The lungs in rheumatoid spondylitis: Gas exchange and lung mechanics in a form of restrictive pulmonary disease

Abstract

Sixteen patients with rheumatoid spondylitis are presented with studies of lung volumes, gas exchange and the mechanics of breathing, and are discussed as representing a form of restrictive pulmonary disease with hyperinflation of the resting chest cage. The restriction, and apparently also the hyperinflation, are the result of fixation of the chest in an expanded position by ankylosis of the spine and ribs. The majority of patients exhibited a relatively straight spine. Eleven of the patients had no complicating cardiac or pulmonary diseases. In these the most significant changes were a reduction in vital capacity (70 per cent of predicted), a markedly increased residual volume and functional residual capacity, and a residual volume to total lung capacity ratio which averaged 49 per cent. In addition the elastic recoil of the lungs at resting mid-position was decreased. Although these findings resemble obstructive pulmonary emphysema, lung function was different in other respects: there were normal ventilation-perfusion relationships, normal intrapulmonary gas mixing, normal one-second vital capacity, normal flow resistance, no air trapping and a restrictive pattern of breathing. In addition, the total lung capacity was normal. Other significant consequences of the immobilization of the thoracic cage were a diminution in the maximum static inspiratory transpulmonary pressure, diminished maximum positive and negative tracheal pressures, and a reduction in maximum breathing capacity. Painful sneezing and coughing, abdominal breathing and absence of dyspnea are important clinical features of rheumatoid spondylitis. The restrictive disease of rheumatoid spondylitis is usually not severe enough to produce alveolar hypoventilation. Pulmonary insufficiency and frequent pulmonary infections are not characteristic of uncomplicated rheumatoid spondylitis, indicating that diaphragmatic breathing is adequate to maintain normal pulmonary function, at least while activity is subdued.