C. Berney

Stabling is associated with airway inflammation in young Arabian horses.

We examined the effect of stabling on upper and lower airway inflammation in 14 yearling Arabian horses that had been at pasture since birth. Horses were divided into 2 groups of 7. One group was stabled for 3 months and the other remained at pasture. The groups were then switched over for another 3 months. The nasopharynx, guttural pouches and trachea were examined endoscopically and bronchoalveolar lavage performed every month. An upper airway inflammation score was devised based on the magnitude of pharyngeal lymphoid hyperplasia and guttural pouch inflammation. During stabling this score remained constant, whereas it decreased during the 3 months at pasture. Stabling was also associated with a higher number and percentage of neutrophils in bronchoalveolar lavage fluid and with a smaller percentage of lymphocytes. There was no correlation between upper airway inflammation score and bronchoalveolar lavage cytology. During a nasal occlusion test, dorsal displacement of the soft palate occurred more times in stabled than in pastured horses, but this was heavily biased by the results from one animal. We conclude that stabling is associated with inflammation of both the upper and lower airway of young horses.

Relationship between clinical signs and lung function in horses with recurrent airway obstruction (heaves) during a bronchodilator trial.

During a trial to determine the dose response to the beta2-adrenergic agonist pirbuterol, we judged the severity of airway obstruction by use of a clinical scoring system and compared this to objective data obtained by quantitative measures of lung function. Six horses affected by recurrent airway obstruction were used in this trial. Four hundred and sixty-eight measurements of lung function and clinical scores were obtained from 13 measurement periods when horses received each of 6 doses of pirbuterol. Scores of 1-4 were assigned to degree of nasal flaring and abdominal effort and summed for a total score. The veterinarian scoring the signs did not know the dose of pirbuterol received by the horse and was unaware of the lung function data. Nasal, abdominal and total scores were significantly related to changes in lung function and changes in breathing pattern. There were significant differences between total scores greater than 5 in indices that reflected changes in breathing strategy (peak inspiratory and expiratory flow), peripheral airway obstruction (dynamic elastance), and effort of breathing (maximal change in pleural pressure). Below a total score of 5, there were fewer significant differences in lung function even though measurements of pulmonary resistance and dynamic elastance indicated considerable airway obstruction. Failure of clinical score to reflect this low-grade airway obstruction suggests that airway disease is underdiagnosed and its detection would be helped by the availability of a convenient lung function test.

Environment and prednisone interactions in the treatment of recurrent airway obstruction (heaves).

Recurrent airway obstruction (RAO) or heaves is a manifestation of a hypersensitivity to dust, moulds, and spores in the environment of a susceptible horse. Although in the majority of RAO-affected horses, clinical remission can be achieved by keeping horses at pasture to reduce their allergen exposure, this often is not practicable. For this reason, we investigated if changing the environment of a single stall in a 4 stall stable was sufficient to improve lung function and reduce inflammation in RAO-affected horses. In addition, we determined if addition of oral prednisone provided additional benefit. Twelve RAO-susceptible horses were stabled, fed hay, and bedded on straw until they developed airway obstruction. At this point, bedding was changed to wood shavings and they were fed a pelleted diet for 2 weeks. Lung function was measured and bronchoalveolar lavage was performed before and 3, 7, and 14 days after environmental modification. In a crossover design, horses were treated for the 14 days with prednisone tablets (2.2 mg/kg bwt, q. 24 h). Horses then returned to pasture for 30 days. Airway obstruction was greatest before environmental modification. Significant improvement in lung function occurred within 3 days of the change in environment and continued to Day 7. Airway function was best after 30 days at pasture. The clinical response achieved by environmental modification was not significantly improved by addition of oral prednisone. The total number of cells, total neutrophils, and percent neutrophils was greatest before environmental modification. In the absence of prednisone, total and percent neutrophils did not decrease until Day 14 and total cell number until 30 days at pasture. In the presence of prednisone, total cells and total and percent neutrophils decreased by Day 3 and again at pasture. The fact that lung function can be improved within 3 days by environmental management alone emphasises the need for allergen reduction as the cornerstone of treatment of RAO. Although prednisone induced a more rapid reduction in airway inflammation, this was not associated with a more rapid improvement in airway function.

