Introduction and Objectives Cough sound analysis is currently used for the assessment of cough frequency; it is not known if it could be used to assess cough intensity. We investigated the optimal Cough Sound Intensity (CSI) measure by validating it against peak cough flow rate (PCFR).
Methods 17 (11 female) patients with stable chronic cough and 15 (8 female) healthy subjects underwent simultaneous measurements of peak cough flow rate and cough sound during voluntary coughs using 2 types of microphones. Subjects were asked to cough voluntarily 10 times at 5 incremental thoracic pressures as measured by an oesophageal balloon catheter. Visual feedback was given to patients. A range of CSI parameters were determined from the cough sound signal. CSI was calculated for the actual cough sound duration and also for a constant duration (time constant) to assess the potential for automation. The repeatability of CSI and the effect of microphone position were assessed. For each subject, PCFRs and CSI data were normalised to values obtained during maximum voluntary cough (MVC).
Results The correlation between the optimal CSI and peak cough flow rate was best for the free-field microphone; median (IQR) correlation coefficient 0.88 (0.79–0.92) (Table 1). The median correlation for all cough sound intensity remained strong for males (r=0.90–0.91), females (r=0.79–0.84), patients with chronic cough (r=0.79–0.82) and healthy subjects (r=0.82–0.89). The intraclass correlation coefficient for repeatability was good, r=0.90, p<0.01. The CSI degraded when the microphone was positioned further away from the mouth, downwards, but not in any other position. The use of a constant cough sound duration to determine CSI did not impact on the association with PCFR (Table 1).
Conclusion Cough sound intensity correlates strongly with PCFR in voluntary cough and is a repeatable measure. The microphone position needs to be standardised as in this study. Further work is needed to automate the analysis of CSI; our preliminary findings suggest this is possible. The CSI has the potential to be developed into a non-invasive, ambulatory outcome measure of cough severity.