Deep Inspiration Avoidance and Airway Response to Methacholine: Influence of Body Mass Index

Abstract

OBJECTIVE: To evaluate the effects of deep inspiration avoidance response to methacholine inhalation in 23 nonobese (body mass index between 18 kg/m2and 30 kg/m2) and 27 obese (body mass index 30 kg/m2or greater), nonatopic, nonasthmatic normal subjects.METHODS: Each subject had four methacholine challenges. In tests A and B, the first postmethacholine forced expiratory volume in 1 s (FEV1) was measured at 30 s and 3 min postinhalation, respectively; tests C and D were single-dose tests (using the final dose of test B), with the first postmethacholine FEV1being obtained at 3 min, without (test C) or with (test D) 20 min of deep inspiration avoidance before inhalation.RESULTS: The mean provocative concentrations inducing a 20% fall in FEV1on tests A and B were 80.6 mg/mL and 28.5 mg/mL (P<0.0001) in nonobese subjects, respectively, and 56.3 mg/mL and 21.5 mg/mL (P<0.0001) in obese subjects, respectively. No significant differences were observed in test A or B between control and obese subjects. Mean falls in FEV1for tests C and D were 20.3% and 40.0% (P=0.0003) in nonobese subjects, respectively, and 18.5% and 23.6% (P>0.05) in obese subjects, respectively.CONCLUSIONS: As previously observed in patients with asthma, the present study found that nonasthmatic obese subjects had no increase in the fall in FEV1after deep inspiration avoidance before methacholine, whereas nonobese subjects did, suggesting that obesity alters airway function. No significant changes were found between groups for symptom perception.