Respiratory mechanics in the anesthetized rat

capacity (FRC) and pressure-volume (PV) curves of the lung, chest wall, and total respiratory system were studied in 15 anesthetized rats, weighing 307 t IO (SE) g. Pleural pressure was estimated from the esophageal pressure measured with a water-filled catheter. The FRC determined by body plethys-mograph was slightly and significantly larger than FRC determined from saline displacement of excised lungs. The difference may be accounted for by 0, uptake by lung tissue, escape of CO, through the pleura, and abdominal gas. Paral-ysis in the prone position did not affect FRC, and abdominal gas content contributed only slightly to the FRC measured by body plethysmograph. Values of various pulmonary parame-ters (mean * SE) were as follows: residual volume, 1.26 k 0.13 ml; FRC, 2.51 t 0.20 ml; total lung capacity, 12.23-t- 0.55 ml; compliance of the lung, 0.90-+ 0.06 ml/cmH,O; chest wal