Relationship between sympathetic nerve activity and aortic wave reflection characteristics in postmenopausal women

Relationships between muscle sympathetic nerve activity and novel indices of arterial stiffness using single oscillometric cuff in patients with hypertension

The arterial velocity pulse index (AVI) and arterial pressure-volume index (API) have been proposed as new arterial stiffness indices that can be measured using an oscillometric cuff. Sympathetic nerve activity (SNA) contributes to arterial stiffness via increasing vascular smooth muscle tone. However, the associations between SNA and the AVI or API are not understood. The purpose of this study was to evaluate the relationships between muscle sympathetic nerve activity (MSNA) and the AVI or API in healthy individuals and patients with hypertension (HT). Forty healthy individuals (40.1 ± 15.2 years, 8 females) (healthy group) and 40 patients with HT (60.2 ± 13.6, 18 females) (HT group) were included in this study. The AVI, API, MSNA, beat-by-beat blood pressure, and heart rate were recorded simultaneously. The AVI and API were higher in the HT group than in the healthy group (AVI, 26.1 ± 7.6 vs. 16.5 ± 4.0, p < 0.001; API, 31.2 ± 8.6 vs. 25.5 ± 7.2, p = 0.002). MSNA in the HT group was also higher than in the healthy group (p < 0.001). MSNA was correlated with the AVI, but not with the API, in both the healthy group (R = 0.52, p = 0.001) and HT group (R = 0.57, p < 0.001). MSNA was independently correlated with the AVI in multivariate analysis (ß = 0.34, p = 0.001). In conclusion, AVI, obtained by a simple and less user-dependent method, was related to the MSNA in healthy individuals and patients with HT.

Aortic haemodynamics: the effects of habitual endurance exercise, age and muscle sympathetic vasomotor outflow in healthy men

PURPOSE

We determined the effect of habitual endurance exercise and age on aortic pulse wave velocity (aPWV), augmentation pressure (AP) and systolic blood pressure (aSBP), with statistical adjustments of aPWV and AP for heart rate and aortic mean arterial pressure, when appropriate. Furthermore, we assessed whether muscle sympathetic nerve activity (MSNA) correlates with AP in young and middle-aged men.

METHODS

Aortic PWV, AP, aortic blood pressure (applanation tonometry; SphygmoCor) and MSNA (peroneal microneurography) were recorded in 46 normotensive men who were either young or middle-aged and endurance-trained runners or recreationally active nonrunners (10 nonrunners and 13 runners within each age-group). Between-group differences and relationships between variables were assessed via ANOVA/ANCOVA and Pearson product-moment correlation coefficients, respectively.

RESULTS

Adjusted aPWV and adjusted AP were similar between runners and nonrunners in both age groups (all, P > 0.05), but higher with age (all, P < 0.001), with a greater effect size for the age-related difference in AP in runners (Hedges' g, 3.6 vs 2.6). aSBP was lower in young (P = 0.009; g = 2.6), but not middle-aged (P = 0.341; g = 1.1), runners compared to nonrunners. MSNA burst frequency did not correlate with AP in either age group (young: r = 0.00, P = 0.994; middle-aged: r = - 0.11, P = 0.604).

CONCLUSION

There is an age-dependent effect of habitual exercise on aortic haemodynamics, with lower aSBP in young runners compared to nonrunners only. Statistical adjustment of aPWV and AP markedly influenced the outcomes of this study, highlighting the importance of performing these analyses. Further, peripheral sympathetic vasomotor outflow and AP were not correlated in young or middle-aged normotensive men.

Effect of Menopause on Arterial Stiffness and Central Hemodynamics: A Pulse Wave Analysis-Based Cross-sectional Study from Gujarat, India

Background:

Menopause, a cardiovascular risk in mid-life women, is studied in terms of blood pressure mostly. Arterial stiffness (AS) and central hemodynamics (CH) are direct surrogates measured by pulse wave analysis (PWA) with no study from our region.

Objective:

We studied AS, CH in relation to menopause using PWA.

Materials and Methods:

A cross-sectional study was performed in 134 middle-aged females divided into groups with or without menopause. Oscillometric PWA done by Mobil-o-Graph (IEM, Germany) gave – AS like augmentation pressure, augmentation index at heart rate (HR) 75, aortic pulse wave velocity (aPWV), and total AS pulse pressure amplification; CH like aortic blood pressure, cardiac output and related parameters, peripheral resistance, stroke work, prevalent brachial/central hypertension, and raised central pulse pressure. They were further compared between groups, in relation to body mass index (BMI) and by multiple regressions with P < 0.05 as statistical significance.

