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  • Author or Editor: N. Edward Robinson x
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Abstract

Objective—To determine the effect of histamine on the contractile elements of the respiratory tract in neonatal calves and young adult cattle.

Sample Population—Samples of trachealis muscle, bronchi, and intrapulmonary arteries and veins dissected from the respiratory tracts of healthy bovids (2 to 8 days and 16 to 20 months old).

Procedure—Histamine cumulative concentrationeffect curves (10–8 to 10–3M) were constructed in duplicate smooth muscle samples mounted in organ baths. Contractile responses to histamine were compared with reference contractions elicited by methacholine (10–5M) for airways or KCl (127mM) for vessels.

Results—In young adult cattle, trachealis muscle had a substantial contractile response to histamine (84% of methacholine-induced contraction), whereas bronchi reacted slightly (15 and 20% for large and small bronchi, respectively). Although contractile responses to KCl were comparable in arteries and veins, histamine-induced contractions were greater for intrapulmonary veins than for arteries (202 vs 48% of KCl-induced contraction). In neonatal calves, histamine- induced contraction of veins also exceeded that of arteries (230 vs 54% of KCl-induced contraction); however, unlike in young adult cattle, histamine produced notable contraction of large and small bronchi (48 and 60% of methacholine-induced contraction, respectively).

Conclusions and Clinical Relevance—Compared with intrapulmonary arteries, intrapulmonary veins have greater contractile responses to histamine in neonatal and young adult cattle. Data suggest loss of histamine responsiveness in bronchial smooth muscle as neonatal calves grow to young adults. Venodilation may be useful in treatment of lung edema in cattle. (Am J Vet Res 2003;64:819–822)

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in American Journal of Veterinary Research

Abstract

Objective—To evaluate leukotriene (LT) biosynthetic capacity in lung tissue from healthy horses and horses with recurrent airway obstruction (RAO).

Sample Population—Lung parenchyma and airway specimens from 8 RAO-affected and 5 healthy horses.

Procedure—Horses were stabled for ≥ 72 hours. Blood was drawn before euthanasia, after which lung specimens were collected. Tissue strips from small airways and parenchyma were incubated in organ baths with the precursor LTA4 or stimulated with calcium ionophore A23187 or the tripeptide N-formyl- Met-Leu-Phe (fMLP), with or without exogenous arachidonic acid, in the presence of isolated blood neutrophils.

Results—Stabling induced typical clinical signs of airway obstruction in RAO-affected horses but not control horses. When lung parenchyma or airway specimens from both groups of horses were incubated with calcium ionophore, with or without arachidonic acid, they did not form LT. In contrast, addition of LTA4 to both tissues resulted in conversion to LTB4, although concentrations of LTC4 were negligible in airways and parenchymal strips from healthy and RAOaffected horses. Incubation of airway and parenchymal strips with suspensions of autologous neutrophils did not influence formation of LT stimulated by calcium ionophore or fMLP, with or without exogenous arachidonic acid.

Conclusion and Clinical Relevance—Results suggest that lung parenchyma and airway tissues themselves are not of substantial importance for LT formation in the lungs, although these tissues possessed some LTA4 hydrolase activity, enabling LTB4 formation. It may be speculated that LTB4 originates primarily from neutrophils and may play a role in the inflammatory events of RAO. (Am J Vet Res 2002; 63:794–798)

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in American Journal of Veterinary Research

Abstract

Objective—To use noninvasive respiratory inductance plethysmography (RIP) to investigate differences in breathing patterns between horses with and without recurrent airway obstruction (RAO) during the onset of airway obstruction induced through confinement to stables.

Animals—12 horses with no history or clinical signs of respiratory disease (control horses) and 7 RAO-affected horses.

Procedures—The study involved 2 phases. In phase 1, the optimal position of RIP bands for recording pulmonary function was investigated in 12 control horses. In phase 2, 7 RAO-affected and 7 control horses were confined to stables. Respiratory inductance plethysmography bands were applied to horses for 24 h/d to record respiratory rate and total displacement in 4-hour periods for 7 days or until RAO-affected horses developed signs of severe RAO that persisted for 2 consecutive days. Lung function was measured once daily.

Results—In phase 1, thoracic and abdominal cavity displacements were best represented by RIP bands positioned at intercostal spaces 6 and 17, respectively. In phase 2, pulmonary function indicated airway obstruction in the RAO-affected group on the final 2 days of stable confinement. Respiratory rate and total degree of respiratory displacement measured by RIP did not differ between the RAO-affected and control groups, but the SDs of these decreased significantly within 8 hours after stable confinement began in RAO-affected horses. Respiratory inductance plethysmography and pulmonary function findings became highly correlated as severity of disease progressed.

Conclusions and Clinical Relevance—The decrease in the SDs of RIP measurements indicated a lower degree of variability in breathing patterns of RAO-affected horses. This loss of variability may provide an early indicator of airway inflammation.

