Ambulatory methods for recording cough
Section snippets
Why do we need and objective measure of cough?
Cough is consistently the commonest symptom for which patients’ seek medical care [1], [2] and yet despite this there is no universally accepted objective measure of cough. The study of cough generally relies upon subjective reporting, measurement of the sensitivity of the cough reflex and more recently cough related quality of life [3], [4].
A patients’ perception of the severity of a symptom and its effect on their well-being are unquestionably important. The processes involved in the
The history of cough monitoring
Recording cough sounds in order to objectively quantify coughing is not a new concept, with the first publications in the 1960s [12]. Using large reel-to-reel tape recorders, hospital in-patients were studied and coughs were counted manually, which is a laborious and time-consuming process (Fig. 1).
As technology progressed ambulatory recording devices became available using sound in combination with chest wall EMG signals to identify coughs [13], [14]. The signals still had to be reviewed and
Challenges in automated cough detection
There are three main challenges in automatically detecting and counting coughs:
- 1.
differentiation from ambient noise,
- 2.
differentiation from other patient sounds, especially speech, laughing sneezing and
- 3.
variability in the acoustics of cough sounds both within and between individuals.
Detection of coughing has most commonly been attempted from sound recordings [15], [16], [17], [18], [19] or sound in combination with a second signal such as EMG [13], [14]/chest wall movement [20], [21]. One of the
Quantifying cough
There is no universally agreed unit of cough. The most intuitive way to quantify cough is to count the expulsive (first phase) of cough sounds (Fig. 3). If long bursts (or peals) of expulsive cough sounds are present, then to identify each expulsive phase can be very difficult. We have devised a new method for quantifying cough, the ‘cough second’ which is the number of seconds containing at least one expulsive cough phase [22]. This gives a representation of the time spent coughing. The main
Performance of objective cough monitors
Any cough monitor will identify some cough events correctly (true positives), mistake non-cough events as cough (false positives), miss some cough events (false negatives) and correctly ignore non-cough (true negatives). The sensitivity is the proportion of coughs correctly detected by the cough monitor (Eq. (1)) as
However, the number and nature of false positive results is also of importance if the monitor is to give clinically useful
Recent developments in cough monitoring
Several groups are currently developing and publishing work in the field of automated cough monitoring and a summary of some of this recent work follows. The soon-to-be-published European Task Force Guidelines on the Measurement of Cough will help to further standardize the reporting of the performance of cough monitors.
Other endpoints in cough monitoring
Cough frequency is the most basic measure of coughing but the objective study of cough signals has the potential to identify further features which may be clinically relevant and hence useful endpoints to study.
The temporal patterns of coughing vary both in the short term (peals or epochs of coughs versus single coughs), from hour to hour and from day to night [24], [25], and can only be appreciated using objective ambulatory measures. Short term patterns could be an indication of individual
Conclusions
In summary, automated detection of coughing is required to make the objective measurement of cough a useful clinical and research tool. If this can be achieved, there are a number of other endpoints which may be important and require exploration. The testing of new cough monitoring systems needs to be rigorous and current systems have not quite achieved the levels of accuracy and consistency in performance necessary. With current progress, ambulatory cough monitoring should be possible in the
Acknowledgements
I would like to thank Alyn Morice, Samantha Barry, Surrinder Birring and Alex Derchak for information about their respective works.
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