Results:

Postmenopausal women were significantly elder, physically inactive with comparable BMI and showed higher AS (only aPWV was significantly different) and CH. BMI was unrelated to AS or CH in postmenopausal group. Age (except for aPWV), BMI, and HR (except for AIx@75) were insignificant predictors, while systolic blood pressure (SBP) in premenopausal and diastolic blood pressure (DBP) in postmenopausal group was major AS predictors. Age, HR, and BMI were insignificant predictors, while SBP more than DBP was significant predictors of CH.

Conclusions:

In obese, predominantly sedentary midlife Gujarati women, menopause negatively affects AS and hemodynamics, central more than peripheral. Menopause accelerates cardiovascular aging, independent of BMI, and age that calls for further studies.

Sympathetic neural modulation of arterial stiffness in humans

Elevated large-artery stiffness is recognized as an independent predictor of cardiovascular and all-cause mortality. The mechanisms responsible for such stiffening are incompletely understood. Several recent cross-sectional and acute experimental studies have examined whether sympathetic outflow, quantified by microneurographic measures of muscle sympathetic nerve activity (MSNA), can modulate large-artery stiffness in humans. A major methodological challenge of this research has been the capacity to evaluate the independent neural contribution without influencing the dynamic blood pressure dependence of arterial stiffness. The focus of this review is to summarize the evidence examining 1) the relationship between resting MSNA and large-artery stiffness, as determined by carotid-femoral pulse wave velocity or pulse wave reflection characteristics (i.e., augmentation index) in men and women; 2) the effects of acute sympathoexcitatory or sympathoinhibitory maneuvers on carotid-femoral pulse wave velocity and augmentation index; and 3) the influence of sustained increases or decreases in sympathetic neurotransmitter release or circulating catecholamines on large-artery stiffness. The present results highlight the growing evidence that the sympathetic nervous system is capable of modulating arterial stiffness independent of prevailing hemodynamics and vasomotor tone.

Autonomic nervous system in Takotsubo syndrome

Takotsubo syndrome (TTS) is an acute and usually reversible heart failure syndrome with symptoms resembling acute myocardial infarction, however, without obstruction of coronary arteries. In the majority of cases, TTS is preceded by emotional or physical stress and the disease concerns mainly postmenopausal women. Although several hypotheses have been introduced, the pathogenesis of TTS is controversial and still remains to be determined. As reported in recent studies, the role of the autonomic nervous system (ANS) seems to be pivotal in the pathogenesis of TTS. Therefore, the aim of this article is to summarize and discuss the current knowledge of the pathogenesis of TTS with a special focus on the ANS.

The Acute Effects of High-Intensity Cycling Exercise on Arterial Stiffness in Adolescent Wrestlers

The aim of this study was to determine the acute effects of high‐intensity cycling exercise on the variables of carotid artery compliance, distensibility and beta stiffness index in elite adolescent wrestlers. The subjects were elite athletes competing in national, European and World Championships, who attended a training camp in the province of Kahramanmaras organized by the Turkish Centre for Olympic Preparation. The study sample comprised 31 male elite wrestlers with a mean age of 15.90 ± 0.87 years, body height of 165.97 ± 9.7 cm and body mass of 66.3 ± 18.45 kg. The arterial stiffness variables of the wrestlers were measured with high‐resolution Doppler ultrasonography before and 5 min after 30 s of high‐intensity cycling exercise (the Wingate Anaerobic Cycling test). The results showed a statistically significant correlation between mean power performance and carotid artery compliance at the 5th min after a single cycling sprint exercise (p < 0.05). No correlation was determined between peak power and the arterial stiffness variables (p > 0.05). The study results indicate that acute changes in arterial stiffness variables are associated with the performance level of high‐intensity cycling exercise in a group of elite adolescent wrestlers.

Age-Associated Differences in Central Artery Responsiveness to Sympathoexcitatory Stimuli

BACKGROUND

Age-associated arterial stiffening may be the result of greater tonic sympathetic nerve activity. However, age-associated changes in central artery responsiveness to sympathoexcitatory stimuli are understudied. Therefore, we examined changes in central artery stiffness and wave reflection in response to sympathoexcitatory stimuli in young and older adults.

