A comparison of laryngoplasty and modified partial arytenoidectomy as treatments for laryngeal hemiplegia in exercising horses

OBJECTIVE: To compare upper airway mechanics, arterial blood gases, and tracheal contamination in horses with induced left laryngeal hemiplegia (recurrent laryngeal neuropathy [RLN]) treated by laryngoplasty/vocal cordectomy (LPVC) or modified partial arytenoidectomy (MPA). STUDY DESIGN: Repeated measures under the following conditions: Control, RLN, LPVC, and MPA. ANIMALS: Six horses. METHODS: Two trials were conducted under all conditions at 80% and 100% of maximal heart rate (HR(max)). In Trial 1, arterial blood gases, tracheal and pharyngeal pressures, and laryngeal videoendoscopy were recorded. In Trial 2, upper airway pressure and airflow were determined. Tracheobronchial aspirates were performed after exercise to quantify airway contamination. RESULTS: Compared with control, RLN significantly increased inspiratory impedance and worsened exercise-induced hypoxemia. At 80% HR(max), LPVC restored most variables to control values. At 100% HR(max), LPVC improved all variables, but did not restore minute volume, arterial pH, and PaCO(2). At 80% HR(max), MPA restored all variables except bicarbonate to control values. At 100% HR(max), MPA improved all variables, but did not statistically restore minute ventilation or bicarbonate level. Only minor differences were noted between LPVC and MPA. Both resulted in equivalent tracheal contamination. CONCLUSIONS: Airway mechanics and arterial blood gas values were not restored to normal after either LPVC or MPA in horses exercising at HR(max). This does not affect ventilation at sub-maximal exercise, but has clinical implications at HR(max). Both procedures diminish normal laryngeal protective mechanisms. CLINICAL RELEVANCE: At sub-maximal exercise intensities both LPVC and MPA restore airway ventilation to normal. At maximal exercise the superiority of LPVC over MPA is slight.     

Evaluation of partial arytenoidectomy as a treatment for equine laryngeal hemiplegia

The efficacy of partial arytenoidectomy was assessed in 6 Standardbred horses, with surgically induced laryngeal hemiplegia, at rest (Period A) and during exercise at speeds corresponding to maximum heart rate (Period C) and 75% of maximum heart rate (Period B). Peak expiratory and inspiratory airflow rate (PEF and PIF), and expiratory and inspiratory transupper airway pressure (P_UE and P_UI) were measured and expiratory and inspiratory impedance (Z_E and Z_I) were calculated. Simultaneously, tidal breathing flow-volume loops (TBFVL) were acquired using a respiratory function computer. Indices derived from TBFVL included airflow rates at 50 and 25% of tidal volume (EF₅₀, IF₅₀, EF₂₅. and IF₂₅) and the ratios of expiratory to inspiratory flows. Measurements were made before left recurrent laryngeal neurectomy (baseline), 2 weeks after left recurrent laryngeal neurectomy (LRLN) and 16 weeks after left partial arytenoidectomy coupled with bilateral ventriculectomy (ARYT). After LRLN, during exercise Periods B and C, Z₁ and the ratio of EF₅₀/IF₅₀ significantly increased and PIF, IF₅₀ and IF₂₅ significantly decreased from baseline values. At 16 weeks after ARYT, Z₁ returned to baseline values during Periods B and C. Although PIF, IF₅₀, IF₂₅, PEF/PIF, and EF₅₀/IF₅₀ returned to baseline values during Period B, these indices remained significantly different from baseline measurements during Period C. After ARYT, TBFVL shapes from horses during Period C approached that seen at the baseline evaluation. Partial arytenoidectomy improved upper airway function in exercising horses with surgically induced left laryngeal hemiplegia, although qualitative and quantitative evaluation of TBFVLs suggested that some flow limitation remains at near maximal airflow rates. These results indicate that, although the procedure does not completely restore the upper airway to normal, partial arytenoidectomy is a viable treatment option for failed laryngoplasty and arytenoid chondropathy in the horse.     

