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- Author or Editor: Susan J. Holcombe x
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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)
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)
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)
Abstract
Objective—To determine the effect of a tongue-tie on upper airway mechanics in exercising horses.
Animals—5 Standardbreds.
Procedure—Peak inspiratory and expiratory tracheal and pharyngeal pressures and airflow were measured while horses exercised on a treadmill with and without a tongue-tie. Respiratory rate was also measured. Horses ran at speeds that corresponded to 50 (HR50), 75, 90 (HR90), and 100% of maximal heart rate. The tongue-tie was applied by pulling the tongue forward out of the mouth as far as possible and tying it at the level of the base of the frenulum to the mandible with an elastic gauze bandage. Peak inspiratory and expiratory tracheal, pharyngeal, and translaryngeal resistance, minute ventilation, and tidal volume were calculated. Data were analyzed by use of 2-way repeated-measures ANOVA. For post hoc comparison of significant data, the Student-Newman- Keuls test was used.
Results—We were unable to detect significant differences between groups for peak inspiratory or expiratory tracheal or pharyngeal resistance, peak pressure, peak expiratory flow, tidal volume, respiratory rate, or minute ventilation. Horses that ran with a tongue-tie had significantly higher peak inspiratory flows, compared with horses that ran without a tongue-tie. In the post hoc comparison, this effect was significant at 4 m/s, HR50, and HR90.
Conclusion and Clinical Relevance—Application of a tongue-tie did not alter upper respiratory mechanics in exercising horses and may be beneficial in exercising horses with certain types of obstructive dysfunction of the upper airways. However, application of a tongue-tie does not improve upper airway mechanics in clinically normal horses. (Am J Vet Res 2001; 62:775-778)
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)
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)
Abstract
Objective
To compare tracheal and pharyngeal inspiratory and expiratory pressures achieved during 60 seconds of nasal occlusion in standing horses with pressures achieved in horses during intense exercise.
Animals
5 Standardbreds.
Procedure
Tracheal and pharyngeal inspiratory and expiratory pressures were obtained from 5 horses during 60 seconds of nasal occlusion and compared with tracheal and pharyngeal pressures achieved during incremental treadmill exercise tests in which horses ran at 50, 75, and 100% of the speed that resulted in maximal heart rate ( HRmax)
Results
Significant difference was not detected between peak tracheal inspiratory pressure during nasal occlusion and peak tracheal inspiratory pressure at HRmax. Peak pharyngeal inspiratory pressure was sig nificantly more negative, and peak tracheal and peak pharyngeal expiratory pressures were sig nificantly more positive during 60 seconds of nasal occlusion than those observed in horses running at HRmax.
Conclusion
During upper airway endoscopy in standing horses, 60-second nasal occlusion induced tracheal and pharyngeal inspiratory pressures that equaled or exceeded pressures achieved during high-intensity exercise.
Clinical Relevance
Nasal occlusion is useful to simulate upper airway pressures achieved during high-intensity exercise. (Am J Vet Res 1996;57:1258–1260)
Abstract
Objective—To determine the effect of desensitization of the laryngeal mucosal mechanoreceptors on upper airway mechanics in exercising horses.
Animals—6 Standardbreds.
Procedure—In study 1, videoendoscopic examinations were performed while horses ran on a treadmill with and without topical anesthesia of the laryngeal mucosa. In study 2, peak tracheal and nasopharyngeal pressures and airflows were obtained from horses during incremental treadmill exercise tests, with and without topical anesthesia of the laryngeal mucosa. A nasal occlusion test was performed on each horse while standing during an endoscopic examination for both trials.
Results—In study 1, horses had nasopharyngeal collapse while running on the treadmill when the laryngeal mucosa was anesthetized. In study 2, inspiratory upper airway and nasopharyngeal impedance were significantly higher, and peak tracheal inspiratory pressure, respiratory frequency, and minute ventilation were significantly lower in horses when the laryngeal mucosa was anesthetized, compared with values obtained when horses exercised without topical anesthesia. Peak inspiratory and expiratory airflows were lower in horses when the laryngeal mucosa was anesthetized, although differences did not quite reach significance (P = 0.06 and 0.09, respectively). During a nasal occlusion test, horses had episodes of nasopharyngeal collapse and dorsal displacement of the soft palate when the laryngeal mucosa was anesthetized. Upper airway function was normal in these horses without laryngeal mucosal anesthesia.
Conclusions and Clinical Relevance—Receptors within the laryngeal mucosa may be important in maintaining upper airway patency in exercising horses. (Am J Vet Res 2001;62:1706–1710)
Summary
The effects of furosemide on the racing times of 79 horses without exercise-induced pulmonary hemorrhage (eiph) and 52 horses with eiph were investigated. Racing times were adjusted to 1-mile equivalent racing times by 2 speed handicapping methods, and analysis of covariance was used to adjust actual racing times by winning time and distance for each race. All 3 methods of determining racing time indicated that geldings without eiph had significantly faster racing times (P < 0.05) when given furosemide before racing than when furosemide was not given before racing. Females and colts without eiph were determined to have faster racing times when furosemide was given before racing, but the difference was not significant. Geldings with eiph had significantly faster racing times (P = 0.0231) when given furosemide before racing, as determined by one of the speed handicapping methods. There was a strong correlation (range 0.9314 to 0.9751) between the 1-mile equivalent racing times, as determined by the 2 speed handicapping methods for horses with and without eiph. Furosemide failed to prevent the development of eiph in many horses that were previously considered to be eiph-negative. When given furosemide, 62 (25.3%) of 235 eiph-negative horses were eiph-positive after racing. Furosemide had questionable efficacy for prevention of eiph in known eiph-positive horses. Thirty-two (61.5%) of 52 eiph-positive horses given furosemide before a race remained eiph-positive after that race.
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)