Objective diagnosis of alar fold collapse in active Standardbred trotting racehorses using nasopharyngeal airway pressure measurements.

Abstract

Background: Clinical evaluation of alar fold (AF) collapse is presently based upon subjective evaluation of improvement in breathing and respiratory noise after suturing the AFs dorsally.

Objectives: To evaluate use of nasopharyngeal airway pressure (NAP) as an objective method of assessing for the presence of AF collapse during exercise. NAPs should also potentially provide a precise means to grade the degree of airway obstruction present and response to surgical treatment.

Study design: Prospective clinical study of actively racing Standardbred horses.

Methods: Standardbreds undergoing this test were outfitted with a heart rate monitor and warmed up on the treadmill for approximately 2000 m, prior to instrumentation with the analogue pressure sensor positioned in the nasopharynx. NAPs were measured continuously before and after the AFs were temporarily sutured dorsally, when horses were trotted at a heart rate ≥200 bpm for 2 min under identical testing circumstances. Peak inspiratory and expiratory NAPs were determined for each horse. A two-way repeated measures ANOVA was performed to analyse the effect of suturing the AFs dorsally on inspiratory and expiratory NAPs. When possible, horses were tested again after AF resection surgery.

Results: Twenty-one consecutive cases with suspected AF collapse were tested. Suturing the AFs dorsally had a significant effect on expiratory NAPs (p < 0.001), but not on inspiratory NAPs. Expiratory NAPs decreased from baseline (mean ± SD) 35.8 ± 8.81 cmH₂O to 20.1 ± 7.04 cmH₂O after suturing AFs dorsally; to 13.3 ± 2.29 cmH₂O after complete AF resection in 13 available horses.

Main limitations: Not all horses were available for NAP testing post-operatively.

Conclusions: NAP measurements provided a precise objective means to determine whether a horse was affected with AF collapse and assess improvement in airway function after surgery. AF collapse caused a moderate to marked expiratory airway obstruction in many affected racehorses.