Address for correspondence: Stephen E. DiCarlo, Ph.D., Department of Physiology, 6213 Scott Hall, 540 E. Canfield Avenue, Detroit, Michigan 48201-1928. Voice: 313-577-1557; fax: 313-577-5494.
sdicarlo{at}med.wayne.edu
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.
