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The severity of dyspnea (MRC scale) was confronted to the blood carbon dioxide tension (PaCO2) in 45 patients with chronic nonspecific lung disease having moderate or severe airway obstruction (FEV1.0 of less than 1.5 liters). The patients were classified as "bronchitic", "emphysematous" and "intermediate" using a 10- criterion (clinical, roentgenologic and biological) "emphysema score". No correlation between dyspnea grade and PaCO2 was found in "bronchitic" and "intermediate" patients; in the "emphysematous" subgroup PaCO2 tended to rise as dyspnea was more severe, but the linear correlation coefficient (r= +0.37) did not reach the significance threshold, which is high (0.468) for such a limited number of observations.

The dyspnea grade (MRC scale) was confronted with the arterial oxygen tension (PaO2) measured at rest in a group of 51 patients with chronic obstructive lung disease with moderate or severe impairment of ventilatory function (FEV 1.0 less than 1.5 1). For the group as a whole no correlation was found, but in the "bronchitic" subgroup (clinical-roentgenologic and biologic criteria) a tendency of PaO2 to decrease with the increase in dyspnea severity was apparent. The linear correlation coefficient did not attain the significance threshold owing to the limited number of observations (r = 0.46; p greater than 0.05).

The measurement of arterial blood oxygen tension (PaO2) in 54 patients with chronic nonspecific lung disease with a FEV1.0 of 1.51 or less, in a stable clinical state, at rest, indicated subnormal results to be more frequent among "bronchitics" (79 per cent with hypoxemia) than than among "emphysematous" patients (63 per cent with hypoxemia). The patients were classified according to a mixed clinical-roentgenologic-biological "score" (Nash et al., 1965). A significant correlation was found between PaO2 and the "emphysema score" (r=0.36; p less than 0.01). The average PaO2 was significantly (p less than 0.02) lower in "bronchitics" (65.5 +/- 8.8 mmHg; n = 14) as compared to the "emphysema" group (71.8 +/- 5.7; n = 19), in agreement with the data of the literature.

The interrelationships of breath holding lung transfer factor (TCO) and transfer coefficient (KCO) with ventilatory obstruction (FEV1.0) and FEV1.0/VC) and hyperinflation (RV and RV/TLC) were studied in 37 patients with chronic nonspecific lung disease with a FEV1.0 of 1.5 litre or less classified as "bronchitic", "emphysematous" or "intermediate" according to Nash, Briscoe and Cournand (1965). No relationships could be found between TCO and airway obstruction or hyperinflation. KCO tended to decrease as RV increased (r=-0.26) and was weakly related to the FEV1.0/VC ratio in "intermediate" (r=0.34) and "emphysema" (r=0.29) patients but these relationships were nonsignificant.