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Twenty-seven horses were treated for epiglottic entrapment by using an oral, hand-assisted bistoury knife technique, under general anaesthesia; 26 of them returned successfully to racing, but one developed a permanently displaced soft palate. After the surgery 13 of the horses had an increased handicap rating and 13 had a decreased rating.

A free-ranging, adult male Florida panther (Puma concolor coryi) was immobilized and evaluated for hematuria following routine capture. Prior to anesthetic recovery, the panther was fitted with a telemetry collar. After an initially quiet recovery, the panther began thrashing in the transport cage, and was again immobilized. Pink foam was evident from the nostrils, and crackles were ausculted over the chest, indicating pulmonary edema. Postobstructive pulmonary edema was diagnosed based on history, clinical signs, radiographic evaluation, and blood gas analysis. The animal was treated intensively for several hours with diuretics, oxygen, and manual ventilation. The panther responded rapidly to therapy and was released back into the wild 48 hr after presentation. Postobstructive pulmonary edema, also called negative-pressure pulmonary edema, may be underrecognized in veterinary medicine. In this case, the telemetry collar, in conjunction with anesthetic recovery in a small transport crate, may have contributed to tracheal obstruction. Wildlife veterinarians and biologists should be aware of the risk of airway obstruction when placing tracking collars, and animals should be continuously monitored during anesthetic recovery to ensure the presence of a patent airway.

Objective: To assess results of surgical correction of brachycephalic syndrome (including stenotic nares, elongated soft palate, and everted laryngeal saccules) in dogs and determine whether dogs with hypoplastic trachea have a less favorable long-term outcome., Design: Retrospective case series., Animals: 62 dogs with brachycephalic syndrome., Procedures: Medical records from 1991 to 2004 were reviewed for information regarding signalment, clinical signs, diagnosis, surgery, and long-term outcome. Surgical outcome was rated by owners as excellent, good, fair, or poor. Common abnormalities, treatments, and long-term outcomes among the 62 dogs were assessed., Results: Predominantly affected breeds included English Bulldog, Pug, and Boston Terrier. Elongated soft palate was the most common abnormality (54/62 [87.1%] dogs); the most common combination of abnormalities was elongated soft palate, stenotic nares, and everted saccules (16/62 [25.8%] dogs). The English Bulldog was the most common breed for all abnormalities, including elongated soft palate (27/54 [50%] dogs), stenotic nares (14/36 [38.9%] dogs), everted saccules (20/36 [55.6%] dogs), hypoplastic trachea (7/13 [53.9%] dogs), and laryngeal collapse (2/5 [40%]). No dogs had everted saccules alone. Outcome did not differ between dogs under-going staphylectomy by use of laser or scissor resection. Follow-up information was obtained for 34 dogs; 16 (47.1%) had an excellent outcome, and 16 (47.1%) had a good outcome. Overall treatment success rate was 94.2%, and overall mortality rate was 3.2%., Conclusions and Clinical Relevance: Surgical treatment of brachycephalic syndrome in dogs appeared to be associated with a favorable long-term outcome, regardless of age, breed, specific diagnoses, or number and combinations of diagnoses.

Unlabelled: REASONS FOR STUDY: Equine recurrent airway obstruction (RAO) is probably dependent on a complex interaction of genetic and environmental factors and shares many characteristic features with human asthma. Interleukin 4 receptor a chain (IL4RA) is a candidate gene because of its role in the development of human asthma, confirmation of this association is therefore required., Methods: The equine BAC clone containing the IL4RA gene was localised to ECA13q13 by the FISH method. Microsatellite markers in this region were investigated for possible association and linkage with RAO in 2 large Warmblood halfsib families. Based on a history of clinical signs (coughing, nasal discharge, abnormal breathing and poor performance), horses were classified in a horse owner assessed respiratory signs index (HOARSI 1-4: from healthy, mild, moderate to severe signs). Four microsatellite markers (AHT133, LEX041, VHL47, ASB037) were analysed in the offspring of Sire 1 (48 unaffected HOARSI 1 vs. 59 affected HOARSI 2-4) and Sire 2 (35 HOARSI 1 vs. 50 HOARSI 2-4), age 07 years., Results: For both sires haplotypes could be established in the order AHT133-LEXO47-VHL47-ASB37. The distances in this order were estimated to be 2.9, 0.9 and 2.3 centiMorgans, respectively. Haplotype association with mild to severe clinical signs of chronic lower airway disease (HOARSI 2-4) was significant in the offspring of Sire 1 (P = 0.026) but not significant for the offspring of Sire 2 (P = 0.32). Linkage analysis showed the ECA13q13 region containing IL4RA to be linked to equine chronic lower airway disease in one family (P<0.01), but not in the second family., Conclusions: This supports a genetic background for equine RAO and indicates that IL4RA is a candidate gene with possible locus heterogeneity for this disease., Potential Relevance: Identification of major genes for RAO may provide a basis for breeding and individual prevention for this important disease.

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.

Recurrent airway obstruction (RAO) is characterized by neutrophilic airway inflammation and obstruction, and stabling of susceptible horses triggers acute disease exacerbations. Stable dust is rich in endotoxin, which is recognized by Toll-like receptor (TLR) 4. In human bronchial epithelium, TLR4 stimulation leads to elevation of interleukin (IL)-8 mRNA expression. The zinc finger protein A20 negatively regulates this pathway. We hypothesized that TLR4 and IL-8 mRNA and neutrophil numbers are elevated and that A20 mRNA is not increased in RAOs during stabling compared with controls and with RAOs on pasture. We measured the maximal change in pleural pressure (DeltaPpl(max)), determined inflammatory cell counts in bronchoalveolar lavage fluid (BAL), and quantified TLR4, IL-8, and A20 mRNA in bronchial epithelium by quantitative RT-PCR. We studied six horse pairs, each pair consisting of one RAO and one control horse. Each pair was studied when the RAO-affected horse had airway obstruction induced by stabling and after 7, 14, and 28 days on pasture. Stabling increased BAL neutrophils, DeltaPpl(max), and TLR4 (4.14-fold change) significantly in RAOs compared with controls and with RAOs on pasture. TLR4 correlated with IL-8 (R2 = 0.75). Whereas stabling increased IL-8 in all horses, A20 was unaffected. IL-8 was positively correlated with BAL neutrophils (R2 = 0.43) and negatively with A20 (R2 = 0.44) only in RAO-affected horses. Elevated TLR4 expression and lack of A20 upregulation in bronchial epithelial cells from RAO-affected horses may contribute to elevated IL-8 production, leading to exaggerated neutrophilic airway inflammation in response to inhalation of stable dust.

