Abstract
Airway hyperresponsiveness (AHR) is linked to airway inflammation and is considered a key manifestation of mild/moderate equine asthma (EA). The study purpose was to determine whether two modalities of non-invasive lung function testing (FOM—forced oscillatory mechanics vs. FP—flowmetric plethysmography) establish the same clinical diagnosis of AHR in horses, using histamine bronchoprovocation. Nineteen horses (3–25 years, 335–650 kg) with clinical signs suggestive of mild/moderate equine asthma were enrolled. FOM and FP testing was performed in each horse on two consecutive days, using a randomized cross-over design. AHR was defined by the histamine dose needed to double FOM baseline resistance, or to achieve a 35% increase in FP delta flow. Bronchoalveolar lavage fluid (BALF) was subsequently collected and stained with modified Wright's and toluidine blue stains. Binary statistical tests (related samples T-test, Mann-Whitney U, Chi-square analyses) were performed to compare study groups, with P < 0.05 considered significant. Abnormal BALF cytology confirmed EA in 14/19 (73.7%) horses. Both FOM and FP revealed AHR in 7/14 (50%) of these EA horses. An additional 4/19 (21.1%) horses showed AHR based on FP but not FOM, including two horses with normal BALF cytology. A diagnosis of AHR was more often associated with FP than FOM (P = 0.013), although the prevalence of AHR was significantly higher in EA vs. non-EA horses, regardless of testing methodology. The phase angle between thoracic and abdominal components of breathing did not differ between test groups. In conclusion, FP diagnosed AHR more frequently than did FOM, including horses with no other diagnostic evidence of EA. Without further evaluation, these two testing modalities of AHR cannot be used interchangeably.
Highlights
Airway hyperresponsiveness (AHR) is linked to airway inflammation and is considered a key manifestation of mild/moderate equine asthma or inflammatory airway disease in horses with chronic cough or exercise intolerance [1] as well as in humans with the similar disease, asthma
The diagnosis of equine asthma [1] requires, in addition to appropriate history, a documentation of lower airway inflammation based on bronchoalveolar lavage fluid (BALF) cytology or abnormal pulmonary function testing (PFT) demonstrating AHR
Various methods of pulmonary function testing to document this bronchoconstrictive response are available in horses; invasive methods are more difficult to use in client-owned animals
Summary
Airway hyperresponsiveness (AHR) is linked to airway inflammation and is considered a key manifestation of mild/moderate equine asthma or inflammatory airway disease (hereafter termed EA) in horses with chronic cough or exercise intolerance [1] as well as in humans with the similar disease, asthma. Despite this well-established link, the exact mechanism is still not fully understood [2]. Airway obstruction is determined by subtracting peak plethysmographic flow from peak nasal flow during expiration—a variable defined as delta flow ( flow) This variable is an established measure of airway obstruction and, similar to respiratory system resistance, increases with bronchoconstriction [4]
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