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Topic:Recurrent Airway Obstruction
Recurrent Airway Obstruction (RAO) is a chronic respiratory condition in horses characterized by airway inflammation, bronchoconstriction, and mucus accumulation. It is often triggered by exposure to environmental allergens such as dust, mold, and pollen. Horses with RAO exhibit symptoms including coughing, nasal discharge, and labored breathing, particularly during exercise or in dusty environments. The condition is comparable to asthma in humans and can significantly impact a horse's respiratory function and performance. This page compiles peer-reviewed research studies and scholarly articles that explore the pathophysiology, diagnosis, management, and treatment of Recurrent Airway Obstruction in equine populations.
Modulation of ACh release from airway cholinergic nerves in horses with recurrent airway obstruction. To evaluate the functional status of neuronal alpha2-adrenoceptors (ARs) and beta2-ARs on ACh release in horses with recurrent airway obstruction (RAO), we examined the effects of the physiological agonists epinephrine (Epi) and norepinephrine (NE) and the beta2-agonists RR- and RR/SS-formoterol on ACh release from airway cholinergic nerves of horses with RAO. Because SS-formoterol, a distomer of the beta2-agonist, increases ACh release from airways of control horses only after the autoinhibitory muscarinic receptors are blocked by atropine, we also tested the hypothesis that if there is an M2...
Variations in systemic and pulmonary endothelin-1 in horses with recurrent airway obstruction (heaves). Recurrent airway obstruction (RAO) is an asthma-like condition of the horse that represents a major cause of morbidity and loss of performance. The exact pathogenesis of asthma in man is unclear but the role of endothelin (ET) is currently under investigation, thus sparking interest in the bronchoconstrictive and vasoconstrictive properties of endothelin in the equine-specific disease entity. In this study, we investigated the levels of ET-1 in systemic blood, as well as in bronchoalveolar lavage (BAL) from horses with RAO. We also studied how these values might correlate with those of lung fu...
Cytologic evaluation of bronchoalveolar lavage fluid from horses with recurrent airway obstruction after aerosol and parenteral administration of beclomethasone dipropionate and dexamethasone, respectively. To determine cytologic changes in horses with recurrent airway obstruction (heaves) after administration of aerosolized beclomethasone dipropionate and dexamethasone parenterally. Methods: 6 horses with inducible and reversible heaves. Methods: Episodes of heaves were induced by exposure to moldy hay and straw for 7 days. Horses were assigned to treatment groups (aerosolized beclomethasone, parenterally administered dexamethasone, aerosolized propellant), and pulmonary inflammation was evaluated by serial cytologic examination of bronchoalveolar lavage (BAL) fluid samples obtained on days 0, 7...
Pulmonary function in horses with recurrent airway obstruction after aerosol and parenteral administration of beclomethasone dipropionate and dexamethasone, respectively. To determine changes in clinical signs of disease and response to pulmonary function testing in horses with recurrent airway obstruction (heaves) after aerosol and parenteral administration of beclomethasone dipropionate and dexamethasone, respectively. Methods: 6 horses with inducible and reversible heaves. Methods: Episodes of heaves were induced by exposure (challenge) to moldy hay and straw for 7 days. Horses were assigned to treatment groups (aerosolized beclomethasone dipropionate, parenterally administered dexamethasone, aerosolized propellant [control]), and respiratory frequency and s...
Alteration in adrenocortical function in horses with recurrent airway obstruction after aerosol and parenteral administration of beclomethasone dipropionate and dexamethasone, respectively. To determine alteration in adrenocortical function in horses with recurrent airway obstruction (heaves) after aerosol and parenteral administration of beclomethasone dipropionate and dexamethasone, respectively. Methods: 6 horses with inducible and reversible heaves. Methods: Episodes of heaves were induced by exposure to moldy hay and straw for 7 days (natural challenge). Horses then underwent treatment (aerosolized beclomethasone, parenterally administered dexamethasone, and aerosolized propellant) for 7 days. Horses remained in the mold-contaminated environment for 7 days after discontinuat...
Epiglottic retroversion as a cause of upper airway obstruction in two horses. Many disorders of the upper respiratory tract which cause severe
respiratory compromise and poor performance have been
described in the equine athlete (Williams et al. 1990; Morris 1991;
King et al. 1994). Until recently, the diagnosis of upper respiratory
tract dysfunction was based on observations made during resting
endoscopic examination; and conclusions regarding the extent and
exact nature of the dysfunction during exercise were often
inaccurate. This report describes 2 horses presented to the George
D. Widener Hospital in which no significant abnormalities were
noted during res...
