Thirty-six patients with chronic obstructive pulmonary disease are analyzed with respect to clinical features, tomograms of the chest and pulmonary function studies. The clinical features are similar in these patients and do not provide any basis for classification into sub-groups. In the majority of patients there is a reduction of the steady state diffusing capacity. Of these, eleven of twenty-seven also had a reduced single breath diffusing capacity for carbon monoxide (Dco). Evidence is presented to support the hypothesis that reduction of the steady state diffusing capacity is a reflection of anatomic emphysema, and it is further suggested that a relatively normal single breath Dco in patients with a reduced steady state Dco reflects the fact that there is some normal lung present which is preferentially sampled by the single breath test. There are no apparent differences between the clinical findings in patients with impaired diffusion as compared to those with normal diffusion.

Only seven of twenty-nine tomograms revealed the presence of “emphysema,” but “emphysema” was only encountered in patients with a reduced steady state Dco.

Although reduction of the maximum midexpiratory flow rate (MMF) is associated with hypercapnia and hypoxemia, there are no differences in symptomatology between the patients with relatively mild and severe airway obstruction. Likewise, grouping the patients with respect to the level of the minute ventilation does not reveal any differences in symptomatology or exercise tolerance between the groups. A history of heart failure is found to be associated with significant abnormality of the arterial blood gas composition, but not with increased abnormality of other measurements of pulmonary function. There are no clinical differences between patients with severe hypoxemia and those with mild hypoxemia. Evidence is presented to support the commonly held view that hypoxemia is largely the result of perfusion of underventilated alveoli.