Laryngeal movements during inspiratory muscle training in healthy subjects

Background: Inspiratory muscle training (IMT) has been used to treat patients with exercise-induced vocal cord dysfunction (VCD); the theoretical basis being the close relationship between the diaphragm and the posterior cricoarytenoid muscle, which is the main abductor of the larynx. Before launching a treatment protocol in patients with VCD, we aimed to substantiate this theory by performing laryngoscopy in healthy subjects during standardized IMT programs.

Methods: Twenty healthy volunteers at mean age 24 years were examined with video-recorded continuous transnasal flexible laryngoscopy while performing standardized training programs using a resistive loading IMT device (Respifit S). All subjects were exposed to two modes of training, that is, the resistance set to generate mouth pressures ≥80% of the maximal attainable inspiratory mouth pressure (PImax) and 60-80% of PImax. Laryngeal movements were scored in retrospect from the video recordings by a senior laryngologist.

Results: At pressure settings of ≥80% of PImax, laryngeal movements could not be assessed in one subject. Abduction was observed in 10 (53%) subjects, six to a maximal extent and four to a moderate extent. At pressure settings of 60-80% of PImax, abduction was observed in 18 (90%) subjects, seven to a maximal extent and 11 to a moderate extent.

Conclusions: IMT can produce laryngeal abduction in healthy subjects, and training programs may conceivably contribute positively in patients suffering from laryngeal adduction during exercise. Individual response patterns varied between subjects and individualized programs seem crucial for effect. Use of high resistances seemed to be counterproductive.