Long-term physiologic consequences of the adult respiratory distress syndrome

Six survivors of the adult respiratory distress syndrome were studied. Measurements were made of lung volumes, flow rates, single-breath diffusing capacity for carbon dioxide (Dsb), arterial blood gas levels at rest and during exercise, the ratio of physiologic dead space to tidal volume (VD/VT), alveolar-arterial oxygen pressure difference (P[A-a]O2) and percent shunt (using an assumed arteriovenous oxygen content difference). At the time of study, which varied from 3 to 16 months after recovery, we found minor and inconsistent abnormalities in the lung volumes (reduced vital capacity in one patient, elevated residual volume [RV] in two, and reduced RV in three) and in the flow rates (reduced instantaneous forced expiratory flow after 50 percent of the forced vital capacity had been exhaled in two patients). In those tests having to do with transfer of gas, there were more abnormalities, consisting of a decreased Dsb in three patients, an elevated P(A-a)O2 in four, a low resting arterial oxygen pressure (PaO2) in two, a decrease in exercise PaO2 in three, an elevated shunt fraction (Qsan/Qt) in three, and an elevated VD/VT in one patient. Clinically, at the time of study, the patients all had returned to their status before illness.