Maximal expiratory flow in the guinea pig

Using the whole body plethysmograph, the maximal expiratory flow-volume (MEFV) curve was performed in anesthetized-paralyzed guinea pigs with intact chest (n = 7) and in anesthetized, chest-open animals following exsanguination (n = 13). The pressure-volume (PV) curve was also measured. Before and after the MEFV and PV maneuvers, lung volume was determined with a neon dilution method. Peak maximal expiratory flow (Vmax) of 178 +/- 7 ml/sec occurring at 83% TLC. After the peak flow, Vmax decreased gradually with reducing lung volume. The Vmax-static recoil pressure curve was relatively linear up to PL = 5 cmH2O. Density-dependence of Vmax (helium-Vmax was significantly higher than air-Vmax) was found at or above 60% TLC but not at lung volume below 60% TLC. For the chest-open postmortem guinea pig, Vmax and TLC decreased while trapped gas volume increased gradually with time after exsanguination, indicating that bronchoconstriction gradually became more severe. The magnitude of this postmortem airway spasm was related to age and anesthetic used.