Decision Making in Severe Equine Asthma-Diagnosis and Monitoring

Decision making consists of gathering quality data in order to correctly assess a situation and determine the best course of action. This process is a fundamental part of medicine and is what enables practitioners to accurately diagnose diseases and select appropriate treatment protocols. Despite severe equine asthma (SEA) being a highly prevalent lower respiratory disease amongst equids, clinicians still struggle with the optimization of routine diagnostic procedures. The use of several ancillary diagnostic tests has been reported for disease identification and monitoring, but many are only suitable for research purposes or lack practicality for everyday use. The aim of this paper is to assist the equine veterinarian in the process of decision making associated with managing SEA-affected patients. This review will focus on disease diagnosis and monitoring, while also presenting a flow-chart which includes the basic data that the clinician must obtain in order to accurately identify severely asthmatic horses in their everyday routine practice. It is important to note that European and American board-certified specialists on equine internal medicine can provide assistance in the diagnosis and treatment plan of SEA-affected horses.

Airway Hyperresponsiveness, but Not Bronchoalveolar Inflammatory Cytokines Profiles, Is Modified at the Subclinical Onset of Severe Equine Asthma

Airway hyperresponsiveness (AHR) and inflammation are both observed in human and equine asthma. The aim of this study was to assess the timeline and relationship of both features at the subclinical onset of severe equine asthma (SEA). First, the repeatability of the pulmonary function test (PFT) using impulse oscillometry system, and the methacholine bronchoprovocation test (BPT) were assessed at a 1-day interval on six SEA horses in clinical remission and six control horses. Then, clinical and ancillary tests were performed before and after a 1-week low-dust environmental challenge, including weighted clinical score, respiratory endoscopy, bronchoalveolar fluid cytology, PFT, and BPT. Both PFT and BPT showed acceptable repeatability. No test allowed SEA horses in clinical remission to be distinguished from control, unlike in human patients. Because of the low-dust environment, no significant difference was observed in the results of clinical and conventional ancillary examinations after the challenge. However, SEA horses showed increased AHR after the environmental challenge. At that stage, no signs of inflammation or changes in pro-inflammatory cytokines profiles (quantification and gene expression) were observed, suggesting AHR is present at an earlier stage of equine asthma than airway inflammation. This feature indicates SEA could present in a different disease pathway than neutrophilic human asthma.

Comparison of electrical impedance tomography and spirometry-based measures of airflow in healthy adult horses

Electrical impedance tomography (EIT) is a non-invasive diagnostic tool for evaluating lung function. The objective of this study was to compare respiratory flow variables calculated from thoracic EIT measurements with corresponding spirometry variables. Ten healthy research horses were sedated and instrumented with spirometry via facemask and a single-plane EIT electrode belt around the thorax. Horses were exposed to sequentially increasing volumes of apparatus dead space between 1,000 and 8,500 mL, in 5-7 steps, to induce carbon dioxide rebreathing, until clinical hyperpnea or a tidal volume of 150% baseline was reached. A 2-min stabilization period followed by 2 minutes of data collection occurred at each timepoint. Peak inspiratory and expiratory flow, inspiratory and expiratory time, and expiratory nadir flow, defined as the lowest expiratory flow between the deceleration of flow of the first passive phase of expiration and the acceleration of flow of the second active phase of expiration were evaluated with EIT and spirometry. Breathing pattern was assessed based on the total impedance curve. Bland-Altman analysis was used to evaluate the agreement where perfect agreement was indicated by a ratio of EIT:spirometry of 1.0. The mean ratio (bias; expressed as a percentage difference from perfect agreement) and the 95% confidence interval of the bias are reported. There was good agreement between EIT-derived and spirometry-derived peak inspiratory [-15% (-46-32)] and expiratory [10% (-32-20)] flows and inspiratory [-6% (-25-18)] and expiratory [5% (-9-20)] times. Agreement for nadir flows was poor [-22% (-87-369)]. Sedated horses intermittently exhibited Cheyne-Stokes variant respiration, and a breath pattern with incomplete expiration in between breaths (crown-like breaths). Electrical impedance tomography can quantify airflow changes over increasing tidal volumes and changing breathing pattern when compared with spirometry in standing sedated horses.

