The effects of several gases (He, N2, N2O, and SF6) on gas trapping in excised lungs.
The effect of the composition of certain gases on the gas trapping mechanism in excised lungs of rats was studied, and the involvement of gaseous diffusion was determined. The gases studied were helium (7440597) (He), nitrogen (7727379) (N2), nitrous-oxide (10024972) (N2O), and sulfur-fluoride (2551624) (SF6). Pressure-volume (PL-VL) curves were recorded using excised rat lungs which were degassed and placed in a plethysmograph filled with isotonic saline solution. As liquid surrounding the lungs was pumped from the chamber, the lungs filled with gas through a cannula; deflation occurred when saline was pumped back into the chamber. In the first part of the study lungs were ventilated with 100 percent of one of the gases. Five 10 cycle PL-VL curves were recorded at a different inflation/deflation rates. Characteristic curves for a given gas were determined. In the second part of the study, four 10 cycle PL-VL curves were recorded for each lung. Lungs were ventilated with one of five different fractions of SF6 and oxygen. The relative volume of trapped gas diffusing across a meniscus was computed. Lungs ventilated with N2O trapped more gas at high ventilation rates. As the ventilation rate was reduced, the order in which the gases began to accumulate in the lungs was N2O, He, N2, and finally SF6. A positive correlation was found between the inflation/deflation rate of trapped gas and the diffusion constant for each gas, suggesting that diffusion through menisci or bubbles was responsible for the trapped gas in the lung.