Resting sympathetic outflow does not predict the morning blood pressure surge in hypertension

Role of basal autonomic functions in patients with increased morning blood pressure surge

BACKGROUND

Morning blood pressure (BP) surge (MS) is associated with cardiovascular events. The autonomic nervous system plays an active role in the regulation of BP and its function can be evaluated by heart rate variability (HRV) analysis. This study aimed to evaluate autonomic nervous system functions in patients with increased MS.

METHODS

Patients who underwent ambulatory BP monitoring (ABPM) and 24-h rhythm Holter in our hospital during the same period between 2017 and 2022 were evaluated. HRV parameters were obtained from 24-h rhythm Holter recordings. MS values of the patients were calculated from ABPM records and patients were divided into four groups according to the MS quartiles. HRV parameters and other parameters were compared between the groups.

RESULTS

A total of 129 patients were included in the study. The mean age of the patients was 57.2 ± 18.2 years, and 63 (48.8%) were male. HF, the square root of the mean squared differences of successive normal-to-normal intervals (rMSSD), and the proportion of adjacent RR intervals differing by >50 ms in the 24-h recording (pNN50) were statistically significant between the groups ( P  = 0.039, P  = 0.013, P  = 0.011, respectively). In univariate regression analysis, low-frequency/high-frequency ratio was positively associated with MS and HF, SDNNi, rMSSD, and pNN50 were negatively associated ( β  = 0.207, P  = 0.019; β  = -0.272, P  = 0.002; β  = -0.201, P  = 0.022; β  = -0.265, P  = 0.002; β  = -0.278, P  = 0.001, respectively). Multiple linear regression analysis showed an independent association between HF, low-frequency/high-frequency ratio, rMSSD, pNN50, and MS ( β  = -0.247, P  = 0.005; β=0.206, P  = 0.017; β  = -0.209, P  = 0.005; β  = -0.227, P  = 0.008, respectively).

CONCLUSION

We found an independent association between HRV parameters associated with vagal tone and MS. The findings of our study suggest that the increased sympathetic activity detected in patients with high MS in previous studies may be due to a decrease in basal vagal tone.

Association of Morning Surge and Postexercise Heart Rate and Blood Pressure Recovery

INTRODUCTION

The autonomic nervous system plays an active role in the regulation of early morning blood pressure (BP) and BP/pulse regulation in the treadmill exercise test (TET).

AIM

We evaluated the relationship between BP/pulse changes during TET and morning blood pressure surge (MS).

METHODS

Patients who underwent ambulatory blood pressure measurement (ABPM) and TET in the same visit between 2017 and 2020 were evaluated retrospectively. Patients with previously diagnosed hypertension and/or using antihypertensives and office BP ≥ 140/90 were excluded from the study.MS values and dipping percentage were calculated from ABPM data. The patients were analyzed by dividing them into two groups according to the MS median, and BP/pulse values during exercise and recovery periods were compared in these groups.

RESULTS

202 patients [median age 45 (39-51), male 134 (66.3%)] were included in the study. MS median was 18.5 (10.75-27) mmHg. TET recovery period 3rd-min systolic blood pressure (RSBP) was higher in the group with high MS (p: 0.017). Systolic and diastolic dipping percentages were higher in the group with higher MS (p: 0.015, p: 0.040, respectively). Peak systolic and diastolic BP, RSBP, and recovery 3rd min diastolic BP were positively correlated with MS (p < 0.05, for all). Additionally, an independent relationship was observed between RSBP and MS (β: 0.205, p: 0.028).

CONCLUSION

We found an independent association between RSBP and MS. Increased RSBP may be associated with target organ damage and cardiovascular events such as MS.

Nocturnal blood pressure is associated with sympathetic nerve activity in patients with chronic kidney disease