Exercise-induced airflow changes in horses with asthma measured by electrical impedance tomography

BACKGROUND

Equine asthma (EA) causes airflow impairment, which increases in severity with exercise. Electrical impedance tomography (EIT) is an imaging technique that can detect airflow changes in standing healthy horses during a histamine provocation test.

OBJECTIVES

To explore EIT-calculated flow variables before and after exercise in healthy horses and horses with mild-to-moderate (MEA) and severe equine asthma (SEA).

ANIMALS

Nine healthy horses 9 horses diagnosed with MEA and 5 with SEA were prospectively included.

METHODS

Recordings were performed before and after 15 minutes of lunging. Absolute values from global and regional peak inspiratory (PIF, positive value) and expiratory (PEF, negative value) flows were calculated. Data were analyzed using a mixed model analysis followed by Bonferroni's multiple comparisons test to evaluate the impact of exercise and diagnosis on flow indices.

RESULTS

Control horses after exercise had significantly lower global PEF and PIF compared to horses with SEA (mean difference [95% confidence interval, CI]: 0.0859 arbitrary units [AU; 0.0339-0.1379], P < .001 and 0.0726 AU [0.0264-0.1188], P = .001, respectively) and horses with MEA (0.0561 AU [0.0129-0.0994], P = .007 and 0.0587 AU [0.0202-0.0973], P = .002, respectively). No other significant differences were detected.

CONCLUSIONS AND CLINICAL IMPORTANCE

Electrical impedance tomography derived PIF and PEF differed significantly between healthy horses and horses with SEA or MEA after exercise, but not before exercise. Differences between MEA and SEA were not observed, but the study population was small.

Comparison of Flowmetric Plethysmography and Forced Oscillatory Mechanics to Measure Airway Hyperresponsiveness in Horses

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.

Bronchoalveolar lavage fluid cytology and airway hyper-reactivity in clinically normal horses

OBJECTIVE

To characterise the relationship between bronchoalveolar lavage fluid (BALF) cytology and pulmonary function testing with histamine bronchoprovocation (HBP) methods in a population of clinically normal horses.

DESIGN

Cross-sectional study METHODS: Clinically normal adult horses (n = 33) underwent pulmonary function testing and HBP with a commercial flowmetric plethysmography system. BAL was performed 1-5 days later. Statistical analysis was used to assess associations between BALF cell concentration, relative inflammatory cell percentages and categorisation, and airway hyper-reactivity (AHR).

RESULTS

AHR (PC₃₅  ≤ 8 mg/mL) was demonstrated in 17 (52%) of the horses. Using current definitions, BALF cytology was consistent with inflammatory airway disease in 14 (42%) of the horses and 7 of those demonstrated either mastocytic and/or eosinophilic responses. There was no correlation between total inflammatory cell counts or relative percentage and AHR. No statistical association was found between BALF inflammatory cell categories and AHR.

CONCLUSION

A direct association between cytological evidence of airway inflammation and AHR was not identified in this population of clinically normal horses. Determining the presence and measuring inflammatory cell mediators in BALF may more accurately reflect AHR. In addition, normal values for cell proportions in BALF may vary between different populations of horses and more appropriate regional reference ranges should be established.

Insect Bite Hypersensitivity in Horses is Associated with Airway Hyperreactivity

Background

Genetic and epidemiologic evidence suggests that in horses, as in other species, different manifestations of hypersensitivity may occur together.

Hypothesis

Horses affected with insect bite hypersensitivity (IBH) show airway hyperreactivity (AH) to inhaled histamine, even in the absence of overt clinical signs of equine asthma (EA).

Animals

Twenty‐two healthy controls (group C), 24 horses suffering from IBH alone (group IBH), and 23 horses suffering from IBH and EA (group IBH/EA).