Case Description: A 1-day-old Standardbred foal with a history of extreme respiratory distress after birth consistent with upper airway obstruction was evaluated. A temporary tracheostomy tube was placed by the referring veterinarian., Clinical Findings: On initial examination, there was evidence of hypoxic-ischemic syndrome, secondary to perinatal asphyxia. Endoscopy revealed obstruction of both nares at the level of the choanae; a diagnosis of bilateral choanal atresia was made., Treatment and Outcome: The foal was anesthetized and underwent transendoscopic laser fenestration of the buccopharyngeal membranes. Three weeks after surgery, cicatricial narrowing of the choanae was apparent and further transendoscopic ablation was performed. Recurrent stenosis necessitated revision surgeries involving a combination of laser ablation with topical administration of mitomycin and, subsequently, a combination of radial incisions into the stenotic tissue and repeated bougienage with a cuffed endotracheal tube. The degree of stenosis decreased, and at 1 year of age, the horse was an appropriate size for its age, had choanae that were almost maximally open (> 85%), and had entered training. Mild stenosis was still evident when the horse was reexamined the following year, although there was no evidence of exercise intolerance or respiratory compromise., Clinical Relevance: Bilateral choanal atresia in a foal can be successfully treated via transendoscopic fenestration of the buccopharyngeal membranes, enabling the horse to subsequently participate in athletic activities. Secondary problems resulting from initial asphyxia and recurrent stenosis at the surgical site can be overcome but may require prolonged and extensive treatment.

Measurements of total, respirable, and real-time airborne particulate were obtained in 12 horse barns in summer and winter. Respirable and total particulate concentrations were measured gravimetrically; real-time particulate was measured with an aerosol photometer. Total particulate (TP) ranged from nondetectable (ND) to 2.1 mg/m3 and from ND to 1.2 mg/m3 for winter and summer sampling, respectively. Respirable particulate (RP) ranged from ND to 0.2 mg/m3 and from ND to 0.7 mg/m3 for winter and summer measurements, respectively. The mean respirable fraction of particulate for summer and winter measurements was 0.63 and 0.34, respectively Real-time particulate (RTP) concentration was significantly correlated with TP for winter measurements and for pooled data but was not significantly correlated with RP for winter, summer, or pooled measurements. Peak, 10-sec average levels of RTP were estimated to range up to 22 mg/m3 in the samples collected. The data suggest that (a) airborne particulate concentrations and particle size distributions vary considerably among horse barns, and (b) real-time sampling, with an aerosol photometer, may be a more reliable measure of airborne TP than airborne RP in these environments.

This study examined the contribution of delayed apoptosis of bronchial mucous cells to mucus accumulation in equine recurrent airway obstruction (RAO). In pilot studies, Bcl-2, an apoptosis inhibitor, was detected in airway mucous cells of RAO-affected horses in remission and during acute disease, when most mucus was secreted. To study whether delayed apoptosis results in an increase in the number of mucous cells during disease recovery, six RAO-affected and six control horses were fed hay for 5 days to induce inflammation and then pellets for 7 days to partially resolve RAO before euthanasia. RAO-affected horses had more airway obstruction and luminal mucus than control horses under both management systems. At the time of euthanasia, RAO-affected horses had more inflammation and Bcl-2-positive bronchial mucous cells than control animals. In horses with >10 and <10 neutrophils per microliter of bronchoalveolar lavage fluid, >50% and <10% of mucous cells stained positive for Bcl-2, respectively. No differences in mucous cell number or amount of stored mucosubstance were observed between RAO-affected and control horses, but in RAO-affected animals, the amount of stored mucosubstance decreased as the number of neutrophils in bronchoalveolar lavage fluid increased. Because the number of mucous cells was similar in both groups of horses but only mucous cells of RAO-affected horses expressed Bcl-2 during recovery from acute disease, a conclusive role for Bcl-2 in prolonging bronchial mucous cell life could not be determined. Future studies are needed to compare horses that are kept in remission for prolonged periods when all mucous cells are fully developed.

Reasons for Performing Study and Objective: To review the prevalence of single and complex forms of dynamic airway obstructions within a large group of Thoroughbred horses in training referred for investigation of poor performance., Methods: Video-endoscopic recordings of the upper respiratory tract made during a standardised treadmill exercise test of 600 Thoroughbred racehorses were reviewed and analysed in real time and slow motion to identify dynamic collapse by the tissues bordering onto the pharyngeal and laryngeal airways., Results: Dynamic collapse within the nasopharynx or larynx was confirmed in 471 of the 600 horses. Dorsal displacement of the soft palate (DDSP; 50%) and palatal instability (33%) were the disorders most frequently identified. It was concluded that deglutition is not a significant event in the triggering of DDSP. Complex forms of dynamic collapse were present in 30% of the horses with upper respiratory tract obstructions. A significant influence of age on the prevalence of DDSP and dynamic laryngeal collapse was identified. There was an increased risk of DDSP in younger horses, and of laryngeal collapse in older horses. No association with gender or format of racing was identified., Conclusions and Potential Relevance: Palatal instability and DDSP comprised the most frequently encountered forms of dynamic collapse within the upper respiratory tract of the Thoroughbred racehorses in this study and are probably expressions of the same nasopharyngeal malfunction. Complex obstructions, i.e. where more than one structure collapses into the airway, occur frequently and therefore treatments that address solitary disorders may often be unsuccessful. Younger horses were found to be at greater risk of sustaining DDSP while older horses seemed more at risk to vocal cord collapse but not to collapse of the arytenoid cartilage itself.

This study was performed to determine if a peripheral sample of lung from the site where biopsy is conducted is representative of the rest of the lung and to investigate the relationship between airway inflammation and intraepithelial mucous production in the peripheral airways. Lung parenchyma samples were collected from five different regions of the lung in five control and five heaves-affected horses. Horse groups were defined by clinical response to stabling. Tissue sections were used for semi-quantitative scoring of lesions, to count the number of airways, to quantify the amount of stored mucosubstances (Vs) within the epithelium, and to count the number of epithelial cells in terminal airways. No significant differences were found between lung regions or between groups of horses. Lack of regional differences in airway structures means that a biopsy sample can be used for diagnosis and investigation of diffusely distributed diseases. Airway inflammation was correlated with mucous cell metaplasia and Vs. Therefore, in horses, mucus accumulation is partly caused by increased number of mucous cells and is associated with airway inflammation. Therapy targeted to reduce airway inflammation will help reduce the excessive mucous accumulation in horses.

