Evaluation of head-out constant volume body plethysmography for measurement of specific airway resistance in conscious, sedated sheep

Objective - To evaluate the use of a modified whole body plethysmograph in awake sheep. Animals - 10 healthy adult sheep. Procedure - Concurrent measurements of specific airway resistance (sR_aw) and pulmonary resistance (R_L) were obtained using a novel noninvasive headout constant-volume plethysmograph and esophageal balloon-pneumotachography, respectively. All data were collected before and after external resistive loading with 1 and 5.6 cm H₂O/L/s. Functional residual capacity (FRC) was measured by helium dilution for computation of airway resistance (R_aw) preloading (R_aw = sR_aw/FRC). Results - The sR_aw and R_L were closely correlated in 10 adult sheep. Additionally, sR_aw and R_L accurately reflected the magnitude of added resistance. The mean FRC was 52 mL/kg and used to calculate R_aw. At baseline, the values for R_aw were significantly correlated with sR_aw and R_L. Conclusions and Clinical Relevance - Precise measurements of sR_aw and R_aw at baseline and sR_aw after external resistive loading were obtained by use of this novel noninvasive plethysmographic technology. This method should have application to veterinary patients or animals used in research in which noninvasive rapid or serial measurements of sR_aw in the conscious state are required.