Human muscle nerve sympathetic activity at rest. Relationship to blood pressure and age

Abstract

SUMMARY1. Recordings of multi-unit sympathetic activity were made from median or peroneal muscle nerve fascicles in thirty-three healthy subjects, resting in recumbent position. Simultaneous recordings of intra-arterial blood pressure were made in seventeen subjects. The neural activity, quantified by counting the number of pulse synchronous sympathetic bursts in the mean voltage neurogram (burst incidence), was plotted against the arterial blood pressure level and the age of the subjects. The effects of spontaneous temporary blood pressure fluctuations were studied by correlating different pressure parameters of individual heart beats to the probability of occurrence of a sympathetic burst and to the amplitude of the occurring burst.2. Between different subjects there were marked differences in burst incidence, from less than 10 to more than 90 bursts/100 heart beats. No correlation was found to interindividual differences in the arterial blood pressure level but there was a slight tendency for increasing burst incidence with increasing age.3. Irrespective of the magnitude of the burst incidence, the bursts always occurred more frequently during spontaneous transient blood pressure reductions than during transient increases in blood pressure. When, for each heart cycle, the occurrence of a sympathetic burst was correlated with different blood pressure parameters there was regularly a close negative correlation to diastolic pressure, a low correlation to systolic and an intermediary negative correlation to mean blood pressure. There was a positive correlation to pulse pressure and to pulse interval.4. When measured for individual heart beats, not only the occurrence but also the mean voltage amplitude of the sympathetic bursts tended to increase with decreasing diastolic pressure.5. In a given subject when comparing heart beats with the same diastolic pressure, the occurrence as well as the amplitude of the sympathetic bursts was higher for heart beats occurring during falling than for heart beats occurring during rising blood pressure. For a given change in diastolic blood pressure, sympathetic activity changed more if pressure was falling than if it was rising.6. The findings suggest that the sympathetic outflow is modulated by arterial baroreflex mechanisms and that transient variations in the strength of the activity are, to a large extent, determined by diastolic blood pressure fluctuations. The intimate correlation with 'dynamic' variations in blood pressure and the absence of correlation to the 'static' blood pressure level suggests that the sympathetic outflow 6. SUNDLJF AND B. G. WALLIN to skeletal muscles is of importance for buffering acute blood pressure changes but has little influence on the long term blood pressure level. The difference in reflex sensitivity between falling and rising pressure indicates that acute blood pressure decreases may be buffered more efficiently than acute blood pressure increases.7. In twenty-seven subjects baroreflex latency was calculated from the QRScomplexes in the e...

Muscle sympathetic nerve activity during cold stress and isometric exercise in healthy older adults

“…To this end, the present investigation examined sympathetic nervous system activation in healthy young and older adults using a standardized whole body skin surface cooling protocol via water-perfused suit (3,30,51,55). Consistent with a wide body of literature examining MSNA at rest in older adults at thermoneutrality (27,39,53), older adults in the present study exhibited increases in basal muscle sympathetic outflow. Furthermore, whole body cold stress elicited pronounced increases in MSNA burst frequency and strength in older, but not young, adults.…”

“…MSNA and plasma norepinephrine concentrations are elevated with advancing age (15,24,27,39,53); therefore, impairments in norepinephrine-mediated vasoconstriction have generally been attributed to sustained agonist-mediated desensitization in ␣-adrenergic receptor responsiveness (24). Conversely, the age-related increase in MSNA during cooling may be a compensatory response as a result of age-associated reductions in ␣-adrenergic receptor responsiveness.…”

The effect of gender on the sympathetic nerve hyperactivity of essential hypertension

“…However, greater arterial blood pressure levels in the EHT groups were associated with a greater rather than smaller sympathetic nerve activity than in the NC groups as has been commonly reported previously. [4][5][6][7][8]14 Also, there were no significant differences in arterial blood pressure levels between women and men within the EHT or the NC groups, although as has previously been reported elsewhere, 6,35,36 we found no significant correlation between sympathetic nerve activity and arterial blood pressure level in individual subjects. Indeed, the differences in sympathetic nerve activity between women and men within the EHT or the NC groups were greater than the variability attending repeated measurements of this activity.…”

Cardiac and peripheral autonomic control in restrictive cardiomyopathy

“…Several studies in heart failure patients show that sympathetic hyperactivity is triggered by lower BRS 33, 34, 35. We observed that spontaneous BRS is decreased either BRS+ or BRS− in patients with RCM.…”