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Summary

The usefulness of tidal breathing flow-volume loops (tbfvl) to evaluate pulmonary function was investigated in 6 Standardbreds during treadmill exercise. Tidal breathing flow-volume loops are a graphic representation of airflow rate vs tidal volume for each individual breath. These tbfvl were obtained from horses exercising at speeds corresponding to 75 and 100% of maximum heart rate. Measurements were recorded in each horse before and after ovalbumin-induced allergic lung disease. Moderate obstructive lung disease, characterized by a significant increase in pulmonary resistance, was observed while the horses were at rest. We found that in horses with airway obstruction exercising at 75 or 100% of maximum heart rate, the quantitative indices describing tbfvl shape and size were not markedly different from those in clinically normal horses exercising at similar speeds.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of manual tongue protrusion on the dimensions of the hyoid apparatus, nasopharynx, and oropharynx in anesthetized horses.

Animals—5 adult horses.

Procedure—Horses were anesthetized and positioned in sternal recumbency for 2 sequential computed tomographic (CT) scans. Images were acquired with the tongue in a natural position inside the mouth. Then, the tongue was pulled rostrally and secured, and a second CT scan was performed. Dorsoventral length of the hyoid apparatus and angles of the basisphenoid, basihyoid, and ceratohyoid were measured on 3-dimensional reconstructed CT images. Cross-sectional diameters and areas of the nasopharynx and oropharynx were determined on reformatted images in the transverse and longitudinal planes, using osseous landmarks for consistency. Results were tested between the 2 groups to determine significant differences.

Results—We were unable to detect a significant difference between any of the lengths or angles of the hyoid apparatus measured with or without rostral protrusion of the tongue. Similarly, nasopharyngeal and oropharyngeal diameters and cross-sectional areas were not significantly different with or without rostral protrusion of the tongue.

Conclusions and Clinical Relevance—Tying the tongue rostrally out of a horse's mouth did not influence the position of the hyoid apparatus or dimensions of the nasopharynx or oropharynx in anesthetized horses. Currently, no data suggest that application of a tongue-tie is effective for maintaining stability and patency of the nasopharyngeal or orolaryngeal airways in horses during races. (Am J Vet Res 2001;62:1865–1869)

Full access
in American Journal of Veterinary Research

Abstract

Objective

To determine the effect of bilateral blockade of the pharyngeal branch of the vagus nerve on soft palate function in horses.

Animals

5 Standardbreds.

Procedure

Peak tracheal inspiratory and expiratory pressures and airflow were measured while horses exercised at the speeds corresponding to 75 and 100% of the speed that resulted in maximal heart rate, with and without pharyngeal branch of the vagus nerve blockade. Respiratory frequency-to-stride frequency coupling ratio was measured by correlating foot fall measurements with respiratory frequency. The pharyngeal branch of the vagus nerve was blocked bilaterally as the nerve coursed through the auditory tube diverticulum (guttural pouch) across the longus capitus muscle.

Results

Persistent, reversible dorsal displacement of the soft palate (DDSP) occurred in all horses after nerve blockade, and lasted from 1 to 3 hours; normal nasopharyngeal function returned within 3 hours. Compared with control values, peak expiratory tracheal pressure increased (P = 0.001), expiratory impedance increased (P = 0.007), and minute ventilation decreased (P = 0.04). Respiratory frequency-to-stride frequency coupling ratio decreased (P = 0.009) so that horses took 1 breath/stride without the nerve block and, approximately, 1 breath/2 strides with the block.

Conclusion

DDSP creates flow-limiting expiratory obstruction and may be caused by neuromuscular dysfunction involving the pharyngeal branch of the vagus nerve. It may alter performance by causing expiratory obstruction and by altering breathing strategy in horses.

Clinical Relevance

A repeatable, reversible model of DDSP exists that allows further study of the disease. Dysfunction of the neuromuscular group, pharyngeal branch of the vagus nerve and palatinus and palatopharyngeus muscles, may be implicated in the pathogenesis of clinical DDSP. (Am J Vet Res 1998;59:504–508)

