Recipient Organization
UNIVERSITY OF MISSOURI
(N/A)
COLUMBIA,MO 65211
Performing Department
Veterinary Medicine & Surgery
Non Technical Summary
Recurrent laryngeal neuropathy (RLN) is a highly prevalent degenerative neurological disease in horses that has been recognized for centuries. The disorder preferentially affects the left side of the larynx (voice box) and occurs most commonly in tall breeds such as Thoroughbreds and Draft horses. While the exact cause remains largely unknown, both environmental and genetic factors are suspected contributors. As the disease progresses, the larynx collapses on the affected side during inspiration, a condition called laryngeal hemiplegia. A telltale clinical sign is a loud roaringnoise during strenuous exercise or working conditions, caused by increased airflow passing through a narrowed larynx; hence, RLN is often called "roaring disease". Definitive diagnosis currently relies on endoscopic examination of the larynx in the context of exertion in conjunction with the 'Slap Test' to elicit the thoraco-laryngeal adductor reflex (TLAR) and/or through rigorous exercise to evoke airway compromise.The clinical problem is that endoscopic test results are entirely subjective, as laryngeal movement is graded using one of many existing Likert scales that rely on clinician judgement rather than objective, quantitativemeasurements, such as the actual timing and distance of laryngeal motion in response to the 'Slap Test' and/or strenuous exercise.Moreover, by the time symptoms become clinically apparent to warrant endoscopic assessment, surgical intervention is the onlytreatment option - either removal of the paralyzed cartilage (arytenoidectomy), a 'tie back' procedure (prosthetic laryngoplasty) to permanently hold the larynx open for unimpeded breathing, or laryngeal by-pass (tracheotomy).Unfortunately, these surgical procedures often result in aspiration pneumonia and lower airway diseases that further compromise breathing and may ultimately necessitate retirement or euthanasia. The ultimate goal of this study is to develop an objective clinical tool to facilitate early endoscopic detection of RLN in horses, long before symptoms become clinically apparent via existing subjective laryngeal grading scales. Toward this goal, our research group has been adapting our previously developed vocal fold (i.e. laryngeal) tracking software, (VFtrack©), originally designed for use with humans and rodent models of recurrent laryngeal nerve pathology, into a prototype 'SlapTrack' software for objective assessment of the TLAR in horses. We are now ready to optimize this software for horses, first with low-risk breeds for RLN (e.g., Quarter Horses, Arabians) in Specific Aim 1, followed by high-risk breeds for RLN (e.g., Thoroughbreds and Draft horses) in Specific Aim 2. Each horse (n=20 per Aim) will be tested at least twice at 1-3-month intervals to measure change (or lack thereof) over time. The endoscopic videos will be analyzed using our 'SlapTrack' software to objectively measure the distance and timing of laryngeal movements bilaterally, and modifications to our software will be made as needed for improved performance. The ultimate goal of this project is to transform the widely-used 'Slap Test' into an objective measurement tool via our 'SlapTrack' software. If successful, we envision marketing our user friendly endoscopy-based software to equine veterinary centers and racehorse veterinarians to facilitate subclinical detection and ongoing monitoring of RLN in horses. We also envision this objective laryngeal measurement tool being used in equine research aimed at elucidating the pathophysiology of RLN as well as the discovery of effective treatments to preserve (or improve) laryngeal function in horses diagnosed with RLN.
Animal Health Component
50%
Research Effort Categories
Basic
(N/A)
Applied
50%
Developmental
50%
Goals / Objectives
Long-term Goals: Our long-term goal is to transform the widely-used subjective equine 'Slap Test' assessment of the TLAR into an objective, software-based measurement tool ('SlapTrack') for early detection of RLN, long-term tracking of disease progression, and unbiased evaluation of treatment response.Specific Objectives: We will complete 2 Specific Aims for this 1-year project.Specific Aim 1: Use our prototype 'SlapTrack' software to establish normative measures of TLAR dynamics (based on timing and distance of left- versus rightsided laryngeal motion) in healthy horses at low risk for RLN. Hypothesis: 'SlapTrack'-based TLAR measurements in low-risk RLN breeds (e.g., Quarter Horses, Arabians) will remain stable over time (i.e., no significant change), with low variability within and between horses.Specific Aim 2: Use our 'SlapTrack' software for detection of subclinical pathology in healthy horses at high risk for RLN.Hypotheses: 1) Compared to low-risk breeds, 'SlapTrack'-based TLAR measurements will be altered in high-risk RLN breeds (e.g., Thoroughbreds and Draft horses), thus providing functional evidence of subclinical laryngeal pathology in Havemeyer Grade 1 horses; and 2) compared to the stable SlapTrack'-based TLAR measurements over time in low-risk RLN breeds, TLAR 'performance' in high-risk RLN breeds will deteriorate over time, thus providing quantitative (rather than qualitative) evidence of RLN disease progression.