A young Golden Retriever dog developed severe respiratory distress following an initial clinical diagnosis of infectious tracheobronchitis. Severe expiratory flow limitation, associated with exertional respiratory distress and hypoxemia was present. Thoracic images obtained with conventional radiography were characterized by hyperinflation and abnormal bronchial and alveolar patterns. Computed tomography was performed and in conjunction with pulmonary functional changes was diagnostic of small airway disease. The dog was treated with a variety of antibiotics, anti-inflammatory agents, and antitussives, but the clinical signs worsened and the puppy was euthanized. Pathologic examination confirmed severe small airway disease, with emphysema and bronchiolitis.

Objective: To describe the seasonal pattern of clinical exacerbation of summer pasture-associated recurrent airway obstruction (SPA-RAO) in relation to climate and aeroallergens in horses., Animals: 19 horses with SPA-RAO and 10 nonaffected horses., Procedures: Daily examinations were performed on all horses while they were kept on pasture for 3 years. Onset and progression of clinical exacerbation based on a clinical score of respiratory effort were evaluated in relation to changes in maximum temperature, minimum temperature, mean temperature, maximum dew-point temperature, minimum dew-point temperature, and delta dew-point temperature. Seasonal pattern of clinical exacerbation was evaluated in relation to aeroallergen counts (20 types of fungal spores and 28 types of pollen)., Results: Seasonal pattern of clinical exacerbation of SPA-RAO was associated with increases in temperature (heat) and dew-point temperature (humidity), counts of fungal spores, and counts of grass pollen grains. Seasonal pattern of clinical exacerbation paralleled and was associated with increases in counts of specific types of fungal spores, particularly Basidiospore, Nigrospora, and Curvularia spp., Conclusions and Clinical Relevance: Although a causal relationship could not be determined, the seasonal pattern of clinical exacerbation of SPA-RAO was associated with hot and humid conditions and high environmental counts for fungal spores and grass pollen grains. It is not known yet whether these are aeroallergens that cause clinical exacerbation of the disease.

Reasons for Performing Study: The reliability of diagnoses of obstructive conditions of the upper respiratory tract (URT) based on examinations performed at rest vs. at exercise is controversial., Objective: To compare diagnosis of URT by endoscopy at rest with that achieved during high-speed treadmill exercise (HSTE)., Hypothesis: Endoscopy of URT at rest, when performed in isolation from other simpler techniques is unreliable in the prediction of dynamic respiratory obstructions., Methods: Endoscopic findings of 600 Thoroughbred racehorses during quiet breathing were compared with findings during high-speed treadmill exercise. Other parameters were also assessed for their specificity in diagnosis., Results: Endoscopy of the resting horse showed low sensitivity (0.15) in the diagnosis of dorsal displacement of the soft palate (DDSP) and palatal instability (PI). When endoscopy and reported noises were taken together there was still a 35% misdiagnosis rate. Although there was significant association between resting laryngeal function score (LFS) and dynamic vocal cord and/or arytenoid cartilage collapse at exercise, 19% of horses with a grade 4/5 LFS were able to attain and maintain full abduction during exercise and 7% of those with 'normal' grades 1 or 2 LFS at rest showed dynamic laryngeal collapse when exerted. Sensitivity of the diagnostic model was greatly increased (80%) when a history of inspiratory noise and palpable intrinsic muscle atrophy were included., Conclusions and Potential Relevance: Endoscopy of the upper respiratory tract of static horses is unreliable in the diagnosis of dynamic obstructions of the URT and should not be used in isolation in surgical decision-making or in the assessment of horses at the time of sale.

Objectives: To determine (1) if the cricothyroid muscle had respiratory-related electromyographic (EMG) activity that increased with respiratory effort and (2) if bilateral cricothyroid myotomy resulted in vocal fold instability and collapse in exercising horses., Study Design: Experimental., Animals: Seven (3 EMG; 4 cricothyroid myotomy) Standardbred horses., Methods: Three horses exercised on a treadmill at speeds corresponding to the speed that produced maximum heart rate (HR(max)), 75% of maximum heart rate (HR(75%max)), and 50% of maximum heart rate (HR(50%max)) for 60 seconds at each speed while EMG activity of the cricothyroid muscle and nasopharyngeal pressures were measured. Another 4 normal horses were exercised on the treadmill at HR(max) and HR(75%max) for 60 seconds at each speed before and after bilateral cricothyroid myotomy. Upper airway pressures were measured and videoendoscopic examinations were performed and videotaped at each speed., Results: Peak phasic EMBG activity of the cricothyroid muscle was coincident with inspiration and increased with treadmill speed. Bilateral cricothyroid myotomy resulted in vocal fold collapse in all horses. Mean peak inspiratory pressures were significantly more negative compared with control values at both HR(max) and HR(75%max)., Conclusions: Cricothyroid muscle dysfunction may be implicated in vocal fold collapse and likely causes inspiratory airway obstruction in exercising horses., Clinical Relevance: Conditions compromising cricothyroid muscle function or motor innervation could result in vocal fold collapse.

Recurrent airway obstruction (RAO) is an environmental respiratory disease affecting horses. A risk-screening questionnaire (RSQ) for RAO would provide a useful tool to investigate the epidemiology of the disease in horses; our aim in this study was to construct and validate such an instrument. Guidance for what questions to include in the RSQ came from three processes: a review of the scientific literature, a survey of equine practitioners in the UK and a consultation with 19 experts using a modified Delphi technique. The latter consultation consisted of two rounds; agreement amongst the experts increased between the rounds. The quantitative outputs provided estimates of the probabilities of a horse having RAO for each particular piece of historical information or clinical sign. The RSQ for RAO was a short questionnaire for completion by horse owners regarding the horse, its health and its management. The likelihood of a horse having RAO (the RAO score) was calculated from a completed RSQ by combining the relevant estimated probabilities. The RSQ was validated against a reference standard of a veterinary diagnosis including respiratory cytology. This was achieved by inviting veterinary surgeons (residing in Great Britain who had taken part in the practitioner survey, and who had indicated that they used respiratory cytology in the diagnosis of respiratory cases) to participate. During 2003 and 2004 these veterinary surgeons returned RSQs for 40 cases that underwent investigation of the respiratory tract and 40 controls; 18 of the cases were given a final diagnosis of RAO. A receiver-operating characteristic (ROC) curve was used to select a positive cut-off of 0.87 for the RSQ for RAO. This suggested that the RSQ had a sensitivity of 0.83 (95% confidence interval=0.59-0.96) and specificity of 0.85 (0.74-0.93) for the diagnosis of apparent RAO (compared to all other diagnoses).

