Respiratory Muscle Function in Myasthenia Gravis

Abstract

Global respiratory muscle function and diaphragmatic strength were assessed and compared with quadriceps femoris muscle strength in 17 patients with generalized mild-to-moderate myasthenia gravis and breathlessness. Initial measurements, made 10 h after the last dose of oral anticholinesterase therapy, demonstrated reduced maximal static expiratory (52.4 +/- 26.8% predicted) and inspiratory (54.0 +/- 23.5% predicted) mouth pressures in 16 patients, and reduced quadriceps femoris muscle strength in all cases. Vital capacity (VC) (70.9 +/- 19.0% predicted) was abnormal in 12 patients. Transdiaphragmatic pressure recorded during maximal sniffs (sniff Pdl) was reduced in eight patients, whereas pressure recorded during bilateral phrenic nerve stimulation at 1 Hz (twitch Pdi) was reduced in only three. There was no relationship between the grade of myasthenia or the severity of dyspnea and any of the measurements of respiratory muscle strength. After the administration of edrophonium hydrochloride (Tensilon), there was a significant increase in maximal static expiratory and inspiratory mouth pressures in quadriceps muscle strength and in sniff Pdi. The small increase in VC was not significant, and twitch Pdi increased in only one patient. Phrenic nerve conduction time was normal before and after Tensilon. Two patients with severe long-standing myasthenia showed no improvement in any measurement after Tensilon. We conclude that expiratory and inspiratory muscle weakness was not uncommon in patients with myasthenia gravis. Respiratory muscle strength improved after Tensilon. Vital capacity was a less sensitive measure of respiratory muscle strength than were respiratory mouth pressures and sniff Pdi. Diaphragmatic involvement was not detected by twitch Pdi unless the weakness was severe.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventilatory muscle strength and endurance in myasthenia gravis

“…Previous studies of pulmonary function and ventilatory muscle strength and endurance have focused on patients with generalized myasthenia gravis [1][2][3][4][5][6]. In our group of four patients with clinical ocular myasthenia gravis, there was no evidence of ventilatory muscle involvement.…”

“…This disorder is characterized by weakness of voluntary muscles, accentuated by repetitive activity, and alleviated by rest and cholinesterase inhibitors. Ventilatory muscle weakness has been demonstrated in patients with generalized myasthenia gravis [1,[3][4][5][6], and increased strength reported following the administration of cholinesterase inhibitors [2][3][4][5][6][7]. Whether clinically significant ventilatory muscle weakness exists in patients with milder or predominantly ocular muscle weakness has not been established.…”

“…Most studies to date have assessed ventilatory muscle involvement in myasthenia gravis by measuring muscle strength using maximal static respiratory pressures [2,[4][5][6]. Given the pathogenesis of myasthenia gravis, an assessment of ventilatory muscle endurance may be a more sensitive indicator.…”

Respiratory Care for Myasthenic Crisis

“…The theoretical curvilinear relation between volume and pressure implies that, in the case of mild respiratory muscle weakness, VC is less sensitive than PImax, and, in more advanced disease, marked reduction in VC can occur with relatively small changes in maximum pressures. One previous study showed that inspiratory and expiratory forces were more sensitive than VC in evaluating muscle strength in MG (Mier-Jedrzejowicz et al, 1988). However, a recent study found that PImax was not more sensitive than VC for early detection of respiratory muscle failure in these patients (Prigent et al, 2011).…”

Adverse effects of myasthenia gravis on rat phrenic diaphragm contractile performance

“…For example, Ringqvist and Ringqvist (25) studied nine subjects with moderate to rather severe generalized disease and found that the maximum inspiratory pressure was reduced to 78% of predicted, whereas the maximum expiratory pressure was reduced to 55% of predicted. MierJedrzejowicz et al (20) studied 17 subjects who had mild to moderate generalized disease with breathlessness and found Fig. 3.…”