This is an article written by Dr. Andrew H. Sparkes, which you may wish to print off and share with your vet.

Since writing these notes, Dr. Sparkes is now testing the Aerokat feline spacer in practice. Next year Dr. Sparkes will be starting a more in depth study of feline asthma, looking at a number of different aspects, including a critical evaluation of the response to therapy. Also, Dr. Padrid is now advocating the use of Serevent in cats.

Chronic Bronchial Disease in Cats
Andrew H Sparkes BVetMed PhD DipECVIM-CA MRCVS
Animal Health Trust Lanwades Park Kentford, Suffolk, UK

Chronic bronchial disease is a common clinical entity in cats with certain well-recognised breed predispositions, for example Siamese cats. Clinical signs are predominantly coughing, wheezing and dyspnoea, signs which may be persistent, intermittent, or episodic. While coughing may predominate in some cats, wheezing (due to narrowing of the airways) may predominate in others with per-acute onset of severe wheezing and dyspnoea being seen in a minority of cases.

Cats with such signs are typically diagnosed as having either ‘chronic bronchitis’ or ‘feline asthma’, but the distinction between these two disease entities is at best difficult, and often completely arbitrary, with some clinicians using the two terms synonymously. However, this is far from ideal. True asthma is characterised by airway hyper-reactivity and reversible bronchoconstriction, whereas in chronic bronchitis (or chronic obstructive pulmonary disease – COPD) the disease is characterised by airway inflammation and excessive mucus production – changes which lead to irreversible narrowing of the airways.

Although presenting signs may be identical in both disease syndromes, unless a distinction can be made between these disease entities, therapy cannot be appropriately targeted to the underlying disease process. There is therefore a requirement for a better understanding of the pathophysiology of chronic bronchial disease in the cat, and the development of diagnostic tests that will help determine the underlying disease and enable targeted therapy to be used.

Routine clinical investigations of chronic bronchial disease in cats
Clinical investigation of chronic bronchial disease in the cat has, to date, been relatively limited. Routine investigations include physical examination, routine blood tests, radiography and cytological assessment of respiratory tract fluids. Pulmonary function tests are rarely employed at present, yet their use is routine and regarded as crucial in the assessment of chronic respiratory disease in humans.

Clinical findings
Studies suggest that coughing is the single most common clinical sign of chronic bronchial disease in cats, with a smaller proportion of cats showing signs of lower airway obstruction (wheezing, dyspnoea, tachypnoea and abnormal/noisy breathing patterns). A proportion of affected cats display both signs of airway obstruction and also chronic coughing. Coughing may be paroxysmal in some cats and may sometimes terminate in an episode of retching or coughing. These signs are of variable severity in affected cats ranging from very mild to very severe. Signs may be persistent in some cats, intermittent/episodic in others and in some the signs will wax and wane. Some cats present with per-acute onset of severe lower respiratory tract obstruction (severe expiratory dyspnoea) that can be life-threatening and appears analogous to status asthmaticus in humans. Rarely a seasonal pattern to the problem may be noticed.
Results of physical examination are variable – there may be wheezes and crackles audible on lung auscultation, and some cats may show reduced compressibility of the thorax, but these findings are variable. A cough may be readily elicited in some cats by tracheal palpation/pinching. In some cats, physical examination results may be unremarkable.

No clear sex predisposition to bronchial disease has been reported but Siamese and other Oriental shorthair breeds do appear predisposed. Affected cats vary in age from a few months to elderly adults, but most are young-middle aged adults when presented.

Laboratory findings
Routine laboratory tests include haematology, a biochemistry panel selected serologies and faecal examination. With chronic bronchial disease these investigations most commonly reveal a circulating eosinophilia, which has been reported in 20% or more of cases. However, the presence of an eosinophilia is not necessarily related to the bronchial disease as concomitant infestation with fleas or endoparasites is not uncommon. Hyperproteinaemia is also reported occasionally in affected cats and some have had a hyperglobulinaemia.

