Establishing a gold standard for manual cough counting: video versus digital audio recordings

Abstract

Background: Manual cough counting is time-consuming and laborious; however it is the standard to which automated cough monitoring devices must be compared. We have compared manual cough counting from video recordings with manual cough counting from digital audio recordings.

Methods: We studied 8 patients with chronic cough, overnight in laboratory conditions (diagnoses were 5 asthma, 1 rhinitis, 1 gastro-oesophageal reflux disease and 1 idiopathic cough). Coughs were recorded simultaneously using a video camera with infrared lighting and digital sound recording. The numbers of coughs in each 8 hour recording were counted manually, by a trained observer, in real time from the video recordings and using audio-editing software from the digital sound recordings.

Results: The median cough frequency was 17.8 (IQR 5.9-28.7) cough sounds per hour in the video recordings and 17.7 (6.0-29.4) coughs per hour in the digital sound recordings. There was excellent agreement between the video and digital audio cough rates; mean difference of -0.3 coughs per hour (SD +/- 0.6), 95% limits of agreement -1.5 to +0.9 coughs per hour. Video recordings had poorer sound quality even in controlled conditions and can only be analysed in real time (8 hours per recording). Digital sound recordings required 2-4 hours of analysis per recording.

Conclusion: Manual counting of cough sounds from digital audio recordings has excellent agreement with simultaneous video recordings in laboratory conditions. We suggest that ambulatory digital audio recording is therefore ideal for validating future cough monitoring devices, as this as this can be performed in the patients own environment.

Figure 1

Two coughs with the explosive phase of the cough sounds marked by the vertical dashed red lines.

Figure 2

Equipment setup for simultaneous video and digital sound recordings. Note the same microphone is used to record audio into both the digital sound recorder and the video recorder. In addition to this an infra red light source is used to illuminate the subject.

Figure 3

Bland Altman plot of difference between video and digital cough counts versus mean cough count. The solid horizontal red line represents the mean difference between the two methods and the red dashed lines the 95% limits of agreement.