Flow interruption compared to forced oscillatory maneuvers and esophageal balloon/pneumotachography for measurement of respiratory resistance in the horse.

Abstract

Pulmonary function testing is critical to the diagnosis of equine asthma (EA), an important cause of respiratory disease in the horse, but its clinical use has remained elusive, unfortunately, due to the complexity of reference methods, esophageal balloon/pneumotachography (EBP), and forced oscillatory mechanics (FOM), so we sought a noninvasive, portable method for use in horses through rapid interruption of airflow for equilibration of alveolar pressure with proximal airway pressure, termed flow interruption (FI). Resistance (R_INT) was computed as the relationship between the change in pressure at the nose before and immediately after interruption and flow immediately before interruption. A pilot study in five healthy university-owned animals using EBP and FI showed good correspondence between the two methods: R_INT (0.33 ± 0.05 cmH₂O/L/s) and R_L (0.31 ± 0.06 cmH₂O/L/s). In two separate populations of client-owned horses, with random assignment of methods to FI versus EBP (n = 8), R_INT showed good correlation with R_L in horses (r_s = 0.995, P = 0.0002) and accords with R_L, with no significant difference between R_INT and R_L. Using FOM (n = 12), R_INT (0.67 ± 0.31 cmH₂O/L/s) has good correlation with R_RS measured with FOM (r = 0.834, P = 0.0001), but is consistently smaller than R_RS (0.74 ± 0.33 cmH₂O/L/s). Histamine bronchoprovocation (HBP) was performed in a subset of these horses: FI classified one horse in six as less reactive than did EBP, and FI classified one horse in seven as less reactive than did FOM.NEW & NOTEWORTHY We developed and document for the first time the use of flow interruption for the rapid and noninvasive measurement of resistance in equine patients and demonstrated short- and long-term stability and accuracy in comparison with the reference methods.