Elevated nocturnal blood pressure (BP) and nocturnal non-dipping are frequently observed in patients with chronic kidney disease (CKD) and are stronger predictors of cardiovascular complications and CKD progression than standard office BP. The sympathetic nervous system (SNS) is thought to modulate diurnal hemodynamic changes and the vascular endothelium plays a fundamental role in BP regulation. We hypothesized that SNS overactivity and endothelial dysfunction in CKD are linked to elevated nocturnal BP and non-dipping. In 32 CKD patients with hypertension (56 ± 7 years), office BP, 24-hr ambulatory BP, muscle sympathetic nerve activity (MSNA) and endothelial function via flow-mediated dilation (FMD) were measured. Participants were subsequently divided into dippers (nighttime average BP > 10% lower than the daytime average BP, n = 8) and non-dippers (n = 24). Non-dippers had higher nighttime BP (p < .05), but not office and daytime BP, compared to dippers. MSNA burst incidence (81 ± 13 versus 67 ± 13 bursts/100 HR, p = .019) was higher and brachial artery FMD (1.7 ± 1.5 versus 4.7 ± 1.9%, p < .001) was lower in non-dippers compared to dippers. MSNA and FMD each predicted nighttime systolic (β = 0.48,-0.46, p = .02, 0.07, respectively) and diastolic BP (β = 0.38,-0.47, p = .04, 0.03, respectively) in multivariate-adjusted analyses. Our novel findings demonstrate that unfavorable nocturnal BP profiles are associated with elevated SNS activity and endothelial dysfunction in CKD. Specifically, CKD patients with higher nighttime BP and the non-dipping pattern have higher MSNA and lower FMD. These support our hypothesis that SNS overactivation and endothelial dysfunction are linked to the dysregulation of nighttime BP as well as the magnitude of BP lowering at nighttime in CKD.

Repeatability and reproducibility of pulse wave velocity in relation to hemodynamics and sodium excretion in stable patients with hypertension

OBJECTIVE

Pulse wave velocity (PWV) is a useful marker for determining subclinical vascular damage and patient risk stratification. Repeatability and reproducibility of PWV in relation to influencing factors have not yet been determined. This study examined the repeatability and reproducibility of PWV, and whether hemodynamics and sodium excretion impact on PWV in hypertensive patients remaining on stable medication.

METHODS

Office blood pressure (BP), heart rate (HR), carotid--femoral PWV and central BP (SphygmoCor device), impedance cardiography (HOTMAN device) and 24-h urinary sodium excretion (UNa) were measured at baseline and after 4 weeks in 74 hypertensive patients (age 56.8 ± 11.5 years, mean ± SD). Two PWV measurements were performed at each visit.

RESULTS

Intraclass correlation coefficient (ICC) and 95% confidence interval (95% CI) between the two PWV measurements were 0.981 (0.970--0.988) at baseline, 0.975 (0.960--0.984) after 4 weeks and 0.851 (0.773--0.903) between both visits. There were no significant changes in BP, HR, thoracic fluid content, stroke volume and UNa between visits. Despite excellent ICC, reproducibility of PWV was related to BP (P < 0.001) and HR (P = 0.07) changes between visits. Nineteen out of 74 patients had a difference in PWV greater than ±1 m/s between both visits.

CONCLUSION

In the medium-term observation, changes in BP and HR seem to affect PWV values. Our findings suggest that the assessment of PWV should be performed under stabilized BP and HR values, particularly in patients with newly diagnosed hypertension and/or low--moderate cardiovascular risk in whom the detection of asymptomatic hypertension-mediated organ damage impact on patient risk stratification.

Morning blood pressure surge is associated with autonomic neuropathy and peripheral vascular disease in patients with diabetes

Although vascular and autonomic nervous system have been involved in the regulation of morning surge in blood pressure (MBPS), data on clinical correlates of MBPS in diabetic population are scarce, in particular with regard to diabetic complications. This study was aimed at investigating predictors and correlates of MBPS in diabetes. In a cross-sectional study including 167 patients with diabetes (age 58.5 ± 11.1 years, duration 15.9 ± 12.1 years), clinical variables, diabetic and neuropathic complications, and MBPS (using 24-h ambulatory blood pressure monitoring) were measured. The upper quartile of MBPS (>30.5 mmHg) was associated with higher values of waist circumference (P = 0.027), triglycerides (P = 0.021), and Michigan Diabetic Neuropathy Score (P = 0.042), with lower HDL cholesterol (P = 0.030), and with the presence of cardiovascular autonomic neuropathy (CAN) (P = 0.016) and peripheral vascular disease (PVD) (P < 0.0001). In a logistic regression analysis, PVD (odds ratio: 10.2, P = 0.001), CAN (odds ratio: 6.09, P = 0.016), and diastolic blood pressure (BP) (odds ratio: 1.06, P = 0.022) predicted MBPS upper quartile (r² = 0.20, P = 0.0005). In a multiple regression analysis, PVD (P = 0.002) and diastolic BP (P = 0.003) were the only determinants of MBPS (r² = 0.20). MBPS upper quartile was associated with BP dipping (systolic BP day-night reduction > 10%) (P = 0.012), and MBPS was positively related to systolic (rho = 0.41, P < 0.0001) and diastolic BP day-night reduction. In conclusion, metabolic syndrome stigmata, diastolic BP, CAN and PVD are the main predictors of MBPS in the diabetic population. Excessive MBPS and nondipping are not concurrent 24-h BP alterations. Autonomic dysfunction might exert an exacerbating effect on MBPS phenomenon.

