDERS

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Abstract
The perception of changes in airflow resistance was examined in normal subjects, asthmatics, and patients with chronic obstructive pulmonary disease (COPD) using the psychophysical tests of just noticeable differences and magnitude estimation. The just noticeable difference in airflow resistance expressed as a percentage of the baseline resistance (JND%) was 18 .+-. 2% SE in normal subjects and this value was not altered by changes in baseline resistance. The exponent for the magnitude estimation (ME) of airflow resistance was 0.93 .+-. 0.04 SE in normal subjects. Neither JND% nor ME wefe significantly different from normal in asthmatics. In patients with COPD; JND% was increased to 49 .+-. 7% SE (P < 0.01) and ME was reduced to 0.64 .+-. 0.10 SE (P < 0.01). In contrast to the abnormalities in the perception of changes in airflow resistance, the perception of heaviness during the lifting of small weights was the same in patients with COPD as in normal subjects and asthmatics. Measures of the perception of changes in airflow resistances were related to the degree of respiratory compensation during ventilatory loading as determined from the change in the occlusion pressure response to hypercapnia during inspiratory resistive loading compared with the response during free rebreathing. Normal subjects and asthmatics with the largest ME and smallest JND% showed the greatest load compensation. Patients with COPD with lower ME and higher JND% demonstrated smaller changes in occlusion pressure response during resistive loading. The results of this study indicated that the perception of changes in airflow resistance is impaired in patients with COPD but not in asthmatics. The impairment was not explained by a generalized defect in perceptual abilities. Abnormalities in the perception of changes in ventilatory loads may be responsible for impaired respiratory responsiveness to increases in airway resistance.