REVIEWSympathetic Neural Mechanisms in Human Cardiovascular Health and Disease
Section snippets
SYMPATHETIC NEURAL MECHANISMS IN THE REGULATION OF BLOOD PRESSURE
Sympathetic neural influences on cardiovascular function can be divided into 4 main categories: the influences of cardiac sympathetic nerves, the influences of vascular sympathetic nerves, adrenal medullary influences caused by circulating epinephrine and norepinephrine, and the sympathetic stimulation of renal juxtaglomerular cells that activates the renin-angiotensin-aldosterone axis. Most sympathetic innervation in the human cardiovascular system is noradrenergic. Norepinephrine is the
Direct Measurement
Because sympathetic postganglionic neurons are small, unmyelinated C fibers, it was originally thought that their activity could not be directly measured in humans. In the late 1960s, a group of Swedish investigators pioneered the method of microneurography for measurement of human neural activity and somewhat accidentally came upon the sympathetic vasoconstrictor nerve signal.14 Since the 1970s, microneurography has been used successfully to elucidate the complex integrative physiology related
INTERINDIVIDUAL VARIABILITY: ROLE IN REGULATION OF BLOOD PRESSURE
Two characteristics of MSNA have perplexed both clinicians and scientists for several decades. The first is the striking interindividual variability in the amount of neuralactivity in resting humans. Muscle sympathetic neural activity can exhibit a 7- to 10-fold variation in healthy humans, a fact that was initially disappointing to investigators who thought that a narrower range of “normal values” would allow the use of MSNA measurements for clinical diagnostic purposes. However, the more
Physiology
Aging. Even in the absence of disease, MSNA increases with age, on average by approximately 1 burst per minute each year.26 This age-related increase in sympathetic activity may contribute to the increase in the risk of hypertension with aging. Indeed, in persons older than 40 years, a strong association exists between resting levels of MSNA and resting arterial blood pressure.28 This association does not exist in younger persons, suggesting that mechanismsthat buffer or balance the
CONCLUSION
The sympathetic nervous system plays a vital role in maintaining cardiovascular health because of its key effects on both short- and long-term regulation of blood pressure and blood flow to organs. In the past several decades, direct measurement of vasoconstrictor SNA by microneurography has provided great insight into sympathetic neural mechanisms in both health and disease. Because microneurography is both technically challenging and time-consuming, its widespread use in the clinical setting
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