Lung volume modulation of sternohyoid muscle function: an anesthetized rat model

Area of Science:

• Physiology
• Respiratory Mechanics
• Sleep Medicine

Background:

• Lung volume influences upper airway patency through passive force transmission.
• Active dilator muscle function may be affected by changes in resting muscle length due to lung volume shifts.

Purpose of the Study:

• To investigate the relationship between end-expiratory lung volume (EELV) and the sternohyoid muscle's (SH) ability to modify pharyngeal airway patency.
• To determine how lung volume affects both passive and active components of upper airway resistance.

Main Methods:

• Measurements in anesthetized Wistar rats included airflow, mask pressure, tracheal pressure, and sternohyoid muscle length and tension.
• End-expiratory lung volume (EELV) was manipulated using plethysmograph pressure changes.
• Upper airway resistance was assessed passively and during electrical stimulation of the sternohyoid muscle.

Main Results:

• Increasing EELV altered passive upper airway resistance and sternohyoid muscle length and passive tension.
• Decreasing EELV significantly increased passive upper airway resistance and altered muscle mechanics.
• Both increasing and decreasing EELV reduced active sternohyoid muscle tension and the change in upper airway resistance during muscle contraction.
• Maximal active dilation and resistance change occurred at baseline EELV.

Conclusions:

• Lung volume shifts impact both passive and active upper airway function.
• Altered resting sternohyoid muscle length at different lung volumes may impair active pharyngeal dilator function.
• Findings suggest a mechanism linking lung volume to airway patency relevant for obstructive sleep apnea treatment strategies.