Rather than yielding specific information about the bronchial disease, routine laboratory investigations will more commonly help to rule out other specific causes of coughing/dyspnoea such as heartworm infection (via serological testing), Aelurostrongylus abstrusus infection (via faecal examination). FeLV and FIV testing may be prudent depending on the background of the cat and the prevalence of these agents, but a specific association between these agents and chronic bronchial disease has not been reported.
Radiographic findings

Radiographic investigation of chronic bronchial disease in cats frequently reveals a marked diffuse bronchial pattern. This is the single most common radiographic change but may be accompanied by a variety of other findings. There may be collapse of the right middle lung lobe or, more rarely, other lung lobes such as the left cranial. Hyper- or over-inflation of the lungs (air-trapping) may be seen, and in severe cases this will lead to flattening of the diaphragm and a barrel-shaped chest. Other reported changes include a patchy alveolar pattern, patchy or diffuse interstitial patterns and emphysema. Severe dyspnoea may also lead to the presence of aerophagia.

Radiographic changes vary from mild to extremely severe, but there is little correlation between the severity of the radiographic changes and the severity of the clinical signs.
In reality, the radiographic investigations confirm the presence of chronic bronchial disease, and rule out other potential causes of coughing (eg, pulmonary neoplasia) but none of the radiographic findings provide information on the aetiopathogenesis of the disease process, and they cannot help to distinguish between chronic bronchitis and bronchial asthma.

Bronchoscopy
Bronchoscopy is of limited value in the investigation of chronic bronchial disease in cats as the narrow airway diameter and size of flexible endoscopes means that in most cases endoscopic evaluation is limited to the trachea and at best the rostral mainstem bronchi. Bronchoscopy can again help to rule out other diseases associated with narrowing of the trachea (tracheal oedema, tracheal collapse), inflammation of the trachea, or intraluminal obstruction such as tracheal neoplasia or a foreign body. IN cases of chronic bronchial disease there may be erythema of the tracheal and bronchial mucosa and in some cases there will be excessive mucus/mucopurulent material present in the airway. When present, it may be possible to aspirate this for culture and cytology via the endoscope.

Bronchial washing and bronchoalveolar lavage
Bronchial washing and bronchoalveolar lavage form a routine part of the investigation of cats with bronchial disease. In our clinic we routinely perform both of these investigations and submit material obtained for both cytology and culture.

Tracheo-bronchial washing
Bronchial washing is most easily achieved via a sterile endotracheal tube using a sterile small diameter catheter such as a dog urinary catheter. The procedure is best performed under a light plane of general anaesthesia, sufficient to allow intubation but not to abolish the cough reflex. After careful intubation, the cat can be positioned in either dorsal or lateral recumbency. The sterile catheter is passed through the endotracheal tube into the distal trachea (carina) where direct aspiration of mucus may be attempted. After direct aspiration of any mucus, one or two small aliquots (approximately 0.5 ml/kg, maximum 2-3ml) of sterile saline are then instilled through the catheter and immediately aspirated. Ideally instillation of saline should induce a cough response

Bronchoalveolar lavage
The technique for BAL is similar, but a longer catheter is required (of narrow diameter) so that it can be lodged in the distal bronchial tree. Again, a long, narrow gauge dog urinary catheter is usually suitable. If radiographically one side of the chest appears more severely affected than the other, it may be possible to pass the catheter via the mainstem bronchus on that side by lying the cat in lateral recumbency with the most severely affected side down. The catheter is passed as far as possible until it lodges in the bronchial tree and then an isolated lung segment distal to the catheter is lavalged by instilling aliquots of sterile saline. We typically infuse 10ml saline followed by aspiration (via a 20-30ml syringe). If the yield of fluid is poor, or appears very clear (poor sample) further aliquots of saline can be infused but we generally use no more than a total of 20-30ml. For both bronchial washing and BAL it is helpful to have the saline warmed to body temperature prior to lavage. IN addition to improving cellular yield, this may help to prevent bronchoconstriction which can be a complication when the fluid is instilled into the airways. Because this procedure is usually undertaken in cats with known airway disease, and because there may be underlying airway hyper-reactivity in a proportion of these it is sensible to ensure the anaesthesia provides 100% O2 during and immediately after the washing and it is also prudent to have emergency bronchodilator therapy available (eg, intravenous terbutaline available).

Handling of aspirated samples
Cytological examination of the bronchial washings is likely to be of most value, although a small aliquot (0.5-1.0 ml) of the fluid should also be submitted in a sterile air-evacuated tube for aerobic and anaerobic bacterial culture. Fluid intended for cytological analysis should be placed immediately in tubes containing EDTA anticoagulant. If large plugs of mucus are present, these can be retrieved with a sterile pipette and smeared directly onto slides (or alternatively the fluid can be filtered through a single layer of sterile gauze to trap the mucus). Ideally, cytological examination of the aspirated fluid should be performed within 30 minutes to minimise cellular degeneration. However if this is not practical, further air-dried smears should be made and submitted to the laboratory with the EDTA fluid. Direct smears can be made from the fluid if it is visibly turbid, but smears of an aliquot sedimented by centrifugation can also be made.