Methods

The clinical histories were assessed using 2 standardized questionnaires, the Horse Owner Assessed Respiratory Signs Index (HOARSI), and IBH scoring. Horses were classified as EA‐affected if their HOARSI was >1 and as IBH‐affected if IBH score was >0. Confounding disorders were excluded by clinical examination. The arterial partial pressure of oxygen (PaO₂) was measured and flowmetric plethysmography used to assess airway reactivity to increasing doses of inhaled histamine.

Results

The median histamine provocation concentration (PC) when ∆_flow values increased by 35% (PC35) was significantly higher in group C (5.94 [1.11–26.33] mg/mL) compared to group IBH (2.95 [0.23–10.13] mg/mL) and group IBH/EA (2.03 [0.43–10.94] mg/mL; P < 0.01). The PC50 and PC75 showed very similar differences between groups. Furthermore, PaO₂ was significantly lower in group IBH (84 ± 8 mmHg) and group IBH/EA (78 ± 11 mmHg) compared to group C (89 ± 6 mmHg; P < 0.01).

Conclusions and Clinical Importance

IBH is associated with AH and decreased PaO₂, even in the absence of overt respiratory clinical signs.

Effect of Dexamethasone and Fluticasone on Airway Hyperresponsiveness in Horses With Inflammatory Airway Disease

Background

Airway hyperresponsiveness (AWHR), expressed as hypersensitivity (PC₇₅R_L) or hyperreactivity (slope of the histamine dose‐response curve), is a feature of inflammatory airway disease (IAD) or mild equine asthma in horses. Glucocorticoids are used empirically to treat IAD.

Objectives

To determine whether dexamethasone (DEX) (0.05 mg/kg IM q24h) and inhaled fluticasone (FLUT) (3,000 μg q12h) administered by inhalation are effective in decreasing AWHR, lung inflammation, and clinical signs in horses with IAD.

Methods

A randomized crossover study design was used. Eight horses with IAD were assigned to a treatment group with either DEX or FLUT. Measured outcomes included lung mechanics during bronchoprovocative challenges, bronchoalveolar lavage fluid (BALF) cytology, and scoring of clinical signs during exercise.

Results

Dexamethasone and FLUT abolished the increase in R_L by 75% at any histamine bronchoprovocative dose in all horses after the first week of treatment. However, after 2 weeks of FLUT treatment, 1 horse redeveloped hypersensitivity. There was a significant decrease in the number of lymphocytes after treatment with both DEX and FLUT (P = .039 for both) but no significant differences in other BALF cell types or total cell counts (P > .05). There was no difference in the scoring of the clinical signs during each treatment and washout period (P > .05).

Conclusions and Clinical Importance

Both DEX and FLUT treatments significantly inhibit airway hypersensitivity and hyperreactivity in horses with IAD. There are no significant effects on the clinical signs or the number of inflammatory cells (except lymphocytes) in BALF. The treatments have no residual effect 3 weeks after discontinuation.

Cardiac and Respiratory Disease in Aged Horses

Respiratory and cardiac diseases are common in older horses. Advancing age is a specific risk factor for cardiac murmurs and these are more likely in males and small horses. Airway inflammation is the most common respiratory diagnosis. Recurrent airway obstruction can lead to irreversible structural change and bronchiectasis; with chronic hypoxia, right heart dysfunction and failure can develop. Valvular heart disease most often affects the aortic and/or the mitral valve. Management of comorbidity is an essential element of the therapeutic approach to cardiac and respiratory disease in older equids.

Inflammatory Airway Disease of Horses--Revised Consensus Statement

The purpose of this manuscript is to revise and update the previous consensus statement on inflammatory airway disease (IAD) in horses. Since 2007, a large number of scientific articles have been published on the topic and these new findings have led to a significant evolution of our understanding of IAD.

