Summary by

Elizabeth Gormley

Dynamic Laryngeal Collapse Associated with Poll Flexion at the World Equine Airways Symposium 2009 (WEAS 09) was presented by Eric Strand, Associate Professor of Equine Surgery, Norwegian School of Veterinary Medicine, University of Oslo, Norway.  The focus of his talk was the recently identified upper respiratory tract obstructive disorder named dynamic laryngeal collapse, and its association with the specific head carriage of poll flexion.

Dynamic laryngeal collapse was defined by Strand as bilateral vocal fold collapse with some degree of concurrent bilateral arytenoid cartilage collapse diagnosed by high speed treadmill video endoscopy with the horse wearing full head gear, including head check rein, and driving them on the treadmill with long reins.

The basic theme of Strand's presentation was to characterize signs of respiratory tract obstruction or abnormal noise problems suffered by Norwegian Coldblooded Trotters in poll flexed head carriage while harness racing.   Complaints of abnormal upper respiratory tract noise and poor performance, Strand said, are associated with periods of poll flexion during training and racing. Although harness racehorses are encouraged to race with an extended head and neck position, poll flexion occurs when horses are restrained onto the bit to prevent premature exhaustion during races, according to earlier research by Strand.  In defining the new diagnostic criteria for dynamic laryngeal collapse Strand focused on whether or not the condition is breed specific to the Norwegian Coldblooded Trotter.  It was concluded by the results of the study that any breed of horse during poll flexion can suffer from dynamic laryngeal collapse.  Diagnosed horses have normal laryngeal function at rest, and when exercised with a free head carriage, but develop dynamic laryngeal collapse when the poll region is flexed. 

Horses were identified as having this respiratory obstructive disorder after being excluded from the following diagnosed conditions: laryngeal hemiplegia, entrapment of the epiglottis, epiglottic fold collapse, cricothyroid muscle dysfunction, and dorsal displacement of the soft palate.  Also ruled out was the possibility that these horses required surgery, as even horses that had  been treated with bilateral ventriculocordectomy operations continued to have collapse of the arytenoid cartilages and other structures despite the absence of the vocal folds and laryngeal ventricles, Strand said.

Although dynamic laryngeal collapse associated with poll flexion is the most common upper respiratory tract disorder in Norwegian Coldblooded Trotters, according to Strand it is also seen in other breeds of horses.  A seemingly identical disorder is diagnosed in “gaited” breeds such as the Saddlebreds, Hackneys, Tennessee Walking horses, and Morgans which perform with a head carriage in “high” poll flexion, Strand stated following a personal communication with Brett Woodie, Rood and Riddle Equine Hospital, Kentucky, USA.  Strand also cites past research studies that have shown that head and neck flexion results in upper airway obstruction in normal Standardbred horses exercised at maximum heart rates.

Comparison of tracheal pressure measurements during alternating phases of free head carriage and poll flexion between horses with and without the diagnosis of dynamic laryngeal collapse led Stand to discard the hypothesis that clinically diagnosed horses could have greater baseline driving pressures due to “smaller” laryngeal internal space.

Both groups according to Strand had significantly “greater negative inspiratory pressures during poll flexion relative to respective free head carriage measurements; however, the affected group had much greater negative inspiratory pressures (-58.4 cmH2O) relative to the elite group (-39.4 cm H2O).  In summary this study demonstrated that even elite racehorses develop a mild airway obstruction during periods of poll flexion, and that dynamic laryngeal collapse associated with poll flexion causes a severe upper respiratory tract obstruction based upon tracheal pressure measurements.  During periods of free head carriage affected horses have inspiratory tracheal pressures which are within normal limits.”

References

1. Strand E, Hanche-Olsen S, Gronvold AMR, Mellum CN (2004) Dynamic bilateral

arytenoid and vocal fold collapse associated with head flexion in 5

Norwegian Coldblooded Trotter racehorses. Equine Vet Educ 16: 242-254.

2. Fjordbakk CT, Strand E, Hanche-Olsen S (2008) Surgical vs conservative

treatment of bilateral dynamic laryngeal collapse associated with poll flexion

in harness race horses. Vet Surgery 37: 501-507.

3. Strand E, Fjordbakk CT, Sundberg K, Olsson L, Lunde H, Hanche-Olsen S

(2009) Relative prevalence of upper respiratory tract disorders in 2 harness

racehorse breeds (185 cases: 1998-2006). To be submitted Equine Vet J.

4. Petsche VM, Derksen FJ, Berney CE, Robinson NE (1995) Effect of head position

on upper airway function in exercising horses. Equine Vet J Suppl.

18: 18-22.

5. Holcombe SJ, Rodriguez K, Lane J, Caron JP (2006) Cricothyroid muscle

function and vocal fold stability in exercising horses. Vet Surg 35 (6): 495-

500.

6. Strand E, Fjordbakk CT, Holcombe SJ, Risberg A, Chalmers HJ (2009) Effect

of poll flexion and dynamic laryngeal collapse on tracheal pressure in

Norwegian Coldblooded Trotter racehorses. Equine Vet J 41 (1): 59-64.

7.  Denise Steffanus, Veterinary Spotlight: Clear the air.  Thoroughbred Times Saturday, July 17, 2004

About Elizabeth Gormley

Elizabeth Gormley provides scientific information on equine health, sports medicine, and genetics for the general public. The information is made available with the understanding that the author and publisher are not providing veterinary or nutritional counseling services on this site. The information should not be used in place of a consultation with a competent veterinarian or equine nutrition professional. Elizabeth does not accept funding from any source with a financial interest in any specific approach to veterinary testing or treatment.

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