Ventilatory impairment and hypoxemia in chronic non-specific lung disease

The relation between arterial oxygen tension at rest (Pao2) and ventilatory performance (VC and FEV1.0) was studied (198 determinations) in a group of 156 patients (11 females) aged 31 to 76 (mean 52.1) years, with chronic non-specific lung disease (asthmatics non included). The average results were 72.7 mmHg for Pao2, 2.87 1 for VC, 1.32 1 for FEV1.0 and 44.9 % for the FEV1.0/VC ratio. Ninety per cent of the patients had ventilatory impairment (FEV1.0 less than 81 % predicted) and 2/3 had hypoxemia (Pao2 less than 75 mmHg). The Pao2 - spirometric variables linear correlation coefficients were of medium value (0.35 to 0.51), but highly significant due to the large number of observations. The correlation was high in patients with severe ventilatory defect (FEV1.0 less than 40% pred.), weak in those with moderate (FEV1.0 41-60 % pred.) and absent in those with minor or absent ventilatory impairment. In respect to the clinical type of obstructive disease, Pao2 and FEV1.0 showed a high correlation (r=0.69) in "bronchitics", a looser one (r=0.45) in "intermediate" patients, and no correlation for "emphysema" patients. The regression equation relating Pao2 and FEV1.0 (Pao2=64.4 + 5.9 X litres) had too high a standard error of estimate (20 % of the mean) to be of practical value.