METHODS

Fourteen young (25 ± 4 years) and 15 older (68 ± 4 years) subjects completed 3 minutes of the cold pressor test (CPT) and lower-body negative pressure (LBNP) separated by 15 minutes. Carotid-femoral pulse wave velocity (cfPWV), central augmentation pressure (cAP), and augmentation index (AIx) were measured in duplicate during rest and the final minute of each perturbation.

RESULTS

Young subjects had lower baseline cfPWV, cAP, and AIx than older subjects (P < 0.05 for all). During the CPT mean arterial pressure (MAP), cfPWV, cAP, and AIx increased in both groups (P < 0.05 for all); however, changes (Δ) in MAP (18 ± 7 vs. 9 ± 5 mm Hg), cfPWV (1.3 ± 0.7 vs. 0.6 ± 0.9 m/s), cAP (4 ± 2 vs. 6 ± 3 mm Hg), and AIx (18 ± 9% vs. 7 ± 4%) were greater in young vs. older subjects, respectively (P < 0.05 for all). With MAP as a covariate, cfPWV, cAP, and AIx responses to the CPT were no longer significantly different between groups. During LBNP, changes in MAP (-1 ± 3 vs. -3 ± 5 mm Hg), cfPWV (0.5 ± 0.3 vs. 0.5 ± 0.7 m/s), cAP (-2 ± 2 vs. -2 ± 3 mm Hg), and AIx (-7 ± 7% vs. -3 ± 6%) were similar between young and older groups, respectively (P > 0.05 for all).

CONCLUSIONS

Collectively, our data suggest the sympathetic nervous system may directly modulate central hemodynamics and that age-associated differences in central artery responsiveness to sympathoexcitatory stimuli are largely attributable to differential blood pressure responses.

Heart Failure-Specific Relationship Between Muscle Sympathetic Nerve Activity and Aortic Wave Reflection

BACKGROUND

Reflected arterial waves contribute to left ventricular (LV) afterload. Heart failure patients with reduced ejection fraction (HFrEF) are afterload sensitive and sympathetically activated. We tested the hypothesis that HFrEF patients exhibit a positive relationship between sympathetic vasoconstrictor discharge and aortic wave reflection.

METHODS

Sixteen treated patients with HFrEF (61 ± 9 years of age, left ventricular ejection fraction 30 ± 7%, 3 women) and 16 similar-aged healthy control subjects (57 ± 7 years of age, 4 women) underwent noninvasive measurements of radial pulse waveforms (applanation tonometry) to calculate central blood pressures and aortic wave reflection characteristics: augmentation pressure (AP), augmentation index (AI_x), and AI_x corrected to a heart rate of 75 beats/min (AI_x@75). Muscle sympathetic nerve activity (MSNA) burst frequency was recorded from the fibular nerve (microneurography).

RESULTS

HFrEF patients had higher AI_x (26 ± 9 vs 17 ± 15%; P < .05) and MSNA burst frequency (48 ± 7 vs 39 ± 11 bursts/min; P < .05) and lower central diastolic pressure than control subjects (64 ± 8 vs 70 ± 9 mm Hg; P = 0.05). There were no between-group differences in heart rate, other measures of blood pressure (brachial and central; P > .05), AP (11 ± 5 vs 7 ± 8 mm Hg; P = 0.11), or AI_x@75 (19 ± 9 vs 13 ± 11%,-P = 0.14). MSNA correlated positively with AP (r = 0.50; P < .05), AI_x (r = 0.51; P < .05), and AI_x@75 (r = 0.54; P < .05) in HFrEF patients but not in control subjects (r = 0.002-0.18; P > 0.49).

CONCLUSIONS

In patients with HFrEF, but not similarly aged healthy subjects, indices of aortic wave reflection correlate positively with MSNA. By increasing LV afterload, such neurovascular coupling could impair LV performance and worsen heart failure symptoms. Therapies that attenuate neurogenic vasoconstriction may benefit HFrEF patients by diminishing arterial wave reflection.

