Comparison of forced oscillation with the conventional method for histamine bronchoprovocation testing in horses

Objective-To compare response of horses to histamine bronchoprovocation (HB P), using total respiratory resistance (R-rs) measured by forced oscillator y mechanics (FOM) with dynamic compliance (C-dyn) and pulmonary resistance (R-L) measured by the esophageal balloon method. Animals-10 horses with various degrees of airway reactivity. Procedure-The 2 methods for measuring airway responses to HBP were performe d on separate days. Endpoints compared were increase of 150 or 200% of base line R-rs (PC150Rrs, PC200Rrs) and to 150% of baseline R-L (PC150RL) or dec rease to 65% of baseline C-dyn (PC65Cdyn). Frequency dependence of respirat ory mechanics, using FOM, was evaluated, using the slope of R-rs over 1 to 3 Hz and the ratios of R-rs at 1 Hz to R-rs at 2 and 3 Hz (R-rs1Hz/R-rs2Hz, R-rs1Hz/R-rs3Hz) and of R-rs at 2 Hz to R-rs at 3 Hz (R-rs2Hz/R-rs3Hz) Eff ect of histamine on frequency dependence was assessed. Results-Correlation with PC65Cdyn was high for PC150Rrs (r(s) = 0.93) and P C200Rrs (r(s) = 0.96). Correlation between PC65Cdyn and PC150RL was weakly positive (r(s) = 0.61). The slope of R-rs over 1 to 3 Hz changed significan tly between baseline (-0.07 +/- 0.09 cm H2O/L/s/Hz) and final histamine dos e (-0.28 +/- 0.10 cm H2O/L/s/Hz). The R-rs1Hz/R-rs3Hz and R-rs2Hz/R-rs3Hz d iffered significantly (P < 0.05 between baseline [1.27 +/- 0.36 and 0.96 +/ - 0.11, respectively] and final histamine dose [1.62 +/- 0.37 and 1.09 +/- 0.14, respectively]). Conclusions-Correlation between histamine-induced changes in respiratory me chanics, as measured by FOM and the pneumotachographesophageal balloon meth od, was good. The FOM results indicated frequency dependence of respiratory mechanics during HBP. Clinical Relevance-A noninvasive method of measuring airway reactivity will facilitate routine evaluation of horses with suspected small airway diseas e and may be suitable for field studies.