Comparison of forced oscillation with the conventional method for histamine bronchoprovocation testing in horses.
OBJECTIVE
To compare response of horses to histamine bronchoprovocation (HBP), using total respiratory resistance (Rrs) measured by forced oscillatory mechanics (FOM) with dynamic compliance (Cdyn) and pulmonary resistance (RL) measured by the esophageal balloon method.


METHODS
10 horses with various degrees of airway reactivity.


METHODS
The 2 methods for measuring airway responses to HBP were performed on separate days. Endpoints compared were increase of 150 or 200% of baseline Rrs (PC150Rrs, PC200Rrs) and to 150% of baseline RL (PC150RL) or decrease to 65% of baseline Cdyn (PC65Cdyn). Frequency dependence of respiratory mechanics, using FOM, was evaluated, using the slope of Rrs over 1 to 3 Hz and the ratios of Rrs at 1 Hz to Rrs at 2 and 3 Hz (Rrs1Hz/Rrs2Hz, Rrs1Hz/Rrs3Hz) and of Rrs at 2 Hz to Rrs at 3 Hz (Rrs2Hz/Rrs3Hz). Effect of histamine on frequency dependence was assessed.


RESULTS
Correlation with PC65Cdyn was high for PC150Rrs (rs = 0.93) and PC200Rrs (rs = 0.96). Correlation between PC65Cdyn and PC150RL was weakly positive (rs = 0.61). The slope of Rrs over 1 to 3 Hz changed significantly between baseline (-0.07+/-0.09 cm H2O/L/s/Hz) and final histamine dose (-0.28+/-0.10 cm H2O/L/s/Hz). The Rrs1Hz/Rrs3Hz and Rrs2Hz/Rrs3Hz differed 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 mechanics, as measured by FOM and the pneumotachograph-esophageal balloon method, was good. The FOM results indicated frequency dependence of respiratory mechanics during HBP.


CONCLUSIONS
A noninvasive method of measuring airway reactivity will facilitate routine evaluation of horses with suspected small airway disease and may be suitable for field studies.
Department of Clinical Sciences, School of Veterinary Medicine, Tufts University, North Grafton, MA 01536, USA.
M R
MR
Mazan
A M
AM
Hoffman
N
N
Manjerovic
D000403:Airway Resistance / Q000502:physiology; D000818:Animals; D016535:Bronchial Hyperreactivity / Q000503:physiopathology / Q000662:veterinary*; D001985:Bronchial Provocation Tests / Q000379:methods / Q000662:veterinary*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006632:Histamine; D006734:Horse Diseases / Q000503:physiopathology*; D006736:Horses; D008173:Lung Diseases, Obstructive / Q000503:physiopathology / Q000662:veterinary*; D008297:Male; D015656:Respiratory Mechanics / Q000502:physiology; D018709:Statistics, Nonparametric
D006632:Histamine