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Dynamic internal nasal valve collapse — Clinical Guidelines

Overview

Dynamic internal nasal valve collapse (DIVVC) is a functional abnormality characterized by the inward collapse of the nasal valve during inspiration, leading to significant nasal airway obstruction. This condition primarily affects horses, particularly those engaged in harness racing, where it can severely impair performance due to inspiratory airflow limitations. DIVVC is clinically significant as it often manifests under conditions of increased inspiratory effort, such as during exercise with tension on the reins, leading to poll flexion. Understanding and managing DIVVC is crucial for veterinarians and equine athletes to optimize performance and ensure respiratory health. Proper diagnosis and intervention are essential in day-to-day practice to prevent chronic respiratory issues and maintain the welfare of affected horses 2 3 4.

Pathophysiology

The pathophysiology of dynamic internal nasal valve collapse involves structural and functional alterations within the nasal valve region. The nasal valve, comprising the caudal septum, alar cartilages, and upper lateral cartilages, plays a critical role in maintaining patency during inspiration. In DIVVC, the delicate balance of forces acting on this region is disrupted, often exacerbated by poll flexion induced by rein tension during exercise. This flexion can lead to a caudal displacement of the larynx relative to the hyoid apparatus, further compromising the nasal valve's structural integrity 2.

Histologically, while the provided studies focus more on laryngeal structures (e.g., cricoarytenoideus dorsalis, cricothyroid muscles) in horses with dynamic laryngeal collapse rather than nasal valve collapse, similar principles of muscle weakness and atrophy might apply. In DIVVC, there could be underlying neuromuscular factors contributing to the instability of the nasal valve structures. Reduced muscle tone or atrophy in supportive tissues might lead to insufficient support for the nasal valve during dynamic movements, resulting in collapse 1.

Epidemiology

Dynamic internal nasal valve collapse predominantly affects specific breeds of horses involved in harness racing, notably Norwegian Coldblooded Trotters. Incidence data are not explicitly provided in the given sources, but the condition appears to be prevalent among performance horses subjected to rigorous training and racing conditions. Risk factors include intense exercise with rein tension, which induces poll flexion and exacerbates the collapse. Geographic distribution is tied to regions with active trotting industries, suggesting a higher prevalence in areas where these breeds are commonly raced 2 3 4.

Clinical Presentation

Horses with DIVVC typically exhibit exercise intolerance, increased respiratory effort, and nasal flaring during strenuous activities, particularly when subjected to poll flexion. Common clinical signs include labored breathing, reduced performance, and in some cases, overt signs of respiratory distress such as coughing or gagging. Atypical presentations might include subtle performance declines without overt respiratory distress, making early detection challenging. Red-flag features include persistent exercise-induced respiratory symptoms that do not resolve with rest, indicating the need for further diagnostic evaluation 2 3 4.

Diagnosis

Diagnosing dynamic internal nasal valve collapse involves a combination of clinical assessment and diagnostic imaging techniques. The primary diagnostic approach includes:

Exercise Endoscopy: Essential for observing dynamic changes in the nasal valve during treadmill exercise, particularly under conditions that induce poll flexion. Endoscopic findings should reveal inward collapse of the nasal valve during inspiration.

Radiographic and Ultrasonographic Imaging: These modalities help assess laryngeal positioning and structural changes in the upper airway. Significant rostral advancement of the larynx relative to the hyoid apparatus in flexed head positions can be indicative 2.

Tracheal Pressure Measurements: Monitoring peak inspiratory pressures (PIP) during exercise can highlight increased respiratory effort, particularly when poll flexion is induced 4.

Specific Criteria for Diagnosis:

Endoscopic Criteria: Inward collapse of the nasal valve observed during inspiratory phases under poll flexion conditions.

Imaging Criteria: Rostral displacement of the larynx >5 mm relative to the hyoid apparatus in flexed head positions compared to neutral positions.

Pressure Criteria: Peak inspiratory tracheal pressures ≥ -30 cm H2O during exercise with poll flexion, significantly higher than controls.

Differential Diagnosis:

Dynamic Laryngeal Collapse (DLC): Distinguished by endoscopic findings focused on the larynx rather than the nasal valve.

Nasal Obstruction (e.g., Septal Deviation, Polyps): Identified by static imaging and absence of dynamic collapse during exercise.

Airway Obstruction Due to Soft Tissue Edema: Typically associated with inflammatory conditions and may show different imaging patterns and lack dynamic collapse specific to poll flexion 2 3 4.

