The relationship between wheezing and lung mechanics during methacholine-induced bronchoconstriction in asthmatic subjects.

Abstract

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.

Analysis of Forced Wheezes in Asthma Patients

“…The mean frequency of wheezes for all our subjects (618.0 ± 195 Hz) was similar to frequencies reported previously for both normal subjects (658 ± 184 Hz) [19 ]and asthma patients (669 ± 100 Hz) [20]. However, in our controls, the mean frequency was significantly higher than the frequency for all asthmatic patients, attributable to the fact that we placed microphones near the trachea whereas previous researchers recorded at the chest, where high-frequency sounds are attenuated.…”

Self-reported Symptoms after Induced and Inhibited Bronchoconstriction in Athletes

“…In swimmers (7), runners (29), and ice-arena athletes (32)—all of whom are frequently exposed to noxious airborne agents (e.g., chlorine derivatives and exhaust gas from cars or from fossil-fueled ice-resurfacing machines)—high prevalence of respiratory symptoms and pulmonary dysfunction has consistently been reported. That hyperpnea of dry air may stimulate cough and mucus hypersecretion independently of a change in airway caliber may explain why wheeze, which is more directly linked to airflow limitation (34), differentiated better EVH-positive athletes from EVH-negative athletes in Part 1 of this study.…”

Changes in the highest frequency of breath sounds without wheezing during methacholine inhalation challenge in children

“…On the other hand, measurement of BHR has been accepted as useful for making a diagnosis and assessing the severity of asthma 5–8 . Although methacholine induces bronchoconstriction and/or airway narrowing, almost all subjects who undergo provocation tests do not experience wheezing or dyspnoea, despite significant increases in airway resistance or decreases in FEV 1 9,10 . Clinicians know that, in patients with a mild asthma attack detected by peak flow measurements, changes in breath sounds are not detected on auscultation.…”