Recidivism in equestrian trauma. A 3-year chart survey and questionnaire was conducted of equestrian-injured patients at a regional trauma center to determine patterns and consequences of injury and rate of recidivism. Ninety-two patients (95 encounters) were treated; most were young (mean age, 27 +/- 11 years) women (84%) riders sustaining falls (80%). Most injuries were orthopedic (47%); 19 per cent of patients required hospital admission. There was one death. Helmet use was documented in only 34 per cent. Eighty-one per cent of patients responded to a follow-up telephone survey; 36 per cent recounted additional accidents (...
Quantification of antigen-specific antibody concentrations in tracheal lavage fluid of horses with summer pasture-associated obstructive pulmonary disease. To determine whether horses with summer pasture-associated obstructive pulmonary disease (SPAOPD) have increased concentrations of antigen-specific IgG and IgE in tracheal lavage fluid, compared with values in clinically normal horses. Methods: 8 horses (6 females, 2 geldings; 6 Quarter Horses, 2 Appaloosas), 14 to 23 years old and with previous diagnosis of SPAOPD, served as the principal group; 8 horses (2 females, 6 geldings; 1 Quarter Horse, 7 Thoroughbreds), 6 to 9 years old, with no evidence of respiratory tract disease, served as the control group. Methods: Data were collected twice dur...
In vitro responses of equine small airways and lung parenchyma. In vitro responses of equine small peripheral airways (SA) and lung parenchyma (LP) were studied. We examined their contractile and relaxant responses and investigated effects of histamine, and endogenous prostanoids as these mediators may play a role in development or recurrent airway obstruction in horses (heaves). SA and LP electrical field stimulation (EFS) induced nearly maximal and partial frequency-dependent contractions, respectively. These contractions were virtually abolished in SA but only partially inhibited in LP by atropine (ATR) and tetrodotoxin (TTX). Methacholine (MCh) contrac...
Frequency dependence of forced oscillatory respiratory mechanics in horses with heaves. The effect of measurement frequency on respiratory mechanics was investigated in six horses with reversible allergic airway disease. Total respiratory impedance was measured at 1.5, 2.0, 3.0, and 5.0 Hz by using the forced oscillation technique with the horses in remission, after acute antigenic challenge producing clinical heaves, and with heaves but after the administration of 2 mg fenoterol by inhalation. The slopes of the magnitude (magnitude of Zrs) and real part (R) of total respiratory impedance over the frequency range 1.5-3 Hz changed significantly after antigenic challenge and fenote...
Pulmonary function measurements during repeated environmental challenge of horses with recurrent airway obstruction (heaves). To evaluate the degree of reproducibility in clinical variables, blood gas measurements, and lung function variables, and the changes in these variables caused by exposure to moldy hay in naturally sensitized and control horses. Methods: The magnitude of variation in arterial blood gas and pulmonary function measurements were evaluated in a model of naturally acquired heaves. Horses with heaves and similarly aged control horses were studied prior to moldy hay challenge and again after the horses with heaves manifested clinical signs of airway obstruction. This cycle of testing was repeated 3 t...
Use of a hand-held, metered-dose aerosol delivery device to administer pirbuterol acetate to horses with ‘heaves’. Aerosol administration of bronchodilators to horses is recommended for treatment of certain airway diseases such as 'heaves'. We have developed a novel, hand-held, metered-dose inhaler and we sought to determine the bronchodilator efficacy of the beta 2 adrenoceptor agonist pirbuterol delivered by this device to horses affected with 'heaves'. To induce airway obstruction, 6 heaves-susceptible horses were stabled, bedded on straw and fed hay. When the maximum change in pleural pressure during tidal breathing (delta Pplmax) was greater than 20 cmH2O on 2 consecutive days, pulmonary function was ...
Effects of hydrogen peroxide on isolated trachealis muscle of horses. During acute bouts of recurrent airway obstruction (heaves) in horses, neutrophils that are capable of increased production of reactive oxygen species accumulate in the airways. In the study reported here, the effect of hydrogen peroxide (H2O2; 1 microM to 0.1M), one of these reactive oxygen species products, on the responses of isolated trachealis muscle of horses was determined. Before and after incubation with H2O2, contractile responses to acetylcholine, electrical field stimulation (EFS), 127 mM KCl, and relaxation responses to isoproterenol and activation of the nonadrenergic noncholiner...