Free access
in American Journal of Veterinary Research

SUMMARY

During acute bouts of recurrent airway obstruction (heaves) in horses, neutrophils that are capable of increased production of reactive oxygen species accumulate in the airways. In the study reported here, the effect of hydrogen peroxide (H2O2; 1 µM to 0.1M), one of these reactive oxygen species products, on the responses of isolated trachealis muscle of horses was determined. Before and after incubation with H2O2, contractile responses to acetylcholine, electrical field stimulation (efs), 127 mM KCl, and relaxation responses to isoproterenol and activation of the nonadrenergic noncholinergic inhibitory response (iNANC) were evaluated. Beginning at 1 mM, H2O2 contracted trachealis muscle in a concentration-dependent manner. This contraction was unaffected by atropine (1 µM), tetrodotoxin (1 µM), or 1 µM meclofenamate. Contraction of trachealis muscle in response to H2O2 is, therefore, not attributable to release of prostaglandins, acetylcholine, or other neurotransmitters. Above a concentration of 0.1 mM, H2O2 depressed the responses to efs, acetylcholine, and KCl in a concentration-dependent manner. At 0.1M, H2O2 decreased the maximal responses to efs, acetylcholine, and KCl by 62.7 ± 7.2, 60.58 ± 6.12, and 37.8 ± 9.54%, respectively. In the presence of meclofenamate (1 µM), partial but significant protection against 1 to 100 mM H2O2 was observed. In tracheal strips contracted with 0.3 µM methacholine, H2O2 had no effect on the isoproterenol concentration-response curve. Up to a concentration of 100 mM, H2O2 had no effect on iNANC response. However, in the presence of 100 mM H2O2, this response was abolished in 2 of 4 horses. We conclude that high concentrations of H2O2 affected the responses of airway smooth muscle by actions on neurotransmission, muscarinic receptors, and downstream from receptors; some of the H2O2 effects were in part mediated by cyclooxygenase products; and H2O2 had no effect on β-adrenergic or iNANC-induced relaxation.

Free access
in American Journal of Veterinary Research

Objective—

To assess the educational value of a practice-based ambulatory program used at a school of veterinary medicine.

Design—

Retrospective cohort study.

Sample Population—

Graduates of US veterinary medical schools between 1987 and 1994.

Procedure—

Phase I involved use of interviews and focus groups to assist in development of the questionnaire used in phase II, a retrospective cohort study. The pretested questionnaire was sent to a study population consisting of all graduates of the University of Wisconsin-Madison, School of Veterinary Medicine, between 1987 and 1994 as well as a control group who were randomly selected from the 1994 AVMA list of veterinarians. Control-group veterinarians were matched on the basis of professional activity, region, and year of graduation.

Results—

728 of 1.067 veterinarians completed the questionnaire in phase II of the study (response rate, 68%). The practice-based ambulatory program at the University of Wisconsin-Madison compared favorably with university-based ambulatory programs in volume of experiences and perceived educational quality. Regardless of rotation type. female students were significantly less likely to observe or perform 12 specific clinical procedures and were significantly less likely to rate instructional quality as excellent or very good. compared with male students.

Clinical Implications—

Practice-based ambulatory rotations can be a good alternative to existing university-based ambulatory rotations. Implementation of these programs should emphasize performance of procedures while striving to ensure participation of female students. (J Am Vet Med Assoc 1997;210:1590–1594

Free access
in Journal of the American Veterinary Medical Association

Summary

Tidal breathing flow-volume (tbfv) loops were determined in a group of control horses and in horses affected with recurrent airway obstruction (heaves). The latter group was studied when the condition was in remission and under increasing amounts of airway obstruction as reflected by measurements of change in pleural pressure, pulmonary resistance, and dynamic compliance. The tbfv loops of control horses had biphasic inspiratory and expiratory patterns; peak inspiratory and peak expiratory flows were detected early in inspiration and expiration, respectively. Tidal volume was unaffected by heaves, but at all stages of heaves, respiratory frequency was increased principally because of shorter inspiratory time, and therefore, inspiratory flow rate was increased. In horses with heaves, tbfv loops did not have a biphasic pattern; peak inspiratory flow was observed late in inspiration, and peak expiratory flow was observed early in expiration. As airway obstruction became more severe, peak expiratory flow increased as pulmonary resistance increased so that, during severe airway obstruction, tbfv loops had a characteristic appearance with high peak expiratory flow early in expiration followed by low flow rate.

Free access
in American Journal of Veterinary Research

SUMMARY

The effect of iv administration of the α2-adrenoceptor agonist xylazine hydrochloride (0.5 mg/kg of body weight) was examined in ponies with recurrent obstructive pulmonary disease, commonly called heaves. Six ponies with the disease (principals) were studied during clinical remission and during an acute attack of airway obstruction precipitated by stabling and feeding of dusty hay. Six control ponies were also studied. In principal ponies with airway obstruction, xylazine administration significantly (P < 0.05) decreased pulmonary resistance and increased dynamic compliance, but did not affect Pa o 2 or Pa co 2 . The α2-antagonist yohimbine blocked the pulmonary effects of xylazine. Administration of saline solution was without effect in both groups of ponies at all periods and xylazine did not have effect in controls or in principals in clinical remission.