Treatment of laryngeal hemiplegia in horses by prosthetic laryngoplasty, ventriculectomy and vocal cordectomy

The medical records of 80 horses treated for left laryngeal hemiplegia by prosthetic laryngoplasty, ventriculectomy and vocal cordectomy were examined, first to compare the subjective and objective success rates for groups of horses of different ages and used for different purposes, and secondly, to compare the efficacy of including vocal cordectomy in the surgical protocol with published success rates for laryngoplasty and ventriculectomy alone. Subjectively, 70 per cent of the horses were said to have had a successful surgical outcome. The success rate for thoroughbred racehorses (66 per cent) was lower than for other breeds (90 per cent) on the basis of a subjective assessment by owners and trainers. Thoroughbreds two years old or younger had a success rate of 69 per cent, but older thoroughbreds had a success rate of 61 per cent. Of the 17 horses for which an objective performance index could be calculated, 10 (59 per cent) had an improved performance postoperatively. There was a nearly significant association between the objective and subjective assessments (P=0.078). Six of 69 horses (8.7 per cent) continued to make a respiratory noise after surgery. The subjective assessment of success did not appear to correlate with the objective measure of success used in this study and age had no apparent association with a successful surgical outcome. Inclusion of a vocal cordectomy in the surgical protocol may be more important in the eradication of postoperative respiratory noise than in improving clinical success rates.     

Effect of laryngoplasty on respiratory noise reduction in horses with laryngeal hemiplegia

REASONS FOR PERFORMING STUDY: Laryngoplasty is the technique of choice for treatment of laryngeal hemiplegia, with the aim of improving airway function and/or eliminating respiratory noise. However, there are no quantitative data in the literature describing the effect of laryngoplasty on upper airway noise or its relationship to upper airway mechanics in horses with laryngeal hemiplegia. OBJECTIVES: To determine whether laryngoplasty reduces respiratory noise in exercising horses with laryngeal hemiplegia; and to establish whether the degree of upper airway obstruction can be predicted by upper airway noise, or the degree of arytenoid abduction correlated with airway obstruction and noise production. METHODS: Six Standardbred horses with normal upper airways during maximal exercise were used. Respiratory sounds and inspiratory transupper airway pressure (Pui) were measured in all horses before and after induction of laryngeal hemiplegia and 30, 60 and 90 days after laryngoplasty. Inspiratory sound level (SL) and the sound intensity of the 3 inspiratory formants (F1, F2 and F3, respectively) were measured using a computer-based sound analysis programme. The degree of abduction was graded by endoscopic visualisation 1, 30, 60 and 90 days post operatively. Linear regression analysis was used to determine correlations between Pui, sound indices and grades of arytenoid abduction. RESULTS: In laryngeal hemiplegia-affected horses, Pui, inspiratory SL and the sound intensity of F1, F2 and F3 were significantly increased. At 30 days following laryngoplasty, the sound intensity of F1 and Pui returned to baseline values. The sound intensities of F2, F3 and SL were significantly improved from laryngeal hemiplegia values at 30 days post operatively, but did not return to baseline at any measurement period. Sound level, F2 and F3 were significantly correlated with Pui (P<0.05), but the correlations were weak (r2 = 0.26, 035 and 0.40, respectively). Grade of abduction and F2 were positively and significantly correlated (P<0.006, r2 = 0.76). Grade of arytenoid abduction and Pui were not correlated (P = 0.12). CONCLUSIONS: Laryngoplasty reduced inspiratory noise in laryngeal hemiplegia-affected horses by 30 days following surgery, but did not return it to baseline values. While upper airway noise and Pui were correlated, this relationship was insufficiently strong to predict Pui from noise in individual animals. The degree of arytenoid abduction was not correlated with Pui, but was positively correlated with noise production. POTENTIAL RELEVANCE: Laryngoplasty reduces upper airway noise in horses with laryngeal hemiplegia, but is not as effective as bilateral ventriculocordectomy in this regard, although respiratory noise reduction occurs more rapidly than with bilateral ventriculocordectomy. Residual noise during exercise cannot be used as a predictor of improvement in upper airway function in individual horses following laryngoplasty. The degree of arytenoid abduction obtained following surgery does not affect upper airway flow mechanics. Interestingly, we found that the greater the arytenoid abduction, the louder the respiratory noise.     

