Temperature and hydration: factor affecting increased recoil of excised rabbit lung.

We have examined two factors which strongly affect the rate and amount by which excised rabbit lungs become stiffer during mechanical hyperventilation, Pressure-volume (PV) curves were compared before and after 3 hr ventilation (tidal volume 50% TLC, frequency 8/min, end-expiratory pressure of zero) in the temperature range 4 degrees C to 37 degrees C. Lungs were separated into three groups according to method of suspension: (A) floated on saline, (B) floated on mineral oil, and (C) suspended from the trachea. Lung wet/dry weight ratios (W/D) were obtained from groups A and C. In all lungs marked stiffening occurred below 22 degrees C, but the effect diminished sharply between 22 and 28 degrees C. Lungs not in contact with saline (Groups B and C) revealed little change in recoil above 28 degrees C, whereas those in Group A once again tended to become stiff near 37 degrees C. Lung water content in Group A at 37 degrees C was found to be more than double that in Group C. We conclude that two factors can contribute to the stiffening induced by ventilation: (a) temperature maintained below 27-28 degrees C, or (b) excess lung water in combination with temperature above 28 degrees C.