Recording of intratracheal pressure in the horse under field conditions as a method for evaluation of upper airway resistance.

Recording of intratracheal pressure during exercise as a method for evaluating upper airway obstruction in the horse has previously been carried out on the treadmill. In the present study the method was applied to normal horses, outdoors under field conditions, to assess its usefulness for analysis of respiratory problems mainly occurring under racing conditions. The horses examined performed a standardized exercise test during which the intratracheal pressure was recorded with a tape recorder receiving amplified signals from a transducer connected to a percutaneously inserted intratracheal catheter. The exercise test was carried out under three different conditions: with (1) sulky or (2) rider outdoors and (3) on treadmill indoors. The latter test was included for comparison between field conditions and treadmill exercise. From the recordings obtained, several respiratory variables were calculated. The pressure graphs essentially resembled those obtained previously in tests performed exclusively on the treadmill. There were, however, some differences between the reactions of the horses to the three tests, which seem to necessitate a control material studied under comparable conditions. The technique is simple and the equipment for the outdoor tests is comparatively inexpensive, qualities which seem to make these tests suitable for studies of upper airway obstructions in clinical routine. Further, the outdoor tests may permit investigations of disorders of the respiratory tract that occur mainly under racing conditions.