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

A video-laryngoscopic method, implemented with an algorithm for the correct ion of the deformation inherent in the endoscope optical system, has been u sed to measure the dorsoventral diameter (D-rg) and the cross-sectional are a (CSA(rg)) of the rima glottidis in five healthy workhorses during conscio us breathing at rest. Simultaneous recording of the respiratory airflow was also obtained in two horses. D-rg measured 82.7 +/- 4.5 mm (mean +/- S.D.) independently of the respiratory phase, and did not differ from the measur ement in post-mortem anatomical specimens of the same horses. CSA(rg) range d from 1130 +/- 117 mm(2) (mean +/- S.D.) during the inspiratory phase to 6 40 +/- 242 mm during the expiratory phase, being always narrower than trach eal cross-sectional area, which was 1616 +/- 224 mm(2), as determined from anatomical specimens. Both inspiratory and expiratory airflow waves display ed a biphasic pattern. Maximal laryngeal opening occurred in phase with the second inspiratory peak, while during expiration CSA(rg) attained a minimu m value during the first expiratory peak which was significantly smaller (P < 0.01) than the area subsequently maintained during the rest of the expir atiory phase. These quantitative measurements of equine laryngeal movements substantiate the important role played by the larynx in regulating upper a irway respiratory resistance and the expiratory airflow pattern at rest.