Exploration of Cough Counts and Epochs in Patients with Asthma and Interstitial Lung Disease

초록

Background: Cough counts are widely used for cough studies in patients with various respiratory diseases. The cough epoch is a cluster of cough counts,1 which may reveal the severity of coughs and cough patterns that are indiscernible with cough count alone. Despite its potential clinical importance, cough epochs are not as commonly investigated. One of the few previous studies was conducted on the nighttime cough epoch focused on COPD patients.2 In this study, we observed both the cough counts and cough epochs in patients with asthma and interstitial lung disease (ILD). Methods: In order to observe the cough epochs in respiratory patients, we retrospectively analyzed the data from two independent clinical studies. Cough sounds were recorded from 21 ILD patients recruited in Seoul National University Bundang Hospital and from 24 patients with asthma exacerbation recruited in 7 academic medical centers in South Korea. The ILD patients recorded coughs for 5 consecutive days on two occasions separated by a 3-month period (10 total days), and the asthmatic patients recorded coughs for 7 consecutive days. Both groups recorded for 2 h in awake time and 5 h in sleep time daily, and they received the standard treatment throughout the study. Cough events from recordings were detected by the Coughy AI algorithm,2 and the cough epochs were calculated by counting the number of continuous coughing sounds without a 2-s pause as defined in Morice et al.1 Finally, the trends of cough and epoch frequency over days were compared in each study group. Results: The cough frequency and the epoch frequency both decreased over the course of treatment in awake and sleep time for patients with asthma exacerbation as shown in Fig. 1(a) and (c). The correlation between the cough frequency and epoch frequency was high with R2 of 0.986 and 0.949, respectively. However, in ILD patients, two cough measures didn’t show a decreasing trend clearly nor moved together over days with no clear correlation (R2) of 0.125 in awake time and 0.521 in sleep time (Fig. 1(b) and (d)). Conclusion: We have observed the trend of cough and epoch frequency over time and how they are correlated. Based on our study, the two cough measures showed different trends over the course of treatment in patients with asthma and ILD. A larger population study will be needed to pursue these initial observations and find a clinical role of the cough epoch for respiratory patients.