PULMONARY SURFACTANT MAINTAINS PATENCY OF CONDUCTING AIRWAYS IN THE RAT

The hypothesis was tested that after extrusion of the liquid columns t hat often block the lumen of conducting airways, the latter will remai n open because of well-functioning pulmonary surfactant preventing the liquid columns from returning. The extirpated lungs of 22 Wistar rats were studied. Via a tracheal tube a very fine catheter (PE 10) was in serted and advanced until it pierced the pleura. It was extracted unti l only 2 mm remained in the lung parenchyma. A pressure transducer mea sured the resistance that met a steady flow of air through the series of tubes: the PE 10 tube, the conducting airway of the lung, and the t racheal tube. The airway resistance was studied for 240 s after three airway flushings, two with saline solution and one with calf lung surf actant extract (CLSE), 3 mg/ml. The pressure recording showed that a l ow pressure, indicating airway patency, occurred for only 31 +/- 8 s ( mean +/- SEM) after the first saline flush, and for 26 +/- 8 s after t he second. After the CLSE flush the airway remained open for 174 +/- 1 2 s, which indicated a significantly reduced resistance (p < 0.0001). The results imply that weil-functioning pulmonary surfactant is requir ed for a low airway resistance.