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in American Journal of Veterinary Research

Abstract

Objective—To determine whether the hyoepiglotticus muscle has respiratory-related electromyographic activity and whether electrical stimulation of this muscle changes the position and conformation of the epiglottis, thereby altering dimensions of the aditus laryngis.

Animals—6 Standardbred horses.

Procedure—Horses were anesthetized, and a bipolar fine-wire electrode was placed in the hyoepiglotticus muscle of each horse. Endoscopic images of the nasopharynx and larynx were recorded during electrical stimulation of the hyoepiglotticus muscle in standing, unsedated horses. Dorsoventral length and area of the aditus laryngis were measured on images obtained before and during electrical stimulation. Electromyographic activity of the hyoepiglotticus muscle and nasopharyngeal pressures were measured while horses exercised on a treadmill at 50, 75, 90, and 100% of the speed that produced maximum heart rate.

Results—Electrical stimulation of the hyoepiglotticus muscle changed the shape of the epiglottis, displaced it ventrally, and significantly increased the dorsoventral length and area of the aditus laryngis. The hyoepiglotticus muscle had inspiratory activity that increased significantly with treadmill speed as a result of an increase in phasic and tonic activity. Expiratory activity of the hyoepiglotticus muscle did not change with treadmill speed in 4 of 6 horses.

Conclusions and Clinical Relevance—Findings reported here suggest that contraction of the hyoepiglotticus muscle increases dimensions of the airway in horses by depressing the epiglottis ventrally during intense breathing efforts. The hyoepiglotticus muscle may be an important muscle for dilating the airway in horses, and contraction of the hyoepiglotticus muscle may induce conformational changes in the epiglottis. (Am J Vet Res 2002;63:1617–1621)

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in American Journal of Veterinary Research

Abstract

Objective—To determine the ex vivo leukotriene (LT) biosynthesis in peripheral blood neutrophils (PBNs) and inflammatory cells in bronchoalveolar lavage fluid (BALF) obtained from horses affected with recurrent airway obstruction (RAO).

Animals—6 RAO-affected and 6 control horses.

Procedure—Before and 6, 24, and 48 hours after stabling, disease severity was determined subjectively by clinical and mucus scores and measurement of the maximal change in pleural pressure (ΔPplmax); PBNs were isolated and BALF samples were examined cytologically. The PBN and BALF cells were activated with a calcium ionophore in the presence of arachidonic acid, and production of LTC4 and LTB4 was measured per 106 cells.

Results—Clinical and mucus scores and ΔPplmax increased during stabling in RAO-affected horses, but not in control horses. In neutrophils and BALF cells from both groups, production of LTB4 exceeded that of LTC4. At all times, LTB4 production by PBNs was less in RAO-affected horses than it was in control horses. Before stabling, LTB4 production by cells in BALF was low in RAO-affected horses, but increased considerably after 6 hours of stabling. This increase coincided with the migration of neutrophils into the airways. In control horses, production of LTB4 did not change during stabling.

Conclusions and Clinical Relevance—Results suggested increased production of LTB4 in airways of RAO-affected horses, compared with control horses, that may contribute to the infiltration of neutrophils into the lungs and the sustained inflammation associated with RAO. ( Am J Vet Res 2004;65:289–295)

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in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of a commercially available nasal strip on airway mechanics in exercising horses.

Animals—6 horses (5 Standardbreds and 1 Thoroughbred).

Procedure—Horses exercised on a treadmill at speeds corresponding to 100 and 120% of maximal heart rate with and without application of a commercially available nasal strip. Concurrently, tracheal pressures, airflow, and heart rate were measured. Peak inspiratory and expiratory tracheal pressures, airflow, respiratory frequency, and tidal volume were recorded. Inspiratory and expiratory airway resistances were calculated by dividing peak pressures by peak flows. Endoscopic examination of the narrowest point of the nasal cavity (ie, nasal valve) was performed in 1 resting horse before, during, and after application of a nasal strip.

Results—During exercise on a treadmill, peak tracheal inspiratory pressure and inspiratory airway resistance were significantly less when nasal strips were applied to horses exercising at speeds corresponding to 100 and 120% of maximal heart rate. Application of the nasal strip pulled the dorsal conchal fold laterally, expanding the dorsal meatus.

Conclusions and Clinical Relevance—The commercially available nasal strip tented the skin over the nasal valve and dilated that section of the nasal passage, resulting in decreased airway resistance during inspiration. The nasal strip probably decreases the amount of work required for respiratory muscles in horses during intense exercise and may reduce the energy required for breathing in these horses. (Am J Vet Res 2002;63:1101–1105)

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in American Journal of Veterinary Research

Abstract

Objective—To evaluate the safety and efficacy of thoracoscopically guided pulmonary wedge resection in horses.

Animals—10 horses (5 control horses and 5 horses affected with recurrent airway obstruction [ie, heaves]).

