Low-dose atropine amplifies cardiac vagal modulation and increases dynamic baroreflex function in humans

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Regulation
• Pharmacological Interventions

Background:

• Low-dose atropine (LDA) is known to enhance vagal outflow to the heart.
• Vagal cardiac modulation plays a crucial role in maintaining arterial blood pressure (ABP) stability.
• Understanding the impact of enhanced vagal activity on ABP regulation during dynamic stimuli is important.

Purpose of the Study:

• To evaluate the effect of vagal cardiac stimulation via LDA on ABP fluctuation.
• To assess ABP stability during dynamic hypertensive and hypotensive stimuli.
• To investigate the role of vagal cardiac modulation in buffering ABP changes.

Main Methods:

• 16 healthy volunteers participated in the study.
• Measurements included RR interval (RRI), ABP, heart rate variability (HRV), ABP variability, and spontaneous baroreflex sensitivity (BRS).
• Dynamic hypertension was induced by phenylephrine, and hypotension by thigh cuff deflation, before and after LDA administration.

Main Results:

• LDA administration resulted in bradycardia and significantly increased high-frequency (HF) HRV and spontaneous BRS.
• LDA attenuated the increase in systolic blood pressure (SBP) during phenylephrine-induced hypertension.
• Increases in HF HRV were negatively correlated with SBP increases during phenylephrine challenge.

Conclusions:

• Increased vagal cardiac function induced by LDA enhances heart rate buffering effects.
• LDA plays a significant role in minimizing ABP fluctuations during dynamic hypertensive stimuli.
• Vagal cardiac modulation is critical for maintaining cardiovascular stability under stress.