Am. J. Respir. Crit. Care Med., Vol 154, No. 2, Aug 1996, 290-294.
The relationship between wheezing and lung mechanics during methacholine-induced bronchoconstriction in asthmatic subjects
DP Spence, DR Graham, G Jamieson, BM Cheetham, PM Calverley and JE Earis
Aintree Chest Centre, Fazakerley Hospital, Liverpool, United Kingdom.
Wheeze is a classic sign of airflow obstruction but relatively little is
known of its mechanism of production or its relationship to the development
of airflow obstruction. We studied eight asthmatic subjects age (mean +/-
5D) 42 +/- 5 yr, FEV1 2.46 +/- 0.36 L during an extended, symptom-limited
methacholine challenge test. Breath sounds were detected by a microphone
over the right upper anterior chest. Spectral analysis was by a fast
Fourier transform algorithm. Mean FEV1 fell by 51 +/- 14% to 1.28 +/- 0.61
L during the challenge and airways resistance increased by 119 +/- 50%.
There were no consistent changes in breathing pattern or tidal volume
during the challenge. Wheeze occurred late in the challenge at the highest
concentration of methacholine administered and only after expiratory tidal
flow limitation had been reached. Five subjects developed wheeze on tidal
breathing, the remaining three only wheezed on deep breathing. Wheezing
sounds were reproducible between breaths, coefficient of variation of
starting sound frequency was 4.2% and ending frequency 12%. Mean frequency
of expiratory wheezes was 669 +/- 100 Hz and inspiratory wheezes 710 +/- 76
Hz. Expiratory wheeze fell in pitch during a breath (mean fall in sound
frequency 187 +/- 43 Hz) but inspiratory wheezes were more variable.
Expiratory wheezes occurred late in the respiratory cycle at a mean of 58%
of the maximal tidal expiratory flow, whereas inspiratory wheezes occurred
around maximal tidal inspiratory flows, suggesting that the mechanisms of
production of inspiratory and expiratory wheezes may be different. In this
model, the presence of wheeze during tidal breathing was a sign of severe
airflow limitation.