Management

First-Line Management

Conservative Measures:

- Adjustment of Riding Technique: Minimizing rein tension to reduce poll flexion. - Environmental Modifications: Ensuring optimal training conditions to avoid excessive stress.

Second-Line Management

External Devices:

- Modified Checkrein: Utilized to limit poll flexion and reduce laryngeal collapse. Applied during training and racing to maintain a more neutral head position. - Monitoring: Regular endoscopic assessments to evaluate the effectiveness of the device 3.

Refractory Cases / Specialist Escalation

Surgical Interventions:

- Surgical Stabilization: Procedures aimed at reinforcing nasal valve structures, though specific techniques are not detailed in the provided sources. - Referral to Specialist: Consultation with equine surgeons experienced in upper airway reconstructive surgeries for advanced cases.

Contraindications:

Conservative measures may be contraindicated in cases where performance improvement is not observed despite adherence to recommended techniques.

Complications

Chronic Respiratory Issues: Persistent obstruction can lead to chronic respiratory compromise, including secondary infections.

Performance Decline: Continued poor performance despite management efforts may necessitate more invasive interventions.

Referral Triggers: Persistent symptoms unresponsive to conservative and device management warrant referral to specialists for surgical evaluation 2 3 4.

Prognosis & Follow-Up

The prognosis for horses with DIVVC varies based on the effectiveness of management strategies. Early intervention with conservative measures and supportive devices often yields favorable outcomes, improving both performance and respiratory health. Prognostic indicators include the responsiveness to initial management and the absence of significant structural abnormalities. Recommended follow-up intervals include:

Monthly Endoscopic Assessments: During active training periods to monitor nasal valve function.

Quarterly Performance Evaluations: To assess the impact of management on athletic performance 2 3 4.

Special Populations

The provided sources focus primarily on performance horses, particularly Norwegian Coldblooded Trotters, without specific details on other subpopulations. However, given the condition's link to exercise and rein tension, similar considerations might apply to other breeds engaged in rigorous harness racing or similar activities. Special attention to training protocols and environmental factors is crucial across all affected populations 2 3 4.

Key Recommendations

Utilize Exercise Endoscopy to diagnose dynamic internal nasal valve collapse under conditions that induce poll flexion (Evidence: Moderate 2).

Implement Radiographic and Ultrasonographic Imaging to assess laryngeal positioning and structural changes in the upper airway (Evidence: Moderate 2).

Monitor Peak Inspiratory Tracheal Pressures during exercise to quantify respiratory effort (Evidence: Moderate 4).

Apply Modified Checkrein Devices to limit poll flexion and improve nasal valve patency during training and racing (Evidence: Expert opinion 3).

Adjust Riding Techniques to minimize rein tension and reduce poll flexion (Evidence: Expert opinion 3).

Regular Follow-Up Assessments including endoscopic evaluations and performance monitoring to ensure management efficacy (Evidence: Expert opinion 2).

Refer to Specialists for Surgical Interventions in cases refractory to conservative and device management (Evidence: Expert opinion 3).

Consider Environmental Modifications to reduce stress and optimize training conditions (Evidence: Expert opinion 3).

Evaluate for Differential Diagnoses such as dynamic laryngeal collapse and nasal obstructions to rule out other causes of respiratory distress (Evidence: Expert opinion 2).

Monitor for Chronic Respiratory Complications and adjust management strategies accordingly (Evidence: Expert opinion 4).

References

1 Fjordbakk CT, Revold T, Goodwin D, Piercy RJ. Histopathological assessment of intrinsic laryngeal musculature in horses with dynamic laryngeal collapse. Equine veterinary journal 2015. link 2 Fjordbakk CT, Chalmers HJ, Holcombe SJ, Strand E. Results of upper airway radiography and ultrasonography predict dynamic laryngeal collapse in affected horses. Equine veterinary journal 2013. link 3 Fjordbakk CT, Holcombe S, Fintl C, Chalmers H, Strand E. A novel treatment for dynamic laryngeal collapse associated with poll flexion: the modified checkrein. Equine veterinary journal 2012. link 4 Strand E, Fjordbakk CT, Holcombe SJ, Risberg A, Chalmers HJ. Effect of poll flexion and dynamic laryngeal collapse on tracheal pressure in Norwegian Coldblooded Trotter racehorses. Equine veterinary journal 2009. link

Dynamic internal nasal valve collapse