Dynamic and static lung volumes, blood gas tensions, and diffusing capacity in patients with cystic fibrosis.

Abstract

In 126 ventilatory studies in 80 patients with cystic fibrosis, the maximal midexpiratory flow was the most sensitive index of airway obstruction. Lung volumes were more accurately measured by the body plethysmograph than by helium dilution techniques. There was a good correlation between both flows and lung volumes and clinical scores. The steady state diffusing capacity for carbon monoxide was low in 51 of 126 studies. Arterial carbon dioxide tensions were greater than the normal range in 37 of 64 studies, but only 7 were greater than 45 mm Hg. Hypoxemia was marked. There was a good correlation between the arterial oxygen tensions and clinical scores; there was also a correlation between the degree of airway obstruction and arterial oxygen tension. Further ventilatory studies showed hyperventilation, large physiologic dead space, and abnormal ratios of physiologic dead space to tidal volume, together with increased alveolar-arterial oxygen differences. Hypoxemia was caused by a combination of alveolar h...