Development of equine upper airway fluid mechanics model for Thoroughbred racehorses.

The research designs a computational fluid dynamics (CFD) model, which evaluates the airflow in the upper airways of a Thoroughbred racehorse during exercise, with the aim of identifying areas that are susceptible to collapse. The study uses data from CT scans and exercise pressure traces, and its insights aim to address a prevalent issue known as dorsal displacement of the soft palate (DDSP), common among racehorses.

Methods

• Images from a CT scan of a 3-year-old intact male Thoroughbred racehorse cadaver were used to create a model of in vivo geometry.
• Airway pressure traces obtained during exercise from a live racehorse were used to set the boundary condition — the condition that the solution of a partial differential equation must satisfy on a boundary of its domain.
• The team solved fluid-flow equations for turbulent flow in the airway during both inhalation and exhalation.
• Studying multiple cross-sections along the airway, they used data on pressure, kinetic energy and velocity distributions to understand the overall flow pattern and identify areas that might be inclined toward dynamic collapse.

Results

• The velocity of the airflow and the static pressure within the trachea were in line with the data from horses exercising on a high-speed treadmill.
• The area of the fully dilated rima glottidis, the opening between the vocal cords, was found to be 7% larger than the trachea.
• During inhalation, the highest turbulence occurred in the larynx, the front part of the nasopharynx experienced the most negative wall pressure, and the highest airflow velocity occurred further toward the tail on the underside of the nasopharynx — the soft palate.
• During exhalation, the highest turbulent areas were in the rostral and mid-nasopharynx, the maximum positive pressure occurred at the tail end of the soft palate, and the highest airflow velocity was at the front of the nasopharynx.

Conclusions

• The portion most susceptible to collapsing pressure, and thus to palatal instability, was the floor of the front part of the nasopharynx — noted for its high average turbulent kinetic energy during inhalation. This instability leads to a common racehorse issue, DDSP.
• The conclusion suggested that for ideal performance, maximal dilation of the arytenoid cartilage, which controls the opening of the larynx, may not be necessary, as the trachea’s cross-sectional area was found to be 7% smaller than the rima glottidis.