Asymmetric recurrent laryngeal nerve conduction velocities and dorsal cricoarytenoid muscle electromyographic characteristics in clinically normal horses.

The dorsal cricoarytenoid (DCA) muscles, are a fundamental component of the athletic horse's respiratory system: as the sole abductors of the airways, they maintain the size of the rima glottis which is essential for enabling maximal air intake during intense exercise. Dysfunction of the DCA muscle leads to arytenoid collapse during exercise, resulting in poor performance. An electrodiagnostic study including electromyography of the dorsal cricoarytenoid muscles and conduction velocity testing of the innervating recurrent laryngeal nerves (RLn) was conducted in horses with normal laryngeal function. We detected reduced nerve conduction velocity of the left RLn, compared to the right, and pathologic spontaneous activity (PSA) of myoelectrical activity within the left DCA muscle in half of this horse population and the horses with the slowest nerve conduction velocities. The findings in this group of horses are consistent with left sided demyelination and axonal loss, consistent with Recurrent Laryngeal Neuropathy (RLN), a highly prevalent degenerative disorder of the RLn in horses that predominantly affects the left side. The detection of electromyographic changes compatible with RLN in clinically unaffected horses is consistent with previous studies that identified "subclinical" subjects, presenting normal laryngeal function despite neuropathologic changes within nerve and muscle confirmed histologically.

Idiopathic Canine Laryngeal Paralysis as One Sign of a Diffuse Polyneuropathy: An Observational Study of 90 Cases (2007-2013).

OBJECTIVE: To determine survival and incidence of complications in dogs with idiopathic laryngeal paralysis (ILP) and concurrent neurologic signs. STUDY DESIGN: Observational study. ANIMALS: Dogs (n = 90) with ILP. METHODS: Medical records (January 2007-June 2013) of dogs with ILP were reviewed. Neurologic comorbidities, including pelvic limb neurologic abnormalities and esophageal abnormalities were identified. Using medical record information and client interviews, the relationship between these comorbidities and postoperative survival (primary outcome measure) and postoperative complications (secondary outcome measure) was identified. RESULTS: Dogs that had surgical correction of ILP had a 2.6-fold reduction in the hazard of death throughout the study period (HR = 2.6; 95% CI: 1.34-4.84, P = .006). Owner assessed patient quality of life (10-point scale) increased by an average of 4.1 ± 1.4 units immediately postoperatively, and 4.9 ± 0.9 units until death or followup compared with preoperative values. Thirty-five of 72 dogs available for followup had evidence of diffuse neurologic comorbidities. Overall complication rate for dogs with neurologic comorbidities was 74%, compared with 32% for dogs without neurologic comorbidities. Presence of any neurologic comorbidity was associated with a significantly greater odds of any complication (OR = 4.04; 95% CI: 1.25-13.90, P = .019) as well as recurring complications (OR = 8.00; 95% CI: 1.49-54.38; P = .015). CONCLUSION: Surgical correction of ILP was positively associated with survival, and dogs with neurologic comorbidities were at greater risk for developing postoperative complications.

Effects of Functional Electrical Stimulation on Denervated Laryngeal Muscle in a Large Animal Model.

Bilateral vocal fold paralysis (BVCP) is a life-threatening condition that follows injury to the Recurrent Laryngeal nerve (RLn) and denervation of the intrinsic laryngeal musculature. Functional electrical stimulation (FES) enables restoration and control of a wide variety of motor functions impaired by lower motor neuron lesions. Here we evaluate the effects of FES on the sole arytenoid abductor, the posterior cricoarytenoid (PCA) muscle in a large animal model of RLn injury. Ten horses were instrumented with two quadripolar intramuscular electrodes in the left PCA muscle. Following a 12-week denervation period, the PCA was stimulated using a once-daily training session for 8 weeks in seven animals. Three animals were used as unstimulated controls. Denervation produced a significant increase in rheobase (P < 0.001). Electrical stimulation produced a 30% increase in fiber diameter in comparison with the unstimulated control group (33.9 ± 2.6 µm FES+, 23.6 ± 4.2 µm FES-, P = 0.04). A trend toward a decrease in the proportion of type 1 (slow) fibers and an increase in type 2a (fast) fibers was also observed. Despite these changes, improvement in PCA function at rest was not observed. These data suggest that electrical stimulation using a relatively conservative set of stimulation parameters can reverse the muscle fiber atrophy produced by complete denervation while avoiding a shift to a slow (type 1) fiber type.

Functional electrical stimulation of intrinsic laryngeal muscles under varying loads in exercising horses.

