Changes in lung volumes and poor perception of bronchoconstriction-induced respiratory symptoms.

Abstract

Changes in lung volumes may contribute to the perception of bronchoconstriction-induced breathlessness. To verify whether histamine-induced increases in lung volumes are more marked in asthmatic subjects with normal compared with low symptom perception scores and whether changes in lung volumes are detected similarly in both groups of subjects. A group of 16 asthmatic subjects with low (< or =1) breathlessness score (scale: 0 to 10) at 20% fall in FEV1 (PS20B) on at least one of 2 histamine inhalation tests (HIT) performed on separate days (hypoperceivers) were studied. They were compared with a group of 12 asthmatic patients with a PS20B >1 on the 2 tests (normoperceivers). Lung volumes were measured before and after the second HIT and changes correlated with PS20B and PS20 for the sensation of chest tightness PS20CT) and with the slopes of these perception scores/% fall in FEV1 (PS B or CT/deltaFEV1). Hypoperceivers had a mean (+/-sem) PS20B of 1.03+/-0.20 on HIT1 and 0.66+/-0.12 on HIT2 (P>.05) and normoperceivers 2.59+/-0.14 on HIT1 and 2.38+/-0.18 on HIT2 (P>.05). Subjects' age, gender, duration of asthma, medication needs, and baseline and post-HIT pulmonary function (FEV1, FVC, FRC) were not significantly different between the two groups. Contrary to PS20B (P<.0001), PS20 for chest tightness (PS20CT) was similar in the two groups (HIT 1/2; hypoperceivers: 1.41/1.07, normoperceivers: 1.57/1.99, both P>.05). Perception of bronchoconstriction-induced breathlessness was not correlated with the degree of reduction in FVC at 20% fall in FEV1. In normoperceivers, (PS B/deltaFEV1) was significantly correlated with the postchallenge increase in FRC (rs = 0.63, P=.036) although there was no significant correlation in hypoperceivers (rs = -0.041, P>.05). Changes in lung volumes were similar in hypoperceivers and hyperperceivers of bronchoconstriction. Perception of breathlessness, however, was positively correlated with changes in lung volumes in normoperceivers but not in hypoperceivers suggesting that normoperceivers have an ability to detect these changes, presumably through proprioception, ability that is lacking or lost in hypoperceivers. More subjects should be studied to confirm this finding.