Interpretation of cytology results
Tracheobronchial washings from healthy dogs and cats typically contain small amounts of mucus with ciliated columnar or cuboidal epithelial cells being the predominant cell type. Occasional macrophages and rare mature neutrophils are also found. Cytology of BAL fluid in healthy cats has been the subject of numerous studies, which have generally revealed a very variable population of cells. Total cell counts in normal cats have been extremely variable in BAL fluid, complicated in part by a lack of standardisation of techniques meaning direct comparison between studies is difficult. In general, from healthy cats alveolar macrophages are the dominant cell type in the fluid, typically accounting for around 70% of the total cell population. However, eosinophils, neutrophils and lymphocytes all make a significant contribution to the total cell population. Studies comparing SPF to conventional cats have, probably not surprisingly, shown a higher proportion of eosinophils and neutrophils in cats kept under conventional conditions but in both groups of cats, eosinophils are typically the second most common cell type found in washings and commonly account for 20-30% of the cells in conventionally reared cats. Although generally macrophages are the dominant cell type, in some individual (healthy) cats, eosinophils are the dominant cell population and may make up as much as 80-85% of the total cell count. The proportion of eosinophils in BAL fluid from healthy cats is unusual and atypical. In other species, including humans, eosinophils generally comprise less than 5% of the cells present. As in healthy cats, cytological findings in cats with chronic bronchial disease are also very variable. Predominant cell types can be eosinophils, neutrophils, macrophages or there may be a very mixed cell population. No correlation has been found between the predominant cell type present and the nature of the clinical signs or radiographic features. Published studies suggest that in cats with chronic bronchial disease, eosinophils are the major inflammatory cell type in airway cytology samples in only 20-30% of cases. Neutrophilic inflammation is a more common finding.

In humans, eosinophilic infiltrates are most commonly associated with asthma, whereas neutrophilic infiltrates are more typical of cases of chronic bronchitis/COPD. However, it is unclear whether a similar distinction can be made in cats, and likely dangerous to make such an assumption, particularly given the marked difference in airway cytology in healthy cats compared with humans.

Bacteriology
Airway washings submitted for bacteriology from dogs and cats with bronchial disease are frequently sterile but may yield positive cultures. However, bacteria can also be cultured form the upper and lower airways of a proportion of healthy dogs and cats and the cultures obtained in bronchial disease are generally thought to represent transient contamination with bacteria as quantitative cultures are usually low. Results of bacterial culture and sensitivity therefore have to be interpreted with particular care, but this information may valuable in assessing rational therapy in cases where a mucopurulent inflammatory response is found. If a heavy bacterial growth is found in the presence neutrophilic inflammation this may be justification for trial therapy with antibiotics. Generally though chronic bronchial disease is not associated with an infectious process. One exception to this rule may be mycoplasma infections. Studies have suggested that mycoplasmas can be isolated from up to 20-25% of cats with chronic bronchial disease but are rarely or never isoplated from the respiratory tract of healthy cats. Mycoplasmas are known to play a pathogenic role in human respiratory disease and can be a contributory cause/trigger factor in asthma cases. More information is required on the prevalence and significance of mycoplasmas in the feline respiratory tract, but trial therapy is warranted whenever mycoplasmas are isolated and as these organisms can be difficult to culture, there is a rationale argument for routine therapy aimed at eliminating mycoplasmas in all cats with chronic bronchial disease.