Effect of laryngeal hemiplegia and laryngoplasty on airway flow mechanics in exercising horses

The effect of left laryngeal hemiplegia on airway flow mechanics in 5 exercising horses was examined, and the efficacy of surgical repair by prosthetic laryngoplasty was evaluated. Measurements of the upper airway flow mechanics were made with horses on a treadmill (incline 6.38 degrees) while standing (period A); walking at 1.3 m/s (period B); trotting at 2.6 m/s (period C); trotting at 4.3 m/s (period D); and standing after exercise (period E). Experiments were done on healthy horses before any surgical manipulation (control), at 10 days after left recurrent laryngeal neurectomy, and at least 14 days after prosthetic larynogoplasty. Increasing treadmill speed from period A to period D progressively increased heart rate, respiratory frequency, peak inspiratory flow, and peak expiratory flow, but inspiratory resistance and expiratory resistance remained unchanged. Neither left recurrent laryngeal neutrectomy nor prosthetic laryngoplasty affected heart rate, respiratory frequency, peak expiratory flow, or expiratory resistance when compared with those values at the control measurement periods. Left recurrent laryngeal neurectomy resulted in inspiratory flow limitation at peak inspiratory flow of approximately 25 L/s, and increased inspiratory resistance at periods D and E. Subsequent prosthetic laryngoplasty alleviated the flow limitation and reduced inspiratory resistance at measurement periods D and E.     

Further evidence for a central nervous system component in equine laryngeal hemiplegia

Evidence for a central nervous system component of the distal axonopathy associated with equine laryngeal hemiplegia was found in this survey of 33 horses (control, 15; subclinical, 8; clinical, 10). Significantly higher numbers of axonal spheroids were present in sections of the lateral cuneate nuclei in layngeal hemiplegic horses than in those unaffected by the disease.     

Further evidence for a central nervous system component in equine laryngeal hemiplegia

Evidence for a central nervous system component of the distal axonopathy associated with equine laryngeal hemiplegia was found in this survey of 33 horses (control, 15; subclinical, 8; clinical, 10). Significantly higher numbers of axonal spheroids were present in sections of the lateral cuneate nuclei in layngeal hemiplegic horses than in those unaffected by the disease.     

Effects of ventriculectomy, prosthetic laryngoplasty, and exercise on upper airway function in horses with induced left laryngeal hemiplegia

Effects of ventriculectomy and prosthetic laryngoplasty on upper airway flow mechanics and blood gas tensions in exercising horses with induced left laryngeal hemiplegia were assessed. Five adult horses were trained to stand, trot (4.5 m/s), and gallop (7.2 m/s) on a treadmill (6.38 degrees incline). Inspiratory and expiratory airflows (VImax, VEmax, respectively) were measured using a 15.2-cm diameter pneumotachograph in a face mask. Inspiratory and expiratory transupper airway pressures (PuI, PuE, respectively) were determined as pressure differences between barometric pressure and lateral tracheal pressure. Blood collected from exteriorized carotid arteries was analyzed for PaO2, PaCO2, pH, hemoglobin (Hb) content, and HCO3- values. Heart rate (HR) was determined with an HR monitor. Measurements were made with horses standing, trotting, and galloping before left recurrent laryngeal neurectomy (LRLN; base line), 14 days after LRLN, 30 days after ventriculectomy (44 days after LRLN), and 14 days after prosthetic laryngoplasty (58 days after LRLN). Before LRLN (base line), increasing treadmill speed for horses from standing to the trot and gallop progressively increased HR, respiratory frequency, VImax, VEmax, PuI, PuE, Hb, and PaCO2 values and decreased PaO2, pH, and HCO3- values; inspiratory and expiratory impedances were unchanged. After LRLN, inspiratory impedance and PuI were significantly (P less than 0.05) increased in horses at the trot and gallop, and PaCO2 was significantly increased in horses at the gallop. The VImax and respiratory frequency were significantly (P less than 0.05) decreased in horses at the gallop. Left recurrent laryngeal neurectomy had no effect on PuE, VEmax, HR, PaO2, pH, Hb, or expiratory impedance values.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vitro evaluation of a novel prosthesis for laryngoplasty of horses with recurrent laryngeal neuropathy

