Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan.
Department of Oral Diagnosis, Faculty of Dentistry, Naresuan University, Phitsanulok, Thailand.
Am J Physiol Gastrointest Liver Physiol. 2024 Oct 1;327(4):G598-G607. doi: 10.1152/ajpgi.00138.2024. Epub 2024 Aug 6.
The sternohyoid muscle depresses the hyoid bone, but it is unclear whether the muscle contributes to respiratory and swallowing mechanisms. This study aimed to clarify whether the sternohyoid muscle participates in the respiration and swallowing reflex and how the activity is modulated in two conditions: with airway stenosis and with a fixed sternohyoid muscle length. Electromyographic activity in the sternohyoid, digastric, thyrohyoid, and diaphragm muscles was recorded in anesthetized rats. The sternohyoid muscle activity was observed in the inspiratory phase and during swallowing, and was well coordinated with digastric and thyrohyoid muscle activity. With airway stenosis, the respiratory activity per respiratory cycle was facilitated in all assessed muscles but the facilitation of activity per second occurred only in the digastric, thyrohyoid, and sternohyoid muscles. With airway stenosis, the swallowing activity was facilitated only in the digastric muscle but not in the thyrohyoid and sternohyoid muscles. Swallowing activity was not observed in the sternohyoid muscle in the condition with the sternohyoid muscle length fixed, although increased inspiratory activity remained. The current results suggest that ) the sternohyoid muscle is slightly activated in the inspiratory phase, ) the effect of airway stenosis on respiratory function may differ between the upper airway muscles and diaphragm, and ) swallowing activity in the sternohyoid muscle is not dominantly controlled by the swallowing central pattern generator but instead occurs as a myotatic reflex. We found that the sternohyoid muscle was activated in the inspiratory phase. However, increased airway resistance had different effects on the extrathoracic muscles than on the diaphragm. The swallowing activity of the sternohyoid disappeared when the muscle length was fixed. These findings suggest that the sternohyoid muscle may be activated not by the swallowing central pattern generator but as a myotatic reflex.
胸骨舌骨肌使舌骨下降，但目前尚不清楚该肌肉是否有助于呼吸和吞咽机制。本研究旨在阐明胸骨舌骨肌是否参与呼吸和吞咽反射，以及在两种情况下（气道狭窄和胸骨舌骨肌长度固定）如何调节其活动：在麻醉大鼠中记录胸骨舌骨肌、二腹肌、甲状舌骨肌和膈肌的肌电图活动。观察到胸骨舌骨肌在吸气相和吞咽时的活动，并与二腹肌和甲状舌骨肌的活动很好地协调。在气道狭窄时，所有评估的肌肉的呼吸周期呼吸活动都得到促进，但每秒的活动促进仅发生在二腹肌、甲状舌骨肌和胸骨舌骨肌中。在气道狭窄时，吞咽活动仅在二腹肌中得到促进，但在甲状舌骨肌和胸骨舌骨肌中没有。在胸骨舌骨肌长度固定的情况下，虽然吸气活动增加，但未观察到胸骨舌骨肌的吞咽活动。目前的结果表明：i）胸骨舌骨肌在吸气相轻微激活；ii）气道狭窄对上气道肌肉和膈肌的呼吸功能的影响可能不同；iii）胸骨舌骨肌的吞咽活动不是由吞咽中枢模式发生器主要控制的，而是作为牵张反射发生的。我们发现胸骨舌骨肌在吸气相被激活。然而，增加气道阻力对胸外肌肉的影响与对膈肌的影响不同。当肌肉长度固定时，胸骨舌骨肌的吞咽活动消失。这些发现表明胸骨舌骨肌的激活可能不是由吞咽中枢模式发生器引起的，而是作为牵张反射引起的。