Association between inflammatory airway disease of horses and exposure to respiratory viruses: a case control study

Background

Inflammatory airway disease (IAD) in horses, similar to asthma in humans, is a common cause of chronic poor respiratory health and exercise intolerance due to airway inflammation and exaggerated airway constrictive responses. Human rhinovirus is an important trigger for the development of asthma; a similar role for viral respiratory disease in equine IAD has not been established yet.

Methods

In a case–control study, horses with IAD (n = 24) were compared to control animals from comparable stabling environments (n = 14). Horses were classified using pulmonary function testing and bronchoalveolar lavage. PCR for equine rhinitis virus A and B (ERAV, ERBV), influenza virus (EIV), and herpesviruses 2, 4, and 5 (EHV-2, EHV-4, EHV-5) was performed on nasal swab, buffy coat from whole blood, and cells from BAL fluid (BALF), and serology were performed. Categorical variables were compared between IAD and control using Fisher’s exact test; continuous variables were compared with an independent t-test. For all analyses, a value of P <0.05 was considered significant.

Results

There was a significant association between diagnosis of IAD and history of cough (P = 0.001) and exercise intolerance (P = 0.003) but not between nasal discharge and IAD. Horses with IAD were significantly more likely to have a positive titer to ERAV (68 %) vs. control horses (32 %). Horses with IAD had higher log-transformed titers to ERAV than did controls (2.28 ± 0.18 v.1.50 ± 0.25, P = 0.038). There was a significant association between nasal shedding (positive PCR) of EHV-2 and diagnosis of IAD (P = 0.002).

Conclusions

IAD remains a persistent problem in the equine population and has strong similarities to the human disease, asthma, for which viral infection is an important trigger. The association between viral respiratory infection and development or exacerbation of IAD in this study suggests that viral infection may contribute to IAD susceptibility; there is, therefore, merit in further investigation into the relationship between respiratory virus exposure and development of IAD.

Age effects on blood gas, spirometry, airway reactivity, and bronchoalveolar lavage fluid cytology in clinically healthy horses

Background

Despite the increasing number of geriatric horses attended by veterinarians, there is a lack of understanding of aging‐related changes on the respiratory system of horses.

Objective

To identify aging‐related changes on the respiratory function and bronchoalveolar lavage fluid (BALF) cytology of horses.

Animals

Fifteen healthy young adult (2–11 years) and 16 healthy aged (≥20 years) horses.

Methods

The respiratory system was examined by measurement of arterial blood gases (ABG), use of respiratory inductive plethysmography (RIP) for assessment of breathing pattern and ventilatory parameters, histamine bronchoprovocation, and BALF cytology.

Results

No significant differences were detected with regard to values obtained by ABG or bronchoprovocation of young adult and aged healthy horses. In aged horses, there were significant differences in mean ± SD of the following parameters when compared to young horses: prolonged expiratory time (Te) measured by RIP (3.9 ± 1.5 s versus 3.0 ± 0.6 s), decreased percentage of alveolar macrophages (40.6 ± 11.3% versus 53.5 ± 9.6%), and increased percentage of lymphocytes (53.4 ± 9.5% versus 43.9 ± 11.0%). No correlations between airway reactivity and ventilatory parameters, ABG, or BALF cytology were found in this asymptomatic population.

Conclusions

These results suggest that aging does not cause changes in the results obtained by ABG, most RIP‐derived variables, and bronchoprovocation in the horse. A decreased percentage of macrophage and an increased percentage of lymphocytes in the BALF cytology may be expected in the asymptomatic geriatric horse and may be a result of aging.

Recurrent airway obstruction: a review

Recurrent airway obstruction is a widely recognised airway disorder, characterised by hypersensitivity-mediated neutrophilic airway inflammation and lower airway obstruction in a subpopulation of horses when exposed to suboptimal environments high in airborne organic dust. Over the past decade, numerous studies have further advanced our understanding of different aspects of the disease. These include clarification of the important inhaled airborne agents responsible for disease induction, improving our understanding of the underlying genetic basis of disease susceptibility and unveiling the fundamental immunological mechanisms leading to establishment of the classic disease phenotype. This review, as well as giving a clinical overview of recurrent airway obstruction, summarises much of the work in these areas that have culminated in a more thorough understanding of this debilitating disease.