Pulmonary function testing in cats
Pulmonary function tests (PFTs) are routinely used in human medicine to characterise respiratory disease and monitor both progression and response to therapy. Forced (maximal) flow-volume loops are very commonly used, but the application of this to veterinary medicine is limited, as this requires maximal voluntary expiration on the part of the patient! Tidal breathing flow-volume loops (TBFVL) which relate airflow and volume during normal respiration have been used in cats and applied to the investigation of cats with bronchial disease. The measurement of TBFVL relies on conscious, unsedated cats tolerating a close-fitting facemask, but this system has allowed demonstration of differences in expiratory flow in cats with bronchial disease compared to healthy cats. However the expense of the equipment necessary to obtain the data, the need for a high level of technical competence and familiarity with such equipment and the fact that some cats will not tolerate a close fitting facemask has limited the clinical application of TBFVL in cats. In anaesthetised intubated cats, it is also possible to measure lung resistance (RL) and dynamic lung compliance (Cdyn) with spirometric tests. Such tests have demonstrated increasing RL in association with increasing severity of bronchial disease (although there is marked variability between individuals) and a corresponding decrease in Cdyn. Assessment of response to bronchodilator (terbutaline) therapy has been documented with this technique in a limited number of cats, with results suggesting that at least some do have genuine reversible airway constriction. On an even more limited scale, provocation testing has been used in some cats to assess airway reactivity with again, results suggesting that at least some affected cats do have airway hyper-reactivity. Both reversible bronchoconstriction and airway hyper-reactivity are key features of human asthma, thus there is no doubt that a proportion of cats with chronic bronchial disease do genuinely have asthma. However, such testing has been extremely limited, and is not suitable for routine clinical use, thus it is impossible to draw conclusions about the prevalence of different aetiopathogeneses of bronchial disease in cats.

Most recently, a completely non-invasive technique using barometric whole-body plethysmography has been described for assessing bronchoconstriction in cats. This technique has the advantage of being very simple to perform, as it only needs the cat to remain in a Perspex chamber for a short period of time and the validity of the technique has been demonstrated in cats with induced bronchoconstriction. Although more work is needed with this technique, and further comparison with results from standard PFT’s, it does provide the possibility of routine, non-invasive assessment of pulmonary function in cats with minimal stress and without the need for anaesthesia, sedation or restraint and thus may become the PFT of choice in this species. These various PFT’s are complimentary to each other, each providing different information. To progress our understanding of chronic bronchial disease in the cat it will be necessary to apply such tests to a large number of cats with naturally occurring disease and to correlate the data obtained with other clinical and laboratory tests characterising the airway inflammation. One of the advantages of lung function testing, as noted above, is that bronchial hyper-responsiveness can be documented with these tests (as can be done in humans) by showing exaggerated responses to low doses of a stimulant such as carbachol or methacholine, and improvements in pulmonary function can be documented with the use of bronchodilators thus helping to characterise the underlying disease process.
A routine non-invasive PFT for use in the cat (such as the whole body plethysmography technique) would offer many potential advantages as although PFT’s do not allow absolute differentiation of asthma and chronic bronchitis, their use is regarded as a crucial part of the diagnostic evaluation of chronic bronchial disease in humans.

Current therapy of chronic bronchial disease in cats
Neurological control of airway calibre is complex. Parasympathetic innervation provides stimulus for normal baseline airway tone mediated via Ach. This is balanced by smooth muscle relaxation (bronchodilation) mediated by sympathetic (adrenergic) innervation and â2 receptors. A third arm of the nervous system – the non-adrenergic, non-cholinergic (NANC) system also plays a role in normal airway physiology but its importance and relevance in feline airways is poorly characterised. Control of airway tone includes a variety of sensory receptors in the airways in addition to the nervous control of smooth muscle tone. Other inflammatory mediators may also be responsible for producing bronchoconstriction (histamine via H1 receptors, serotonin, prostaglandins, leukotrienes etc.) or bronchodilation (histamine via H2 receptors). Both central and peripheral airways in cats are very sensitive to serotonin, and in contrast to humans and dogs there is evidence that this may be an important inflammatory mediator of bronchoconstriction in cats. Coughing, sneezing, bronchoconstriction, mucociliary clearance and the mononuclear phagocytic cells are all part of the non-specific defence mechanisms of the airways against irritants.

Traditionally, therapy for non-infectious chronic bronchial disease in cats has relied on the use of oral anti-inflammatory agents (glucocorticoids) and/or bronchodilators such as the methylxanthenes (e.g. theophyline) or â2-agonists such as terbutaline (see table for doses). Glucocorticoids generally remain the main therapeutic agents as they reduce the underlying inflammation in the airways and also promote bronchodilation by sensitizing â2 receptors, increasing their numbers and increasing their affinity. Glucocorticoids reduce the formation of leukotrienes and prostaglandins and part of their anti-inflammatory activity is mediated in this way while this also may contribute to bronchodilation. Soluble glucocorticoids can be given intravenously for immediate effect and are valuable by this route in the treatment of acute bronchoconstriction (an ‘asthma attack’). Although true asthma is characterised by reversible bronchoconstriction, treatment with bronchodilators alone can be dangerous as the underlying inflammatory disease is not being treated and there may therefore be other changes in the airways left untreated (altered mucous production, inflammatory infiltrates etc.).

