Hemodynamic similarities between the trigeminal and aortic vasodepressor responses

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Regulation

Background:

• The trigeminal depressor response (TDR) and aortic depressor reflex (ADR) are known to lower blood pressure.
• Understanding the specific hemodynamic patterns of these reflexes is crucial for comprehending cardiovascular control.

Purpose of the Study:

• To compare the hemodynamic alterations induced by TDR and ADR in rabbits.
• To determine if the TDR elicits a hemodynamic profile comparable to the established ADR.

Main Methods:

• Rabbits anesthetized with urethane were subjected to electrical stimulation of the spinal trigeminal complex (TDR) or aortic nerve (ADR).
• Hemodynamic variables including heart rate, cardiac output, total peripheral resistance, and regional vascular resistances (femoral, mesenteric, renal) were measured.
• Regression analysis was used to compare the relationships between hemodynamic changes and arterial pressure fall during both TDR and ADR.

Main Results:

• Both TDR and ADR induced hypotension, bradycardia, a significant decrease in total peripheral resistance, and a small decrease in cardiac output.
• Regional vascular resistance decreased non-uniformly, with femoral > mesenteric > renal.
• No significant differences were found in the regression slopes or intercepts for heart rate, total peripheral resistance, or regional resistances between TDR and ADR.
• The femoral resistance/arterial pressure relationship showed a significantly greater slope than the renal resistance/arterial pressure relationship in both responses.

Conclusions:

• The trigeminal depressor response (TDR) is characterized by a hemodynamic pattern that is similar to the aortic depressor reflex (ADR).
• Both reflexes demonstrate a comparable differential effect on regional vascular beds, with greater changes in femoral than renal resistance.