BREATHING PATTERN AND CENTRAL VENTILATORY DRIVE IN MILD AND MODERATE GENERALIZED MYASTHENIA-GRAVIS

Background - Myasthenia gravis is a specific autoimmune disease charac terised by weakness and fatigue. Respiratory muscle weakness has been studied using the determination of maximal respiratory pressures, but the response of respiratory centres is not well characterised. This st udy was undertaken to determine the breathing pattern and the central ventilatory drive in patients with mild and moderate generalised myast henia gravis. Methods - Twenty four patients with myasthenia gravis we re studied, divided into two groups. Group 1 included 13 subjects (eig ht women and five men aged 23-64) with mild generalised myasthenia gra vis, and group 2 was composed of 15 patients (11 women and four men ag ed 23-69) with moderate generalised myasthenia gravis. A control group comprised 15 healthy persons with a similar age and sex distribution. Spirometric measurements and maximal respiratory pressures were perfo rmed under basal conditions in all subjects, and the rate and depth of breathing and the inspiratory occlusion pressure in the mouth in the first 0.1 second (P-0.1) were measured. Results - No difference was de tected for parameters of breathing pattern between patients in group 1 and control subjects, although P-0.1 was higher in those in group 1. Subjects in group 2 had a lower tidal ventilation, shorter inspiratory time, and a higher frequency with a higher P-0.1 than control subject s.Conclusions - Mild myasthenia gravis causes increased neuromuscular drive with a normal breathing pattern. Moderate myasthenia gravis is c haracterised by a more rapid shallow breathing pattern.