Implications of different degrees of arytenoid cartilage abduction on equine upper airway characteristics.

This research examines the degree to which arytenoid cartilage abduction (ACA) affects airway function in horses during exercise. It uses computational fluid dynamics to study the impact of varying the degree of ACA on airflow and pressure in horses with laryngeal hemiplegia, a condition in which half the larynx is paralyzed.

Research Purpose and Objectives

• This research aimed to assess the effect of different degrees of ACA on upper airway characteristics of Thoroughbred racehorses with laryngeal hemiplegia during exercise.
• The researchers aimed to determine the necessary degree of ACA required to restore normal peak airflow and pressure.

Methods Used

• The upper airway was modeled with varying degrees of ACA, using computational fluid dynamics to measure and analyze the outcomes.
• Three different arytenoid positions were considered: maximal abduction; 88% cross-sectional area of the rima glottis; and 75% cross-sectional area of the rima glottis.
• Two models were assumed: one without any compensation of airway pressures (Model 1), and one where airway pressure compensation occurs to maintain peak airflow (Model 2).
• The cross-sectional pressure and velocity distributions for turbulent flow were studied at peak flow and at different positions along the airway.

Key Findings

• In Model 1, where no change in driving pressure was assumed, a reduction in the cross-sectional area of the larynx resulted in a decrease in peak airflow and tidal volume, with only mild changes in wall pressure.
• In Model 2, where an increase in driving pressure was assumed to compensate for reduction in cross-sectional area, an increase in negative driving pressure resulted in areas with low intraluminal and wall pressures.
• The reduction of left ACA decreased airflow and tidal volume if no increase in driving pressure was assumed. However, an increase in driving pressure changed the wall pressure profile – the area around the submaximally abducted arytenoid cartilage became susceptible to collapse.

Conclusion

• Based on the models and simulations, the researchers concluded that a surgical target of ACA resulting in 88% of maximum cross-sectional area appears to be appropriate for restoration of normal peak airflow and pressure.