Laryngeal movements during the respiratory cycle measured with an endoscopic imaging technique in the conscious horse at rest.

The research explores the use of a video-laryngoscopic method to measure and analyze the laryngeal movements of horses during resting respiration. This aids understanding of the larynx’s role in managing airflow resistance in horses.

Methodology

• The study used a specialized endoscopic imaging method, complemented by an algorithm designed to correct inherent deformations in the optical system of the endoscope. This enabled precise measurement of parameters such as the dorsoventral diameter (Drg) and the cross-sectional area (CSArg) of the rima glottidis (the opening between the vocal folds in the larynx) in five healthy horses.
• At the same time, respiratory airflow was recorded for two of these horses. This comprehensive approach provided a nuanced view of laryngeal function during respiration.

Results and Findings

• Drg was found to be 82.7 +/- 4.5 mm, not varying by respiratory phase and consistent with post-mortem measurements taken from the same horses.
• CSArg was found to range from 1130 +/- 117 mm2 during the inspiration phase to 640 +/- 242 mm2 during the expiration phase. It was consistently smaller than the tracheal cross-sectional area, measured at 1616 +/- 224 mm2. These differences were derived from anatomical specimens.
• The measurements revealed a biphasic pattern in both inspiratory and expiratory airflow waves. The larynx’s largest opening coincided with the second inspiratory peak, while the smallest CSArg was measured during the first expiratory peak.
• In the expiration phase, the minimum measured area was significantly smaller (P < 0.01) than the area subsequently maintained during the rest of the expiration phase.

Conclusion

• The results from the recordings substantiate the larynx’s crucial role in controlling upper airway respiratory resistance and the expiratory airflow pattern in horses while at rest.
• This study, therefore, offers quantifiable insights into equine respiratory physiology, particularly the laryngeal movements during a respiratory cycle.