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 not affect PaO2 or PaCO2. The alpha 2-antagonist yohimbine blocked the pulmonary effects of xylazine. Administration of saline solution was without effect in both groups of ponies at all periods and xylazine did not have effect in controls or in principals in clinical remission.     

Inflammatory airway disease of horses

The purpose of this consensus statement is to provide a review of current knowledge and opinions concerning inflammatory airway disease (IAD) and to help practitioners differentiate IAD from heaves (or recurrent airway obstruction; RAO) and other inflammatory respiratory diseases of horses.     

Brachycephalic airway syndrome.

The range of clinical syndromes and the pathophysiology of respiratory disorders in brachycephalic animals are presented. The problem of deciding which patients require surgical management is reviewed in the light of recent studies and the author's clinical experience. Newer information from related disorders in humans suggests that serious problems can be subclinical and difficult to diagnose. The index of suspicion and guidelines for providing surgical relief to veterinary patients may need to undergo revision.     

Recurrent airway obstruction--heaves.

Heaves, or recurrent airway obstruction (RAO), is a chronic respiratory disease featuring lower airway inflammation, bronchoconstriction, and mucus accumulation. Inhaled organic dusts and T helper 2 type immunologic reactions are involved in the complex pathophysiology of RAO. Clinical signs vary and alternate with remission periods. The diagnosis is often based on history and clinical examination in severe cases, but bronchoalveolar lavage may be useful for the detection of early cases. The most important aspect of treatment is to avoid exposure to allergens. Corticosteroids may be administered systemically or by inhalation in combination with bronchodilators and environmental control.     

Coughing,mucus accumulation,airway obstruction,and airway inflammation in control horses and horses affected with recurrent airway obstruction

OBJECTIVE: To investigate relationships between cough frequency and mucus accumulation, airway obstruction, and airway inflammation and to determine effects of dexamethasone on coughing and mucus score. ANIMALS: 13 horses with recurrent airway obstruction (RAO) and 6 control horses. PROCEDURE: 6 RAO-affected and 6 control horses were stabled for 3 days. Coughing was counted for 4 hours before and on each day horses were stabled. Before and on day 3 of stabling, tracheal mucus accumulation was scored, airway obstruction was assessed via maximal change in pleural pressure (deltaPpl(max)), and airway inflammation was evaluated by use of cytologic examination of bronchoalveolar lavage fluid (BALF). Effects of dexamethasone (0.1 mg/kg, IV, q 24 h for 7 days) were determined in 12 RAO-affected horses. RESULTS: To assess frequency, coughing had to be counted for 1 hour. In RAO-affected horses, stabling was associated with increases in cough frequency, mucus score, and deltaPpl(max). Control horses coughed transiently when first stabled. In RAO-affected horses, coughing was correlated with deltaPpl(max), mucus score, and airway inflammation and was a sensitive and specific indicator of deltaPpl(max) > 6 cm H2O, mucus score > 1.0, and > 100 neutrophils/microL and > 20% neutrophils in BALF Dexamethasone reduced cough frequency, mucus score, and deltaPpl(max), but BALF neutrophil count remained increased. CONCLUSIONS AND CLINICAL RELEVANCE: Because of its sporadic nature, coughing cannot be assessed accurately by counting during brief periods. In RAO-affected horses, coughing is an indicator of airway inflammation and obstruction. Corticosteroid treatment reduces cough frequency concurrently with reductions in deltaPpl(max) and mucus accumulation in RAO-affected horses.     

Inherited and congenital airway conditions

Brachycephalic airway obstruction can take the form of several clinical entities, eg, overlong soft palate, tracheal hypoplasia and laryngeal paralysis. These, and other major congenital airways diseases are discussed together with possible methods of surgical correction.     