Dorsal displacement of the soft palate is a common cause of upper airway obstruction in racehorses and is of unknown aetiology. To determine whether the palate may displace for structural reasons, knowledge of the normal soft palate is required. The present study aimed to describe, qualitatively and quantitatively, the structure of the normal equine soft palate using histomorphometry. In soft palates from 12 Thoroughbreds, glandular tissue predominated (ca. 40% of total area), located mainly in the rostral and ventral regions. Rostrally, muscles attached to a tendinous aponeurosis located dorsal to the glandular tissue. Muscle was most abundant in the dorsal mid region and decreased caudally. The oral mucosa consisted of a non-keratinised stratified squamous epithelium whereas the nasopharyngeal mucosa was pseudostratified, columnar and ciliated. Elastin fibres were observed in the nasopharyngeal submucosa, becoming more prevalent caudally. The palates were bilaterally symmetrical although the proportion of tissue types varied considerably between individuals.

Reasons for Performing Study: The presence of abnormal respiratory sounds is commonly associated with obstructions of the upper respiratory tract. In order to establish their clinical significance measurements are required of both normal and abnormal respiratory sounds produced by horses exercising over-ground., Objectives: To determine whether high quality recordings of respiratory sound can be made during over-ground exercise, and to develop a convenient measurement system that can be used to obtain respiratory sounds from horses exercising in field conditions., Methods: A range of prototypes was evaluated against the requirements that the system must be easy to use under field conditions and produce high-quality recordings of respiratory sound. The chosen design incorporated a miniature microphone and an air-flow direction sensor mounted on a lightweight plastic face mask. The mask was attached to the horse's head using nylon straps secured by velcro fastenings. Sound and flow signals were recorded on a portable minidisc player carried by the jockey., Results: The system fulfilled the design criteria. High quality recordings of respiratory sounds were obtained from Thoroughbred horse exercising on a training gallop under a variety of weather conditions. Intermittently occurring abnormal sounds were readily identified from the data., Conclusions: High quality measurements of respiratory sounds during over-ground exercise can be made relatively easily., Potential Relevance: The system enables measurement of respiratory sounds outside a laboratory environment creating new opportunities for scientific research and clinical assessment. The study demonstrated that diagnostic systems based on respiratory sound analysis could potentially be manufactured at relatively low cost and be convenient and simple to use.

Objective: To evaluate time-dependent alterations in gene expression of chemokines in bronchial epithelium of recurrent airway obstruction (RAO)-affected horses and whether alterations resulted from increases in gene expression of interleukin (IL)-17 in cells isolated from bronchoalveolar lavage fluid (BALF)., Animals: 8 RAO-susceptible horses and 9 control horses., Procedure: In 2 experiments, both groups of horses were evaluated after being maintained on pasture and after being stabled and fed dusty hay for 1, 14, 35, and 49 days (experiment 1) or 14 and 28 days (experiment 2). In experiment 1, gene expression of IL-8, chemokine (C-X-C motif) ligand 1 (CXCL1), granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), and Toll-like receptor 4 (TLR4) in epithelium and IL-8, IL-17, and TLR4 in BALF cells was measured. In experiment 2, bronchial biopsy specimens were evaluated for IL-8 immunoreactivity., Results: In RAO-susceptible horses after 14 days of challenge exposure, there was a 3- and 10-fold increase in gene expression of IL-8 for epithelial and BALF cells and an increase in IL-8 immunoreactivity in epithelial cells. Challenge exposure failed to alter gene expression of CXCL1, GM-CSF, G-CSF, and TLR4 in epithelial cells of any horses at any time point. During challenge exposure, gene expression of BALF cell IL-17 was downregulated in control horses (day 1) and upregulated in RAO-affected horses (day 35)., Conclusions and Clinical Relevance: Epithelial-derived IL-8 may promote airway neutrophilia, but the inciting stimulus is unlikely to be IL-17 because upregulation of this gene is subsequent to that of IL-8 in epithelial cells.

Objectives: To describe clinical features of brachycephalic airway obstructive disease in dogs, the incidence of laryngeal collapse in dogs presenting for surgery and the outcome after surgery in dogs with laryngeal collapse., Methods: Basic clinical details were reviewed retrospectively in 73 dogs. Presence of laryngeal collapse and short-term outcomes after surgery were determined for 64 dogs with complete medical records. Long-term outcomes were reviewed for 46 dogs by telephone survey between 19 and 77 months following surgery., Results: Stenotic nares were present in 31 dogs (42.5 per cent), elongated soft palate in 63 (86.3 per cent) and everted laryngeal saccules in 43 (58.9 per cent). The most common breeds were the pug (19 dogs, 26 per cent), Cavalier King Charles spaniel (15 dogs, 20.5 per cent), British bulldog (14 dogs, 19.2 per cent) and Staffordshire bull terrier (4 dogs, 5.5 per cent). Laryngeal collapse was present in 34 of 64 (53 per cent) dogs. No dogs died perioperatively and only one dog was euthanased as a result of its respiratory disease three years after surgery. Telephone interviews indicated that 26 dogs (56.5 per cent) were much improved after surgery, 15 (32.6 per cent) had some improvement and 5 (10.9 per cent) showed no improvement. Signs that persisted after surgery were snoring during sleep (34 dogs, 73.9 per cent), stertor/stridor while conscious (23 dogs, 50 per cent), excessive panting (13 dogs, 28.3 per cent) and dyspnoea (10 dogs, 21.7 per cent). Long-term outcome was considered good, even in dogs with laryngeal collapse., Clinical Significance: Laryngeal collapse is relatively common in dogs presented for surgical correction of brachycephalic airway obstructive disease. Dogs with severe laryngeal collapse often respond well to surgery. Clinical signs rarely resolve completely following surgery.

