PURPOSE: To determine if time based parameters of lung sounds differed in patients with chronic obstructive lung disease (COPD) as compared to normal subjects and patients with other disorders.
METHODS: A 16-channel lung sound analyzer (Stethographics Model STG1602) was used to collect 20s samples of sound from patients with COPD (n=103), normals (n=379), pneumonia (PN, n=118), congestive heart failure (CHF, n=92), bronchial asthma (n=62), and interstitial pulmonary fibrosis (IPF, n=39) during deeper than normal breathing. The difference in timing between the start of the inspiration at the trachea and the start at each chest wall site was calculated. The inhomogeneity of the start of the inspiration (SI) was defined as the ratio of the mean of these starting time differences to the duration of the inspiration at the trachea. The negative sign indicates that chest microphones detected inspiration before the tracheal microphone. The end of inspiration inhomogeneity (EI) was defined similarly.
RESULTS: The SI and EI are presented in Table 1. Notice that inhomogeneity of the start and end of inspiration was significantly more common in COPD (p<0.05).
CONCLUSION: The mechanism of the Inter-channel inhomogeneity is unknown, but a possible explanation is regional variations in elasticity and airway resistance. In other words in a normal subject as the chest wall moves outward on inspiration the airways dilate relatively uniformly and the lung is uniformly expanded. In COPD, airway dilatation is less likely to be uniform and dilatation more inhomogeneous secondary to regional variations in elasticity and resistance.
CLINICAL IMPLICATIONS: A long-term goal of studies with multichannel lung sound analyzers is to provide useful diagnostic information at the bedside. The increase in the inter-channel Inhomogeneity together with other features of COPD, such as decreased amplitude of sound and relatively prolonged inspiratory phases can help provide evidence that COPD is present. This can be done using a simple test using that requires little patient cooperation.
DISCLOSURE: Raymond Murphy, Grant monies (from sources other than industry) Supported in part by grant from NIH SBIR (1R43HL70480–01); Grant monies (from industry related sources) Supported in part by grant from Stethographics, Inc.; Shareholder Dr. Murphy and Dr. Vyshedskiy have financial interests in Stethographics, Inc.; Employee Dr. Murphy and Dr. Vyshedskiy have financial interests in Stethographics, Inc.; No Product/Research Disclosure Information