Acoustic parameters of voluntary cough in healthy non-smoking subjects

The aim of this study was to explore cough in healthy subjects.

We studied 234 coughs generated by 24 (12 males) healthy non-smokers (forced expiratory volume in 1 s (FEV1) 103+/-8% of predicted), who had no significant differences in FEV1 and age between males and females. For each subject, several bouts of voluntary coughing were recorded using a personal computer with an A/D converter (sampling rate 10 kHz, 8 bit resolution) and the first and second coughs of each bout were analysed using short-time Fast Fourier Transformation. For each cough we studied the three phases that are produced. In particular, we studied the duration of the three parts, loudest frequency in the first part, lowest and highest frequencies, number of continuous frequencies and lowest and highest continuous frequencies in the second part, and the loudest frequency of the third part if present.

We found significant differences between males and females in length of the first part (41.4+/-14 vs 44.7+/-10.4 msec, P = 0.04), loudest frequency of the first part (362+/-145 vs 449+/-145 Hz), lowest frequencies (282+/-100 vs 348+/-135 Hz) and highest continuous frequencies (3877+/-571 vs 4147+/-362 Hz; P < 0.001) of the second part. An interesting finding was that healthy males and females had the same number of continuous frequencies. Different frequencies are probably a consequence of anatomical differences in airway geometry involved in the cough.

In cough frequency spectrum studies the differences between the two sexes should be taken into account to reduce the variability of the results.