Changes in selected pulmonary functions in patients diagnosed with myasthenia gravis.

Patients with myasthenia gravis (MG) face major pulmonary problems as a part of the disease process. In this descriptive study, changes in selected pulmonary functions (respiratory rate, negative inspiratory force, tidal volume and forced vital capacity) in 14 patients diagnosed with mild or moderate MG were measured every two hours from 8:00 a.m. to 8:00 p.m. Females comprised 64% of the sample while 36% were males. All subjects received anticholinesterase medication, and some subjects received additional treatment modalities. Most of the subjects were nonsmokers or previous smokers, but two subjects continued to smoke. Ninety-three percent of the sample had forced vital capacities less than 60% of their predicted values. Myasthenic forced vital capacities were significantly lower (p = .0000) than those predicted for normal subjects. The inspiratory force for the sample was low at 8:00 a.m. as well as in females over 55 years of age. There was a wide variation in tidal volume. The comparison of myasthenic values for respiratory rate, inspiratory force and tidal volume to normal values derived from random tables and prediction equations was not significant. The major implications from this study are the need to assess pulmonary function in the hospitalized myasthenic every two hours, and the need for a program of coughing, deep breathing and sighing after medication administration when muscles are strongest.