Influence of lung inflation reflex on vascular capacitance in the systemic circulation

Area of Science:

• Physiology
• Cardiovascular System
• Respiratory System

Background:

• Understanding the cardiovascular reflexes initiated by lung inflation is crucial for managing respiratory and cardiac conditions.
• Previous research has explored the effects of lung mechanics on cardiovascular parameters, but the specific neural pathways involved require further elucidation.

Purpose of the Study:

• To investigate the impact of sustained lung inflation on systemic vascular capacitance (SVC), systemic vascular resistance (SVR), and cardiac sympathetic efferent nerve activity (SENA).
• To determine the role of vagal afferent nerve fibers in mediating the observed cardiovascular responses to lung inflation.

Main Methods:

• Anesthetized dogs were subjected to total cardiopulmonary bypass.
• Sustained lung inflation was induced by inflating lungs to tracheal pressures of 10, 15, and 20 mmHg.
• Measurements of SVC, SVR, and SENA were recorded, with and without bilateral vagotomy, at a low carotid sinus pressure (CSP) of 41 mmHg.

Main Results:

• Lung inflation significantly increased SVC and decreased SVR in a pressure-dependent manner.
• Cardiac sympathetic efferent nerve activity (SENA) decreased concurrently with lung inflation.
• Bilateral vagotomy substantially attenuated the changes in SVR, SVC, and SENA, indicating a primary role for vagal afferents.

Conclusions:

• Lung inflation elicits a reflex that increases systemic vascular capacitance and reduces systemic vascular resistance and sympathetic nerve activity.
• The lung inflation reflex is predominantly mediated by vagal afferent nerve fibers, with a minor contribution from other afferent pathways.