Whole-Body Barometric Plethysmography Characterizes Upper Airway Obstruction in 3 Brachycephalic Breeds of Dogs

Abstract

Background: A novel test using whole-body barometric plethysmography (WBBP) was developed recently to diagnose brachycephalic obstructive airway syndrome (BOAS) in unsedated French bulldogs.

Hypothesis/objectives: The hypotheses of this study were: (1) respiratory characteristics are different between healthy nonbrachycephalic dogs and brachycephalic dogs; and among pugs, French bulldogs, and bulldogs; and (2) obesity and stenotic nares are risk factors for BOAS. The main objective was to establish a diagnostic test for BOAS in these 3 breeds.

Animals: A total of 266 brachycephalic dogs (100 pugs, 100 French bulldogs, and 66 bulldogs) and 28 nonbrachycephalic dogs.

Methods: Prospective study. Exercise tolerance tests with respiratory functional grading, and WBBP were performed on all dogs. Data from WBBP were associated with functional grades to train quadratic discriminant analysis tools to assign dogs to BOAS+ and BOAS- groups. A BOAS index (0-100%) was calculated for each dog. Receiver operating characteristic (ROC) curves were used to evaluate classification ability.

Results: Minute volume was decreased significantly in asymptomatic pugs (P = .009), French bulldogs (P = .026), and bulldogs (P < .0001) when compared to nonbrachycephalic controls. Respiratory characteristics were different among breeds and affected dogs had a significant increase in trace variation. The BOAS index predicted BOAS status for each breed with 94-97% (95% confidence interval [CI], 88.9-100%) accuracy (area under the ROC curve). Both obesity (P = .04) and stenotic nares (P = .004) were significantly associated with BOAS.

Conclusions and clinical importance: The WBBP can be used as a clinical tool to diagnose BOAS noninvasively and objectively.

Keywords: Brachycephalic obstructive airway syndrome; Quadratic discriminant analysis; Respiratory function test; Whole-body barometric plethysmography.

Figure 1

Definition of the degree of nostril stenosis in brachycephalic dogs. Representative nostrils of French bulldogs with different degrees of stenosis. (A) Open nostrils: nostrils are wide open; (B) Mild stenotic nostrils: slightly narrowed nostrils but the lateral nostril wall does not touch the medial nostril wall. Immediately after the exercise tolerance test (ETT), the nostril wings should move dorsolaterally to open on inspiration. (C) Moderately stenotic nostrils: the lateral nostril wall touches the medial nostril wall at the dorsal part of the nostrils and the nostrils are only open at the bottom. Immediately after the ETT, the nostril wings are not able to move dorsolaterally and there may be nasal flaring (ie, muscle constraction around the nose trying to enlarge the nostrils); (D) Severely stenotic nostrils: nostrils are almost closed. The dog may switch to oral breathing from nasal breathing with stress or very gentle exercise such as playing.

Figure 2

Breaths plotted against three selected respiratory parameters. Twenty representative breaths per dog (represented as crosses), assigned colors for each group with a marked centroid (co‐ordinates of each axis). (A) Nonbrachycephalic control dogs vs Grade 0 brachycephalic dogs; (B) Grade III brachycephalic dogs to be compared with Grade 0 groups in (A); (C)–(E), breed‐specific comparisons between Grade 0 and Grade III dogs. PEF/PIF = peak expiratory flow rate (mL/s)/peak inspiratory flow rate (mL/s); MV/BW = minute volume (mL)/bodyweight (kg); Te/Ti = expiratory time (s)/inspiratory time (s).

Figure 3

Respiratory flow trace samples. (A) Flow traces of a nonbrachycephalic control; (B) Flow trace samples of Grade 0 brachycephalic dogs; (C) Flow trace samples of Grade II/III brachycephalic dogs, showing variations in amplitude, flow pattern, and noise within the trace. Take French bulldog as an example, Type A shows extremely low amplitude when compared to Type B and C; however, the peak flow rates of inspiration and expiration are equal while they are significantly different in Type B. Noise, low amplitude high frequency fluctuations can be seen in all three types mainly during inspiration.

Figure 4

Receiver operating curves (ROC) assess the classification accuracy on diagnostic models for brachycephalic obstructive airway syndrome. The area between 95%CI for the curve is shaded. A cross and the associated values show the cut‐off values chosen for use in the diagnostic test. AUC, area under the curve.