Characterisation of Brachycephalic Obstructive Airway Syndrome in French Bulldogs Using Whole-Body Barometric Plethysmography

Assessment of computed tomography derived cricoid cartilage and tracheal dimensions to evaluate degree of cricoid narrowing in brachycephalic dogs

The aims of this observational, analytical, retrospective study were to (i) obtain computed tomographic (CT) cricoid dimensions (height, width, and transverse-sectional area), (ii) compare the cricoid dimensions between brachycephalic and mesaticephalic breeds, and (iii) compare cricoid cartilage dimensions between dogs without and affected with brachycephalic airway syndrome. The study is important to help to further evaluate and understand the anatomical components of brachycephalic airway syndrome. Measurements were performed in 147 brachycephalic and 59 mesaticephalic dogs. The cricoid cartilage was found to be significantly more oval in Pugs and French Bulldogs compared to mesaticephalic breeds. The cricoid cartilage transverse-sectional area was smallest for the Pug and, after adjusting for weight, significantly smaller for Pugs (P < 0.001), Boston Terriers (P = 0.001), and French Bulldogs (P < 0.001) compared to Jack Russell Terriers. The tracheal transverse-sectional area at C4 of English Bulldogs was significantly smaller than for Jack Russell Terriers (P = 0.005) and Labradors (P < 0.001). The cricoid cartilage transverse-sectional area:weight ratio was significantly lower in brachycephalic breeds compared to mesaticephalic breeds (P < 0.001). The cricoid cartilage:trachea at C4 transverse-sectional area for brachycephalic dogs was significantly larger than for mesaticephalic dogs (<0.001), demonstrating that the trachea was the narrowest part of the airway. No significant differences were found for cricoid dimensions between dogs affected with and without brachycephalic airway syndrome. However, large individual variation was found among the brachycephalic breeds and further studies investigating the relationship between cricoid cartilage size, laryngeal collapse, concurrent tracheal hypoplasia, and/or severity of brachycephalic airway syndrome are warranted.

Outcomes and prognostic factors of surgical treatments for brachycephalic obstructive airway syndrome in 3 breeds

OBJECTIVE

To determine prognostic indicators for the surgical treatment of brachycephalic obstructive airway syndrome (BOAS) and to compare the prognosis of 2 multilevel surgical procedures.

STUDY DESIGN

Prospective clinical study.

SAMPLE POPULATION

Client-owned pugs, French bulldogs, and bulldogs (n = 50).

METHODS

Noninvasive whole-body barometric plethysmography (WBBP) was used to assess respiratory function before, 1 month and 6 months after upper airway corrective surgery. Postoperatively, BOAS indices (ie, ascending severity score generated from WBBP data, 0%-100%) that equaled to or exceeded the cut-off values of BOAS in the diagnostic models were considered to have a "poor prognosis." A multivariate logistic regression was used to assess predictors for prognosis.

RESULTS

The median BOAS indices decreased after surgery (from 76% to 63%, P < .0001), although dogs with indices in this range would still be considered clinically affected. Age (odds ratios [OR] = 0.96, 95% confidence interval [CI]: 0.93-0.99, P < .05), body condition (OR = 0.06, 95% CI: 0.01-0.39, P < .01), laryngeal collapse (OR = 6.1, 95% CI: 1-37.22, P < .05), and surgical techniques (OR = 7.94, 95% CI: 1.17-54.01, P < .05) were associated with postoperative prognosis. The multivariate model suggests modified multilevel surgery (MMS) may have a better outcome than traditional multilevel surgery (TMS) (P = .034). The positive predictive value of the logistic model was 84% (95% CI: 68-94%) and the area under the receiver operating characteristic (ROC) curve was 89% (95% CI: 78-99%, P <.0001).

CONCLUSIONS

Younger age, normal body condition, presence of laryngeal collapse, and treatment with TMS were negative prognostic factors after surgical treatment of BOAS. MMS is recommended, particularly in dogs with a higher probability of poor prognosis.

