Muscle activation and sound during voluntary single coughs and cough peals in healthy volunteers: Insights into cough intensity

Abstract

Very few studies have addressed how coughing varies in intensity. We assessed the influence of cough effort and operating volume on the mechanics of coughing using respiratory muscle surface electromyography (EMG), oesophageal/gastric pressures and cough sounds recorded from 15 healthy subjects [8 female, median age 30 (IQR 30-50)years] performing 120 voluntary coughs from controlled operating volume/effort and three cough peals. For single coughs, low operating volumes and high efforts were associated with the highest EMG activity (p < 0.001); the resultant pressures increased with effort but volume had little influence. In contrast, cough sounds increased with both volume and effort. During cough peals, EMG fell initially, increasing towards the end of peals, pressures remained stable and sound parameters fell steadily to the end of the peal. In conclusion, effort and operating volume have important influences on cough mechanics but modulate muscle activation, pressure and cough sound amplitude and energy differently. Consequently, these cough sound parameters poorly represent voluntary cough mechanics and have limited potential as a surrogate intensity measure.

Global Physiology and Pathophysiology of Cough

“…However, when voluntary coughs are studied from a range of different lung volumes and with different efforts applied, then unlike flow, the EMG activity is largely independent of lung volume and is mainly determined by cough effort. The exceptions are coughs performed from below FRC, such as those occurring at the end of cough bouts; these are associated with the highest EMG signals [72]. The study of EMG has allowed the observation that voluntary cough is associated with coordinated sequential activation of the main expiratory and accessory muscles, whereas induced cough is associated with simultaneous activation of both muscle groups with greater EMG activity but shorter duration [67].…”

“…A limitation of EMG is the inability to compare values between subjects or between experimental sessions and normalization methods are required for data analysis [67,69,72,73]. Factors such as electrode position, contact between electrode and skin, resting muscle state and inherent skin resistance can affect the measures and signal contamination from ECG and limited potential for automation has also made EMG challenging to develop as a clinical measure [74].…”

“…In health, the duration of a typical cough sound is approximately 410 ms but in disease it can be longer, up to 600 ms in asthma or bronchitis and up to 1 s in acute viral cough [79][80][81][82]. The sound signal amplitude and power (calculated after transforming the sound signal into its frequency domain) have been shown to correlate with flow, pressure and with cough EMG during voluntary cough, although the strength of the relationships has varied among studies [72,78,83,84].…”

“…The impracticalities of measuring EMG or pressure or flow in the ambulatory setting have prompted the study of sound as a potential cough intensity monitoring measure but further studies are needed to determine if this is a clinically useful outcome measure [72,83,84,99].…”

The present and future of cough counting tools

“…The most studied signal for cough evaluation is sound, acquired by means of microphones. Other investigated m o d a l i t i e s i n c l u d e : e l e c t r o m y o g r a p h y ( E M G ) , electrocardiography (ECG), nasal thermocouple sensors, effort belts, and accelerometry (21), individually or together (38)(39)(40)(41)(42). Microphones can be classified as contact, and noncontact (43,44).…”