DEFECTIVE MOTOR CONTROL OF COUGHING IN PARKINSONS-DISEASE

The high incidence of serious chest infections in patients with Parkin son's disease is unexplained, but an impairment in cough reflex may ha ve a role. Maximal voluntary cough (MVC) and reflex cough (RC) to inha lation of ultrasonically nebulized distilled water were analyzed in pa tients with Parkinson's disease and age-matched control subjects by mo nitoring the integrated electromyographic activity (IEMG) of abdominal muscles. The peak amplitude of IEMG activity (IEMG(p)) was expressed as a fraction of the highest IEMG(p) value observed during MVC correct ed to account for possible losses in abdominal muscle force due to red uced central muscle activation. Cough intensity was indexed in terms o f both the IEMG(p) and the ratio of IEMG(p) to the duration of the exp iratory ramp (TEC), i.e., the rate of rise of IEMG activity. Cough thr eshold was slightly higher in patients than in control subjects, but t he difference failed to reach statistical significance. Compared with control subjects, patients displayed a lower IEMG(p) during maximal ex piratory pressure maneuvers (PEmax), MVC, and RC (p always < 0.01); TE C during RC was longer (p < 0.01) than in controls. Consequently, the rate of rise of IEMG activity during cough was always lower in patient s (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 coefficien t, r(s) = -0.88, -0.86, and -0.85, respectively, p always < 0.01). The results indicate that the central neural mechanisms subserving the re cruitment of motor units and/or the increase in their frequency of dis charge during voluntary and, even more markedly, RC are impaired in pa tients with Parkinson's disease.