A prosthesis, composed of a steel cable and stress-reducing washers, was developed to prevent failure of laryngoplasty, a common treatment for horses affected by recurrent laryngeal neuropathy. Laryngoplasties were performed on 15 cadaveric larynges using a polyester suture on one side and the cable prosthesis on the other. Each prosthesis was distracted at a displacement rate of 20 mm/s using a servohydraulic materials testing machine until laryngoplasty failed. Distraction force and actuator displacement were recorded and analysed. All 15 laryngoplasties performed with a suture failed at the muscular process at a mean +/- s.d. force of 55.8 +/- 13.1 N. Six laryngoplasties performed with the cable prosthesis failed at the muscular process at mean force 219.6 +/- 125.0 N. In the other 9, the arytenoid cartilage was avulsed from the larynx at mean force 206.4 +/- 75.3 N, and the cable then tore through the muscular process at mean force 357.0 +/- 32.0 N. The difference in force required to cause failure of laryngoplasty was significant (P<0.0001). Although the prosthesis resisted substantially higher forces than did the suture, the effects of the prosthesis in vivo must be evaluated.     

In vitro effect of ventriculocordectomy before laryngoplasty on abduction of the equine arytenoid cartilage

Objective: To determine whether ventriculocordectomy (VCE) performed before prosthetic laryngoplasty (PL) results in increased rima glottidis size compared with PL alone. Study Design: Experimental study. Animals: Equine cadaver larynges (n=13). Methods: Right arytenoid cartilages were maximally abducted using a standard PL technique. Standard PLs were then performed on the left side and the force required to maximally abduct the left arytenoid cartilage recorded (F_max). Photographs were taken of the rima glottidis at zero force and at five equal levels of force up to F_max. The force applied was released, left VCE performed, and photographs repeated. Arytenoid left:right angle quotients (LRQ) and glottic cross‐sectional area ratios (CSAR) were calculated at each force level in each condition (PL and VCE‐PL). Results: Mean LRQ and CSAR for both PL and VCE‐PL increased with increasing force, initially rapidly before plateauing at ～50% of F_max. LRQ and CSAR were significantly greater for VCE‐PL than for PL (P<.001). When VCE was performed before PL, 12% less force was required to achieve an LRQ of 0.8, and 45% less for a CSAR of 0.8. Conclusions: In vitro, VCE performed before PL enables the arytenoid cartilage to be abducted to a greater degree for a given PL suture force.     

An in vitro biomechanical comparison of two interlocking-nail systems for fixation of ostectomized equine third metacarpal bones

OBJECTIVE--To compare the mechanical properties of 2 interlocking-nail systems for fixation of ostectomized equine third metacarpi (MC3): (1) a standard interlocking nail with 2 parallel screws proximal and distal to a 1-cm ostectomy; and (2) a modified interlocking nail with 2 screws proximal and distal to a 1-cm ostectomy with the screws offset by 30 degrees. ANIMAL OR SAMPLE POPULATION--Twelve pairs of adult equine forelimbs intact from the midradius distally. METHODS--Twelve pairs of equine MC3 were divided into 2 test groups (6 pairs each): torsion and caudocranial 4-point bending. Standard interlocking nails (6-hole, 13-mm diameter, 230-mm length) were placed in 1 randomly selected bone from each pair. Modified interlocking nails (6-hole, 13-mm, 230-mm length, screw holes offset by 30 degrees) were placed in the contralateral bone from each pair. All bones had 1-cm mid-diaphyseal ostectomies. Six construct pairs were tested in caudocranial 4-point bending to determine stiffness and failure properties. The remaining 6 construct pairs were tested in torsion to determine torsional stiffness and yield load. Mean values for each fixation method were compared using a paired t test within each group. Significance was set at P <.05. RESULTS--Mean (+/-SEM) values for the MC3-standard interlocking-nail composite and the MC3-modified interlocking-nail composite, respectively, in 4-point bending were: composite rigidity, 3,119 +/- 334.5 Nm/rad (newton. meter/radian) and 3,185 +/- 401.2 Nm/rad; yield bending moment, 205.0 +/- 18.46 Nm and 186.7 +/- 6.17 Nm; and failure bending moment, 366.4 +/- 21.82 Nm and 378.1 +/- 20.41 Nm. There were no significant differences in the biomechanical values for bending between the 2 fixation methods. In torsion, mean (+/-SEM) values for the MC3-standard interlocking-nail composite and the MC3-modified interlocking-nail composite were: composite rigidity, 135.5 +/- 7.128 Nm/rad and 112.5 +/- 7.432 Nm/rad; gap stiffness, 207.6 +/- 10.57 Nm/rad and 181.7 +/- 12.89 Nm/rad; and yield load, 123.3 +/- 2.563 Nm and 107.5 +/- 8.353 Nm, respectively. Composite rigidity and gap stiffness for standard interlocking-nail fixations were significantly higher than the modified interlocking-nail fixation technique in torsion. Yield load had a tendency to be higher for the standard interlocking-nail fixation (P =.15). CONCLUSIONS--No significant differences in biomechanical properties were identified between a standard interlocking nail and one with the screw holes offset by 30 degrees in caudocranial 4-point bending. The standard interlocking nail was superior to the modified interlocking nail in torsional gap stiffness and composite rigidity. The torsional yield load also tended to be higher for the standard interlocking nail. CLINICAL RELEVANCE--The standard interlocking nail with parallel screw holes is superior to a modified interlocking nail with the screw holes offset by 30 degrees in ostectomized equine MC3 bones in vitro when tested in torsion.     