Acetylcholine release from airway cholinergic nerves in horses with heaves, an airway obstructive disease. The present study was conducted to determine if acetylcholine (ACh) release from airway cholinergic nerves is increased and if modulation of ACh release by prejunctional receptors is altered in horses with heaves, an obstructive airway disease characterized by airway inflammation and bronchospasm. Trachealis strips and bronchial segments of normal horses and horses affected with heaves were suspended in 2-ml tissue baths. ACh release was induced by electrical field stimulation and the bath ACh content was measured by high performance liquid chromatography (HPLC) with electrochemical detection....
Modulation of bronchial smooth muscle function in horses with heaves. Four mechanisms that modulate airway smooth muscle function in normal horses were studied in the bronchi of horses affected by the airway obstructive disease heaves. Results were compared with data from historical controls studied by the same personnel in the same laboratory. Rings from the left cranial lobar bronchus (LB1) and small bronchi (5 mm OD) were suspended in muscle baths, and the isometric tension were measured. The inhibitory nonadrenergic noncholinergic (iNANC) function was studied in LB1. After the LB1 segments were pretreated with atropine and contracted with histamine, electric...
Tidal breathing flow-volume loops in horses with recurrent airway obstruction (heaves). Tidal breathing flow-volume (TBFV) loops were determined in a group of control horses and in horses affected with recurrent airway obstruction (heaves). The latter group was studied when the condition was in remission and under increasing amounts of airway obstruction as reflected by measurements of change in pleural pressure, pulmonary resistance, and dynamic compliance. The TBFV loops of control horses had biphasic inspiratory and expiratory patterns; peak inspiratory and peak expiratory flows were detected early in inspiration and expiration, respectively. Tidal volume was unaffected by hea...
Tidal breathing flow-volume loop analysis as a test of pulmonary function in exercising horses. The usefulness of tidal breathing flow-volume loops (TBFVL) to evaluate pulmonary function was investigated in 6 Standardbreds during treadmill exercise. Tidal breathing flow-volume loops are a graphic representation of airflow rate vs tidal volume for each individual breath. These TBFVL were obtained from horses exercising at speeds corresponding to 75 and 100% of maximum heart rate. Measurements were recorded in each horse before and after ovalbumin-induced allergic lung disease. Moderate obstructive lung disease, characterized by a significant increase in pulmonary resistance, was observed ...
The rapid and effective administration of a beta 2-agonist to horses with heaves using a compact inhalation device and metered-dose inhalers. The purpose of the study was to administer therapeutic aerosol generated by metered-dose inhalers to horses exhibiting clinical signs of heaves using a compact inhalation device developed for human medicine. It was fitted to a custom face mask in order to study the effect of an inhaled beta 2-agonist, fenoterol. Pulmonary function testing was performed on six horses following an acute exacerbation of heaves, characterized by tachypnea, wheezes, crackles, and spasmodic cough. Horses inhaled fenoterol in 1 mg increments administered as one 200 microgram puff every 5-10 s with the recording of da...
The airway response of horses with recurrent airway obstruction (heaves) to aerosol administration of ipratropium bromide. The airway response to aerosol administration of the anticholinergic agent ipratropium bromide was determined in 8 horses with recurrent airway obstruction (heaves). The reversibility of airway obstruction was confirmed by measuring lung function before and during stabling; and by determining the response to atropine administration (0.02 mg/kg bwt intravenously). The dose-response to ipratropium bromide was determined using a Williams square design experiment in which 25, 50 or 75 micrograms ipratropium bromide/ml (4 ml/100 kg bwt) or the same volume of vehicle was administered to each horse b...
Antibody to a recombinant merozoite protein epitope identifies horses infected with Babesia equi. Horses infected with Babesia equi were previously identified by the presence of antibodies reactive with a merozoite surface protein epitope (D. P. Knowles, Jr., L. E. Perryman, L. S. Kappmeyer, and S. G. Hennager. J. Clin. Microbiol. 29:2056-2058, 1991). The antibodies were detected in a competitive inhibition enzyme-linked immunosorbent assay (CI ELISA) by using monoclonal antibody 36/133.97, which defines a protein epitope on the merozoite surface. The gene encoding this B. equi merozoite epitope was cloned and expressed in Escherichia coli. The recombinant merozoite protein, designated equ...
Effects of xylazine on airway function in ponies with recurrent airway obstruction. The effect of IV administration of the alpha 2-adrenoceptor agonist xylazine hydrochloride (0.5 mg/kg of body weight) was examined in ponies with recurrent obstructive pulmonary disease, commonly called heaves. Six ponies with the disease (principals) were studied during clinical remission and during an acute attack of airway obstruction precipitated by stabling and feeding of dusty hay. Six control ponies were also studied. In principal ponies with airway obstruction, xylazine administration significantly (P < 0.05) decreased pulmonary resistance and increased dynamic compliance, but did n...