The effect of acute maximal exercise on postexercise hemodynamics and central arterial stiffness in obese and normal-weight individuals

Central arterial stiffness is associated with incident hypertension and negative cardiovascular outcomes. Obese individuals have higher central blood pressure (BP) and central arterial stiffness than their normal‐weight counterparts, but it is unclear whether obesity also affects hemodynamics and central arterial stiffness after maximal exercise. We evaluated central hemodynamics and arterial stiffness during recovery from acute maximal aerobic exercise in obese and normal‐weight individuals. Forty‐six normal‐weight and twenty‐one obese individuals underwent measurements of central BP and central arterial stiffness at rest and 15 and 30 min following acute maximal exercise. Central BP and normalized augmentation index (AIx@75) were derived from radial artery applanation tonometry, and central arterial stiffness was obtained via carotid‐femoral pulse wave velocity (cPWV) and corrected for central mean arterial pressure (cPWV/cMAP). Central arterial stiffness increased in obese individuals but decreased in normal‐weight individuals following acute maximal exercise, after adjusting for fitness. Obese individuals also exhibited an overall higher central BP (P < 0.05), with no exercise effect. The increase in heart rate was greater in obese versus normal‐weight individuals following exercise (P < 0.05), but there was no group differences or exercise effect for AIx@75. In conclusion, obese (but not normal‐weight) individuals increased central arterial stiffness following acute maximal exercise. An assessment of arterial stiffness response to acute exercise may serve a useful detection tool for subclinical vascular dysfunction.

Inorganic nitrate supplementation attenuates peripheral chemoreflex sensitivity but does not improve cardiovagal baroreflex sensitivity in older adults

Aging is associated with increased peripheral chemoreceptor activity, reduced nitric oxide (NO) bioavailability, and attenuation of cardiovagal baroreflex sensitivity (BRS), collectively increasing the risk of cardiovascular disease. Evidence suggests that NO may attenuate peripheral chemoreflex sensitivity and increase BRS. Exogenous inorganic nitrate ([Formula: see text]) increases NO bioavailability via the [Formula: see text]-[Formula: see text]-NO pathway. Our hypothesis was that inorganic [Formula: see text] supplementation would attenuate peripheral chemoreflex sensitivity and enhance spontaneous cardiovagal BRS in older adults. We used a randomized, placebo-controlled crossover design in which 13 older (67 ± 3 yr old) adults ingested beetroot powder containing (BR_A) or devoid of (BR_P) [Formula: see text] and [Formula: see text] daily over 4 wk. Spontaneous cardiovagal BRS was assessed over 15 min of rest and was quantified using the sequence method. Chemoreflex sensitivity was assessed via ~5 min of hypoxia (10% fraction of inspired O₂) and reported as the slope of the relationship between O₂ saturation (%[Formula: see text]) and minute ventilation (in l/min) or heart rate (in beats/min). Ventilatory responsiveness to hypoxia was reduced after BR_A (from -0.14 ± 0.04 to -0.05 ± 0.02 l·min^-1·%[Formula: see text]^-1, P = 0.01) versus BR_P (from -0.10 ± 0.05 to -0.11 ± 0.05 l·min^-1·%[Formula: see text]^-1, P = 0.80), with no differences in heart rate responsiveness (BR_A: from -0.47 ± 0.06 to -0.33 ± 0.04 beats·min^-1·%[Formula: see text]^-1, BR_P: from -0.48 ± 0.07 to -0.42 ± 0.06 beats·min^-1·%[Formula: see text]^-1) between conditions (interaction effect, P = 0.41). Spontaneous cardiovagal BRS was unchanged after BR_A and BR_P (interaction effects, P = 0.69, 0.94, and 0.39 for all, up, and down sequences, respectively), despite a reduction in resting systolic and mean arterial blood pressure in the experimental (BR_A) group ( P < 0.01 for both). These findings illustrate that inorganic [Formula: see text] supplementation attenuates peripheral chemoreflex sensitivity without concomitant change in spontaneous cardiovagal BRS in older adults. NEW & NOTEWORTHY Exogenous inorganic nitrate supplementation attenuates ventilatory, but not heart rate, responsiveness to abbreviated hypoxic exposure in older adults. Additionally, inorganic nitrate reduces systolic and mean arterial blood pressure without affecting spontaneous cardiovagal baroreflex sensitivity. These findings suggest that inorganic nitrate may attenuate sympathetically oriented pathologies associated with aging.