Efficacy of three corticosteroids for the treatment of heaves

This study used a cross-over design to compare the efficacy of 3 corticosteroids for the relief of airway obstruction and inflammation in 9 heaves-affected horses. The severity of airway obstruction and inflammation was quantified by measurement of lung function and by bronchoalveolar lavage fluid (BALF) cytology, respectively. Airway obstruction was induced by stabling the horses and they remained stabled during the 10 day treatment period. Lung function was measured before treatment (baseline), at Days 3, 7, and 10 of treatment, and after 30 days at pasture. BALF cytology was investigated at baseline, Day 10, and at pasture. All 9 horses received the following 4 treatments in random order: no treatment, daily oral prednisone tablets (1 mg/kg), daily i.v. dexamethasone solution (0.1 mg/kg), and i.m. dexamethasone-21-isonicotinate (0.04 mg/kg) every 3 days. When horses received no treatment, lung function did not change significantly during stabling but improved at pasture. In all horses, daily i.v. administration of dexamethasone solution improved lung function within 3 days to levels as good as or better than those measured at pasture. Dexamethasone-21-isonicotinate was rapidly effective in 8 of 9 horses. The other horse did not respond to this drug. Prednisone tablets were without effect on Days 3 and 7 of treatment, but by Day 10, 5 of 9 horses showed some improvement in lung function. Dexamethasone i.v. solution decreased the percent neutrophils in BALF at Day 10. Other treatments had no effect on BALF cytology. These results demonstrate that dexamethasone rapidly relieved airway obstruction in heaves-affected horses. Oral prednisone had inconsistent effects but may be beneficial in some horses after more than a week of treatment.

Effects of stylopharyngeus muscle dysfunction on the nasopharynx in exercising horses

REASONS FOR PERFORMING STUDY Nasopharyngeal collapse has been observed in horses as a potential cause of exercise intolerance and upper respiratory noise. No treatment is currently available and affected horses are often retired from performance. OBJECTIVE To determine the effect of bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction on nasopharyngeal function and airway pressures in exercising horses. METHODS Endoscopic examinations were performed on horses at rest and while running on a treadmill at speeds corresponding to HRmax50, HRmax75 and HRmax, with upper airway pressures measured with and without bilateral glossopharyngeal nerve block. RESULTS Bilateral glossopharyngeal nerve block caused stylopharyngeus muscle dysfunction and dorsal nasopharyngeal collapse in all horses. Peak inspiratory upper airway pressure was significantly (P = 0.0069) more negative at all speeds and respiratory frequency was lower (P = 0.017) in horses with bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction compared to control values. CONCLUSIONS Bilateral glossopharyngeal nerve anaesthesia produced stylopharyngeus muscle dysfunction, dorsal pharyngeal collapse and airway obstruction in all horses. POTENTIAL RELEVANCE The stylopharyngeus muscle is probably an important nasopharyngeal dilating muscle in horses and dysfunction of this muscle may be implicated in clinical cases of dorsal nasopharyngeal collapse. Before this information can be clinically useful, further research on the possible aetiology of stylopharyngeus dysfunction and dysfunction of other muscles that dilate the dorsal and lateral walls of the nasopharynx in horses is needed.

Efficacy of oral and intravenous dexamethasone in horses with recurrent airway obstruction

