EFFECT OF TEMPERATURE ON PRESSURE-VOLUME HYSTERESIS OF EXCISED LUNGS

The objective of this study was to determine if the effect of temperat ure on excised lung pressure-volume (P-V) hysteresis during various P- V maneuvers would be consistent with predicted effects based on the re cruitment-derecruitment (R-D) model of lung P-V hysteresis. Three sets of P-V curves were recorded for excised rat lungs at (1) 24 degrees C , (2) either 42 degrees or 45 degrees C, and (3) 24 degrees C. After f ull inflation of the lung, deflation-inflation (D-I) cycles were perfo rmed between total lung capacity (30 cmH(2)O) and successively decreas ing end-expiratory pressures (EEPs). Normalized hysteresis (K) was plo tted vs EEP. K remained relatively constant at EEPs greater than or eq ual to +5 cmH(2)O at 24 degrees C and 42 degrees C and > +5 cmH(2)O at 45 degrees C. Large increases in K occurred as the EEP was further re duced, with the relationship of K vs EEP being shifted to the right at 42 degrees C and 45 degrees C relative to 24 degrees C, with the grea ter shift occurring at 45 degrees C. Previous work has shown that the R-D of lung units contributes to P-V hysteresis and is EEP-dependent, increasing at EEPs less than or equal to +4 +/- 1 cmH(2)O at room temp erature (Cheng et al., 1995). This study suggests that at increased te mperatures, R-D of lung units is initiated at higher EEPs and is more extensive than at room temperature.