Geniohyoid muscle function in awake canines.

Area of Science:

• Physiology
• Respiratory Mechanics
• Upper Airway Function

Background:

• The geniohyoid muscle's role in breathing is unclear in awake mammals.
• Previous studies in anesthetized cats showed no activity, contrasting with awake humans.

Purpose of the Study:

• To investigate the mechanical action and electrical activity of the geniohyoid muscle in awake, nonanesthetized canines during respiration and swallowing.
• To determine if the geniohyoid muscle contributes to breathing mechanics in awake mammals.

Main Methods:

• Sonomicrometry transducers and EMG electrodes were implanted in four canines.
• Muscle length, shortening, and EMG activity were recorded during quiet breathing, CO2-stimulated breathing, inspiratory-resisted breathing, and airway occlusion.
• Measurements were also taken during swallowing.

Main Results:

• The geniohyoid muscle showed no phasic EMG activity and minimal lengthening during quiet and CO2-stimulated breathing.
• During inspiratory-resisted breathing and airway occlusion, the geniohyoid exhibited phasic EMG activity but still lengthened.
• The geniohyoid muscle shortened significantly (9.31% change) with increased EMG activity (6.44 V) during swallowing.

Conclusions:

• The geniohyoid muscle in awake canines is electrically inactive and passively lengthens during resting and stimulated breathing.
• Geniohyoid muscle contraction and electrical activity are primarily associated with swallowing, not respiration in awake dogs.
• Even against inspiratory resistance, the geniohyoid muscle lengthens during inspiration, suggesting a passive role in breathing mechanics.