REASONS FOR PERFORMING STUDY Although the efficacy of dexamethasone for the treatment of recurrent airway obstruction (RAO) has been documented, the speed of onset of effect and duration of action are unknown, as is the efficacy of orally administered dexamethasone with or without fasting. OBJECTIVES To document the time of onset of effect and duration of action of a dexamethasone solution i.v. or orally with and without fasting. METHODS Protocol 1 used 8 RAO-affected horses with airway obstruction in a crossover design experiment that compared the effect of i.v. saline and dexamethasone (0.1 mg/kg bwt) on pulmonary function over 4 h. Protocol 2 used 6 similar horses to compare, in a crossover design, the effects of dexamethasone i.v. (0.1 mg/kg bwt), dexamethasone per os (0.164 mg/kg bwt) with and without prior fasting, and dexamethasone per os (0.082 mg/kg) with fasting. RESULTS Dexamethasone i.v. caused significant improvement in lung function within 2 h with a peak effect at 4-6 h. Dexamethasone per os was effective within 6 h with peak effect at 24 h at a dose of 0.164 mg/kg bwt prior to feeding. The duration of effect was, for all dexamethasone treatments, statistically significant for 30 h when compared to saline and tended to have a longer duration of effect when used orally. Dexamethasone per os at a dose of 0.164 mg/kg bwt to fed horses had mean effects comparable to dexamethasone at a dose of 0.082 mg/kg bwt per os given to fasted horses, indicating that feeding decreases bioavailability. CONCLUSIONS Dexamethasone administered i.v. has a rapid onset of action in RAO-affected horses. Oral administration of a bioequivalent dose of the same solution to fasted horses is as effective as i.v. administration and tends to have longer duration of action. Fasting horses before oral administration of dexamethasone improves the efficacy of treatment. POTENTIAL RELEVANCE Oral administration to fasted horses of a dexamethasone solution intended for i.v. use provides an effective treatment for RAO-affected animals.

Response to nasopharyngeal oxygen administration in horses with lung disease

REASONS FOR PERFORMING STUDY Guidelines for administration of oxygen to standing horses are unavailable because previous investigations of the efficacy of oxygen administration to increase arterial oxygenation in standing horses have produced equivocal results. OBJECTIVE To determine the effect of nasal oxygen supplementation on inspired and arterial blood gas tensions in control horses and those with moderate to severe recurrent airway obstruction (RAO). METHODS Normal horses (n = 6) and horses during an attack of RAO induced by stabling (n = 6) were studied. Oxygen was administered through either one or 2 cannulae, passed via the nares into the nasopharynx to the level of the medial canthus of each eye. Intratracheal inspired oxygen and carbon dioxide concentration and arterial blood gas tensions were measured at baseline and during delivery of 5, 10, 15, 20 and 30 l/min oxygen. RESULTS Nasal cannulae and all but the highest oxygen flow rates were well tolerated. Fractional inspired oxygen concentration (F(I)O2) increased with flow but was significantly lower at all flow rates in horses with RAO compared with controls. Arterial oxygen tension (PaO2) was significantly increased (P < 0.001) by all flow rates, but was always lower in RAO-affected animals. At 30 l/min, PaO2 increased to 319 +/- 31 mmHg in control horses and 264 +/- 69 mmHg in horses with RAO. Additionally, a large arterial to end-tidal gradient for CO2 in RAO-affected horses was observed, indicating increased alveolar deadspace ventilation in these animals. CONCLUSIONS The use of nasal cannulae to deliver oxygen effectively increases both F(I)O2 and PaO2 in horses with moderate to severe RAO. Oxygen flow rates up to 20 l/min are well tolerated, but flow rates of 30 l/min produce occasional coughing or gagging. POTENTIAL RELEVANCE Oxygen therapy delivered by means of an intranasal cannula is a highly effective means of increasing arterial oxygen tension in horses with respiratory disease. Generally, flows of 10-20 l/min should be effective. If higher flows (20-30 l/min) are necessary, they should be delivered by means of 2 cannulae.

The effects of a single acupuncture treatment in horses with severe recurrent airway obstruction

Summary Reasons for performing study: Acupuncture may be recommended for horses with ‘heaves’ because it is being increasingly applied to treat human asthma. Therefore, its efficacy was investigated in horses with this asthmalike disease. Objective: To evaluate the efficacy of a single acupuncture treatment for the relief of airway obstruction in heaves-affected horses. Methods: The efficacy of a single acupuncture treatment was tested in 10 heaves-affected horses, and the effect of removal from the dusty stall environment in 5 heaves-affected horses. Before treatment, horses were stabled to induce airway obstruction and, apart from trips to the laboratory for pulmonary function measurements, they remained stabled for the duration of each treatment. The severity of airway obstruction was quantified by measurement of lung function before treatment (baseline), and at 20, 60, 120 and 240 mins and 24 h after the following treatments administered in random order: halter restraint and patting, a single acupuncture treatment by an experienced acupuncturist, and a single acupuncture treatment using predetermined points (recipe) by a veterinarian with no acupuncture training. In a second study, horses were untreated and remained either in their stall or in a paddock for all measurements of lung function, after baseline readings were made. Results: In the first study, after all treatments, there was a temporal improvement in maximal change in pleural pressure, pulmonary resistance, dynamic compliance, respiratory rate, and tidal volume that lasted less than 24 h. There was no specific effect of acupuncture treatment. In the second study, removal from the dusty environment did not produce an improvement in lung function in the first 6 h. We conclude that most of the improvements in lung function observed in the study were due to handling. Conclusions: Assessed objectively, a single acupuncture treatment during an attack of heaves causes no more improvement in lung function than does handling the horse. Potential relevance: Acupuncture should not replace conventional medical treatments for heaves.

