Defective Motor Control of Coughing in Parkinson's Disease

Abstract

The high incidence of serious chest infections in patients with Parkinson's disease is unexplained, but an impairment in cough reflex may have a role. Maximal voluntary cough (MVC) and reflex cough (RC) to inhalation of ultrasonically nebulized distilled water were analyzed in patients with Parkinson's disease and age-matched control subjects by monitoring the integrated electromyographic activity (IEMG) of abdominal muscles. The peak amplitude of IEMG activity (IEMGP) was expressed as a fraction of the highest IEMGP value observed during MVC corrected to account for possible losses in abdominal muscle force due to reduced central muscle activation. Cough intensity was indexed in terms of both the IEMGP and the ratio of IEMGP to the duration of the expiratory ramp (TEC), i.e., the rate of rise of IEMG activity. Cough threshold was slightly higher in patients than in control subjects, but the difference failed to reach statistical significance. Compared with control subjects, patients displayed a lower IEMGP during maximal expiratory pressure maneuvers (PEmax), MVC, and RC (p always < 0.01); TEC during RC was longer (p < 0.01) than in controls. Consequently, the rate of rise of IEMG activity during cough was always lower in patients (p < 0. 01), especially during RC. Finally, PEmax, and both the peak and rate of rise of IEMG activity during RC were inversely related to the level of clinical disability (Spearman rank correlation coefficient, rs = -0.88, -0.86, and -0.85, respectively, p always < 0.01). The results indicate that the central neural mechanisms subserving the recruitment of motor units and/or the increase in their frequency of discharge during voluntary and, even more markedly, RC are impaired in patients with Parkinson's disease.

Capsaicin exposure elicits complex airway defensive motor patterns in normal humans in a concentration-dependent manner

“…Lasserson et al [10] showed a much higher activation of 79.7±41.6% following tartaric acid inhalation. Normalizing peak EMG activity for EO produced a 50% increase in cats with mechanical stimulation of the larynx [23] and 78-83% in humans using fog [5,17,19]. In addition to method of analysis, the type of tussive agent used and the species of the test subject will also add variability to the data.…”

“…The EMG response is likely a function of frequency since the number of expulsive events plotted over capsaicin concentration exhibited the same curvilinear trend. The shape of the EMG response curve is particularly relevant if EMG recordings are used to assess cough strength in people with reduced muscle fibre content such as older adults [26,27], or patients with neuromuscular diseases such as Parkinson's and muscular dystrophy [4,5,28].…”

“…With this technique, capsaicin concentrations (or other tussives such as citric acid and distilled water) are doubled until two and five "cough events" (typically defined by the number of expulsive events, or "cough sounds") are achieved, representing the threshold and suprathreshold response, respectively. These studies have shown differences in the cough response between ages [13], genders [14][15][16] and diseases [4,5,13,17]. However, these data cannot infer changes in expiratory muscle activation, duration of expulsive phases and the airflow dynamics with increasing capsaicin concentration, all which are essential components in defining the cough response.…”

“…Hypoxic hypercapnia, a hallmark of several respiratory diseases, reduces cough strength (as determined by intrapleural pressure) but not cough number [3]. Cough in patients with motor neural disease, such as Parkinson's disease, are reduced in strength but higher in frequency [4,5]. Cough strength can vary with or independently of cough frequency; thus it is difficult to infer cough strength from only cough frequency measurements.…”

What is cough and what should be measured?

“…One important aspect of using EMGs to assess cough is that they give important information about cough in neuromuscular diseases, such as stroke, Parkinson's disease and motoneurone disease, where cough may be severely affected [33].…”