Bilateral vocal fold paralysis (BVCP) is a life threatening condition and appears to be a good candidate for therapy using functional electrical stimulation (FES). Developing a working FES system has been technically difficult due to the inaccessible location and small size of the sole arytenoid abductor, the posterior cricoarytenoid (PCA) muscle. A naturally-occurring disease in horses shares many functional and etiological features with BVCP. In this study, the feasibility of FES for equine vocal fold paralysis was explored by testing arytenoid abduction evoked by electrical stimulation of the PCA muscle. Rheobase and chronaxie were determined for innervated PCA muscle. We then tested the hypothesis that direct muscle stimulation can maintain airway patency during strenuous exercise in horses with induced transient conduction block of the laryngeal motor nerve. Six adult horses were instrumented with a single bipolar intra-muscular electrode in the left PCA muscle. Rheobase and chronaxie were within the normal range for innervated muscle at 0.55±0.38 v and 0.38±0.19 ms respectively. Intramuscular stimulation of the PCA muscle significantly improved arytenoid abduction at all levels of exercise intensity and there was no significant difference between the level of abduction achieved with stimulation and control values under moderate loads. The equine larynx may provide a useful model for the study of bilateral fold paralysis.

Effects of epidural morphine on gastrointestinal transit in unmedicated horses.

OBJECTIVE: To evaluate the effect of epidural morphine on gastrointestinal (GI) motility in horses. STUDY DESIGN: Randomly ordered crossover design. ANIMALS: Six healthy adult horses weighing 585± 48 kg (mean±SD). METHODS: Horses were randomly assigned to receive either 0.2 mg kg(-1) morphine or an equal volume (0.04 mL kg(-1)) of saline epidurally (the first inter coccygeal space) with 2 weeks between treatments. The horses were stabled, fed a standardized diet and allowed water ad libitum throughout the duration of the study. Radiopaque spheres were administered by stomach tube. Xylazine 0.2 mg kg(-1) intravenously was administered prior to epidural injection. Heart rate, respiratory rate, GI sounds score and behavior score were recorded before drug administration and after epidural injection at 4, 8, 12, 18, 24 hours and every 12 hours thereafter for 6 days. Feces were weighed, radiographed and the number of spheres counted. Data were analyzed using a mixed effect model. RESULTS: At no time did horses exhibit signs of colic or show significant differences between treatments regarding heart rate, respiratory rate, GI sounds score, behavior score, or cumulative number of spheres. The concentration of spheres per kg of feces was significantly lower (p<0.05) for the morphine group at 18 and 24 hours. Using the centroid of the curves (spheres kg(-1) plotted versus time) the average transit time after saline epidural was 38 hours and after morphine it was 43 hours. The weight of feces hour(-1) was significantly lower (p<0.05) at only 4 and 8 hours after morphine. CONCLUSIONS AND CLINICAL RELEVANCE: Epidural morphine, at a dose of 0.2 mg kg(-1) , temporarily reduced GI motility but did not cause ileus or colic in this small group of healthy unfasted horses. Care should be taken when extrapolating these data to situations in which other factors may also affect GI motility.

Equine laryngoplasty sutures undergo increased loading during coughing and swallowing.

OBJECTIVES: To report (1) the force required on a single laryngoplasty suture to achieve optimal abduction of the left arytenoid cartilage, (2) peak forces experienced by the suture during induced swallowing and coughing, and during 24-hour resting activity in a stall, and (3) peak forces during induced swallowing and coughing after left recurrent laryngeal nerve blockade. STUDY DESIGN: Experimental study. ANIMALS: Horses (n=8). METHODS: Each laryngoplasty suture was instrumented with an E-type buckle force transducer to measure the force required for optimal intraoperative left arytenoid cartilage abduction. This was correlated with abduction observed postoperatively. Change in suture force from baseline was measured during induced coughing and swallowing, and during normal stall activity. RESULTS: Optimal intraoperative arytenoid abduction was achieved with a mean (±SD) force of 27.6±7.5 N. During saline-induced swallowing and coughing mean force on the suture increased by 19.0±5.6 N (n=233 measurements; 7 horses) and 12.1±3.6 N (n=31; 4 horses), respectively. Sutures underwent increased loading a mean of 1152 times in 24 hours. No change in suture force was observed with respiratory rhythm. CONCLUSION: Swallowing increases laryngoplasty suture force to a greater extent than coughing.

Concentrated bone marrow aspirate improves full-thickness cartilage repair compared with microfracture in the equine model.