Assessment of the efficacy of an abductor muscle prosthesis for treatment of laryngeal hemiplegia in horses

Four variations of abductor muscle prosthesis for treating laryngeal hemiplegia were evaluated in 153 horses by questionnaire, and in the 100 Thoroughbred racehorses in this group survival analysis was used to compare their racing performances and earnings with those of 400 control horses. The questionnaire indicated that the technique which included a ventriculectomy and 2 prostheses was regarded as being the most successful (P less than 0.01) and resulted in the least residual stertor (P less than 0.001). Survival analysis showed that there was no significant difference between the treated group of horses and the control horses (P greater than 0.05).     

Cohort study examining long‐term respiratory health,career duration and racing performance in racehorses that undergo left‐sided prosthetic laryngoplasty and ventriculocordectomy surgery for treatment of left‐sided laryngeal hemiplegia

Reasons for performing study: The risk of respiratory conditions, such as inflammatory airway disease (IAD) and exercise‐induced pulmonary haemorrhage (EIPH), are thought to be higher in racehorses that undergo prosthetic laryngoplasty with ventriculocordectomy (PLVC) surgery to treat left‐sided laryngeal hemiplegia (LLH) than in racehorses with normal laryngeal function. However, this has not been investigated formally owing to the difficulty of obtaining reliable follow‐up data. Objectives: To determine the incidence of respiratory conditions (IAD and EIPH), duration of racing career, number of starts and number of starts for which stakes money was earned in racehorses that had undergone PLVC surgery to treat LLH, compared with racehorses that did not have LLH or undergo any laryngeal surgery. Methods: A retrospective cohort study design was used, with surgical, clinical and race data of Thoroughbred racehorses obtained from the time of importation until retirement. The surgical cohort consisted of racehorses that had undergone PLVC for LLH and met specific inclusion criteria. Every surgical case was matched, according to trainer, year of import into Hong Kong and pre‐import international handicap rating, to 2 unexposed racehorses. Results: Respiratory conditions, such as excessive tracheal mucus and epistaxis due to severe EIPH, were significantly increased in the surgical cohort, compared with the matched unexposed cohort (P values <0.001 and <0.004, respectively). Racing career duration in the surgical cohort was significantly shorter than in the unexposed cohort, which was primarily due to retirement because of epistaxis. The number of race starts was fewer in the surgical than in the unexposed cohort after surgery/matching, but the number of starts for which stakes money was earned was not significantly different. Conclusions and potential relevance: Owners and trainers should be advised that racehorses with LLH that undergo PLVC surgery are at an increased risk of respiratory conditions (IAD and severe EIPH), which is likely to shorten their racing career compared to racehorses with normal laryngeal function. Racing performance in terms of race starts was significantly less in racehorses that had undergone PLVC surgery; however, the number of starts for which stakes money was earned was similar to those racehorses that were unexposed.     

