Patients with Vocal Cord Dysfunction (VCD) present with wheezing and shortness of breath and are often misdiagnosed as having bronchial asthma. Since the wheezes of asthma are primarily generated peripherally and wheezes of VCD are generated centrally, a method based on the site of wheeze generation could be of value in the differential diagnosis of these disorders. The goal of this study was to determine whether centrally generated wheezes could be distinguished from wheezes of bronchial asthma and chronic obstructive lung disease (COPD) using computerized acoustic techniques.
A multichannel lung sound analyzer was used to collect 20 second samples of sound from the trachea and from 14 chest sites from 2 patients with VCD, 32 of patients with asthma who were wheezing, and 44 patients with COPD. Under the assumption that centrally generated wheezes are more likely to have more symmetrical acoustic characteristics than peripherally generated wheezes we calculated an acoustic symmetry coefficient (ASC) using a technique that crosscorrelated the signal between all symmetrical channels; ASC=0% when sounds are completely different between left and right lungs, ASC=100% when sounds in left and right lungs are identical. As vocal sounds provide a surrogate of centrally generated wheezes we also calculated the ASC of vocal sounds in all participants in this study.
The ASC in patients with asthma averaged 27±11% for inspiratory and 31±8% for expiratory wheezing compared to 74±9% for vocal sounds (p<0.0001). The ASC in patients with COPD averaged 29±9% for inspiratory and 34±8% for expiratory wheezing compared to 70±12% for vocal sounds (p<0.0001). The ASC of wheezing in asthma and COPD patients was never greater than 50%. The ASC of wheezing in patients with VCD was always greater than 55%. The ASC of the spoken voice was always greater than 47%.
These differences in ASC offer the promise of helping to distinguish the wheezing patients with VCD from that of BA.
Automated lung sound analysis may help in distinguishing these often diagnostically perplexing conditions.
Raymond Murphy, Shareholder Dr. Raymond Murphy is founder and CEO of Stethographics, Inc.; No Product/Research Disclosure Information