The effect of intravenous lidocaine infusion on bronchoalveolar lavage cytology in equine recurrent airway obstruction.

BACKGROUND Lidocaine decreases neutrophilic inflammation in models of acute lung injury and decreases inflammation in asthmatic patients. Neutrophilic bronchiolitis develops in recurrent airway obstruction (RAO), but it remains unknown if lidocaine infusion decreases neutrophil migration into the airways. HYPOTHESIS Lidocaine decreases neutrophilic inflammation as measured in BALF in RAO-affected horses. ANIMALS Six RAO-susceptible horses in remission. METHODS In a randomized cross-over design, horses received lactated Ringers solution (LRS) IV or lidocaine hydrochloride IV with a minimum of 4 weeks at pasture between treatments. Treatments were delivered as continuous infusions beginning 4 hours before and for 68 hours during exposure to hay and straw challenge. Clinical score (CS, grade 0-8), maximal change in pleural pressure (∆Ppl(max) ), and bronchoalveolar lavage fluid (BALF) cytology were measured at baseline and the end of challenge (day 4). Plasma lidocaine concentrations were monitored daily. RESULTS At baseline, there were no significant differences in variables between treatments. Plasma lidocaine concentration was consistently > 1100 ng/mL. After challenge, CS increased significantly [baseline: 2/8 (2-3), [median (interquartile range)]; day 4: 4/8 (4-5) P = .0006] as did ∆Ppl(max) [baseline: 3.6 (2.63-4.95) cmH(2) 0; day 4: 9.62 (6.5-16) P = .0036], but there was no difference between treatments. Percentage of neutrophils was not different between treatments, but lidocaine infusion significantly increased BALF total cells [baseline: LRS 2.18 ± 0.82 × 10(5) cells/mL (mean ± SD), lidocaine 1.6 ± 0.3 × 10(5) , day 4: LRS 2.0 ± 0.88 × 10(5) , lidocaine 4.4 ± 2 × 10(5) (P = .0045)]. CONCLUSIONS AND CLINICAL IMPORTANCE Lidocaine does not decrease neutrophilic inflammation in RAO.

Trimetoquinol: bronchodilator effects in horses with heaves following aerosolised and oral administration

REASON FOR PERFORMING STUDY The bronchodilator effects of trimetoquinol (TMQ) have been studied when administered i.v. or intratracheally, but not in an aerosolised form. OBJECTIVES To define the relationship between the therapeutic and adverse responses (therapeutic index) of TMQ when administered as an aerosol or by the oral route. METHODS Increasing doses of TMQ were administered to horses with heaves as an aerosol and by the oral route. Dose ranged 100-1000 microg/horse for aerosolised TMQ and from 6-60 microg/kg bwt for the oral route. Airway and cardiac effects were assessed by measurement of maximal change in pleural pressure (deltaPplmax) and heart rate (HR), respectively. Side effects of sweating, agitation and muscle trembling were scored subjectively. Duration of action of aerosolised (1000 pg/horse) and oral (6-60 microg/kg bwt) TMQ was evaluated over 6 h. RESULTS Aerosol administration of TMQ caused dose-dependent bronchodilation but did not change HR or cause other observable side effects. When 1000 microg/horse was administered via aerosol, TMQ produced a 2-phase bronchodilation; an immediate effect lasting up to 30 min and a second phase between 2 and 4 h. Oral TMQ was therapeutically ineffective. CONCLUSION Aerosol administration of TMQ is a safe and effective method of producing bronchodilation in horses.