Sympathetic Nervous System and Blood Pressure in Humans

Abstract

The autonomic nervous system and its sympathetic arm play important roles in the regulation of blood pressure.1–3⇓⇓ Their role in the short-term regulation of blood pressure, especially in responses to transient changes in arterial pressure, via baroreflex mechanisms is well known.4 However, the role of the sympathetic branch in longer-term (days, months, and years) blood pressure regulation has been a focus of debate since at least the 1970s.1,4⇓ Our goal in this Hypertension Highlights is to summarize and integrate our ideas on the role of the sympathetic nervous system in long-term blood pressure regulation in humans.1–3,5–9⇓⇓⇓⇓⇓⇓⇓ We will focus primarily on information from studies conducted in humans and use data from animal studies to emphasize key points. In this context, we want to address 4 key questions. The first 3 focus on our recent work. The final issue is an emerging one and more speculative. First, what is the role of the sympathetic nervous system in long-term blood pressure regulation in young (18- to 40-year–old) normotensive men? Second, does the role of the sympathetic nervous system in long-term blood pressure regulation change as a function of age in men? Third, does sex influence the role of the sympathetic nervous system in long-term blood pressure regulation, and are sex differences modified by aging? Fourth, are we entering an era of sympathetically driven hypertension? Before we address these questions, we share a few thoughts about how to assess the overall activity of sympathetic nerves in humans. Various approaches used to assess sympathetic activity in humans have been reviewed recently by Grassi.10 We focus primarily on studies that use direct measurements of muscle sympathetic nerve activity (MSNA) as an overall marker of sympathetic outflow in humans and, to …