Sex-specific factors regulating pressure and flow

NEW FINDINGS

What is the topic of this review? There are sex- and sex-hormone-specific differences in autonomic control of blood pressure, central haemodynamics and cerebral blood flow. What advances does it highlight? Sex differences in autonomic control of blood pressure may underlie other sex-specific characteristics associated with cerebral blood flow, which can, in turn, affect tissue function. Over the last decade, there have been many published reports on sex differences in blood pressure regulation between young men and young women. The autonomic nervous system is a primary contributor to both acute and long-term blood pressure regulation. Sex differences in blood pressure regulation are likely to have effects that extend beyond mean arterial pressure and that can affect blood flow and tissue function. This short review includes recent literature from our laboratory focusing on autonomic control of the circulation, specifically age- and sex-hormone-related differences in central haemodynamics and cerebral blood flow, and discusses potential clinical implications.

Influence of sympathetic nerve activity on aortic hemodynamics and pulse wave velocity in women

Central (aortic) blood pressure, arterial stiffness, and sympathetic nerve activity increase with age in women. However, it is unknown if the age-related increase in sympathetic activity influences aortic hemodynamics and carotid-femoral pulse wave velocity (cfPWV), an index of central aortic stiffness. The goal of this study was to determine if aortic hemodynamics and cfPWV are directly influenced by sympathetic nerve activity by measuring aortic hemodynamics, cfPWV, and muscle sympathetic nerve activity (MSNA) in women before and during autonomic ganglionic blockade with trimethaphan camsylate. We studied 12 young premenopausal (23 ± 4 yr) and 12 older postmenopausal (57 ± 3 yr) women. These women did not differ in body mass index or mean arterial pressure (P > 0.05 for both). At baseline, postmenopausal women had higher aortic pulse pressure, augmented pressure, augmentation index adjusted for a heart rate of 75 beats/min, wasted left ventricular pressure energy, and cfPWV than young women (P < 0.05). During ganglionic blockade, postmenopausal women had a greater decrease in these variables in comparison to young women (P < 0.05). Additionally, baseline MSNA was negatively correlated with the reductions in aortic pulse pressure, augmented pressure, and wasted left ventricular pressure energy during ganglionic blockade in postmenopausal women (P < 0.05) but not young women. Baseline MSNA was not correlated with the changes in augmentation index adjusted for a heart rate of 75 beats/min or cfPWV in either group (P > 0.05 for all). Our results suggest that some aortic hemodynamic parameters are influenced by sympathetic activity to a greater extent in older postmenopausal women than in young premenopausal women.NEW & NOTEWORTHY Autonomic ganglionic blockade results in significant decreases in multiple aortic pulse wave characteristics (e.g., augmented pressure) and central pulse wave velocity in older postmenopausal women but not in young premenopausal women. Certain aortic pulse wave parameters are negatively influenced by sympathetic activity to a greater extent in older postmenopausal women.

Sympathetic regulation of blood pressure in normotension and hypertension: when sex matters

NEW FINDINGS

What is the topic of this review? Hypertension is a major problem in Western society. Risk of hypertension increases with age, especially in women, who have lower risk compared with men until menopause. This review outlines the sex differences in the sympathetic control of blood pressure and how these mechanisms change with age. What advances does it highlight? It has recently been recognized that men and women regulate blood pressure by different physiological mechanisms. This is important for both the understanding and the clinical management of individual patients with hypertension. This review summarizes recent advances in understanding how the regulation of blood pressure in hypertension by the sympathetic nervous system differs between men and women. The sympathetic nervous system has a central role in the regulation of arterial blood pressure (BP) and in the development of hypertension in humans. Recent evidence points to differences between the sexes in the integrative mechanisms by which BP is controlled, suggesting that the development of hypertension may follow distinct pathways in women compared with men. An important aspect of sympathetic control of BP is its substantial interindividual variability. In healthy young men, the variability in sympathetic nerve activity (SNA) is balanced by variability in cardiac output and vascular adrenergic responses, such that BP remains similar, and normal, across a severalfold range of resting SNA values. In young women, variability in resting SNA is similar to that seen in men, but the 'balancing' mechanisms are strikingly different; women exhibit greater β-adrenergic vasodilatation compared with men, which minimizes the pressor effects of a given level of SNA. Ageing is associated with increased SNA and a loss of the balancing factors seen in younger people, leading to an increased risk of hypertension in older people. Loss of oestrogen with menopause in women appears to be linked mechanistically with the decrease in β-adrenergic vasodilatation and the increased risk of hypertension in older women. Other important factors contributing to hypertension via sympathetic mechanisms are obesity and arterial stiffening, both of which increase with ageing. We conclude with a discussion of important areas in which more work is needed to understand and manage appropriately the sex-specific mechanisms in the development and maintenance of hypertension.

