Bronchoconstriction: upper airway dilating muscle and diaphragm activity

Area of Science:

• Respiratory Physiology
• Neuroscience

Background:

• Bronchoconstriction, a narrowing of the airways, poses a significant challenge to respiratory function.
• The compensatory mechanisms involving respiratory muscles, including the diaphragm and upper airway muscles, are crucial for maintaining airflow during such conditions.

Purpose of the Study:

• To investigate the impact of induced bronchoconstriction on the electrical activity of the diaphragm and key upper airway muscles (genioglossus, posterior cricoarytenoid, alae nasi).
• To determine if vagotomy alters the response of these muscles to bronchoconstriction.

Main Methods:

• Anesthetized dogs spontaneously breathing oxygen were administered graded doses of methacholine to induce bronchoconstriction.
• Electrical activity of the genioglossus, posterior cricoarytenoid, alae nasi, and diaphragm was recorded and compared at varying levels of pulmonary resistance.
• Bilateral cervical vagotomy was performed to assess its effect on the observed muscle responses.

Main Results:

• Methacholine-induced bronchoconstriction led to increased electrical activity in all examined muscles, including the diaphragm and upper airway muscles.
• Bilateral cervical vagotomy reduced, but did not abolish, the bronchoconstrictor effects on muscle activity.
• Even after vagotomy, increased methacholine concentrations comparable to pre-vagotomy levels resulted in heightened genioglossus and diaphragm activity.

Conclusions:

• The diaphragm and upper airway muscles are activated in response to bronchoconstriction.
• Activation of upper airway muscles during bronchoconstriction may serve to decrease upper airway resistance, partially counteracting increased pulmonary resistance.
• These findings suggest a protective role for upper airway muscle recruitment in modulating airflow during bronchoconstriction.