Reflex modulation of airflow dynamics through the upper airway

Area of Science:

• Respiratory Physiology
• Upper Airway Mechanics

Background:

• Maximal inspiratory flow (VImax) is critical for breathing.
• Upper airway collapsibility, determined by pharyngeal critical pressure (Pcrit), influences VImax.
• The role of respiratory reflexes in modulating upper airway mechanics is not fully understood.

Purpose of the Study:

• To investigate the effect of respiratory reflexes on VImax and its mechanical determinants.
• To evaluate the influence of chemoreceptor reflexes (CO2 and O2) on pharyngeal collapsibility and nasal resistance.
• To examine the impact of vagal afferents and upper airway mucosal receptors on airflow dynamics.

Main Methods:

• Used an isolated feline upper airway preparation.
• Varied inspired oxygen and end-tidal CO2 concentrations to stimulate chemoreceptors.
• Assessed pharyngeal critical pressure (Pcrit) and nasal resistance.
• Examined the effects of vagal and airway mucosal afferents under varying CO2 levels.

Main Results:

• Increased CO2 reduced pharyngeal collapsibility (more subatmospheric Pcrit) and increased VImax.
• Hypoxia did not affect Pcrit.
• Airway mucosal afferents decreased pharyngeal collapsibility, while vagal afferents increased it under hypercapnia.
• CO2 effects on VImax and Pcrit persisted despite altered afferent activity.

Conclusions:

• CO2 significantly influences pharyngeal collapsibility, impacting upper airway patency.
• Vagal and mucosal afferents modulate the effects of CO2 on airway mechanics.
• Reflex CO2 responses are crucial for maintaining airway patency.