Objectives: After a first clinical study showing a high prevalence of gastrointestinal tract diseases in brachycephalic dogs presented for upper respiratory syndrome, a prospective study was performed to determine the influence of medical treatment for gastrointestinal tract disorders associated with upper respiratory syndrome surgery., Methods: The gastrointestinal tract and respiratory disorders of 61 brachycephalic dogs presented for upper respiratory syndrome were evaluated. Together with surgery of the upper respiratory tract, a specific gastrointestinal medical treatment was administered. A minimal follow-up of six months was required for inclusion., Results: Palatoplasty with rhinoplasty was the most common surgical correction (88.5 per cent). The mortality rate in the perioperative period was 3.3 per cent. Minor complications accounted for 26.2 per cent of cases. No aspiration pneumonia was encountered. A sufficient follow-up was obtained in 51 dogs. The improvement was judged by the owners as excellent or good in 88.3 per cent of the respiratory disorders and in 91.4 per cent of the gastrointestinal disorders. Clinically, a statistically significant improvement was obtained for both respiratory and gastrointestinal disorders., Clinical Significance: In comparison with other studies, digestive tract medical treatment combined with upper respiratory surgery seems to decrease the complication rate and improve the prognosis of dogs presented for upper respiratory syndrome.

Respiratory obstruction resulting from a discrete haematoma within the dorsal tracheal membrane was seen in an 11-year-old neutered female greyhound that had been involved in a fight two days earlier. There was no history or evidence of rodenticide toxicity or other coagulopathy, and it is suggested that the tracheal haematoma resulted from trauma. A right third intercostal thoracotomy was performed and this allowed resection of the haematoma from within the dorsal membrane of the cranial thoracic trachea, relieving the obstruction with no subsequent signs of dyspnoea. Intramural haematoma should be considered as a rare differential diagnosis for dogs presenting with acute respiratory obstruction.

Objectives: To document the histories, clinical findings, and management of seven puppies with laryngeal collapse occurring secondarily to brachycephalic airway syndrome., Methods: Seven brachycephalic puppies aged between 4.5 and six months underwent surgery for management of brachycephalic airway syndrome following presentation for exercise intolerance and increased respiratory noise and effort., Results: Stenotic nares of varying severity and an elongated soft palate were common to all dogs. All dogs had tracheal hypoplasia and this was severe in four dogs. Laryngeal collapse was present in all dogs. Two dogs had stage I, four dogs stage II, and one dog stage III laryngeal collapse. The dog with stage III laryngeal collapse and one dog with stage II laryngeal collapse died. There was no apparent association between the changes evident on thoracic radiographs or the degree of tracheal hypoplasia and postoperative outcome., Clinical Significance: The development of severe secondary laryngeal changes in dogs aged six months or less supports the suggestion that immature brachycephalic dogs should undergo assessment and, if indicated, surgery as soon as any clinical signs of BAS are apparent.

Reasons for Performing Study: The long-established conventional reference technique (CRT) for measuring respiratory mechanics in horses lacks sensitivity and there is a need for further refinement in new technology, such as the impulse oscillometry system (IOS)., Objectives: To evaluate the potential use of the IOS as a clinical respiratory function test and compare it to the current CRT in horses suffering from common upper and lower airway dysfunctions., Methods: Six healthy horses were tested before and after induction of a unilateral nasal obstruction (UNO) or transient left laryngeal hemiplegia (LLH). Six heaves-affected horses were tested in clinical remission and during a heaves crisis, before and after nebulisation of cumulative doses of a bronchodilator therapy (ipratropium bromide; IPB)., Results: As opposed to the CRT, the IOS was able to detect partial upper airway obstruction (UAO) caused by UNO or LLH in resting horses, without differentiating both conditions. Upper airway obstruction caused an upward shift of resistance (R(rs)) from 5 to 35 Hz without altering reactance (X(rs)). As for the CRT, IOS respiratory parameters measured in heaves-affected horses in crisis differed significantly from values measured during remission. The difference in frequency-dependent behaviour of R(rs) and X(rs) allowed discrimination between upper and lower airway obstructions. Bronchodilator treatment induced significant dose-dependent changes in X(rs) at 5 and 10 Hz, from the first dose. Total pulmonary resistance (RL) and R(rs) at 5 Hz were affected from the second dose and displayed similar sensitivity. Although post treatment RL values were comparable to remission, R(rs) and X(rs) remained significantly different, characterising persistent peripheral obstruction., Conclusions: The IOS was more sensitive than the CRT in detecting partial UAO in resting horses and persistent post treatment peripheral dysfunction in heaves-affected horses. The IOS is a sensitive test that provides graded quantitative and qualitative information on disease-induced respiratory dysfunctions as well as on treatment efficiency in horses., Potential Relevance: The IOS could represent a practical and sensitive alternative respiratory function test for routine clinical investigations of common airway obstructive diseases and therapy in horses.

The effects of an oral preparation containing a mixture of extracts from yellow gentian, garden sorrel, cowslip, verbena and common elder on the lung function of nine horses suffering from heaves were determined in a longitudinal crossover study. The horses were divided at random into a group of five (group 1) and a group of four (group 2). The horses in group 1 were each given 15 tablets of the preparation twice daily, while the horses in group 2 were left untreated. Fourteen days later, the horses in group 2 were given the same course of treatment while the horses in group 1 were left untreated. On being subjected to a histamine inhalation provocation test, five of eight horses tested appeared to be hyperresponsive to histamine. The treatment decreased the histamine sensitivity of three of them; it also caused a significant decrease in maximal intrapleural pressure difference of all the horses. The treatment had no significant effects on the clinical signs, the mucociliary activity or the cytology of the bronchoalveolar lavage fluid of the horses.

The mechanism of recurrent airway obstruction (RAO) in horses was investigated by measuring the membrane domain structure and oxy-redoxy activity in phagocytes isolated from bronchoalveolar lavage fluid (BAL) and from the blood of healthy and RAO horses by electron paramagnetic resonance (EPR). Differences in the activity of intracellular antioxidant enzymes CAT, GPx, and SOD measured in phagocytes of RAO horses in comparison to healthy horses showed that the phagocytes were affected by oxidative stress. In comparison with polymorphonuclear leukocytes (phagocytes) from the blood of healthy horses the reduction mechanisms in BAL were faster and coincided with the merging of disordered membrane domains, while in horses with RAO the reduction and membrane domain structure remained unchanged. We assume that the merging of lipid domains observed in phagocytes from BAL of healthy horses could promote cluster formation of membrane proteins or ligands, which could trigger the activation process in phagocytes of healthy horses and consequently the physiological response that probably did not happen in phagocytes of RAO horses.