Tachycardia: The hidden cardiovascular risk factor in uncomplicated arterial hypertension

Early detection and management of elevated blood pressure is crucial in reducing the burden of cardiovascular disease (CVD). The importance of an absolute risk assessment and patient risk stratification has been highlighted in the European hypertension guidelines since 2003. Amongst numerous risk factors influencing patient prognosis, elevated heart rate (HR) has been indicated as important predictor of future risk of hypertension, coronary heart disease, sudden cardiac death, heart failure, CVD, stroke, total cancer and mortality. Given that resting HR can be easily determined in clinical practice and modified by lifestyle changes as well as beta-blocker therapy, it seems reasonable that lowering resting HR should be a potential target to reduce disease burden and premature mortality. However, there is a lack of outcome studies of HR lowering in tachycardia-related hypertension. This review outlines the underlying mechanisms of early course hypertension pathophysiology with the critical role of the sympathetic nervous system activation, the prognostic significance of fast HR and the mechanistic rationale for the use of non-pharmacological approaches and/or highly long-acting cardioselective beta-blockers with some consideration given to betaxolol properties.

Long-term effects of device-guided slow breathing in stable heart failure patients with reduced ejection fraction

Background

Slow breathing (SLOWB) alleviates symptoms of chronic heart failure (HF) but its long-term effects are unknown. We examined the acute and long-term impact of device-guided breathing on hemodynamics and prognostic parameters in HF patients with reduced ejection fraction (HFrEF).

Methods and results

Twenty-one patients with HFrEF (23.9 ± 5.8%, SD ± mean) on optimal medical therapy underwent blood pressure (BP), heart rate (HR), HR variability, 6-min walk test (6MWT), cardiopulmonary exercise testing (CPET), and echocardiography measurements before and 3 months after SLOWB home training (30 min daily). After 3 months, all patients were assigned to continue SLOWB (Group 1) or no-SLOWB (Group 2). All tests were repeated after 6 months. Acute SLOWB (18 ± 5 vs 8 ± 2 breaths/min, P < 0.001) had no influence on BP and HR but improved saturation (97 ± 2 vs 98 ± 2%, P = 0.01). Long-term SLOWB reduced office systolic BP (P < 0.001) but not central or ambulatory systolic BP. SLOWB reduced SDNN/RMSSD ratio (P < 0.05) after 3 months. One-way repeated measures of ANOVA revealed a significant increase in 6MWT and peak RER (respiratory exchange ratio) from baseline to 6-month follow-up in group 1 (P < 0.05) but not group 2 (P = 0.85 for 6MWT, P = 0.69 for RER). No significant changes in echocardiography were noted at follow-up. No HF worsening, rehospitalisation or death occurred in group 1 out to 6-month follow-up. Two hospitalizations for HF decompensation and two deaths ensued in group 2 between 3- and 6-month follow-up.

Conclusions

SLOWB training improves cardiorespiratory capacity and appears to slow the progression of HFrEF. Further long-term outcome studies are required to confirm the benefits of paced breathing in HFrEF.

Morning blood pressure surge: pathophysiology, clinical relevance and therapeutic aspects

Morning hours are the period of the day characterized by the highest incidence of major cardiovascular events including myocardial infarction, sudden death or stroke. They are also characterized by important neurohormonal changes, in particular, the activation of sympathetic nervous system which usually leads to a rapid increase in blood pressure (BP), known as morning blood pressure surge (MBPS). It was hypothesized that excessive MBPS may be causally involved in the pathogenesis of cardiovascular events occurring in the morning by inducing hemodynamic stress. A number of studies support an independent relationship of MBPS with organ damage, cerebrovascular complications and mortality, although some heterogeneity exists in the available evidence. This may be due to ethnic differences, methodological issues and the confounding relationship of MBPS with other features of 24-hour BP profile, such as nocturnal dipping or BP variability. Several studies are also available dealing with treatment effects on MBPS and indicating the importance of long-acting antihypertensive drugs in this regard. This paper provides an overview of pathophysiologic, methodological, prognostic and therapeutic aspects related to MBPS.

