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Published on: December 1, 2023
Implications of different degrees of arytenoid cartilage abduction on equine upper airway characteristics
V Rakesh1, N G Ducharme, J Cheetham
1Department of Biological and Environmental Engineering, College of Agriculture and Life Sciences, North Carolina State University, Raleigh, North Carolina 27606, USA.
Reason For Performing Study:
The necessary degree of arytenoid cartilage abduction (ACA) to restore airway patency at maximal exercise has not been determined.
Objectives:
Use computational fluid dynamics modelling to measure the effects of different degrees of ACA on upper airway characteristics of horses during exercise.
Hypothesis:
Maximal ACA by laryngoplasty is necessary to restore normal peak airflow and pressure in Thoroughbred racehorses with laryngeal hemiplegia.
Methods:
The upper airway was modeled with the left arytenoid in 3 different positions: maximal abduction; 88% cross-sectional area of the rima glottis; and 75% cross-sectional area of the rima glottis. The right arytenoid cartilage was maximally abducted. Two models were assumed: Model 1: no compensation of airway pressures; and Model 2: airway pressure compensation occurs to maintain peak airflow. The cross-sectional pressure and velocity distributions for turbulent flow were studied at peak flow and at different positions along the airway.
Results:
Model 1: In the absence of a change in driving pressure, 12 and 25% reductions in cross-sectional area of the larynx resulted in 4.11 and 5.65% reductions in peak airflow and 3.68 and 5.64% in tidal volume, respectively, with mild changes in wall pressure. Model 2: To maintain peak flow, a 6.27% increase in driving tracheal pressure was required to compensate for a cross-sectional reduction of 12% and a 13.63% increase in driving tracheal pressure was needed for a cross-sectional area reduction of 25%. This increase in negative driving pressure resulted in regions with low intraluminal and wall pressures, depending on the degree of airway diameter reduction.
Conclusion:
Assuming no increase in driving pressure, the decrease in left ACA reduced airflow and tidal volume. With increasing driving pressure, a decrease in left ACA changed the wall pressure profile, subjecting the submaximally abducted arytenoid cartilage and adjacent areas to airway collapse.
Clinical Relevance:
The surgical target of ACA resulting in 88 % of maximal cross-sectional area seems to be appropriate.
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