Abstract

Deep inspiration avoidance and airway response to methacholine: Influence of body mass index

OBJECTIVE: To evaluate the effects of deep inspiration avoidance response to methacholine inhalation in 23 nonobese (body mass index between 18 kg/m² and 30 kg/m²) and 27 obese (body mass index 30 kg/m² or 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 FEV₁ being 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 FEV₁ on 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 FEV₁ for 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 FEV₁ after 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.