Airflow mechanics in models of equine obstructive airway disease under conditions simulating exercise.

The research aims to study the effects of respiratory tract obstructions on the airflow mechanics in horses when engaged in intense exercise. They used a model of a horse’s respiratory system to study how severe pharyngeal lymphoid hyperplasia (PLH) and partial bronchial obstruction would impact the flow of air.

Methodology

• A replica of the airways of a horse, made from fiberglass, was used. The model was designed to represent the airways from the external nares (nostrils) to the main bronchi.
• Researchers recorded pressures at six points along the model under four different flows of air, ranging between 1300 to 4100 liters per minute.
• The model was adjusted to simulate severe PLH, which is overgrowth of lymphoid tissue in the pharynx, and partial bronchial obstruction to assess the variance of pressure at different points.
• To mimic the natural breathing of a horse, two 16-liter anaesthetic rebreathing bags were attached to the bronchial end of the model, and tidal ventilation was generated by a piston pump.

Findings

• The nares and the larynx contributed most to the total resistance to airflow when there was no obstruction.
• Simulating severe PLH did not impact the resistance at the larynx or any point in the trachea under these flow conditions.
• However, when airflow was simulated that would match high frequency, high volume ventilation, like that seen in galloping horses, there was an influence on the resistance for RL (lower part of the airway, from larynx to bronchi), RTOT (total resistance from nostrils to bronchi) and dynamic compliance under PLH simulated condition.
• When partial bronchial obstruction was simulated, the resistance for RM and RTOT increased at pumping frequencies greater than 34 with each volume of pump (Vp).
• The results from the unobstructed state were verified by comparing them with results from normal horses exercising on a treadmill.

Conclusions

• The research suggests that in high-intensity exercises, severe PLH can affect the airflow in the lower areas of the respiratory tract.
• Partial bronchial obstructions can have an increased effect on resistance to airflow.
• Therefore, obstructions in the respiratory tract can significantly impact high performance in activities like racing that require intense exercise and high respiratory rates.