Bronchodilators can be very valuable in addition to glucocorticoids. â2-agonists are probably the most effective class of drugs and due to the effect of glucocorticoids on â2-receptors, the combined use of these agents can be synergistic. Terbutaline is a selective â2-agonist and the pharmacokinetics of this drug have been reasonably well established in cats leading to a known effective and safe dose. This is generally regarded as the systemic bronchodilator of choice in this species.

|Theophylline pharmacokinetics has also been studied in cats. Theophylline is also a bronchodilator, but has additional potential benefits in stabilising mast cells, increasing mucociliary clearance and increasing the strength of respiratory muscle contractions. Whether bronchodilator therapy will benefit an individual patient with chronic bronchial disease is difficult to determine – pulmonary function tests are not generally available and do not therefore form the basis of rational therapy in cats. While most cats will therefore benefit from anti-inflammatory therapy, the value of bronchodilator therapy has to be assessed according to response.

Many other drugs have been advocated for therapeutic use in cats, particularly in cases of purported ‘asthma’. These include the leukotriene receptor antagonists such as zafirlukast, serotonin antagonists such as cyproheptadine, new generation anti-histamines such as cetirizine, anti-cholinergics such as ipratropium and T-lymphocyte modulators such as cyclosporine A. However, although some of these agents have been widely used in feline medicine, reported efficacy has been very variable and clinical use is based only on anecdotal evidence. It is possible, and even probable, that the variable success observed with some of these agents reflects different types of underlying bronchial disease that have been grouped together by clinicians under the ‘umbrella’ term of feline ‘asthma’. Experimental data suggests that leukotriene antagonists are unlikely to be of major benefit in cats, whereas serotonin antagonists (eg, cyproheptadine) could be of value. If response to glucocorticoids and standard bronchodilators is poor, there is rational therefore to try serotonin antagonists as an additional therapeutic option.

Drug Indications Dose Route Frequency
Betamethasone sodium phosphate Glucocorticoid 0.8 mg/kg IV, IM, SQ Acute emergency Rx

Cyproheptadine Serotonin antagonist 1 – 2 mg/cat PO SID – BID

Dexamethasone sodium phosphate Glucocorticoid 1 mg/kg IV, IM, SQ Acute emergency Rx

Doxycycline Antibiotic (for mycoplasmosis) 5 mg/kg PO BID

Epinephrine (adrenaline) Bronchodilator, mixed adrenergic 0.1 ml of 1:1,000 dilution IV, IM, SQ, via ET tube Acute emergency Rx

Methylprednisolone sodium succinate Glucocorticoid 50-100 mg/cat IV, IM, SQ Acute emergency Rx

Prednisolone Glucocorticoid 1 – 2 mg/kg PO BID to start; taper as possible

Terbutaline Selective (â2 agonist) bronchodilator 0.01 mg/kg IV, IM, SQ q4h
0.625-1.25 mg/cat PO BID

Theophylline (sustained release) Bronchodilator 20 – 25 mg/kg PO SID

Zafirlukast Leukotriene receptor antagonist 10 mg/cat PO BID

Therapy with inhaled drugs
Traditional systemic therapy with corticosteroids and beta-agonists can be associated with significant side effects. More recently, inhaled medications have been recommended for the treatment of cats although again, objective data on their efficacy is currently lacking.
Nevertheless, using a human paediatric spacer device, aerosol (metered dose inhaler – MDI) therapy can be effectively administered to cats and clinical experience suggests this may prove to be a valuable form of therapy. A spacer device (chamber into which the MDI is actuated) with a face mask is required to allow the cat to inhale the medication and in the current absence of a specific device designed for use in cats, human paediatric spacers are generally used. The paediatric spacers are preferred as it is important that the incorporated non-return valves are of very low resistance allowing the cat to effectively move the air through the chamber. In our clinic we usually use a product called a ‘Babyhaler’ – a human device made by Glaxo (Allen & Hanbury).

Administration of both bronchodilators and glucocorticoids can be achieved with MDIs in cats and both have advantages being administered in this way. Bronchodilators are more rapidly acting when given by inhalation than either oral or SQ/IM products. Glucocorticoids are also potentially more effective given by the inhaled route and systemic side-effects can be avoided. We generally give a single actuation of the MDI into the spacer device and allow the cat to breathe the medication via the face mask for approximately 10-30 seconds (depending on what the cat will tolerate). If higher doses are required it is better to give to separate doses rather than to give to actuations into the chamber at the same time.

