Doctoral Thesis
Diagnosis of mild to moderate equine asthma in Australian horses: Investigation of the diagnostic confirmatory tests of bronchoalveolar lavage cytology and pulmonary function testing
Doctor of Philosophy (PhD), Murdoch University
2023
Abstract
Mild to moderate equine asthma (mEA) occurs commonly and clinical signs can be vague. Conformation is usually made with bronchoalveolar lavage fluid (BALF) cytology. This test provides indirect evidence of pulmonary dysfunction, but has a number of limitations. Direct testing of pulmonary function is difficult in clinical practice. This thesis aimed to explore diagnostic techniques of mEA in Australian horses, with particular emphasis on the mast cell variant.
The first aim was to explore prevalence, seasonality and relationships between clinical signs, BALF cytology and pulmonary dysfunction. A mixed mast cell phenotype of mEA occurred commonly. An association with BALF cytology and nasal discharge and the presence of a cough was identified. Cytological phenotypes were significantly associated with season. Pulmonary dysfunction was assessed using histamine induced airway reactivity measured by flowmetric plethysmography (FP). In horses with mEA characterised using higher cut off BALF relative cell percentages, airway hyperreactivity (AHR) was evident. Mixed cell responses were more likely to display AHR when mast cells exceeded 2%, whereas AHR was only evident when sole mast cell percentages were ³5%.
The second aim of the thesis was to explore the feasibility of electrical impedance tomography (EIT) an emerging clinically applicable pulmonary function test to demonstrate airflow alteration, a feature of equine asthma. It was demonstrated EIT could detect histamine-induced changes in gas flow at the level of the lungs. The studies explored regional assessment of pulmonary function by EIT, evaluation of subsequent airflow changes after drug-induced bronchodilatation, and novel EIT variables which provide additional information on changes in breathing pattern during bronchoconstriction.
A mixed mast cell phenotype of mEA occurs commonly in Australian horses and is associated with AHR. The associations differed from other studies and provided evidence of the challenges in using BALF cytology as a sole confirmatory test of mEA. Diagnostic conformation of mEA should be through assessment of pulmonary function. Electrical impedance tomography shows great potential as diagnostic tool to assess equine asthma in clinical practice.
Details
- Title
- Diagnosis of mild to moderate equine asthma in Australian horses: Investigation of the diagnostic confirmatory tests of bronchoalveolar lavage cytology and pulmonary function testing
- Authors/Creators
- Cristy J Secombe
- Contributors
- Martina Mosing (Supervisor) - Murdoch University, Centre for Sustainable Aquatic EcosystemsGuy Lester (Supervisor)Ian Robertson (Supervisor)
- Awarding Institution
- Murdoch University; Doctor of Philosophy (PhD)
- Identifiers
- 991005575464807891
- Murdoch Affiliation
- School of Veterinary Medicine
- Resource Type
- Doctoral Thesis
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