Lung volumes and compliance in myasthenia gravis and reversible airway obstruction

A patient with myasthenia gravis, reversible airway obstruction, and a vertical chest wall pressure-volume curve was shown to inflate his lungs to 12 liter during the night. During the day, either spontaneously or after isoproterenol, his functional residual capacity decreased by more than 2 liter. The large lung volume changes occurred without a change in slope of the static pressure-volume curve of the lung above functional residual capacity. The changes in the position of this curve might be due to the the very slow filling and emptying of bullae or to unexplained alterations in the length-tension characteristics of the alveoli. The vertical pressure-volume curve of the chest wall suggested that, unlike other patients who have normal or decreased chest wall compliance, this patient's chest wal was not a factor that limited ventilation at high lung volumes.