Pulmonary alveolar microlithiasis: lung function in five cases

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Abstract
Pulmonary function was investigated in five patients with pulmonary alveolar microlithiasis. Four male cases occurred in two families. This contrasts with previous reports that females predominate in familial cases. Only one patient had respiratory symptoms. Total lung capacity was reduced in all patients and vital capacity was less than normal in four of five patients. The ratio of residual volume to total lung capacity and the one second forced expiratory volume was normal in all patients. Frequency of respiration and ventilatory equivalent were greater than normal and tidal volume was less than normal in the symptomatic patient. Minute volume of ventilation, O2 consumption, and alveolar O2 tension were normal in all patients. Arterial O2 tension was less than normal in one patient and became less than normal during exercise in another patient. Arterial CO2 was low in one patient and arterial pH was normal in all. The alveolar arterial O2 gradient was greater than normal in all patients; and the venous admixture-like effect was increased in three patients. The ratio of physiological dead space to tidal volume was greater than normal in two patients and the O2 diffusing capacity was less than normal in one of three patients. Pulmonary function studies reported previously showed no specific pattern. All patients reported herein revealed a definite restrictive pattern with decreased lung volumes, absent airway obstruction, and uneven distribution of pulmonary capillary blood evidenced by an increased alveolar arterial O2 tension gradient.