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

Jugular venous thrombosis as a risk factor for exercise-induced pulmonary hemorrhage in thoroughbred racehorses

Background

Exercise-induced pulmonary hemorrhage (EIPH) is one of the most commonly diagnosed disorders in racehorses. Many EIPH risk factors such as breed, age, high or low environmental temperature, and distance of the race have been studied in racehorses.

Aim

The aim of this study was to study the relationship between EIPH and the presence of jugular vein thrombose in racehorses.

Methods

Forty-eight thoroughbred racehorses randomly selected from animals with exercise intolerance due to respiratory disorders were enrolled in the present study. Clinical and tracheobronchoscopy examinations were done for EIPH grading. In addition, both jugular veins were examined using ultrasonography for vein thrombosis.

Results

It was noted during endoscopy that many cases suffered from laryngeal paralysis, and we were not able to assess the degree of laryngeal paralysis under sedation. About 40% of horses with exercise intolerance suffered from EIPH of varying degrees. Most cases of jugular vein thrombosis were of the chronic type, as local heat and pain were not observed. About 42% of the exercise-intolerant horses had jugular vein thrombose with most jugular vein thrombosis on the left side. Combined jugular veins thrombose and EIPH were found in about 25% of exercise intolerance horses, while 17% showed jugular vein thrombose without EIPH, and 41% showed no EIPH with the absence of jugular vein thrombose.

Conclusion

The present study revealed that jugular vein thrombosis may cause disorders-associated damage to the vessels and anatomical structures close to it, such as the trachea causing EIPH.

Laryngeal reinnervation using the spinal accessory nerve: Electromyographic study of the sternomandibularis muscle

BACKGROUND

Selective laryngeal reinnervation using the first and second cervical nerve (C1C2) is a treatment option for recurrent laryngeal neuropathy that aims to restore the function of the cricoarytenoideus dorsalis muscle (CAD). Despite the technique's satisfying success rate, it has several limitations. These triggered the search for another potential donor nerve that could reduce CAD muscle fatigue and shorten rehabilitation. The ventral branch of the spinal accessory nerve, providing motor innervation to the sternomandibularis (SM) muscle, was identified as a potentially well adapted nerve.

OBJECTIVES

To gather normative data from SM muscle activity induced by physiological spinal accessory nerve stimulation at rest and during exercise, and to determine SM muscle activity and fibre type recruitment relative to posture, gait, and respiratory cycle.

STUDY DESIGN

Clinical observational study.

METHODS

Surface electromyography of the SM muscle was performed in 9 horses: trained warmbloods, Thoroughbreds and Standardbreds. Signals were recorded in different feeding postures and at exercise, which included standardised treadmill exercise tests, lungeing and ridden work.

RESULTS

Timing of the SM muscle contraction coincided with inspiration at gallop. Intra-individual mean SM muscle activity increased with exercising speed (4 times higher in Thoroughbreds at gallop compared to walk and 7 times higher in Standardbreds at high-speed trot compared to walk). Moreover, the SM muscle was strongly activated at rest when the horse was grazing (7 times more compared to when it was eating out of a hay net or stable feeder). Frequency domain analysis revealed a predominant type I muscle fibre recruitment during feeding and at exercise (Type I muscle fibre activity was at least 2.5 times higher than type II muscle fibre activity).

MAIN LIMITATIONS

Lack of reference data on equine electromyography.

CONCLUSIONS

This study confirmed the potentially advantageous properties of the spinal accessory nerve for laryngeal reinnervation.

Immunohistochemical analysis of laryngeal muscle of horses clinically affected with recurrent laryngeal neuropathy

BACKGROUND

As myosin heavy chain (MyHC) profile of muscle fibres is heavily influenced by neural input, changes in MyHC expression are expected in horses clinically affected with recurrent laryngeal neuropathy (RLN) yet, this has not been thoroughly investigated.

OBJECTIVES

To describe the changes in MyHC and fibre diameter in left cricoarytenoideus dorsalis (L-CAD) muscle of horses with clinical signs of RLN.

STUDY DESIGN

Observational cohort study.

METHODS

Immunohistochemistry was used to assess the MyHC-based fibre-type proportion, size and grouping in the L-CAD of 10 Thoroughbred horses, five clinically affected with RLN and five unaffected controls based on resting endoscopic examination. The Mann-Whitney U test was used to compare the two groups.

RESULTS

Compared to controls (of mean age 3.0 ± 1.7 years) which only expressed type I, IIA and IIX MyHC, the L-CAD of affected horses (of mean age 2.8 ± 0.8 years) had obvious fibre-type grouping, and despite apparent compensatory hypertrophy of a small number of fibres, a decrease in overall fibre diameter (median difference -35.2 µm, 95% CI -47.4 to -7.9, P = .02) and diameter of type IIA fibres (median difference -46.8 µm, 95% CI -52.1 to -5.0, P = .03) was observed. Anti-fast MyHC (MY32) cross-immunoreacted with embryonic-MyHC. Whereas MY32-positive fibres were identified as type IIX in controls, in affected horses these fibres were less than 50 µm diameter with internal nuclei and were MYH3-positive for embryonic myosin indicating depletion of type IIX fibres, yet active regeneration and fibre renewal.

MAIN LIMITATIONS

Small sample size that did not include subclinical cases. Fibre size and appearance rather than staining colour were relied upon to differentiate embryonic from type IIX MyHC.

CONCLUSIONS

Horses clinically affected with RLN have overall atrophy of fibres, loss of IIX fibres and expression of embryonic myosin indicating regenerative capacity. Despite hypertrophy of some remaining fibres, the overall decline in the bulk of fibres, including those most fatigue-resistant, may be the critical change that results in failure to maintain arytenoid abduction during exercise although direct comparison to subclinical cases is needed to confirm this.