The effect of high oxygen tensions on the mechanical properties of rat lungs.

1. The average mechanical properties of groups of lungs or lung-thorax systems from pathogen-free rats weighing approximately 200 g were determined. Static pressure-volume curves and resistances to air-flow were obtained.2. Six series, each of sixteen rats, were studied. Eight experimental rats in each series were exposed to 4 atm O(2) (OHP) in a transparent pressure chamber; the other eight rats, which served as controls, were obtained from the breeder at the same time and studied at the same time.3. In four series, the experimental animals were killed 10 min after gasping due to OHP had been definitely established. One series was a control in which experimental animals were exposed to 4 atm of pressure in an atmosphere containing oxygen at a tension of 150 mm Hg for 190 min. The experimental animals in the sixth series were exposed to 4 atm O(2) for 2 hr and none of them gasped.4. Gross and histological examination of sixteen rats, eight of which were killed after 10 min of gasping at 4 atm O(2), showed that at this stage of intoxication there was no evidence of pulmonary pathology.5. In none of the series studied were the static pressure-volume curves for deflation shifted, i.e. OHP did not affect the elastic properties of the lungs or the alveolar surfactant.6. In two series studied 10 min after gasping behaviour had been established there was a significant decrease of resistance to air-flow and a shift to the left of the static pressure-volume curve for inflation with air. The rats in both these series were sedated with pentobarbitone and then killed with pentobarbitone injected into the jugular vein.7. The decrease in resistance to air-flow was interpreted as broncho-dilatation and a possible mechanism whereby OHP produces broncho-dilatation is discussed.