Combined whole-body vibration training and l-citrulline supplementation improves pressure wave reflection in obese postmenopausal women

Postmenopausal women have increased wave reflection (augmentation pressure (AP) and index (AIx)) and reduced muscle function that predispose them to cardiac diseases and disability. Our aim was to examine the combined and independent effects of whole-body vibration training (WBVT) and l-citrulline supplementation on aortic hemodynamics and plasma nitric oxide metabolites (NOx) in postmenopausal women. Forty-one obese postmenopausal women were randomized to 3 groups: l-citrulline, WBVT+l-citrulline and WBVT+Placebo for 8 weeks. Brachial and aortic systolic blood pressure, diastolic blood pressure, AP, AIx, AIx adjusted to 75 beats/min (AIx@75), and NOx were measured before and after 8 weeks. All groups similarly decreased (P < 0.05) brachial and aortic pressures as well as AP, and similarly increased (P < 0.05) NOx levels. AIx and AIx@75 decreased (P < 0.01) in the WBVT+l-citrulline and WBVT+Placebo groups, but not in the l-citrulline group. The improvement in AIx@75 (−10.5% ± 8.8%, P < 0.05) in the WBVT+l-citrulline group was significant compared with the l-citrulline group. l-Citrulline supplementation and WBVT alone and combined decreased blood pressures. The combined intervention reduced AIx@75. This study supports the effectiveness of WBVT+l-citrulline as a potential intervention for prevention of hypertension-related cardiac diseases in obese postmenopausal women.

Tetrahydrobiopterin lowers muscle sympathetic nerve activity and improves augmentation index in patients with chronic kidney disease

Chronic kidney disease (CKD) is characterized by overactivation of the sympathetic nervous system (SNS) that contributes to cardiovascular risk. Decreased nitric oxide (NO) bioavailability is a major factor contributing to SNS overactivity in CKD, since reduced neuronal NO leads to increased central SNS activity. Tetrahydrobiopterin (BH4) is an essential cofactor for nitric oxide synthase that increases NO bioavailability in experimental models of CKD. We conducted a randomized, double-blinded, placebo-controlled trial testing the benefits of oral sapropterin dihydrochloride (6R-BH4, a synthetic form of BH4) in CKD. 36 patients with CKD and hypertension were randomized to 12 wk of 1) 200 mg 6R-BH4 twice daily + 1 mg folic acid once daily; vs. 2) placebo + folic acid. The primary endpoint was a change in resting muscle sympathetic nerve activity (MSNA). Secondary endpoints included arterial stiffness using pulse wave velocity (PWV) and augmentation index (AIx), endothelial function using brachial artery flow-mediated dilation and endothelial progenitor cells, endothelium-independent vasodilatation (EID), microalbuminuria, and blood pressure. We observed a significant reduction in MSNA after 12 wk of 6R-BH4 (-7.5 ± 2.1 bursts/min vs. +3.2 ± 1.3 bursts/min; P = 0.003). We also observed a significant improvement in AIx (by -5.8 ± 2.0% vs. +1.8 ± 1.7 in the placebo group, P = 0.007). EID increased significantly (by +2.0 ± 0.59%; P = 0.004) in the 6R-BH4 group, but there was no change in endothelial function. There was a trend toward a reduction in diastolic blood pressure by -4 ± 3 mmHg at 12 wk with 6R-BH4 (P = 0.055). 6R-BH4 treatment may have beneficial effects on SNS activity and central pulse wave reflections in hypertensive patients with CKD.

Sympathetic neural regulation of blood pressure: influences of sex and aging

Sex and age have important influences on sympathetic neural control of blood pressure in humans. Young women are relatively protected against risk of hypertension due to greater peripheral vasodilator influences compared with young men and older people. This protective effect is lost at menopause. Older men and women have higher sympathetic nerve activity and tighter coupling between SNA and blood pressure, contributing to the increased risk of hypertension with aging.