Using plethysmography to determine erythropoietin's impact on neural control of ventilation

The evaluation of respiratory parameters often requires the use of anesthetics (that depress the neural -network controlling respiration), and/or ways to restrain the animal's mobility (that produces a stress-dependent increase of respiration). Consequently, the establishment of plethysmography represented an invaluable technique in respiratory physiology. Plethysmography, indeed, allows the assessment of ventilatory parameters on living, unanesthetized, and unrestrained animals. The conception of the barometric plethysmography relies on the fact that an animal placed inside a hermetically closed chamber generates through its breathing a fluctuation of pressure in the chamber than can be recorded. Thus, the respiratory frequency and the tidal volume can be directly measured, while the animal's ventilation is calculated indirectly by the multiplication of these two parameters. In our hands, plethysmography was a key tool to investigate the impact of erythropoietin (Epo) on the neural control of hypoxic ventilation in mice.

Respiratory mechanics and results of cytologic examination of bronchoalveolar lavage fluid in healthy adult alpacas

OBJECTIVE

To evaluate respiratory mechanical function and bronchoalveolar lavage (BAL) cytologic results in healthy alpacas.

ANIMALS

16 client-owned adult alpacas.

PROCEDURES

Measurements of pulmonary function were performed, including functional residual capacity (FRC) via helium dilution, respiratory system resistance via forced oscillatory technique (FOT), and assessment of breathing pattern by use of respiratory inductive plethysmography (RIP) in standing and sternally recumbent alpacas. Bronchoalveolar lavage was performed orotracheally during short-term anesthesia.

RESULTS

Mean ± SD measurements of respiratory function were obtained in standing alpacas for FRC (3.19 ± 0.53 L), tidal volume (0.8 ± 0.13 L), and respiratory system resistance at 1 Hz (2.70 ± 0.88 cm H(2)O/L/s), 2 Hz (2.98 ± 0.70 cm H(2)O/L/s), 3 Hz (3.14 ± 0.77 cm H(2)O/L/s), 5 Hz (3.45 ± 0.91 cm H(2)O/L/s), and 7 Hz (3.84 ± 0.93 cm H(2)O/L/s). Mean phase angle, as a measurement of thoracoabdominal asynchrony, was 19.59 ± 10.06°, and mean difference between nasal and plethysmographic flow measurements was 0.18 ± 0.07 L/s. Tidal volume, peak inspiratory flow, and peak expiratory flow were significantly higher in sternally recumbent alpacas than in standing alpacas. Cytologic examination of BAL fluid revealed 58.52 ± 12.36% alveolar macrophages, 30.53 ± 13.78% lymphocytes, 10.95 ± 9.29% neutrophils, 0% mast cells, and several ciliated epithelial cells.

CONCLUSIONS AND CLINICAL RELEVANCE

Pulmonary function testing was tolerated well in nonsedated untrained alpacas. Bronchoalveolar lavage in alpacas yielded samples with adequate cellularity that had a greater abundance of neutrophils than has been reported in horses.

Pulmonary function measurements immediately after exercise are correlated with neutrophil percentage in tracheal aspirates in horses with poor racing performance

Inflammatory airway disease (IAD) is common in racehorses, and is a cause of wastage in the industry. IAD has been diagnosed by measurement of percent neutrophils (N%) in tracheal aspirates (TA). The aim of this study was to investigate whether spirometric indices of pulmonary function were correlated with N% in TAs. Limits to breathing were measured by analyses of relationships between relative times and relative respiratory gas flows during inspiration and expiration in individual breaths recorded after exercise. Horses with higher N% had significantly lower relative gas flows at the same relative times during inspiration and expiration, suggesting a limit to breathing. These findings confirm a physiological basis for the measurement of N% in TA after exercise for diagnosis of IAD. Spirometric pulmonary function testing using analyses of individual breaths after exercise has application for assessment of pulmonary function and poor exercise performance.