Procedure—Each horse underwent a thoracoscopically guided pulmonary wedge resection. Before, during, and after surgery, heart rate, respiratory rate, arterial blood gases, and systemic and pulmonary arterial pressures were measured. Physical examination, CBC, and thoracic radiography and ultrasonography were performed 24 hours before and 2 and 48 hours after surgery. Pulmonary specimens were assessed by histologic examination. A second thoracoscopic procedure 14 days later was used to evaluate the resection site.

Results—The technique provided excellent specimens for histologic evaluation of the lung. Heart and respiratory rates decreased significantly after horses were administered sedatives. A significant transient decrease in PaO2 was detected immediately after pulmonary wedge resection, but we did not detect significant effects on arterial pH, Paco2, or mean arterial and pulmonary arterial pressures. All horses except 1 were clinically normal after thoracoscopic surgery; that horse developed hemothorax attributable to iatrogenic injury to the diaphragm. The second thoracoscopy revealed minimal inflammation, and there were no adhesions.

Conclusion and Clinical Relevance—Thoracoscopically guided pulmonary wedge resection provides a minimally invasive method for use in obtaining specimens of lung tissues from healthy horses and those with lung disease. This technique may be useful for the diagnosis of diseases of the lungs and thoracic cavity. (Am J Vet Res 2002;63:1232–1240)

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in American Journal of Veterinary Research

Abstract

Objective—To record respiratory sounds in exercising horses and determine whether spectrum analysis could be use to identify sounds specific for laryngeal hemiplegia (LH) and dorsal displacement of the soft palate (DDSP).

Animals—5 Standardbred horses.

Procedure—Respiratory sounds were recorded and pharyngeal pressure and stride frequency were measured while horses exercised at speeds corresponding to maximum heart rate, before and after induction of LH and DDSP.

Results—When airway function was normal, expiratory sounds predominated and lasted throughout exhalation. After induction of LH, expiratory sounds were unaffected; however, all horses produced inspiratory sounds characterized by 3 frequency bands centered at approximately 0.3, 1.6, and 3.8 kHz. After induction of DDSP, inspiratory sounds were unaffected, but a broad-frequency expiratory sound, characterized by rapid periodicity (rattling) was heard throughout expiration. This sound was not consistently detected in all horses.

Conclusions and Clinical Relevance—The technique used to record respiratory sounds was well tolerated by the horses, easy, and inexpensive. Spectrum analysis of respiratory sounds from exercising horses after experimental induction of LH or DDSP revealed unique sound patterns. If other conditions causing airway obstruction are also associated with unique sound patterns, spectrum analysis of respiratory sounds may prove to be useful in the diagnosis of airway abnormalities in horses. (Am J Vet Res 2001;62:659–664)

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in American Journal of Veterinary Research

Abstract

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 (ΔPplmax), 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 ΔPplmax. Control horses coughed transiently when first stabled. In RAO-affected horses, coughing was correlated with ΔPplmax, mucus score, and airway inflammation and was a sensitive and specific indicator of ΔPplmax > 6 cm H2O, mucus score > 1.0, and > 100 neutrophils/µL and > 20% neutrophils in BALF. Dexamethasone reduced cough frequency, mucus score, and ΔPplmax, 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 ΔPplmax and mucus accumulation in RAO-affected horses. ( Am J Vet Res 2003;64:550–557)

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in American Journal of Veterinary Research

Abstract

Objective—To determine the effects of 2 weeks of intense exercise on expression of markers of pulmonary venous remodeling in the caudodorsal and cranioventral regions of the lungs of horses.

Animals—6 horses.

Procedures—Tissue samples of the caudodorsal and cranioventral regions of lungs were obtained before and after conditioning and 2 weeks of intense exercise. Pulmonary veins were isolated, and a quantitative real-time PCR assay was used to determine mRNA expression of matrix metalloproteinase-2 and −9, tissue inhibitor of metalloproteinase-1 and −2, collagen type I, tenascin-C, endothelin-1, platelet-derived growth factor, transforming growth factor (TGF)-β, and vascular endothelial growth factor (VEGF). Protein expression of collagen (via morphometric analysis) and tenascin-C, TGF-β, and VEGF (via immunohistochemistry) was determined.

Results—Exercise-induced pulmonary hemorrhage was detected in 2 horses after exercise. The mRNA expression of matrix metalloproteinase-2 and −9, tissue inhibitor of metalloproteinase-2, TGF-β, and VEGF was significantly lower in pulmonary veins obtained after exercise versus those obtained before exercise for both the caudodorsal and cranioventral regions of the lungs. Collagen content was significantly higher in tissue samples obtained from the caudodorsal regions of the lungs versus content in samples obtained from the cranioventral regions of the lungs both before and after exercise. Exercise did not alter protein expression of tenascin-C, TGF-β, or VEGF.

Conclusions and Clinical Relevance—Results of this study indicated 2 weeks of intense exercise did not alter expression of marker genes in a manner expected to favor venous remodeling. Pulmonary venous remodeling is complex, and > 2 weeks of intense exercise may be required to induce such remodeling.

Full access
in American Journal of Veterinary Research