A first step towards objective grading of equine laryngeal function

Due to concerns about disagreement between veterinarians when grading resting laryngeal function (LF), a diagnostic decision tree (DDT) has been developed by codifying the Havemeyer grading system and objectively defining certain terms to remove ambiguity. Videoendoscopic examinations of the equine larynx that had previously been assigned a unanimous LF grade by 3 experienced observers were used to develop the DDT and determine the cut-off values. The DDT is a flow chart consisting of a series of dichotomous (yes/no) decisions, to dictate the order of decision making and direct the observer down a pathway towards the most appropriate LF grade. To use the DDT, the observer must know the frame rate of the video and use frame-by-frame video playback when reviewing the videos. The first decision involves determining if full left arytenoid cartilage (LAC) abduction is achieved (≤ grade III.1), or not achieved (> grade III.1). Maintained full LAC abduction (≤ grade II.2) is defined as maintenance of full abduction for ≥ 0.2 seconds. Full LAC abduction that is achieved but not maintained (grade III.1) is defined as maintenance of full abduction for < 0.2 seconds. Arytenoid abductor deficit is categorized into left arytenoid abduction ≥45° from vertical midline (grade III.2) and <45° abduction (grade III.3). The DDT could be used as a first step towards computer assisted laryngeal function grading.