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in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

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)

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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 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)

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in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of a tongue-tie on upper airway mechanics in clinically normal horses exercising on a treadmill following sternothyrohyoid myectomy.

Animals—6 Standardbreds.

Procedure—Upper airway mechanics were measured with horses exercising on a treadmill at 5, 8, and 10 m/s 4 weeks after a sternothyrohyoid myectomy was performed. Pharyngeal and tracheal inspiratory and expiratory pressures were measured by use of transnasal pharyngeal and tracheal catheters connected to differential pressure transducers. Horses were fitted with a facemask and airflow was measured by use of a pneumotachograph. Horses underwent a standardized exercise protocol on a treadmill at 5, 8, and 10 m/s with and without a tongue-tie in a randomized cross-over design. Inspiratory and expiratory airflow, tracheal pressure, and pharyngeal pressure were measured, and inspiratory and expiratory resistances were calculated.

Results—We were unable to detect an effect of a tongue-tie on any of the respiratory variables measured.

Conclusions and Clinical Relevance—Results indicate that a tongue-tie does not alter upper airway mechanics following sternothyrohyoid myectomy in clinically normal horses during exercise. (Am J Vet Res 2001;62:779–782)

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in American Journal of Veterinary Research

Abstract

Objective

To investigate the effect of a mask and pneumotachograph on ventilation, respiratory frequency, and tracheal and nasopharyngeal pressures in horses running on a treadmill.

Design

Six horses ran at 50, 75, and 100% of the speed that resulted in maximum oxygen consumption, with and without a mask and pneumotachograph. Tracheal and pharyngeal inspiratory and expiratory pressures, respiratory frequency, and arterial blood gases were measured.

Animals

Six Standardbred horses.

Procedure

Oxygen consumption was measured during an incremental exercise test to determine the speed that resulted in maximal oxygen consumption for each horse. Tracheal and pharyngeal pressures were measured, using transnasal tracheal and pharyngeal side-hole catheters connected to differential pressure transducers. Carotid arterial blood samples were collected and PaO2 , PaCO2 , and pH were measured with a blood gas analyzer.

Results

Peak tracheal and pharyngeal inspiratory pressures were significantly more negative, peak tracheal and pharyngeal expiratory pressures were significantly more positive and respiratory frequency was significantly lower (all P < 0.05) at all speeds when horses wore a mask The PaCO2 , was higher and arterial pH and PaO2 , were lower (P < 0.05) when horses wore a mask.

Conclusions

The mask and pneumotachograph altered upper airway pressures, respiratory frequency, and ventilation in horses running on a treadmill.(Am J Vet Res 1996; 57: 250-253)

Free access
in American Journal of Veterinary Research

Objective

To evaluate the clinical efficacy of antibiotic-impregnated polymethyl methacrylate (PMMA) in horses with open or infected fractures or joints in which internal fixation or external coaptation devices were used.

Design

Retrospective case series,

Animals

19 horses in which antibiotic-impregnated PMMA was used as part of the treatment regimen.

Procedures

Medical records of each horse were reviewed, and owners and trainers were contacted to provide additional information.

Results

Musculoskeletal problems in these horses included 10 fractures of long bones, 2 comminuted phalangeal fractures, 5 joint injuries, and 2 chronically septic joints in which ankylosis was stimulated. Nine horses had open fractures, 8 had closed wounds and developed infection after internal fixation of fractures, and 2 had chronically septic joints. Bony union was achieved in 15 of 19 horses. Twelve horses were discharged from the hospital and survived long term. Gentamicin sulfate, tobramycin sulfate, amikacin sulfate, and cefazolin sodium were used in PMMA.

Clinical Implications

Use of antibiotic-impregnated PMMA provided high local concentrations of antibiotics and should be considered in the treatment of horses with open fractures and acute and chronic bone and joint infections. (J Am Vet Med Assoc 1997; 211:889–893)

Free access
in Journal of the American Veterinary Medical Association

Summary

Frequency of aerobic and anaerobic isolates in 327 aspirates and in 123 pleural fluid samples from 327 horses with pneumonia or pleuropneumonia and antimicrobial susceptibility patterns of the aerobes were reported. Of the 327 horses, 75% survived, 20% were euthanatized, and 5% died. Tracheobronchial aspirates or pleural fluid specimens from 25 of the horses did not yield growth. Of the remaining 302 horses, 221 had only aerobic organisms isolated, whereas only anaerobes were isolated from 6 of the 302 horses. The remaining 75 horses had mixed aerobic and anaerobic bacterial infections. The survival rates for horses with aerobic only isolates was twice that of horses with anaerobic isolates. The aerobic bacteria most frequently isolated were β-Streptococcus spp, Pasteurella spp, Escherichia coli, and Enterobacter spp. The anaerobic species most frequently isolated were Bacteroides spp and Clostridium spp.

Free access
in Journal of the American Veterinary Medical Association

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)

Full access
in American Journal of Veterinary Research