Project Methods
General scientific methods and unique aspects:Animals: This project entails an endoscopic examination of the larynx of 40 healthy adult horses (either sex), with equal representation of low-risk (e.g., Quarter Horses, Arabians) versus high-risk (e.g., Thoroughbreds and Draft horses) RLN breeds. We intend to primarily test horses owned by the University of Missouri, such as those in the teaching herd at Middlebush Farm. If needed, we will add horses through incentivized recruitment (e.g., offering free endoscopic examinations for client-owned animals). Each horse will be tested at least twice at 1-3-month intervals to evaluate for change (or lack thereof) over time. Following establishment of the normative measures of TLAR dynamics in normal horses (Specific Aim 1), we will then proceed to collecting data from horses at high risk for RLN. For this purpose, high-risk RLN breeds will be recruited through active communication (incentivized recruitment drive) with practicing veterinarians who work in the equine field of veterinary medicine. We will undertake endoscopic examination of horses in both low-risk (Specific Aim 1) and high risk (Specific Aim 2) RLN breeds.Endoscopic Laryngeal Examination Protocol: Endoscopic laryngeal examination is routinely performed in standing awake horses using a flexible video-endoscope. Horses generally tolerate transnasal endoscopy very well. In some (refractory) cases, a routine nose twitch may be applied in order to facilitate compliance. For this study, we will use endoscopy equipment that is available in the Veterinary Health Center and was used during pilot testing (see Preliminary Studies/Data section, above). Briefly, each horse will be accommodated/restrained in stocks and the endoscope will be passed trans-nasally and positioned in the nasopharynx for viewing and recording of the larynx. Following passage and placement of the endoscope, a trained individual will perform the 'Slap Test' by administering slaps to the saddle region, just caudal to the withers. Slaps will be administered 10-15 times on the right saddle area, and then 10-15 times on the left saddle area; at least five slaps will be administered at a light force and an additional five slaps will be delivered with a greater force. Slap-induced TLAR responses will be videorecorded using the recording system built into the endoscope. Following these manipulations, the endoscope will be withdrawn, and the horse will be allowed to resume normal activity. Each endoscopy/'Slap Test' session typically requires approximately 5 - 10 minutes. The digital video-endoscopy recordings will be analyzed at a later date. A description of the endoscopic appearance of each horse's larynx will be noted and any (subjectively evident) abnormalities (morphological or functional) will be noted.Analysis of videoendoscopic recordings: First, videos will be reviewed to apply the 4- point subjective Havemeyer laryngeal grading scale (Figure 1). Next, short video clips will be spliced from the original video recording such that the TLAR event is randomly located within a 3 second video clip. Then, using 'SlapTrack', we will characterize the TLAR using dynamic measures based on the timing and distance of left- versus rightsided laryngeal motion. Based on pilot testing (See Preliminary Studies/Data section), we expect that precise tracking of the diamond-shaped equine larynx will require modeling by four lines -- two lines for tracking the left versus right arytenoid cartilages, and two lines for tracking the left versus right vocal folds. This equine-specific approach will permit independent versus coordinated motion tracking of the arytenoids and vocal folds bilaterally during the TLAR, thus permitting automated quantification of the entire laryngeal airspace. Thus, we will refine our prototype 'SlapTrack' software to accommodate 4-line tracking, editing, and graphic visualization capabilities. Doing so will allow us to design and compute novel TLAR motion dynamics (e.g., distance, velocity, symmetry, and synchrony of left/right laryngeal motion) for improved RLN detection and diagnostic capabilities. Validation of our added software features and quantitative TLAR motion dynamics will occur in Specific Aim 1, which will establish normative value ranges (mean ± standard error) for comparison with high-risk RLN breeds in Specific Aim 2. In addition, correlations between 'SlapTrack' and Havemeyer grading results will be explored using statistical approaches capable of comparing continuous versus discrete variables, respectively. Statistical analyses will be performed in consultation with the MU Biostatistics Department.Analysis, evaluation, and interpretation of the results: Characterization of 'SlapTrack'-based TLAR dynamic measures from healthy adult horses at low risk for RLN (Specific Aim 1) will be used to establish a normative database for comparison with high-risk RLN breeds (Specific Aim 2). As each horse will be tested at least twice, a repeated measure analysis of variance (RMANOVA) statistical model will be used to investigate differences within and between groups (low- versus high-risk RLN breeds) over time, along with post-hoc pairwise comparisons (Bonferroni-adjusted). To our knowledge, this quantitative TLAR analysis approach has never been undertaken previously in horses - all earlier publications pertaining to the use of the 'Slap Test' in horses (either for diagnosis of laryngeal disease or for characterization of spinal cord disease) have relied on subjective assessment by the observer via grading scales. Uniquely, we anticipate that the objective digital evaluation of this rapid laryngeal reflex will yield much more information and usable data that simple reliance on 'naked eye' observation of a movement phenomenon that lasts less than one second.Efforts (instruction, outreach, etc.) that will be used to cause a change in knowledge, actions, or conditions of a target audience:Results from this study will be shared (via journal publications and scientific/professional conference presentation) with the racing community and equine veterinarians who perform equine laryngeal endoscopy. Our group also will provide lectures to MU veterinary faculty and students to facilitate adoption of quantitative evaluation of upper airway function and neurological status in horses.How the output(s) will be evaluated and/or quantified for its impact on the intended audience(s)?We anticipate that, successfully prosecuted, the results of this work will become more broadly available and adopted by equine veterinarians concerned with both normal laryngeal function (assessment of athletic performance) and the diagnostic characterization of spinal cord disease. Specific measured of success in this regard would include observation of the employment of this technology in new veterinary literature derived both from this and other equine veterinary research centers around the world. Filtration of the impact of this new technology in the future could be quantified through selective literature screening.How success of the project will be measured - key milestones and measurable or quantitative indicators of success.We will consider the project successfully if we are able to distinguish low- versus highrisk RLN breeds based on 'SlapTrack'-based measurement of the TLAR. A further measure of success will be the publication of these results in a manuscript submitted to a high impact peer-reviewed scientific journal.