Age-dependent sympathetic neural responses to ß1 selective beta-blockade in untreated hypertension-related tachycardia

BACKGROUND

Elevated heart rate (HR) increases cardiovascular morbidity and mortality in hypertension. The impact of beta-blockers on patient prognosis in hypertension is controversial. This study examined the age-related effects of betaxolol on HR, muscle sympathetic nerve activity (MSNA), blood pressure (BP) and sympathovagal balance in untreated males with hypertension and tachycardia.

METHODS

Ten young (age 26 ± 1 years) and seven older (age 50 ± 4 years) males underwent measurement of BP, HR, HR variability (Poincare plot) and MSNA before and after 8 weeks treatment with betaxolol at the initial starting dose of 10 mg/day, which was increased to 20 mg/day once daily after 4 weeks in all subjects.

RESULTS

In younger subjects, betaxolol decreased systolic BP (-13 ± 4 mm Hg, p = .01) and HR (-29 ± 4 bpm, p < .001) but not MSNA (3 ± 3 burst/min., p = 0.47) after 8 weeks. In older subjects a pronounced reduction in BP (-27 ± 7, p = .007) was accompanied by a significant decrease in MSNA (-13 ± 5 burst/min., p < .05) and HR (-17 ± 4 bpm, p = .002). SD1/SD2 ratio of Poincare plot increased in younger (0.36 ± 0.03 vs 0.51 ± 0.05, p = .004), but not in older (0.43 ± 0.08 vs 0.54 ± 0.12, p = .50) subjects.

CONCLUSION

Autonomic neural responses to betaxolol are age-dependent in hypertension-related tachycardia. Betaxolol reduces sympathetic drive to the heart, but not to the peripheral vessels confirming the contribution of augmented cardiac sympathetic activity to disease pathophysiology in younger adults. In older hypertensives, the sympathovagal balance is not influenced by betaxolol. The paradoxical reduction in MSNA despite lowering of BP and HR in older patients may suggest age-related functional decrements in autonomic control and/or inhibitory effects of betaxolol on the central nervous system.

Magnitude of Morning Surge in Blood Pressure Is Associated with Sympathetic but Not Cardiac Baroreflex Sensitivity

The ability of the arterial baroreflex to regulate blood pressure may influence the magnitude of the morning surge in blood pressure (MSBP). The aim was to investigate the relationships between sympathetic and cardiac baroreflex sensitivity (BRS) and the morning surge. Twenty-four hour ambulatory blood pressure was recorded in 14 young individuals. The morning surge was defined via the pre-awakening method, which is calculated as the difference between mean blood pressure values 2 h before and 2 h after rising from sleep. The mean systolic morning surge, diastolic morning surge, and morning surge in mean arterial pressures were 15 ± 2, 13 ± 1, and 11 ± 1 mmHg, respectively. During the laboratory protocol, continuous measurements of blood pressure, heart rate, and muscle sympathetic nerve activity (MSNA) were made over a 10-min period of rest. Sympathetic BRS was quantified by plotting MSNA burst incidence against diastolic pressure (sympathetic BRS_inc), and by plotting total MSNA against diastolic pressure (sympathetic BRS_total). Cardiac BRS was quantified using the sequence method. The mean values for sympathetic BRS_inc, sympathetic BRS_total and cardiac BRS were −1.26 ± 0.26 bursts/100 hb/mmHg, −1.60 ± 0.37 AU/beat/mmHg, and 13.1 ± 1.5 ms/mmHg respectively. Significant relationships were identified between sympathetic BRS_inc and the diastolic morning surge (r = 0.62, p = 0.02) and the morning surge in mean arterial pressure (r = 0.57, p = 0.03). Low sympathetic BRS was associated with a larger morning surge in mean arterial and diastolic blood pressure. Trends for relationships were identified between sympathetic BRS_total and the diastolic morning surge (r = 0.52, p = 0.066) and the morning surge in mean arterial pressure (r = 0.48, p = 0.095) but these did not reach significance. There were no significant relationships between cardiac BRS and the morning surge. These findings indicate that the ability of the baroreflex to buffer increases in blood pressure via reflexive changes in MSNA may play a role in determining the magnitude of the MSBP.

