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Summary

In this double-blind study, the effectiveness of and dose response to intra-articular administration of modified hyaluronan (hylan) was determined in an equine carpal lameness model over a 23-day period, using a computerized three-dimensional motion analysis system, synovial fluid variables, and synovial histologic examination.

In 24 clinically sound horses, baseline motion data was acquired from horses trotting at 4 m/s on a high-speed treadmill. Then, to induce lameness, 25 mg of amphotericin B in 5 ml of sterile water was injected into the left middle carpal joint of each horse every other day for 3 treatments. Phenybutazone (2.2 mg/kg of body weight, PO, once) and butorphanol tartrate (0.1 mg/kg, IM, q 6 h, for 36 hours) were used to control signs of discomfort. Horses were assigned at random to 4 equal groups and received intracarpal administration of either 1, 2, 4 ml of hylan (8 mg/ml), or 2 ml of balanced electrolyte solution (control).

Intracarpal administration of amphotericin B caused significant (P ≤ 0.01) increase in subjective lameness grades over the 2-week evaluation period, and hylan administration did not significantly (P ≤ 0.01) change the subjective lameness grade. Lameness induction caused significant (P ≤ 0.01) decrease in head and withers excursions during the lame forelimb support phase and significant (P ≤ 0.05) increase in head and withers excursions during the sound forelimb support phase. Synovitis induction was further characterized by significant (P ≤ 0.05) increases in total wbc, polymorphonuclear, and large and small mononuclear cell numbers, and synovial fluid total protein concentrations. Also, subjective scores for synovial sections were significantly (P ≤ 0.05) different from baseline values, but hylan treatment at the 1-, 2-, or 4-ml dose did not significantly (P ≤ 0.05) alter these variables, compared with baseline values or values in control horses. Hyaluronan concentrations were not altered by induction of synovitis or hylan treatment.

Although clinical use of hyaluronan for treatment of traumatic joint disease in horses is well accepted, the beneficial effect of hylan was not detectable in this study. Further studies are required to more fully characterize the possible beneficial effects of hyaluronan-based products for treatment of joint disease in equids.

Free access
in American Journal of Veterinary Research

SUMMARY

Upper airway flow mechanics and arterial blood gas measurements were used to assess the efficacy of subtotal arytenoidectomy for treatment of induced left laryngeal hemiplegia in horses. Measurements were collected with the horses at rest, and trotting or pacing on a treadmill (6.38° incline) at speeds of 4.2 and 7.0 m/s. Experimental protocols were performed after right common carotid artery exteriorization (baseline), after left recurrent laryngeal neurectomy (lrln), and after left subtotal arytenoidectomy.

At baseline, increasing treadmill speed progressively increased peak inspiratory and expiratory flow (Vi max and Ve max respectively), peak inspiratory and expiratory transupper airway pressure (PuI and PuE, respectively), respiratory frequency (f), tidal volume (VT), minute volume (VE), and heart rate. Inspiratory and expiratory times (TI and TE, respectively) and arterial oxygen tension (Pao2) decreased with increased treadmill speed; inspiratory and expiratory impedance (ZI and ZE, respectively) did not change.

After lrln, Vi max, f, and Pao 2 significantly (P < 0.05) decreased at exercise, whereas PuI, TI, and ZI significantly increased. Minute volume decreased at exercise after lrln, but the changes were not significant; lrln had no effect on Ve max PuE, ZE, heart rate, arterial carbon dioxide tension (Paco 2), or VT.

Subtotal arytenoidectomy did not improve upper airway flow mechanics or blood gas measurements impaired by laryngeal hemiplegia.

Free access
in American Journal of Veterinary Research

Summary

The efficacy of a nerve muscle pedicle (nmp) graft in restoring upper airway function was evaluated in exercising horses with induced left laryngeal hemiplegia. The nmp graft was created from the first cervical nerve and the omohyoideus muscle and transplanted into the left cricoarytenoideus dorsalis muscle. Seven adult Standardbreds were trained to exercise on a treadmill inclined at 6.38°. With the horses at rest and exercising at 4.2 and 7.0 m/s, the following variables were recorded: peak inspiratory and expiratory transupper airway pressures (defined as the pressure difference between a lateral tracheal catheter and a mask catheter), peak inspiratory and expiratory air flow, inspiratory and expiratory impedance, tidal volume, minute ventilation, heart rate, and respiratory frequency. Measurements were made before left recurrent laryngeal neurectomy (lrln), 28 days after lrln, and 12, 24, and 52 weeks after the nmp graft (n = 5) or sham operation (n = 2). Before lrln, exercise increased inspiratory and expiratory air flow and transupper airway pressure, whereas the impedance was unchanged. After lrln, transupper airway inspiratory pressure and impedance were significantly greater and inspiratory air flow was significantly less than baseline values at 7.0 m/s. The sham operation did not improve airway function. Twelve weeks after insertion of the nmp graft, inspiratory impedance and inspiratory air flow were significantly different (improved) from lrln values. Twenty-four weeks after insertion of the nmp graft, inspiratory impedance was not significantly different from lrln values. Fifty-two weeks after insertion of the nmp graft, inspiratory impedance was not significantly different from the baseline value and was significantly less than the value after lrln. We conclude that the nerve muscle pedicle graft can restore upper airway function within 52 weeks in horses with induced left laryngeal hemiplegia.

