Time course of lung function changes in atypical pneumonia.

We measured pulmonary function in each of 21 patients suffering from "atypical", non-bacterial pneumonia during the acute illness and during convalescence (two to 18 months) to study the course and the nature of functional impairment at different stages of the disease. In six patients, no aetiological agent was found. An aetiological agent was identified in 15 of the patients: Mycoplasma pneumoniae (seven patients), influenza A (three patients), parainfluenza 3 (one patient), varicella (two patients), Q fever (one patient), coxsackie B3 (one patient). At the time of admission we observed a restrictive pattern in 52%, an obstructive pattern (decreased FEV1/FVC ratio) in 52% abnormalities in distribution of ventilation (abnormal slope of phase 3) in 63%, and abnormalities in gas exchange (increased AaDO2) in 75% of the patients. The frequency of abnormalities in these pulmonary function tests decreased dramatically after two to four weeks and nearly disappeared in most patients during convalescence. The only major residual abnormality was a decreased FEV1/FVC ratio in five subjects, four of whom were smokers. However, when MMEF and V75 were measured at this stage, their average value for all the groups of patients with the exclusion of the Mycoplasma pneumoniae group, was markedly reduced. These data suggest that small airways involvement can be demonstrated during the convalescence of patients recovering from various types of atypical pneumonia other than those caused by Mycoplasma pneumoniae.