Functional Residual Capacity and Airway Resistance of the Rat Measured with a Heat- and Temperature-Adjusted Body Plethysmograph

Abstract

The functional residual capacity (FRC) and airway resistance (R_aw) of the rat were measured, using a newly designed body plethysmograph (BPG), the inner environment of which was maintained at body temperature and was water-vapor saturated. The subjects were anesthetized and tracheally intubated male Wistar rats (n = 15). After measuring the FRC and R_aw, we analyzed the effects of inhaled methacholine (Mch, 0–8 mg/ml) on R_aw.The determined FRC was 5.37 ± 0.22 ml (mean ± SE). An almost linear relationship between box pressure and respiratory flow was obtained when the difference between box-gas temperature and the rectal temperature of the rat was less than 1.0°C. The R_aw at FRC was 0.230 ± 0.017 cmH₂O/ml/s. It increased proportionally with increases in the Mch concentration. When the dynamic changes in R_aw were analyzed, the R_aw was found to progressively increase during expiration; this increase continued throughout inspiration. Thus in the rat, R_aw is not simply a function of changes in lung volume. In conclusion, the humidity- and temperature-adjusted BPG provided an absolute and possibly dynamic value of R_aw.