Free access
in American Journal of Veterinary Research

Summary

Flow-volume loops generated from 6 Standardbreds at rest and during treadmill exercise were evaluated for their use in detecting upper airway obstruction. Tidal breathing flow-volume loops (tbfvl) were obtained from horses at rest and exercising at speeds corresponding to 75% of maximal heart rate and at maximal heart rate. The tbfvl were evaluated, using a pulmonary function computer; calculated indices describing airflow rate and expiratory-to-inspiratory airflow ratio for individual loops were determined. In addition to tbfvl indices, standard variables of upper airway function also were measured: peak airflow, peak pressure, and calculated inspiratory and expiratory impedances. Measurements were recorded before left recurrent laryngeal neurectomy (lrln; baseline) and 14 days after surgically induced left laryngeal hemiplegia.

When horses were at rest, tbfvl shape and indices describing the loop were highly variable. In contrast, in exercising horses, tbfvl shape was consistent and coefficients of variation of loop indices were less during exercise than at rest. After lrln, tbfvl from exercising horses indicated marked inspiratory airflow limitation, while the expiratory airflow curve was preserved. Peak inspiratory flow rate and inspiratory flow at 50 and 25% of tidal volume decreased, and the ratio of peak expiratory to inspiratory airflow and that of midtidal volume expiratory and inspiratory airflow rates increased significantly (P < 0.05). Inspiratory impedance also increased after lrln.

Although in resting horses tbfvl were not a useful indicator of upper airway obstruction, examination of tbfvl from exercising horses allowed objective, specific, and repeatable detection of upper airway obstruction. The technique was noninvasive, rapid, and well tolerated by horses; thus, it is a potentially valuable clinical diagnostic test.

Free access
in American Journal of Veterinary Research

Summary

The lungs of sensitized horses were exposed to aerosolized ovalbumin. Some horses (n = 4) were given ovalbumin in 1 lung only, whereas in others (n = 7), ovalbumin or vehicle were inoculated in the cranial, ventral, and caudal regions of the caudal lung lobe. Horses were exercised 5 hours after ovalbumin exposure. Immediately before exercise, endoscopy failed to reveal any abnormality. After exercise, endoscopic examination of horses subjected to unilateral ovalbumin exposure revealed extensive blood in airways leading to the exposed lung in all horses. Blood was not observed in the airways leading to the control lung. Mean (± sem) minimum volume of the exposed and control lungs was 9.5 ± 1.5 and 5.5 ± 1.6 L, respectively; this difference was statistically significant (P< 0.05). Bronchoscopy of horses subjected to regional ovalbumin or vehicle exposure and exercise revealed a small amount of blood-tinged fluid in the bronchi serving the regions of the lung inoculated with ovalbumin. Minimum volumes of such regions were not significantly different from one another. However, their minimum volume was significantly (P<0.05) larger than that of vehicle-inoculated regions. Gross and histologic examination confirmed inflammation and hemorrhage in the ovalbumin-exposed, but not the control lungs or lung regions. Thus, exercise can cause blood from an injured region of lung to appear in the larger airways. Regional differences in lung structure and function do not influence the appearance of blood in the airways.

Free access
in American Journal of Veterinary Research

Summary

Pulmonary function measurements were made in control ponies and in ponies with recurrent obstructive pulmonary disease (principals) during clinical remission and during an attack of acute airway obstruction. The ponies were given β-adrenergic antagonists and agonists to determine the role of β receptors in recurrent obstructive pulmonary disease, and to determine the subtypes of β receptors mediating bronchodilation in ponies. Aerosol administration of the β antagonists, propranolol (β1 and β2), atenolol (β1), and butoxamine (β2) decreased dynamic compliance (Cdyn) and increased pulmonary resistance (RL) in the principal ponies during airway obstruction, but were without effect when the ponies were in clinical remission. Intravenous administration of atropine reversed the effect of atenolol on Cdyn and RL, but was without effect on the decrease in Cdyn and increase in RL observed after butoxamine administration. The β antagonists did not affect airway function in the control ponies. The effect of β blockade on Cdyn and RL suggests β-adrenergic activation in the central and peripheral airways of principal ponies, mediated through both β2- and β1-adrenergic receptors. The aerosol β agonists, isoproterenol (β1 and β2), and clenbuterol (β2) attenuated histamine-induced airway obstruction to a similar extent in control ponies that were given histamine iv. In addition, the β1 antagonist, atenolol, did not attenuate the bronchodilation observed with isoproterenol. We concluded that, although β1- and β2-adrenergic receptors exist in pony airways and are activated during acute airway obstruction, bronchodilation in response to β agonists in ponies seems to be mediated primarily by β2-adrenergic receptors.

Free access
in American Journal of Veterinary Research