Aerosol pirbuterol: bronchodilator activity and side effects in ponies with recurrent airway obstruction (heaves). The dose of aerosol pirbuterol that could be administered safely to ponies (weight approximately 200 kg) was determined by observation for sweating, trembling and excitement and measurement of heart and respiratory rates during cumulative administration of the drug. Sweating, trembling and excitement were first observed following a dose of 2,400 micrograms and became more severe at 3,200 micrograms. These effects were accompanied by an increase in heart rate but not a change in respiratory rate. When 3200 micrograms was administered without prior administration of lower doses, side effects wer...
Intradermal testing of horses with chronic obstructive pulmonary disease and recurrent urticaria. Six horses with chronic obstructive pulmonary disease (COPD) and 8 horses with recurrent urticaria were skin tested with 67 extracts from 58 allergens, including pollens, epidermals, cultivated farm plants, dusts, molds, and insects. Reactions were evaluated 3 times over a 24-hour period immediately after the injections. Results were compared with those obtained from 11 clinically normal horses. All horses had positive skin test reactions. Significant differences was evident between horses with COPD and clinically normal horses for only 3.0% of the possible extract reactions, and between horse...
Beta-adrenergic receptor activity in ponies with recurrent obstructive pulmonary disease. Pulmonary function measurements were made in control ponies and in ponies with recurrent obstructive pulmonary disease (principals) during clinical remission and during an attack of acute airway obstruction. The ponies were given beta-adrenergic antagonists and agonists to determine the role of beta receptors in recurrent obstructive pulmonary disease, and to determine the subtypes of beta receptors mediating bronchodilation in ponies. Aerosol administration of the beta antagonists, propranolol (beta 1 and beta 2), atenolol (beta 1), and butoxamine (beta 2) decreased dynamic compliance (Cdyn) ...
In vitro responses of distal airways in horses with recurrent airway obstruction. Distal airway segments (ID, 3 to 4 mm; length, 5 mm) from 2 groups of horses were isolated and suspended in tissue baths filled with Krebs solution, aerated with 5% CO2 in oxygen and maintained at 37 degrees C. Responses to exogenous acetylcholine, isoproterenol, or electrical field stimulation were compared. Control horses (n = 30) had no history of recurrent airway obstruction, whereas principal horses (n = 15) had recurrent airway obstruction and were studied during an acute episode of airway obstruction. Although the distal airways contracted in response to the cumulative half-logarithmic ...
Upper airway obstruction in performance horses. Differential diagnoses and treatment. Abnormalities of the nasal cavity, pharynx, larynx, and trachea result in respiratory noise and exercise intolerance. Clinical features of common upper respiratory conditions of performance horses are reviewed with emphasis on diagnosis, treatment, and risk factors that affect the outcome of surgical treatment.
In vitro responses of airway smooth muscle from horses with recurrent airway obstruction. The in vitro contractile and relaxant responses of tracheal smooth muscle strips (TSM) and third-generation bronchi (3B) of control horses and horses with recurrent obstructive disease (heaves) were compared. Acetylcholine (ACH) sensitivity of the diseased tissues was less than that of tissues from control horses, especially at the level of the third generation (EC50 controls 15 +/- 11 microM vs 81 +/- 17 microM for heaveys). Despite tracheal and bronchial hyporesponsiveness to ACH, these tissues from heavey horses were hyperresponsive to EFS. The inhibitory effect of isoproterenol and electri...
Effects of furosemide on ponies with recurrent airway obstruction. The effect of aerosol and intravenous administrations of furosemide was examined in ponies with recurrent obstructive pulmonary disease, commonly called 'heaves'. This recurrent airway disease bears many similarities to human asthma. Six ponies with the disease (principal animals) were studied during clinical remission and during an acute attack of airway obstruction precipitated by stabling and feeding dusty hay. Six control animals were also studied. Furosemide (1.0 mg/kg) or vehicle was administered by aerosol in the first study, and intravenously in a second study. In principal ponies with...
Plasma theophylline concentration and lung function in ponies with recurrent obstructive lung disease. Six ponies with recurrent obstructive lung disease were studied during two separate 60 min periods while receiving constant equal volume infusions of either aminophylline or sterile water. Dynamic lung compliance, pulmonary resistance, respiratory rate, tidal volume, blood gas tensions and heart rate were measured. Plasma samples were obtained for determination of theophylline concentrations before, and at 10 min intervals during, the infusion period. Excitability was assessed subjectively at these same time periods. The plasma theophylline concentrations in ponies were well predicted by a pre...
