Role of atelectasis in surfactant abnormalities following extracorporeal circulation. A clinical and experimental study

Surface activity of lung extracts was determined in 36 patients and 28 dogs following extracorporeal circulation. Normal results were usually found. Abnormal surface tension was demonstrated only in a few samples obtained from grossly atelectatic or congested portions of lung, normal surface tension being present in adjoining areas of the same lung. Sources of error in surface-tension measurements and factors to be considered in the interpretation of results are discussed. A possible explanation for the discrepancies in results obtained by various investigators is presented.

Effects of atelectasis on pulmonary surfactant and quasi-static lung mechanics

The effects of unilateral atelectasis on pulmonary surfactant activity and lung mechanics have been studied in rabbits. Total left lung collapse was produced by pneumothorax and maintained from 90 min to 8 days. Quasi-static pressure-volume relationships were determined with air and saline after varying intervals. Surface activity of minced lung extracts and of dried foam obtained by tracheal washings was measured on a surface balance. A marked decrease in lung inflatability progressing with duration of collapse was noted during air and saline pressure-volume studies. However, deflation characteristics of all atelectatic lungs were normal. Extracts from minced, in vitro reinflated atelectatic lung showed a variable but significant loss of surface activity compared to the right (normal) lung of the same animal. However, highly surface-active material could be demonstrated in the collapsed lungs by the more efficient extraction procedure of tracheal foaming. Correlation exists therefore between normal volume stability of alveoli after initial inflation and presence of surfactant activity in atelectatic lungs.

pressure-volume relationships; rabbit lung surface activity

Submitted on July 27, 1964

THE CURRENT STATUS OF THE RESPIRATORY DISTRESS SYNDROME OF THE NEWLY BORN

The respiratory distress syndrome (RDS) occurs in 14% of premature infants and is twice as common and twice as lethal in males as in females. Recent work suggests that, during the intrauterine period a disturbance in nutrition of the lung resulting from fetal pulmonary vascular constriction results in alveolar-cell damage and a decrease in pulmonary surface activity with resultant atelectasis. Data on respiratory work levels, oxygen consumption and arterial oxygen tension suggest that there is an oxygen debt in the acute stage of the disease. Such data have further clarified the pathogenesis of the metabolic and respiratory components of the acidosis and the secondary effects thereof. In prevention, prophylaxis of prematurity is of major importance. A program of treatment designed to combat the various aspects of the pathophysiological disturbances is described in the form of a case profile. Modern methods of observation, biochemical control and treatment, as well as the necessity for critical evaluation, suggest that infants with RDS are best cared for in special centres.

Pulmonary Vascular Changes with Chronic Unilateral Pulmonary Hypoxia

One main bronchus was ligated in each of twelve dogs and three calves. In eight of the animals, the bronchus reopened spontaneously with a 2 to 4 mm aperture permitting re-expansion of the associated lung. Both smooth muscle hyperplasia and hypertrophy developed in small arteries of the poorly ventilated dog lungs. In the calves, muscular hyperplasia and hypertrophy developed in small pulmonary veins of the hypoxic lungs. Since arterial pressures and pulmonary arterial oxygen saturation were presumably identical in hypoxic and control lungs, changes in vascular muscle are postulated to be the result of altered oxygen tension of the surrounding alveolar gas.