Salbutamol (albuterol, ‘Ventolin’) is the bronchodilator that has been most used via MDIs in cats. Salbutamol comes in a single strength MDI and can be given as required being effective within 5-10 minutes. It has been recommended that for moderately affected cats (cats with daily clinical signs) one or two doses of salbutamol can be given 2-4 times daily as a routine and more frequently where necessary. For more mildly affected cats, it can simply be given as required and in severe ‘attacks’ of respiratory disease, two doses of salbutamol may be given every 30 minutes for up to two to four hours. In humans, salmeterol is commonly used for long-term bronchodilation as this product lasts approximately 12 hours compared to 2-4 hours maximum for salbutamol. However, there are no reports yet of the use of salmeterol in cats, although it is likely to be safe and beneficial. The disadvantage of salmeterol is that it can take up to 60 minutes to take effect, thus albuterol may still be required for control of acute signs.

Fluticasone propionate is the glucocorticoid that has most commonly been used in cats. This is a highly effective but expensive inhaled steroid, with an advantage of virtually no systemic effects whatsoever. Where cost is an issue we have used beclomethasone dipropionate instead of fluticasone propionate. The highest strength MDIs of these products (generally 200-250 µg/actuation) has generally been used in cats, and typical recommendations are to administer one or two doses twice daily. Although very effective, inhaled steroids may take up to 1-2 weeks to achieve maximal effect and thus in severely affected cats, systemic steroids may also be required initially, and when switching from systemic to inhaled therapy it may be sensible to use the two therapies concurrently for around 10 days before beginning to wean down the systemic steroid dose.
As with the initial investigations of the disease process, response of cats to specific inhaled (or oral) therapeutic agents is poorly documented at present, but the development of non-invasive methods of characterising airway inflammation and performing PFT’s will allow collection of objective data in the future.

References and Further reading
Boothe DM, McKiernan BC (1992) Respiratory therapeutics. Vet Clin N Am 22;1231-1258
Corcoran BM, Foster DJ, Fuentes VL (1995) Feline asthma syndrome: a retrospective study of the clinical presentation in 29 cats. J Small Anim Pract 36;481-488
Dye JA, McKiernan BC, Rozanski EA, Hoffmann WE, Losonsky JM, Homco LD, Weisiger RM, Kakoma I (1996) Bronchopulmonary disease in the cat: historical, physical, radiographic, clinicopathologic, and pulmonary function evaluation of 24 affected and 15 healthy cats. J Vet Intern Med 10;385-400
Hawkins EC, Kennedy-Stoskopf S, Levy J, Meuten DJ, Cullins L, DeNicola D, Tompkins WA, Tompkins MB (1994) Cytologic characterization of bronchoalveolar lavage fluid collected through an endotracheal tube in cats. Am J Vet Res 55;795-802
Hoffman AM, Dhupa N, Cimetti L (1999) Airway reactivity measured by barometric whole-body plethysmography in healthy cats. Am J Vet Res 60;1487-1492
Moise NS, Wiedenkeller D, Yeager AE, Blue JT, Scarlett J (1989) Clinical, radiographic, and bronchial cytologic features of cats with bronchial diseae: 65 cases (1980-1986). J Am Vet Med Assoc 194;1467-1473
McCarthy G, Quinn PJ (1989) Bronchoalveolar lavage in the cat: cytologic findings. Can J Vet Res 53;259-263
McKiernan BC, Dye JA, Rozanski EA (1993) Tidal breathing flow-volume loops in healthy and bronchitic cats. J Vet Intern Med 6;388-393
McKiernan BC, Johnson LR (1992) Clinical pulmonary function testing in dogs and cats. Vet Clinics N Am 30;1357-1367
Mandelker L (2000) Experimental drug therapy for respiratory disorders in dogs and cats. Vet Clinics N Am 22;1087-1099
Padrid PA (2000) Feline asthma – diagnosis and treatment. Vet Clin N Am 30;1279-1293
Padrid PA, Feldman BF, Funk K, Samitz EM, Reil D, Cross CE (1991) Cytologic, microbiologic and biochemical analysis of bronchoalveolar lavage fluid obtained from 24 cats. Am J Vet Res 52;1300-1307