BACKGROUND: The purpose of this study was to compare the outcomes of treatment with bone marrow aspirate concentrate, a simple, one-step, autogenous, and arthroscopically applicable method, with the outcomes of microfracture with regard to the repair of full-thickness cartilage defects in an equine model. METHODS: Extensive (15-mm-diameter) full-thickness cartilage defects were created on the lateral trochlear ridge of the femur in twelve horses. Bone marrow was aspirated from the sternum and centrifuged to generate the bone marrow concentrate. The defects were treated with bone marrow concentrate and microfracture or with microfracture alone. Second-look arthroscopy was performed at three months, and the horses were killed at eight months. Repair was assessed with use of macroscopic and histological scoring systems as well as with quantitative magnetic resonance imaging. RESULTS: No adverse reactions due to the microfracture or the bone marrow concentrate were observed. At eight months, macroscopic scores (mean and standard error of the mean, 9.4 + or - 1.2 compared with 4.4 + or - 1.2; p = 0.009) and histological scores (11.1 + or - 1.6 compared with 6.4 + or - 1.2; p = 0.02) indicated improvement in the repair tissue in the bone marrow concentrate group compared with that in the microfracture group. All scoring systems and magnetic resonance imaging data indicated that delivery of the bone marrow concentrate resulted in increased fill of the defects and improved integration of repair tissue into surrounding normal cartilage. In addition, there was greater type-II collagen content and improved orientation of the collagen as well as significantly more glycosaminoglycan in the bone marrow concentrate-treated defects than in the microfracture-treated defects. CONCLUSIONS: Delivery of bone marrow concentrate can result in healing of acute full-thickness cartilage defects that is superior to that after microfracture alone in an equine model. CLINICAL RELEVANCE: Delivery of bone marrow concentrate to cartilage defects has the clinical potential to improve cartilage healing, providing a simple, cost-effective, arthroscopically applicable, and clinically effective approach for cartilage repair.

In vitro model for testing novel implants for equine laryngoplasty.

OBJECTIVE: To develop an in vitro laryngeal model to mimic airflow and pressures experienced by horses at maximal exercise with which to test laryngoplasty techniques. STUDY DESIGN: Randomized complete block. SAMPLE POPULATION: Cadaveric equine larynges (n=10). METHODS: Equine larynges were collected at necropsy and a bilateral prosthetic laryngoplasty suture was placed with #5 Fiberwire suture to achieve bilateral maximal arytenoid abduction. Each larynx was positioned in a flow chamber and subjected to static flow and dynamic flow cycling at 2 Hz. Tracheal pressure and flow, and pressure within the flow chamber were recorded at a sampling frequency of 500 Hz. Data obtained were compared with the published physiologic values for horses exercising at maximal exercise. RESULTS: Under static flow conditions, the testing system produced inspiratory tracheal pressures (mean+/-SEM) of -33.0+/-0.98 mm Hg at a flow of 54.48+/-1.8 L/s. Pressure in the flow chamber was -8.1+/-2.2 mm Hg producing a translaryngeal impedance of 0.56+/-0.15 mm Hg/L/s. Under dynamic conditions, cycling flow and pressure were reproduced at a frequency of 2 Hz, the peak inspiratory (mean+/-SEM) pharyngeal and tracheal pressures across all larynges were -8.85+/-2.5 and -35.54+/-1.6 mm Hg, respectively. Peak inspiratory flow was 51.65+/-2.3 L/s and impedance was 0.57+/-0.06 mm Hg/L/s. CONCLUSIONS: The model produced inspiratory pressures similar to those in horses at maximal exercise when airflows experienced at exercise were used. CLINICAL RELEVANCE: This model will allow testing of multiple novel techniques and may facilitate development of improved techniques for prosthetic laryngoplasty.

Arthroscopic removal of palmar/plantar osteochondral fragments from the proximal interphalangeal joint in four horses.

OBJECTIVE: To describe anatomic considerations and arthroscopic technique in horses for arthroscopic removal of palmar/plantar osteochondral fragments from the proximal interphalangeal (PIP) joint. STUDY DESIGN: Retrospective study. ANIMALS: Adult horses (n=4) with osteochondral fragments of the palmar/plantar PIP joint. METHODS: Arthroscopic removal of palmar/plantar osteochondral fragments within the PIP joint was performed with horses in dorsal recumbency under general anesthesia. Medical records of affected horses were reviewed to determine history; physical, lameness, and radiological findings; surgical technique; complications and outcome. RESULTS: Two horses had lameness localized to the PIP joint. Two other horses had lameness suspected, but not confirmed to the pastern region. One of these horses had a history of intermittent lameness, but was not lame on admission. All horses had radiographic evidence of palmar/plantar osteochondral fragmentation within the PIP joint. Fragmentation was located abaxially in 2 horses in the hind limb and axially in 2 horses in the left forelimb. Osteochondral fragments were successfully removed via a palmar/plantar arthroscopic approach in all horses. Three horses returned to previous levels of athletic performance; 1 horse was used for trail riding instead of reining. CONCLUSIONS: Arthroscopy of the palmar/plantar pouch of the PIP joint allowed limited assessment of the joint and removal of osteochondral fragments. CLINICAL RELEVANCE: Arthroscopy of the palmar/plantar PIP joint pouch for assessment and removal of osteochondral fragments is possible and should be considered when lameness is localized to this joint.