Free access
in American Journal of Veterinary Research

Summary

A nerve muscle pedicle (nmp) graft was placed in the cricoarytenoideus dorsalis (cad) muscle of 6 horses with induced left laryngeal hemiplegia. The nmp graft was created by use of the first cervical nerve and omohyoideus muscle. In 1 horse (control), the first cervical nerve was transected after placement of the nmp graft. One year after the surgical procedure, horses were examined endoscopically and then anesthetized. While the larynx was observed endoscopically, the first cervical nerve was stimulated. Horses were subsequently euthanatized, and the larynx was harvested.

Prior to anesthesia, the endoscopic appearance of the larynx of all horses was typical of laryngeal hemiplegia. During anesthesia, stimulation of the first cervical nerve produced vigorous abduction of the left aiytenoid in principal horses but not in the control horse. The right cricoarytenoideus lateralis and cad muscles were grossly and histologically normal. Also, the left cricoarytenoideus lateralis was atrophic in all horses as was the left cad muscle of the control horse. In contrast, the left cad muscle harvested from principal horses had evidence of reinnervation with type 1 or type 2 fiber grouping. One year after the nmp graft procedure, horses with left laryngeal hemiplegia had reinnervation of the left cad muscle. In another study, reinnervation was sufficient to allow normal laryngeal function during exercise. Combined, these data suggest that the nmp graft procedure is a viable technique for the treatment of left laryngeal hemiplegia in horses.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To evaluate the efficacy of prosthetic laryngoplasty with and without bilateral ventriculocordectomy for treatment of experimentally induced left laryngeal hemiplegia (LLH).

Animals

15 adult Standardbreds.

Procedure

Horses were allotted to 3 equal groups. Sham operation (group 1), prosthetic laryngoplasty (group 2), or prosthetic laryngoplasty with bilateral ventriculocordectomy (group 3) was performed after induction of LLH. Upper airway function testing was performed prior to left recurrent laryngeal neurectomy (LRLN), 14 days after LRLN, and 60 and 180 days after surgical treatment. Measurements were obtained at rest and at treadmill speeds corresponding to 75 and 100% of maximal heart rate. Videoendoscopy was performed at rest and during exercise in all horses prior to LRLN and 60 and 180 days after surgical treatment. Upper airway endoscopy was performed immediately after LRLN to document induction of grade-IV LLH. Also, horses in group 3 were endoscopically examined at 7, 14, 21, 28, and 120 days after surgical treatment to evaluate healing of the ventriculocordectomy sites.

Results

When horses were at rest, significant differences were not apparent between groups at any period or between periods for any measured variable. LRLN induced airway obstruction in all horses during exercise. In sham-operated horses, this obstruction was unaffected by time. In contrast, 60 and 180 days after surgical treatment, inspiratory flow limitations induced by LRLN were reversed in horses of groups 2 and 3. There were no significant differences between the 2 treatment groups. Endoscopy revealed the left arytenoid cartilage abducted beyond the intermediate position, but not touching the pharyngeal wall in all horses with a laryngeal prosthesis. After surgical treatment, 4 group-2 horses had filling of both ventricles with air during exercise. There was moderate to marked swelling of the ventriculocordectomy sites immediately after surgery, and this swelling resolved by 7 days after surgery. The ventriculocordectomy sites looked best at 14 and 180 days.

Conclusions

60 and 180 days after prosthetic laryngoplasty, upper airway function returned to pre-LRLN values in horses with experimentally induced LLH exercising at 100% of maximal heart rate. Combining ventriculocordectomy with prosthetic laryngoplasty does not further improve upper airway function in these horses. (Am J Vet Res 1996;57:1668–1673)

Free access
in American Journal of Veterinary Research