Acute and chronic inflammation of the airway remains an important health problem for equids. "Heaves" or recurrent airway obstruction (RAO) remains one of the most commonly diagnosed conditions affecting the lung of older horses in Europe and the United States. The typical clinical signs of RAO include non-productive coughing, serous nasal discharge, labored expiratory effort, and flaring of the nostrils. Auscultation of the lungs of the affected horse often reveals abnormal respiratory sounds, described as crackles and wheezes, throughout the area of the lung field. These clinical signs occur secondary to an inflammatory response that results in bronchospasm, excessive mucus production and airway obstruction. This inflammatory response is characterized by the presence of excessive mucus and inflammatory cells, primarily neutrophils, in the small airways. Most evidence suggests that RAO is the result of a pulmonary hypersensitivity to inhaled antigens. Exposure of affected horses to hay dust, pollens, and mold spores leads to neutrophil accumulation in the lung and bronchospasm. The identification of allergen-specific IgE in bronchoalveolar lavage (BAL) fluid and sera of affected horses supports the involvement of a late phase, IgE-mediated, hypersensitivity reaction in the pathogenesis of equine RAO. The production of IgE antibodies is regulated by the cytokines IL-4 and IL-13. Using a quantitative PCR method we have reported that horses with RAO exhibit a modified Type 2 cytokine response characterized by the production of IL-4 and IL-13 mRNA, but not IL-5 mRNA in BAL cells. Interferon-gamma mRNA was also elevated, suggesting a mixed response. While these results are consistent with equine RAO being the result of an aberrant Type 2 cytokine response to inhaled allergens, others have failed to find any evidence of elevated Type 2 cytokine mRNA in BAL from horses with "heaves". It is likely that these disparate results could be the result of differences in the clinical stage of the affected animals or the timing of sample collection. Here, we report a diverse pattern of cytokine gene expression when sampling a group of affected horses over a period of time.

The aim of this study was to assess the effects of changes to the stable environment on exhaled markers of respiratory inflammation in six horses with clinical histories of recurrent airway obstruction. The horses were maintained for two weeks under conventional stable management (straw bedding and hay) and for two weeks on a reduced-dust regimen (paper bedding and ensiled grass), in a crossover study design. Exhaled ethane and carbon monoxide (CO) and exhaled breath condensate hydrogen peroxide (H(2)O(2)) were measured every three days under each regimen. The presence of clinical signs of airway inflammation (nasal discharge and cough) was monitored daily. The reduced-dust regimen was associated with fewer clinical signs of airway inflammation than the conventional regimen. Exhaled ethane and CO were significantly lower on the reduced-dust regimen and these markers were correlated with clinical signs of respiratory inflammation, but exhaled H(2)O(2) was not affected by the management regimen.

Effects of acute airway inflammation induced by organic dust inhalation on pulmonary antioxidant status were investigated in healthy horses and horses affected by recurrent airway obstruction. Exposure to organic dust induced acute airway neutrophilia, which was associated with increases in elastase and decreases in ascorbic acid concentrations in bronchoalveolar lavage fluid. However, markers of oxidative stress were unaffected, as was hydrogen peroxide in breath condensate. Decreases in ascorbic acid correlated with increased respiratory resistance (P = .001) when both groups were combined. In conclusion, acute neutrophilic airway inflammation does not result in significant evidence of oxidative stress in horses affected by recurrent airway obstruction.

Objective: To evaluate cytokine production by equine alveolar macrophages after exposure to lipopolysaccharide (LPS), Aspergillus fumigatus, and hay dust, and determine the effect of clenbuterol on the cytokine response., Animals: 6 horses., Procedure: Alveolar macrophages were exposed to PBS solution (negative control), LPS, hyphae and conidia of Aspergillus fumigatus (AF), or a suspension of hay dust (HDS) and incubated for 24 hours at 37 degrees C. Concentrations of tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta were measured in the supernatant. The procedure was repeated with cells that were concurrently incubated with 0.5 microM clenbuterol., Results: Exposure to HDS and AF significantly increased production of TNF-alpha by equine alveolar macrophages. The increase in TNF-alpha produced in response to HDS and AF was 5 and 7 times as great, respectively, as the increase measured in response to LPS. The concentration of IL-1beta in the supernatant was significantly increased after exposure of cells to AF. Clenbuterol was effective at inhibiting TNF-alpha production by cells exposed to LPS, HDS, or AF., Conclusions and Clinical Relevance: Increased production of TNF-alpha and IL-1 indicated that the pro-inflammatory cytokines produced by alveolar macrophages in response to allergens may play a role in recurrent airway obstruction (RAO) in horses. Equine alveolar macrophages are not only a primary pulmonary defense mechanism but may also influence the pathogenesis of equine RAO. The beta2-adrenoceptor agonist clenbuterol, a drug that is commonly used for treatment of equine RAO, promotes immediate bronchodilation and may also contribute to downward modulation of the inflammatory response.

Reasons for Performing Study: Dorsal displacement of the soft palate (DDSP) is a common condition in racehorses for which various surgical treatments are often performed. In light of recent findings that suggested the position of the larynx may influence the occurrence of DDSP, we investigated whether a noninvasive mean of affecting the position of the larynx could be effective in the management of DDSP., Hypothesis: An external device (laryngohyoid support; LHS) positioning the larynx in a more rostral and dorsal location and preventing caudal displacement of the basihyoid bone would be effective in preventing DDSP during strenuous exercise., Methods: Ten horses were exercised on a high-speed treadmill under 4 different treatment conditions: control (n = 10); control with external device (n = 10); after bilateral resection of thyrohyoid (TH) muscles (n = 7); and after bilateral resection of TH muscles with external device (n = 7). Two trials were performed randomly for each of the 4 conditions. In Trial 1, videoendoscopic images of the upper airway, pharyngeal and tracheal static pressures, and arterial blood gases were collected. In Trial 2, airflow measurement combined with mask and tracheal static pressure was obtained, and upper airway impedance calculated. The trials allowed calculation of airway impedance and respiratory frequency, and assessment of ventilation using arterial PO2 and PCO2., Results: Under control conditions, none of the 10 horses developed DDSP. There was no statistically significant effect from the LHS on airway impedance or respiratory frequency, nor on arterial PO2 and PCO2. Seven of the 10 horses developed DDSP during exercise after resection of the TH muscles. None of these 7 horses continued to experience DDSP during exercise with the external device. In the latter group and condition, the LHS significantly improved inspiratory and expiratory flow and impedance., Conclusions: The LHS helped prevent experimentally induced DDSP at exercise, probably by statically positioning the larynx in a more rostral and dorsal position., Potential Relevance: Field studies are required to investigate whether the LHS can successfully prevent DDSP in horses with naturally occurring disease.

