Deep Inspiration Avoidance and Methacholine Response in Normal Subjects and Patients With Asthma

Background Deep inspiration (DI) avoidance and time intervals between inhalation and measurement of FEV 1 may influence methacholine challenges. Objectives (1) To compare the degree of airway response to methacholine when the initial FEV 1 measurements are obtained either 30 s or 3 min after inhalation, (2) to evaluate a simplified method to study the influence of DI avoidance before inhalation on the fall in FEV 1 , and (3) to determine if methacholine has a cumulative effect. Participants/methods Twenty-five patients with asthma and 21 normal subjects without asthma. Four methacholine inhalation tests (MITs) were performed: two standard tidal-breathing MITs, with the first FEV 1 measured 30 s (test A) and 3 min (test B) after the end of inhalation; a single-dose MIT, using the last concentration from test B, with no control of DI and the first FEV 1 obtained 3 min after inhalation (test C); and an identical single-dose MIT preceded by 20-min of DI avoidance (test D). We compared the provocative concentration of methacholine causing a 20% fall in FEV 1 (PC 20 ) from tests A and B (aim 1), the percentage fall in FEV 1 from tests C and D (aim 2), and the percentage fall in FEV 1 from tests B and C (aim 3). Results Mean PC 20 values from tests A and B were 1.5 mg/mL and 1.0 mg/mL (p = 0.002) in patients with asthma, and 69.8 mg/mL and 29.9 mg/mL (p 1 for tests C and D were 22.0% and 24.5% (p > 0.05) in patients with asthma, and 22.1% and 38.9% (p = 0.0005) in control subjects, respectively. The mean falls in FEV 1 for tests B and C were 30.2% and 22.0% (p = 0.01) in patients with asthma, and 27.5% and 22.1% (p > 0.05) in control subjects, respectively. Conclusions In both groups, the longer the time interval between the end of inhalation and the first FEV 1 measurement, the greater the fall in FEV 1 (lower PC 20 ). DI avoidance before inhalation does not enhance the fall in FEV 1 in subjects with asthma, while it does in control subjects. Methacholine has a slight cumulative effect that is significant in patients with asthma (p = 0.007).