The surface tension of upper airway secretions in patients with and without respiratory disease.

The alveolar-arterial oxygen partial pressure (PAaO2) difference and surface tension of upper airway secretions (UASST) were simultaneously measured in 33 intubated patients. Patients without respiratory disease had UASST and PAaO2 gradients significantly lower than those with chronic obstructive lung disease. Patients in respiratory failure had UASST and PAaO2 gradients significantly higher than when they were out of failure. Correlation of UASST with PAaO2 was good (r = 0.81). These findings demonstrate that UASST closely correlate with the severity of pulmonary disease and suggest that their measurement may be a simple, clinically applicable method of assessing alveolar surfactant function.