Coupling of spontaneous changes in muscle sympathetic nerve activity to blood pressure in humans : potential influence of age [abstract]

Previous studies indicate a 5.5 second latency between a burst of muscle sympathetic nerve activity (MSNA) and the resultant peak blood pressure response, which averages up to 3 mmHg. Aging may attenuate α-adrenergic sensitivity, impair baroreflex function, and hence affect the ability to sympathetically modulate blood pressure. Yet a thorough examination of these relationships in older adults has not been performed. Purpose: To compare the relationship between spontaneous changes in MSNA to changes in blood pressure in young and older men

Selective attenuation of carotid-cardiac responses to hypertension at the onset of static handgrip in humans [abstract]

Previous studies have indicated that at the onset of exercise cardiac baroreflex function is reduced in an intensity-dependent manner, which appears to be mediated by a blunted ability to buffer hypertensive challenges. However, whether cardiac baroreflex responses to a hypotensive stimulus are altered at exercise onset is unclear

The role of spontaneous bursts of muscle sympathetic nerve activity in mediating peripheral vascular responses and cardiovascular hemodynamics in resting man

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The ability for sympathetic nerve activity to dynamically evoke vasoconstriction is paramount for the regulation of blood flow and blood pressure. However, very little information is available to characterize the influence of spontaneously occurring sympathetic nerve activity on human blood vessels during rest. We employed spike-triggered averaging to assess the systematic influence of resting muscle sympathetic nerve activity (MSNA) bursts to determine: 1) their influence on leg and forearm vascular conductance as well as on conduit artery diameter in resting young healthy men. We demonstrate that spontaneous MSNA bursts exert a robust and dynamic vasoconstrictor influence on forearm and leg skeletal muscle blood resistance arteries that occur in close association with vasoconstriction of the systemic vasculature, to subsequently increase arterial blood pressure during rest. Vasoconstriction was greater in leg resistance arteries compared to that observed in the forearm, and conduit arteries did not exhibit any decreases in diameter following spontaneous MSNA bursts. Variations in the amplitude and pattern of MSNA bursts modulated the magnitude of responses via α-adrenergic receptor mechanisms. Collectively, these are the first data to describe the influence of spontaneously occurring MSNA on the human vasculature during rest, suggesting that the dynamic control of skeletal muscle blood flow importantly participates in the control of systemic hemodynamics and blood pressure

Influence of age and sex on the pressor response following a spontaneous burst of muscle sympathetic nerve activity

The sympathetic nervous system is critical for the beat-to-beat regulation of arterial blood pressure (BP). Although studies have examined age- and sex-related effects on BP control, findings are inconsistent and limited data are available in postmenopausal women. In addition, the majority of studies have focused on time-averaged responses without consideration for potential beat-to-beat alterations. Thus we examined whether the ability of muscle sympathetic nerve activity (MSNA) to modulate BP on a beat-to-beat basis is affected by age or sex. BP and MSNA were measured during supine rest in 40 young (20 men) and 40 older (20 men) healthy subjects. Beat-to-beat fluctuations in mean arterial pressure (MAP) were characterized for 15 cardiac cycles after each MSNA burst using signal averaging. The rise in MAP following an MSNA burst was similar between young men and women (+2.64 ± 0.3 vs. +2.57 ± 0.3 mmHg, respectively). However, the magnitude of the increase in MAP after an MSNA burst was reduced in older compared with young subjects (P < 0.05). Moreover, the attenuation of the pressor response was greater in older women (+1.20 ± 0.1 mmHg) compared with older men (+1.72 ± 0.2 mmHg; P < 0.05). Interestingly, in all groups, MAP consistently decreased after cardiac cycles without MSNA bursts (nonbursts) with the magnitude of fall greatest in older men. In summary, healthy aging is associated with an attenuated beat-to-beat increase in BP after a spontaneous MSNA burst, and this attenuation is more pronounced in postmenopausal women. Furthermore, our nonburst findings highlight the importance of sympathetic vasoconstrictor activity to maintain beat-to-beat BP, particularly in older men