Immunological characterization of the equine airway epithelium and of a primary equine airway epithelial cell culture model

Our understanding of innate immunity within the equine respiratory tract is limited despite growing evidence for its key role in both the immediate defense and the shaping of downstream adaptive immune responses to respiratory disease. As the first interface to undergo pathogen invasion, the respiratory epithelium is a key player in these early events and our goal was to examine the innate immune characteristics of equine respiratory epithelia and compare them to an in vitro equine respiratory epithelial cell model cultured at the air-fluid interface (AFI). Respiratory epithelial tissues, isolated epithelial cells, and four-week old cultured differentiated airway epithelial cells collected from five locations of the equine respiratory tract were examined for the expression of toll-like receptors (TLRs) and host defense peptides (HDPs) using conventional polymerase chain reaction (PCR). Cultured, differentiated, respiratory epithelial cells and freshly isolated respiratory epithelial cells were also examined for the expression of TLR3, TLR9 and major histocompatibility complex (MHC) class I and class II using fluorescence-activated cell sorting (FACS) analysis. In addition, cytokine and chemokine profiles from respiratory epithelial tissues, freshly isolated respiratory epithelial cells, and cultured, differentiated, epithelial cells from the upper respiratory tract were examined using real-time PCR. We found that respiratory epithelial tissues and isolated epithelial cells expressed TLRs 1-4 and 6-10 as well as HDPs, MxA, 2'5' OAS, β-defensin-1, and lactoferrin. In contrast, epithelial cells cultured at the AFI expressed TLRs 1-4 and 6 and 7 as well as MxA, 2'5' OAS, β-defensin-1, but had lost expression of TLRs 8-10 and lactoferrin. In addition, MHC-I and MHC-II surface expression decreased in epithelial cells cultured at the AFI compared to isolated epithelial cells whereas TLR3 and TLR9 were expressed at similar levels. Lastly, we found that equine respiratory epithelial cells express an array of pro-inflammatory, antiviral and regulatory cytokines and that after four weeks of in vitro growth conditions, equine respiratory epithelial cells cultured at the AFI retained expression of GM-CSF, IL-10, IL-8, TGF-β, TNF-α, and IL-6. In summary, we describe the development of an in vitro equine respiratory epithelial cell culture model that is morphologically similar to the equine airway epithelium and retains several key immunological properties. In the future this model will be a used to study equine respiratory viral pathogenesis and cell-to-cell interactions.     

Association of treadmill upper airway endoscopic evaluation with results of ultrasonography and resting upper airway endoscopic evaluation

Reasons for performing study: Assessment of arytenoid movement has traditionally been performed using upper airway (UA) endoscopy. However, recent work suggests that laryngeal ultrasonography may provide additional complementary information. Objective: To determine the value of laryngeal ultrasonography for the diagnosis of recurrent laryngeal neuropathy in the horse. Hypotheses: Horses with abnormal arytenoid movement (AM) during treadmill UA endoscopy would have increased echogenicity of the left cricoarytenoideus lateralis muscle (CALM) and smaller left CALM and vocalis size while horses with normal AM during treadmill UA endoscopy would have normal echogenicity of the left CALM and similar left and right CALM and vocalis muscle size. Laryngeal ultrasonography would be more accurate than resting endoscopy at predicting abnormal AM. Methods: Medical records were examined to identify Thoroughbred racehorses aged ≥2 years that had undergone resting and treadmill UA endoscopy and laryngeal ultrasonography. Resting and treadmill AM was graded using accepted scales. The treadmill examination was used as the criterion standard for AM. Laryngeal ultrasonography was performed and the relative echogenicity of the left and right CALM and the cross‐sectional area (CSA) of the CALM and vocalis muscle determined. Data analysis included Chi‐squared tests, paired t tests and one‐way ANOVA. Results: The presence of abnormal AM was associated with relative hyperechogenicity of the CALM while normal AM was not. Laryngeal ultrasonography had a sensitivity of 90% and specificity of 98% and resting UA endoscopy had a sensitivity of 80% and specificity of 81% for diagnosis of abnormal AM. CSA of the left CALM and vocalis muscle was not different between groups. Conclusions: Laryngeal ultrasonography has high accuracy for diagnosing abnormal AM. Potential relevance: Ultrasonography is a valuable addition to the diagnostic evaluation of the equine UA.     