A 10-yr-old female black bear (Ursus americanus) at the North Carolina Zoological Park presented with a 2-wk history of intermittent coughing and stertor. The animal was anesthetized for examination, and at intubation, a large mass associated with the tonsils and larynx was observed obstructing the airway. Cardiopulmonary collapse occurred during the procedure, and efforts at resuscitation were ineffective. At necropsy, an 8 cm times 6 cm times 5 cm mass was present in the larynx, infiltrating the epiglottis and obstructing the airway. Regional lymph nodes were mildly enlarged and contained tan inspissated substance. Histologically, the neoplasm was composed of nests of keratinizing squamous epithelial cells with evidence of lymphatic invasion and metastases to regional lymph nodes.

Objective: To evaluate differences in response to ID injection of histamine, phytohemagglutinin (PHA), and Aspergillus organisms between clinically normal horses and horses with recurrent airway obstruction (RAO)., Animals: 5 healthy adult horses and 5 adult horses with RAO., Procedure: Intradermal testing (IDT) was performed on the neck with 2 positive control substances (histamine and PHA) and a mixture comprising 5 Aspergillus species. Four concentrations of each test substance plus a negative control substance were used. Equal volumes (0.1 mL) of each test substance were prepared to yield 15 syringes ([4 concentrations of each test substance plus 1 negative control substance] times 3 test substances) for each side of each horse (ie, 30 syringes/horse). Intradermal injections were administered; diameter of wheals was recorded 0.5, 4, and 24 hours after injection., Results: Hypersensitive responses to ID injection of histamine were detected 0.5 hours after injection, and a delay in wheal formation after ID injection of Aspergillus mixture 24 hours after injection was detected in RAO-affected horses but was not observed in clinically normal horses. No differences were detected between the 2 groups after ID injection of PHA., Conclusions and Clinical Relevance: RAO-affected horses are hypersensitive to histamine, suggesting that RAO is associated with a heightened vascular response to histamine. Higher concentrations of Aspergillus mixture may be needed to detect horses that are sensitive to this group of antigens. Wheal reactions to Aspergillus may be a delayed response, suggesting that IDT results should be evaluated 0.5, 4, and 24 hours after ID injection.

Objectives: To determine the prevalence of gastrointestinal tract lesions in brachycephalic dogs with upper respiratory tract disease., Methods: The gastrointestinal tract and respiratory disorders of 73 brachycephalic dogs presented with upper respiratory signs were evaluated. Clinical signs and endoscopic and histological anomalies of the upper digestive tract were analysed., Results: A very high prevalence of gastrointestinal tract problems in brachycephalic dogs presented with upper respiratory problems was observed clinically, endoscopically and histologically. Endoscopic anomalies of the upper digestive tract were present even in dogs without digestive clinical signs. Furthermore, histological evaluation of the digestive tract sometimes showed inflammatory lesions not macroscopically visible at endoscopy. Statistical analysis showed a relationship between the severity of the respiratory and digestive signs. This was significant in French bulldogs, males and heavy brachycephalic dogs., Clinical Significance: These observations show a correlation between upper respiratory and gastrointestinal tract problems in brachycephalic breeds with upper respiratory disease. Surgical treatment of respiratory disease could improve the digestive clinical signs, and/or gastro-oesophageal medical treatment could improve the outcome for surgically treated brachycephalic dogs.

Tracheal trauma with resultant rupture is uncommonly reported in veterinary literature. We report the case of a 16-year-old Thoroughbred gelding that sustained a 1 cm longitudinal perforation of the dorsal tracheal membrane in the proximal cervical region. The horse subsequently developed dyspnoea due to acute upper respiratory obstruction secondary to severe emphysema of the guttural pouches. A temporary tracheostomy caudal to the site of tracheal perforation was performed under local anaesthesia. This procedure helped relieve the upper airway obstruction and aided resolution of the injury by diverting air away from the site of tracheal perforation. After conservative management, the gelding recovered completely.

The objective of this study was to describe a standardised and non-invasive method for exhaled breath condensate (EBC) collection in cats and to test whether determination of hydrogen peroxide (H(2)O(2)) in EBC might be used as marker of lower airway inflammation. The technique of barometric whole body plethysmography for cats was combined with a system to condense the effluent air from the plethysmograph, allowing simultaneous EBC collection and respiratory pattern measurement. H(2)O(2) was determined spectrophotometrically. Eighteen experimental cats were used to investigate the impact on EBC volume and EBC H(2)O(2) of plethysmograph ventilation rate, collection duration, sample stability, within-day and day-to-day variability. After determination of a standardised EBC collection procedure, correlation analyses between EBC H(2)O(2) and bronchoalveolar lavage (BAL) cytology of healthy and allergen-challenged Ascaris suum (AS)-sensitised cats were performed. A significant and positive correlation between EBC H(2)O(2) and bronchoalveolar lavage (BAL) neutrophil% was found in healthy cats (P < 0.001, r = 0.55), whereas in AS-sensitised cats, correlation with BAL eosinophil% was significant (P < 0.005, r = 0.61). H(2)O(2) was increased after an allergen challenge in AS-sensitised cats (n = 6, 0.56+/-0.12 versus 1.08+/-0.35 micromol/L, P < 0.05). This study proposes a non-invasive, well tolerated and repeatable method of EBC collection for cats and suggests that EBC H(2)O(2) might be used as non-invasive biomarker for monitoring lower airway inflammation.