Evaluation of a canine cranial cruciate ligament repair system for use in equine laryngoplasty

OBJECTIVE: To report the use of a nylon suture system (Canine Cranial Cruciate Ligament Repair System; Securos Inc Veterinary Orthopedics) as a prosthesis for equine laryngoplasty. STUDY DESIGN: Experimental and prospective clinical study. ANIMALS: Cadaver specimens (n = 5) and 7 horses with left laryngeal hemiplegia. METHODS: A commercially available monofilament nylon suture system was implanted as a laryngeal prosthesis. Arytenoid cartilage abduction was achieved with a tensioning device applied to the suture prosthesis during transnasal endoscopic observation. Suture fixation was achieved with crimping clamps and a crimping device. RESULTS: The nylon suture system was suitable as a laryngeal prosthesis for arytenoid cartilage abduction. The ratchet mechanism of the tensioning device facilitated abduction of the arytenoid cartilage and suture fixation was achieved by the crimped clamp without any loss of tension. Postoperatively, there was a slight loss of tension in 4 horses and complete loss of tension in 1 horse because of cartilage failure. After convalescence, none of the horses had abnormal respiratory noise, exercise intolerance or cough. CONCLUSIONS: A nylon suture system designed for canine cranial cruciate ligament repair was used successfully as a laryngeal prosthesis and facilitated control of the degree of arytenoid cartilage abduction during laryngoplasty. CLINICAL RELEVANCE: For improved control of the degree of arytenoid cartilage abduction during laryngoplasty, use of a nylon suture system with metal crimps should be considered.     

A comparison of techniques to enhance the evaluation of equine laryngeal function

This study was designed to define a simple, unequivocal test for the evaluation of laryngeal function and the diagnosis of idiopathic laryngeal hemiplegia (ILH). ILH is a disorder that results from left recurrent laryngeal neuropathy and in which there is no movement of the left arytenoid cartilage and vocal fold. Laryngeal function was evaluated in seven horses using four techniques designed to stimulate laryngeal movements:-nasal occlusion, exercise, swallowing and administration of a respiratory stimulant. In addition, the effects of sedation and twitching on the endoscopic examination were also examined. The cross-sectional area of the rima glottidis was measured in each horse at rest and after each technique was performed. There was no statistically significant difference in the increase in area seen after nasal occlusion or exercise. Doxapram hydrochloride increased the cross-sectional area of the rima glottidis, whereas xylazine caused a decrease. Neither of these pharmacological agents exaggerated or decreased the amount of asynchronous movement or tremoring of the arytenoid cartilages. Manual occlusion of the external nares during endoscopy is a simple, yet effective method of stimulating arytenoid function and hence diagnosing ILH.     

Transendoscopic, laser-assisted ventriculocordectomy for treatment of left laryngeal hemiplegia in horses: 22 cases (1999-2005)

OBJECTIVE: To determine long-term effects of transendoscopic, laser-assisted ventriculocordectomy (LAVC) on airway noise and performance in horses with naturally occurring left laryngeal hemiplegia. DESIGN: Retrospective case series. ANIMALS: 22 horses with left laryngeal hemiplegia treated by means of LAVC. PROCEDURES: Medical records were reviewed and initial complaint, intended use of the horse, duration of abnormal airway noise, preoperative performance level, endoscopic findings, surgical procedure, postoperative treatment, and complications were recorded. Follow-up telephone interviews with owners and trainers were conducted to determine time for return to intended use, level of postoperative performance, and percentage reduction in airway noise. RESULTS: All horses were examined because of excessive airway noise; 10 (45%) had concurrent exercise intolerance. Left ventriculocordectomy was performed in all 22 horses; bilateral ventriculocordectomy (right ventriculocordectomy was done 1 year later) was performed in 1 horse (5%). Complications occurred in 3 (14%) horses. Twenty (91%) horses returned to their intended use. Excessive airway noise was eliminated after surgery in 18 (82%) horses; exercise intolerance improved postoperatively in 8 of 10 horses. Three racing Thoroughbreds returned to racing; 1 additional racehorse returned to racing but required a laryngoplasty 1 year later to continue racing. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that LAVC was an effective procedure for elimination of excessive airway noise and improvement of performance in horses with left laryngeal hemiplegia.