• Conny P Herholz, Vinzenz Gerber, Peter Tschudi, Reto Straub, Andrea Imhof, and André Busato.
• Department of Equine Internal Medicine, Faculty of Veterinary Medicine, University of Berne, Länggasstr 124, CH-3012 Berne, Switzerland.
• Am. J. Vet. Res. 2003 Mar 1;64(3):338-45.

ObjectiveTo investigate whether volumetric capnography indices could be used to differentiate between horses without recurrent airway obstruction (RAO) and horses with RAO that were in clinical remission or that had clinically apparent RAO.Animals70 adult Swiss Warmblood horses (20 used for pleasure riding and 50 used for dressage or show jumping).ProcedureHorses were allocated to 4 groups on the basis of history, clinical signs, results of endoscopy, and cytologic findings (group 1, 21 healthy horses; group 2, 22 horses with RAO that were in remission; group 3, 16 horses with mild RAO; group 4, 11 horses with exacerbated RAO). Expiratory volume and CO2 curves were recorded by use of a computerized ultrasonic spirometer. Volumetric capnograms were plotted, and derived indices were calculated.ResultsDead-space volume (VD) was calculated by use of the Bohr equation (VD(Bohr)) and for physiologic VD (VD(phys)). Ratios for VD(Bohr) to expiratory tidal volume (VT) and VD(phys) to V(T) as well as an index of effective CO2 elimination were significantly different among groups of horses. Age and use of the horses also significantly affected volumetric capnography indices.Conclusions And Clinical RelevanceRatios of VD(Bohr) to VT and VD(phys) to VT as well as an index of effective CO2 elimination were sufficiently sensitive measures to distinguish between healthy horses and horses with RAO in remission. To optimize the ability of volumetric capnography indices to differentiate among horses in heterogeneous populations, it is important to account for effects of age and specific use of the horses.

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