Central Baroreflex Resetting as a Means of Increasing and Decreasing Sympathetic Outflow and Arterial Pressure

The arterial baroreflex has two important functions. First, the arterial baroreflex is a negative feedback reflex that regulates arterial pressure around a preset value called a set or operating point. Second, the arterial baroreflex also establishes the prevailing systemic arterial pressure when the operating point is reset. That is, modulating the response of barosensitive neurons in the central nervous system (CNS) establishes the operating point or prevailing systemic arterial pressure. Therefore, the operating point of the arterial baroreflex is not fixed, but is variable over a wide range of pressures and is determined by a variety of inputs from the peripheral and central nervous systems. At the onset of dynamic exercise, heart rate (HR) and sympathetic nerve activity (SNA) increase abruptly and dramatically. The initial increase in HR and SNA is mediated by central command. Central command operates by resetting the operating point of the arterial baroreflex to a higher pressure. In this situation, the operating point of the arterial baroreflex is above the prevailing arterial pressure, which elicits a blood pressure error. This error is corrected by activating SNA and inhibiting parasympathetic nerve activity, which increases cardiac output and peripheral resistance and, consequently, arterial pressure. After exercise, loss of central command and enhanced activity of the cardiopulmonary reflex resets the operating point of the arterial baroreflex to a lower pressure. In this situation, the operating point of the arterial baroreflex is below the prevailing arterial pressure, which elicits a blood pressure error. This error is corrected by inhibiting SNA, which decreases peripheral resistance and consequently arterial pressure. In these situations, central resetting of the arterial baroreflex is a means of increasing and decreasing sympathetic outflow and arterial pressure.