Recent finding suggests that T-cells may be involved in the pathogenesis of heaves in horses. However, little is known concerning their possible contribution to pulmonary neutrophilia, a characteristic finding in heaves. Interleukin (IL)-17 is a cytokine secreted by activated T-cells that indirectly promotes the maturation, chemotaxis and activation of neutrophils. We therefore hypothesized that IL-17 may be involved in the recruitment of neutrophils into the airways and that its mRNA expression would be increased in bronchoalveolar lavage (BAL) cells of horses with heaves. Heaves susceptible horses (n=4) and control horses (n=4) when in pasture (clinical remission) and after 35 days of continuous exposure to moldy hay were studied. BAL and respiratory mechanics measurements were performed at both time periods. The mRNA expression of IL-17 in BAL was studied using real-time polymerase chain reaction (PCR) and CD3-zeta was used as a marker of T-cell numbers. There was no significant difference in IL-17 mRNA expression between groups of horses while in pasture. However, stabling resulted in an increased expression of IL-17 in all horses with heaves but in none of the control horses. These preliminary results suggest that IL-17 may contribute in the pathogenesis of horses with heaves following chronic antigen challenge.

A novel endoscopic approach for the removal of nasal polyps from a cat with upper respiratory obstruction is described. The cat's small oral cavity prevented polyp removal via traditional nasopharyngoscopy and the owner declined rhinotomy because of concerns about postoperative morbidity. Access to the nasopharynx was achieved by introducing an endoscope via gastrotomy and passing the instrument orad through the esophagus into the nasopharynx. Compared with traditional endoscopic approaches, this approach provided superior exposure of the nasopharynx and facilitated use of a larger scope and instruments than would have been possible using retroflexed nasopharyngoscopy. Multiple polyps were readily removed using this approach. The procedure was well tolerated, with minimal surgical morbidity.

Equine recurrent airway obstruction (RAO) is thought to result from an aberrant immune response to inhaled antigens, modulated by T lymphocytes via the secretion of pro-inflammatory cytokines. However data relating to the phenotypes of the T lymphocytes present in peripheral blood and bronchoalveolar lavage fluid of RAO horses and their cytokine profiles are contradictory. The aim of this study was to further investigate the cytokine (IL-4, IL-5, IL-13 and INF-gamma) mRNA expression profile in peripheral blood lymphocytes and bronchoalveolar lavage lymphocytes from RAO and control horses, before and at 48 h after horses were exposed to hay/straw. In contrast to previous studies, cytokine expression was quantified in populations of CD4 and CD8 T lymphocytes which were purified using magnetic bead antibody cell separation. Hay/straw exposure induced clinical airway obstruction, airway neutrophilia and airway lymphocytosis in RAO horses, and, induced a mild, but significant, airway neutrophilia in controls. However, hay/straw exposure had no significant effect on peripheral blood lymphocyte or bronchoalveolar lavage lymphocyte cytokine expression in either group. In conclusion, RAO was not associated with alterations in lymphocyte cytokine expression that are consistent with Th1 or Th2 responses, but rather with a general down-regulation in expression of the measured cytokines in peripheral blood lymphocytes and bronchoalveolar lavage lymphocytes.

During anaesthesia for elective procedures, 2 dogs developed acute airway obstruction caused by herniation of the endotracheal cuff. This is an uncommon but potentially fatal complication especially when minimal monitoring of the patient leads to late recognition of the condition. The most typical symptoms are decreased thoracic excursions and tidal volume, absence of gas flow through the endotracheal tube, change in the capnographic waves morphology and increased airway pressures. In both cases desaturation of haemoglobin (measured by pulse oximetry) occurred in-between 6 and 8 minutes after cuff herniation. All signs normalised following partial deflation of the cuff. Careful management of cuff pressures especially when nitrous oxide is used, awareness of the condition and monitoring of the patient can prevent fatal consequences.

Reasons for Performing Study: It has been suggested that rapid administration of isotonic saline solution relieves airway obstruction in heaves-affected horses, but the efficacy and tolerability of this treatment is poorly documented., Objectives: To determine the respiratory and metabolic effects of a rapid administration of isotonic saline solution in control horses and those with heaves., Methods: Thirty litres isotonic saline solution were administered i.v. to 5 control (Group C) and 9 heaves-affected horses (Group H). Pulmonary function testing and arterial blood gas analysis were performed prior to saline infusion, at 90 and 180 mins after starting the infusion, and 1, 3, 6 and 10 days later. PCV, plasma total solids, plasma electrolytes (Na+, Cl- and K+) and venous blood gas analysis were performed prior, during and after saline infusion., Results: Rapid saline administration was shown to have no beneficial effects on lung function during infusion in Group H. On the contrary, they had significantly increased pulmonary resistance (RL) at 180 mins following the initiation of saline administration compared to baseline. In Group C, saline administration resulted in a significant increase in RL at 180 mins and a significant decrease in PaO2 at 90 mins. These results suggest a transient decrement in lung function caused by rapid saline administration. Group H had a metabolic alkalosis with hypochloraemia at baseline compared to control horses. This resolved following i.v. saline administration and returned to baseline within 6 h after treatment had been discontinued., Conclusion: The administration of saline to Group H did not improve airway function significantly, but resulted in mild and transient side effects., Potential Relevance: Rapid administration of isotonic saline alone is not an effective therapy for heaves in horses.

The objective of this paper was to determine if changes in ventilation patterns could influence the outcome of respiratory function measurements performed with our impulse oscillometry system (IOS) in horses. In a first study, IOS tests were performed in vitro on six isolated equine lungs. Lung inflation levels were controlled by modifying depressurisation inside an artificial thorax and different ventilation patterns were imposed. In a second in vivo study, transient variations in breathing pattern were evaluated both with the IOS and a current reference technique (CRT) in five healthy mature horses after an intravenous (i.v.) injection of lobeline hydrochloride. In both studies, respiratory rate (RR, range: 7-42 breaths/min.) and tidal volume (V(T), range: 0.4-25 L) had minor or no influence on IOS parameters. The influence of lung inflation, most marked for resistance at 5 Hz (R(5 Hz)), was limited for the considered physiological range. In vivo, statistical models indicated that maximal changes in pleural pressure (Max Delta Ppl) and peak flows were the main determinants of the variability of the resistance (R(rs)) and the reactance (X(rs)) of the respiratory system. The fourfold increase in baseline Max Delta Ppl and peak flows obtained during hyperpnoea caused a significant increase in R(rs) at 5 and 10 Hz and a decrease in X(rs) at all frequencies. We conclude that IOS parameters are not influenced by tachypnoea, but will reflect alterations in respiratory mechanics caused by hyperpnoeic breathing.