Temperature effects on lung mechanics in air- and liquid-filled rabbit lungs

Effects of temperature on lung pressure-volume (PV) curves and on the reversibility of changes were studied in the range of 4-52 degrees C. Air curves were obtained first at 21 degrees C, then after 60 min equilibration at one of seven test temperatures (4, 21, 32, 37, 42, 47, and 52 degrees C) and finally again at 21 degrees C. In a given lung, peak inflation volume was made identical at all temperatures. Warming from 4 to 42 degrees C steadily diminished both inflation and deflation pressures, but thereafter the trend reversed except on the upper part of the inflation curve. On returning to 21 degrees C, all PV curves were indistinguishable except from 52 degrees C. Liquid PV curves were obtained in a similar way at four temperatures (4, 21, 37, and 52 degrees C). Warming from 4 to 52 degrees C diminished tissue elastic recoil at total lung capacity (TLC) from 17 to 5 cmH2O but raised recoil slightly at lower lung volumes. Liquid PV curves were also reversible except after 52 degrees C. At 37 degrees C the estimated tissue component of the total recoil of air-filled lungs exceeded 95% at 40-60% TLC, and at 21 degrees was 85-90%. This fraction fell to 50% or less at 4 and 52 degrees C, where surface forces failed to reach low levels and alveolar instability resulted.