Reflex apnea induced by high-frequency oscillatory ventilation in rabbits

Area of Science:

• Respiratory Physiology
• Autonomic Nervous System Regulation
• Vagal Nerve Function

Background:

• High-frequency oscillatory ventilation (HFOV) can induce apnea in rabbits with intact vagus nerves.
• The specific vagal mechanisms underlying HFOV-induced apnea and associated diaphragmatic activity remain unclear.

Purpose of the Study:

• To elucidate the vagal mechanisms responsible for HFOV-induced apnea in rabbits.
• To differentiate the roles of pulmonary stretch receptors in HFOV-induced respiratory arrest and diaphragmatic responses.

Main Methods:

• Vagus nerves in anesthetized rabbits were gradually cooled to selectively block nerve fibers based on diameter.
• The effects of HFOV, static lung inflation, and deflation on spontaneous breathing were compared at different temperatures.
• Pulmonary slowly adapting stretch receptors (PSR) and rapidly adapting stretch receptors (RAR) involvement was assessed.

Main Results:

• Cooling the vagus nerves weakened or abolished the lung inflation reflex (PSR) and reinforced the lung deflation reflex (RAR).
• HFOV-induced apnea frequency decreased as PSR function was blocked, but diaphragmatic activity increased.
• At lower temperatures, apnea persisted in some animals, accompanied by pronounced tonic diaphragmatic activity, suggesting RAR involvement.

Conclusions:

• HFOV-induced apnea in rabbits is primarily mediated by the stimulation of pulmonary slowly adapting stretch receptors (PSR).
• The accompanying tonic diaphragmatic activity during HFOV-induced apnea is mainly due to the stimulation of rapidly adapting stretch receptors (RAR).
• Differential blockade of vagal fibers revealed distinct roles for PSR and RAR in HFOV's respiratory effects.