Subclinical airway inflammation despite high-dose oral corticosteroid therapy in cats with lower airway disease

Management of feline chronic lower airway disease focuses on controlling clinical signs and decreasing airway inflammation. This retrospective study evaluated the correlation between the resolution of clinical signs in cats with lower airway disease receiving oral glucocorticoids with the resolution of inflammation based on bronchoalveolar lavage fluid (BALF) cytology. Ten cats diagnosed with lower airway disease based on characteristic clinical signs and inflammatory BALF cytology received oral glucocorticoids for at least 3 weeks. They were required to have resolution of clinical signs and BALF collected while asymptomatic and still receiving glucocorticoids. Cats received prednisolone or prednisone (average dose of 1.8±0.2mg/kg daily) for 35.7±5.5 days. Three cats had resolution of clinical signs and lacked inflammatory BALF cytology; seven had persistent inflammatory BALF cytology despite resolution of clinical signs. Given that subclinical inflammation during high-dose glucocorticoid treatment was common, current recommendations to taper therapy based on resolution of clinical signs should be re-evaluated.     

Equine emergency upper airway management

Respiratory distress due to acute upper respiratory tract obstruction is an uncommon emergency in equine practice. However, clinicians should be confident with the approach to this truly life-threatening scenario. Clinical signs are obvious at rest and include increased respiratory effort, loud respiratory noise and recumbency as asphyxiation progresses. Many cases of upper respiratory tract obstruction involve the pharynx or larynx, though obstruction in other regions of the upper respiratory tract and other causes of respiratory distress should be considered. Generally, the obstruction can be bypassed by placing a nasotracheal tube under endoscopic guidance or by making a temporary tracheotomy to ensure a patent airway. Following this stabilisation, further investigation into the cause of airway obstruction can be performed. Endoscopy is usually the most valuable diagnostic tool, though other imaging modalities can be useful. Further empirical treatment is often required, though the specific management will vary depending on the pathology present.     

Equine recurrent airway obstruction does not alter airway muscarinic acetylcholine receptor expression and subtype distribution

In recurrent airway obstruction (RAO) or heaves, bronchospasm has been attributed to enhanced cholinergic activity. However, the expression and function of muscarinic acetylcholine receptors (mAChR) and their signaling components are not yet known. Thus, we examined the expression, subtype distribution and postreceptor signaling pathways of mAChR in the peripheral lung, bronchial and tracheal epithelia with the underlying smooth muscle from nine horses with RAO and 11 healthy control horses. In RAO horses, no significant segment-dependent alteration in mAChR density and subtype distribution (assessed by [N-methyl-3H]-scopolamine binding; ([3H]-NMS)), was found, except a trend in receptor down-regulation in some peripheral parts of the lung. The total number of high mAChR binding sites (assessed by carbachol-displacement experiments in the presence or absence of guanosine 5'-triphosphate) was not changed in RAO, suggesting that the functional coupling of mAChR to the corresponding G-proteins is intact. The M2-mediated inhibition of adenylate cyclase (AC) as well as the M3-receptor-G(q/11)-phospholipase C (PLC) activity was not different between RAO and control airway tissues. In conclusion, in equine RAO airways, mAChR expression and function were not altered, and thus appear not to account for the enhanced cholinergic activity in RAO.     

Transendoscopic biopsy of the horse's airway mucosa

Transtracheal wash and bronchoalveolar lavage are diagnostic techniques that have been adopted from human medicine for monitoring inflammatory changes in the airway of the horse. Transendoscopic biopsy has also proven to be a valuable tool for obtaining samples of the airway mucosa in human patients. A transendoscopic technique was developed in this study for obtaining a respiratory mucosal biopsy from standing, sedated horses. Six normal adult horses were sampled at eight-week intervals for a total of three sample periods. Horses were monitored for adverse effects of the technique and none were noted. Sample sites were completely healed after eight weeks with no gross or histologic abnormalities. Biopsy samples were 3 to 4 millimeters in diameter, and 17 of 18 samples provided interpretable histological sections. Methods for handling, staining and evaluating tissue were also developed. The results of this study demonstrated that airway mucosal biopsy is a safe, repeatable technique that can be performed in the sedated, standing horse.