Acoustic vs. spirometric assessment of bronchial responsiveness to methacholine in children.

To study wheezing as an indicator of bronchial responsiveness during methacholine challenge (MC) in children, we used computer analysis of respiratory sounds and compared wheeze measurements to routine spirometry. MC was performed in 30 symptomatic subjects (sympt), age 11 ± 3.1 years (mean ± SD), with suspected asthma and in 12 controls (contr), age 10 ± 3.4 years. Respiratory rate (RR), spirometry, arterial oxygen saturation (Sa, O2 ), and cough were registered until the concentration provoking a ≥ 20% fall in forced expiratory flow in 1 second (FEV 1 ; PC 20 ), or the end point (8 mg/mL) was reached. For 1 min after each inhalation, sounds over the trachea and posterior right lower lobe were recorded together with calibrated airflow. Computer analysis of respiratory sounds was used for objective wheeze quantification. Wheezing was measured as its duration relative to inspiration (T w /T i ,) and expiration (T w /T e ,). Seventeen of the sympt group developed wheezing (sympt/W) with ≥ T w /T i , or ≥ 5% T w /T e Thirteen of the sympt did not wheeze (sympt/no W). Three contr developed wheeze (contr/w) while 9 did not (contr/no W). In sympt/W, RR increased from 20 ± 6.2 per min at baseline to 25 ± 9.2 ( P < 0.05) at the MC concentration provoking wheeze (PC w ), and Sa O 2 , decreased from 97.4 ± 1.2% to 95.3 ± 2.4 ( P < 0.05). In contr/W, RR did not change, but Sa O 2 , decreased from 97.3 ± 1.5% to 95.7% ± 1.2% ( P < 0.05). Wheezing occurred at both recording sites and was as common during inspiration as during expiration. In subjects who had both PC w and PC 20 , these variables correlated well (r = 0.82, P < 0.0001). Three SW did not reach PC 20 (maximum fall in FEV 1 8%, 12%, and 18%). On the other hand, 6 of 13 sympt/no W and 2 of 12 contr/no W had a positive MC. Thus, wheezing during MC had a sensitivity of 68% and a specificity of 82%. Acoustic measurements were reproducible in 14 subjects who performed a second MC within 2–10 months. We conclude that wheezing during MC in children strongly suggests airway hyperresponsiveness; however, wheeze detection cannot fully replace spirometry in bronchial provocation testing.