Blood Pressure Variability

This chapter explains blood pressure variability and physiologic control of sympathetic nervous system (SNS) outflow. Control of SNS outflow is generated from complex bidirectional signals among interconnected centers within the central nervous system and peripheral tissues. Given the wide range of responses observed in normal human physiology, it is difficult to identify discrete boundaries of abnormal BP variation. From a clinical perspective, such variation can confound the diagnosis and management of hypertension and may contribute directly to cardiovascular disease (CVD). During normal respiration, breathing is not usually coupled tightly with systemic BP, in part because variations in stroke volume are buffered by baroreflex adjustments as well as vascular damping mechanisms. Maintenance of adequate cerebral perfusion during upright posture requires an instantaneous integrated response of the heart and vasculature that is mediated by the SNS. Physical exercise requires a series of complex neurophysiologic and hemodynamic responses. Centrally regulated increased SNS outflow increases cardiac output and muscle blood flow; stimulatory metaboreceptors in skeletal muscle sustain the response.