Objective—To determine the effect of manual
tongue protrusion on the dimensions of the hyoid
apparatus, nasopharynx, and oropharynx in anesthetized
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
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
Objective—To determine the effect of a commercially
available nasal strip on airway mechanics in exercising
Animals—6 horses (5 Standardbreds and 1
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)
Objective—To determine the effect of a tongue-tie on
upper airway mechanics in exercising horses.
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;
Objective—To determine the effect of desensitization
of the laryngeal mucosal mechanoreceptors on
upper airway mechanics in exercising horses.
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)
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
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
Objective—To evaluate the safety and efficacy of thoracoscopically
guided pulmonary wedge resection in
Animals—10 horses (5 control horses and 5 horses
affected with recurrent airway obstruction [ie,
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)
Objective—To compare endoscopic findings of the
upper portion of the respiratory tract in Thoroughbred
yearlings with their subsequent race records to determine
whether subjective assessment of airway function
may be used as a predictor of future racing performance.
Animals—427 Thoroughbred yearlings.
Procedures—Endoscopic examination findings were
obtained from the medical records and the videoendoscopic
repository of the Keeneland 1996
September yearling sales. Racing records were
requested for the yearlings through the end of their 4-year-old racing season (1997–2000). Twenty-nine measures
of racing performance were correlated with
endoscopic findings. Subjective arytenoid cartilage
movement grades were determined, using a 4-point
grading scale (grade 1 = symmetrical synchronous
abduction of the arytenoid cartilages; grade 4 = no
substantial movement of the left arytenoid cartilage).
Results—Of the 427 Thoroughbred yearlings included
in this study, 364 established race records, and 63 did
not. Opinions regarding suitability for purchase, meeting
conditions of the sale, and the presence of
epiglottic abnormalities had no significant association
with racing performance. Arytenoid cartilage movement
grades were significantly associated with many
of the dependent variables. However, palatine abnormalities
were not predictive of inferior racing performance.
Conclusions and Clinical Relevance—Thoroughbred
yearlings with grade-1 and -2 arytenoid cartilage
movements had significantly better racing performance
as adults, compared with yearlings with grade-
3 arytenoid cartilage movements. In contrast, epiglottic
and palatine abnormalities were not predictive of
inferior racing performance. Therefore, evaluation of
laryngeal function, but not epiglottic or palatine abnormalities,
using the 4-point grading system, should be
the major factor in developing recommendations for
prospective buyers. (J Am Vet Med Assoc 2001;219:
Objective—To investigate relationships between
cough frequency and mucus accumulation, airway
obstruction, and airway inflammation and to determine
effects of dexamethasone on coughing and
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
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
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.
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.