Reflex control of expiratory airflow and duration

Area of Science:

• Physiology
• Respiratory System Mechanics

Background:

• The upper airway plays a crucial role in regulating breathing, particularly during expiration.
• Understanding the neural control of respiratory muscles is essential for respiratory physiology.

Purpose of the Study:

• To investigate reflex responses of respiratory muscles to alterations in upper airway function.
• To determine the role of upper airway resistance in respiratory muscle activity during breathing.

Main Methods:

• Unanesthetized cats were instrumented with a permanent tracheostomy, respiratory pressure catheters, and electromyography (EMG) electrodes.
• The tracheostomy was remotely opened or closed to manipulate airflow and upper airway resistance.
• Respiratory muscle activity (diaphragm, laryngeal abductor, abdominal expiratory muscles) and tracheal pressure were recorded.

Main Results:

• Opening the tracheostomy during expiration elicited sustained compensatory (tracking) responses in respiratory muscles, offsetting the loss of upper airway resistance.
• These responses often overcompensated, suggesting potential involvement of extrathoracic tracheal receptors.
• Changes in expiratory lung volume profiles were accompanied by altered expiration durations (triggering responses), operating independently of tracking responses.
• Both tracking and triggering responses were abolished by vagotomy.

Conclusions:

• Respiratory muscles exhibit robust reflex responses to changes in upper airway resistance, crucial for maintaining breathing stability.
• Tracheal receptors may play a significant role in these compensatory breathing adjustments.
• Distinct tracking and triggering responses contribute to respiratory control, modulated by the vagus nerve.