# Characterization of Brachycephalic Obstructive Airway Syndrome in Cats Using Barometric Whole-Body Plethysmography

## TL;DR

This study shows that a non-invasive breathing test can detect and measure airway issues in short-faced cats, helping assess their breathing problems and welfare.

## Contribution

The study demonstrates that barometric whole-body plethysmography is a valid tool for diagnosing and grading upper airway obstruction in brachycephalic cats.

## Key findings

- Brachycephalic cats had significantly lower minute ventilation compared to non-brachycephalic controls.
- High-grade UAO cats showed increased upper airway resistance and altered flow patterns.
- BWBP effectively detected physiological impairments in brachycephalic cats.

## Abstract

Brachycephalic cat breeds refer to cats with a short-nosed or flat-faced conformation, which can be associated with variable severity of upper airway obstruction (UAO) known as brachycephalic obstructive airway syndrome (BOAS). These structural abnormalities may restrict airflow through the upper airway and reduce effective ventilation. This study evaluated whether barometric whole-body plethysmography (BWBP), a non-invasive test that records breathing signals while a cat rests in a chamber after an adaptation period in a quiet environment, can be used clinically to identify and grade UAO severity in brachycephalic cats. Forty-three client-owned cats were enrolled, classified as having high-grade UAO (clinically evident effects on clinical signs or physical examination findings) or low-grade UAO (no clinically evident problems), and compared with healthy non-brachycephalic control cats. Both brachycephalic groups had lower minute ventilation than non-brachycephalic controls, suggesting impaired ventilation. Cats with high-grade UAO also showed additional evidence of limited inspiratory flow and increased upper airway resistance. These results suggest that brachycephalic conformation in cats is associated with functional impairment of ventilation. This study demonstrates that brachycephalic conformation has physiological impacts and should be recognized as a welfare concern in cats. Additionally, BWBP’s ability to detect these changes highlights its value as a diagnostic and grading tool for assessing UAO in cats.

Objectives: To confirm the utility of barometric whole-body plethysmography (BWBP) as a non-invasive, clinical diagnostic test for brachycephalic obstructive airway syndrome (BOAS) in cats. Methods: Client-owned cats belonging to brachycephalic breeds were enrolled and classified into two clinical severity grades of upper airway obstruction (UAO). Brachycephalic cats with high-grade UAO severity (Brachy-H-UAO) represented those with clinically evident effects on clinical signs or physical examination findings, whereas brachycephalic cats with low-grade UAO severity (Brachy-L-UAO) represented those without clinically evident problems. A group of non-brachycephalic (NB) cats that were respiratory disease-free and with neither a history of cardiac or systemic diseases nor exposure to cigarette smoke was used as the control group. Cats were placed in the BWBP chamber, and breathing signals were obtained after an adaptation period in a quiet and silent environment. The ventilatory variables obtained were respiratory rate (RR; [bpm]), tidal and minute volume per kilogram bodyweight (MV/BW and TV/BW; [mL/kg]), inspiratory (Ti; [s]) and expiratory (Te; [s]) intervals, airway obstruction index enhanced pause (Penh), and peak inspiratory and expiratory flows per kilogram (PIF and PEF; [mL/s/kg]). Results: Forty-three client-owned cats (11 Brachy-H-UAO, 7 Brachy-L-UAO, and 25 NB) were included. Brachycephalic cats (Brachy-H-UAO: 311 mL/kg; Brachy-L-UAO: 253 mL/kg) showed significantly lower median MV/BW than NB cats (503 mL/kg) (p = 0.01). Brachy-H-UAO cats demonstrated significantly higher median PEF/PIF ratios (Brachy-H-UAO: 1.46, minimum–maximum 0.82–2.48; Brachy-L-UAO: 0.76, 0.52–1.11; NB: 0.73, 0.56–1.00) and Penh (Brachy-H-UAO: 2.37, minimum–maximum 0.57–23.82; Brachy-L-UAO: 0.57, 0.27–1.11; NB: 0.53, 0.21–0.68) than Brachy-L-UAO and NB cats (p < 0.001). No significant differences were observed among the three groups for RR, TV/BW, Ti, Te, or Te/Ti. Conclusions and Relevance: Cats affected by BOAS demonstrate impaired ventilatory function, with reduced minute ventilation and a distinctive flow pattern and parameters reflecting limited inspiratory flow and increased upper airway resistance. BWBP can serve as a useful tool to diagnose and characterize the severity of BOAS in cats.