Title: Respiratory Muscle Fatigue and the Effects on Swallowing
Description: The relationship between respiratory muscle fatigue and the function of swallowing is examined here. The main objective of this study is to examine the effects of respiratory muscle fatigue on swallowing physiology in healthy young adults. Specifically, this study aims to determine if differences exist in several swallowing-related parameters (a. the muscle recruitment pattern of the submentals and infrahyoids associated with swallowing, b. the pattern of breathing and swallowing coordination, c. the duration of the breath phases associated with swallowing, d. the duration of swallowing apnea, and e. the secondary swallow frequency) during several different swallowing conditions before, following respiratory muscle fatigue and following recovery. Fifty-four healthy young adults were randomly assigned into two groups, either an inspiratory (MIP) or an expiratory (MEP) muscle fatigue group. Respiratory and swallowing measurements were obtained, during 3 experimental conditions: a baseline condition, after exercise-induced fatigue, and finally, after a 15min rest period.

A loaded breathing device was used in order to induce fatigue to the respiratory muscles. Presence of fatigue was determined with the assessment of Maximum Expiratory (PEmax)/Maximum Inspiratory (PImax) Pressures measured with a mouth pressure manometer. Electrophysiologic data were obtained with the use of sEMG on the submental and infrahyoid muscle groups, and with the use of three respiratory belt transducers, placed around the thorax, abdomen and neck. The Borg Scale was used to behaviourally assess perceived sense of breathing effort. Descriptive and inferential statistics were conducted to allow for detailed analysis of differing measures and variances between individuals. Results revealed significant differences between the three experimental conditions in the muscle recruitment patterns of the submental and infrahyoids, in the pattern of breathing and swallowing coordination, in the duration of the swallow-related respiratory cycle and in the frequency of secondary swallows. The duration of the deglutitive apnea was not affected by the presence of respiratory muscle fatigue.

In particular, the sEMG Integral of the infahyoids was significantly reduced during the fatigued condition compared to the baseline and post-rest conditions, as opposed to an increase in sEMG integral of the submental muscles observed only in the MEP subject group. Additionally, the occurrence of swallows followed by inspiration was significantly increased during the fatigued condition. Secondary swallow frequency was significantly increased during the fatigued condition. These results suggest an effect of respiratory muscle fatigue on selective swallowing related parameters. These results are of great clinical importance since the observed patterns may increase the risk of aspiration. Results will be discussed with respects to the implications for patients and their therapeutic interventions.