Temperature affects mechanics and stability during initial inflation-deflation of mature fetal lung.

Volume-pressure (VP) curves of initial aeration of mature (0.94-0.97 term) rabbit fetuses were compared in three groups, respectively, at 37 degrees C, with maximal inflation pressure of 25 cm H2O (P25); 22 degrees C, P25; and 22 degrees C, P30. Anesthetized fetuses were delivered through uterotomy; chest was opened; trachea of fetal pulmonary liquid (FPL)-filled lungs cannulated; and lungs inflated-deflated in 5 cm H2O, 2 min steps under continuous microscopic observation. As distending pressure was increased, FPL moved peripherally with airways inflation by free gas and with saccular recruitment by free gas and bubbles. Saccular aeration continued during initial reduction of P from Pmax. At end-deflation, air was retained in saccules virtually exclusively as bubbles. Airways inflation required less P at 37 degrees C, though airways volume (V) was the same at both temperatures. Opening P was lower, and saccular aeration was larger and more rapid at 37 degrees C. The apparently higher distensibility at 37 degrees C was most likely due to temperature effects on fluid dynamics rather than on tissue elasticity. Maximal V attained during early P reduction in all groups, was total lung capacity (TLC) at 37 degrees C and less than TLC at 22 degrees C. Air retention at end-deflation, with films of near-zero surface tension, was greatest at 37 degrees C and least at 22 degrees C, P25. Lung stability, greater at 37 degrees C than at 22 degrees C, was best discriminated when V at P0 was taken into account.(ABSTRACT TRUNCATED AT 250 WORDS)