Severe brachycephalic obstructive airway syndrome is associated with hypercoagulability in dogs

We evaluated whether dogs with severe brachycephalic obstructive airway syndrome (BOAS) developed a hypercoagulable state similar to people with obstructive sleep apnea. Five dogs with grade 3 BOAS were included as well as 5 healthy control Labrador Retrievers. Venous blood samples were collected from each dog for performance of thromboelastography and determination of hematocrit and platelet count. Groups were compared using a t-test, with p < 0.05 considered significant. Thromboelastography results identified that all BOAS dogs were hypercoagulable compared to the Labradors, having significantly shortened clotting time with increased angle, maximal amplitude, and clot rigidity. BOAS dogs also had evidence of delayed fibrinolysis. These results are consistent with, but more severe than, those previously documented in apparently healthy Bulldogs. Together, these findings support the presence of a hypercoagulable state in brachycephalic dogs, and suggest that this state is amplified by increasing severity of BOAS.

Comparison of submaximal exercise test results and severity of brachycephalic obstructive airway syndrome in English bulldogs

Canine brachycephalic obstructive airway syndrome (BOAS) is a complex respiratory disease related to congenitally flattened facial and skull anatomy. BOAS causes respiratory distress, heat and exercise intolerance, and gastrointestinal signs. English bulldogs (EB) have a high prevalence of BOAS. Currently, the severity of BOAS signs in veterinary practice is assessed subjectively. To reduce BOAS in brachycephalic breeds, an objective and easy-to-use tool could help breeders select healthier animals. Exercise tests, such as the 6 min walk test (distance walked measured) or the 1000 m walk test (duration measured), could be used to assess the severity of BOAS, as exercise intolerance and impaired recovery are key features of BOAS. This study evaluated the severity of signs and anatomic components of BOAS in a group of prospectively recruited young adult EBs (n = 28) and investigated the correlations of the 6 min walk test or the 1000 m walk test with a veterinary assessment of BOAS severity, using an ordinal 4 level scale of respiratory signs. EBs with more severe BOAS walked a shorter distance, more slowly and their recovery from exercise took longer than those with only mild signs of BOAS. Control dogs of different breeds (n = 10) performed the exercise tests significantly better (i.e. longer distance, faster time and recovery) than EBs. Increases in body temperature during exercise were significantly higher in EBs than in controls. The results of this study support the use of exercise tests for objective evaluation of the severity of BOAS in EBs.

Flat Feline Faces: Is Brachycephaly Associated with Respiratory Abnormalities in the Domestic Cat (Felis catus)?

There has been little research into brachycephalism and associated disorders in cats. A questionnaire aimed at cat owners was used to determine the relationship between feline facial conformation and owner-reported cat management requirements and respiratory abnormalities. Owner-submitted photographs of cats were used to develop novel measures of skull conformation. One thousand valid questionnaires were received. Within these there were 373 valid photographs that allowed measurement of muzzle ratio (M%) and 494 that allowed nose position ratio (NP%). The data included 239 cats for which both measurements were available. Owners reported lifestyle factors (e.g. feeding type, grooming routine, activity level), physical characteristics (e.g. hair length) and other health characteristics of their cat (e.g. tear staining, body condition score). A composite respiratory score (RS) was calculated for each cat using their owner’s assessment of respiratory noise whilst their cat was asleep and then breathing difficulty following activity. Multivariate analyses were carried out using linear models to explore the relationship between RS and facial conformation, and lifestyle risk factors. The results showed that reductions in NP% and M% were significantly associated with RS (P < 0.001 and P = 0.026, respectively) and that the relationship was significantly negatively correlated (r = -0.56, P < 0.001 for both). Respiratory score was also significantly associated with increased presence of tear staining (P < 0.001) and a sedentary lifestyle (P = 0.01). This study improves current knowledge concerning cats with breeding-related alterations in skull confirmation and indicates that brachycephalism may have negative respiratory implications for cat health and welfare, as has been previously shown in dogs.

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

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.