Longitudinal tracking of muscle sympathetic nerve activity and its relationship with blood pressure in subjects with prehypertension

Prehypertension is associated with increased cardiovascular events. While the "tracking phenomenon" is an important longitudinal characteristic of blood pressure (BP), changes in muscle sympathetic nerve activity (MSNA) over time remain unclear. This study tested the hypothesis that MSNA tracking contributes to BP trends in prehypertension. BP and MSNA were assessed in 13 prehypertensive males at rest, during hand grip and mental stressors at baseline and after 8 years. Baseline office BP averaged 127 ± 2/81 ± 2 mmHg and MSNA 24 ± 4 bursts/min. BP increased by 7 ± 2/5 ± 2 mmHg (P < 0.01) and MSNA by 11 ± 2 bursts/min (P < 0.001) at follow-up. SBP and DBP were interrelated at baseline (r = 0.65, P = 0.02) and at follow-up (r = 0.78, P = 0.002). MSNA tracking (r = 0.82; P < 0.001) was similar to BP. MSNA was strongly related to DBP at baseline (r = 0.73; P < 0.01) and follow-up (r = 0.64; P = 0.01), more so than SBP. BMI increased (P < 0.001) at follow-up but was unrelated to BP or MSNA. Despite comparable pressor and cardiac increases to handgrip and mental stressors, sympathetic responses were blunted, more pronounced to isometric test (P < 0.006) at follow-up. In conclusion, the trend in MSNA corresponds with BP changes over time suggesting that tonic sympathetic activation may contribute to time-related increase in resting BP and the development of sustained hypertension in prehypertension.

Blood pressure morning surge, exercise blood pressure response and autonomic nervous system

OBJECTIVE

We investigated blood pressure (BP) response to exercise with respect to BP morning surge (MS), and the association between MS, exercise treadmill test (ETT) and heart rate variability (HRV) indices.

DESIGN

Eighty-four healthy subjects without hypertension were enrolled. Ambulatory BP monitoring and 24-hour Holter recordings were obtained for sleep-trough MS and HRV indices: low-frequency (LF) component, high-frequency (HF) component and LF/HF ratio. ETT was performed, and BPs were obtained at rest, end of each stage, and recovery. Third-minute heart rate recovery (HRR) and BP recovery ratio (BPRR) were calculated.

RESULTS

When analysed in quartiles of MS, systolic BP at low workloads was higher in the highest than in the lowest quartile, although maximum BPs at maximum exercise were not significantly different. BPRR was highest in the highest quartile in contrast to HRR, which was lowest in the highest quartile. LF/HF was highest during both at daytime and night-time in the highest quartile. BPRR and LF/HF were positively, and HRR was inversely associated with MS.

CONCLUSIONS

Subjects with a high MS have higher BP at low workloads, at which most daily activities are performed, and impairment in some indices, which indirectly reflect the autonomic nervous system.

Chemoreflexes, sleep apnea, and sympathetic dysregulation

Obstructive sleep apnea (OSA) and hypertension are closely linked conditions. Disordered breathing events in OSA are characterized by increasing efforts against an occluded airway while asleep, resulting in a marked sympathetic response. This is predominantly due to hypoxemia activating the chemoreflexes, resulting in reflex increases in sympathetic neural outflow. In addition, apnea - and the consequent lack of inhibition of the sympathetic system that occurs with lung inflation during normal breathing - potentiates central sympathetic outflow. Sympathetic activation persists into the daytime, and is thought to contribute to hypertension and other adverse cardiovascular outcomes. This review discusses chemoreflex physiology and sympathetic modulation during normal sleep, as well as the sympathetic dysregulation seen in OSA, its extension into wakefulness, and changes after treatment. Evidence supporting the role of the peripheral chemoreflex in the sympathetic dysregulation seen in OSA, including in the context of comorbid obesity, metabolic syndrome, and systemic hypertension, is reviewed. Finally, alterations in cardiovascular variability and other potential mechanisms that may play a role in the autonomic imbalance in OSA are also discussed.

Morning blood pressure surge is associated with serum gamma-glutamyltransferase activity in essential hypertensive patients

The phenomenon that blood pressure rises sharply in the morning is called 'Morning Blood Pressure Surge' (MBPS). Serum gamma-glutamyltransferase (GGT) is a proinflammatory marker involved in the pathogenesis of cardiovascular diseases. Although both are novel cardiovascular risk factors associated with inflammation and atherosclerosis, the specific relationship between MBPS and serum GGT is unknown. This study investigates the relationship between MBPS and serum GGT activity in essential hypertensive patients. Totally, 320 hypertensive patients were recruited. Mean MBPS was 17.0 ± 12.9 mm Hg. MBPS was positively correlated with age (r = +0.222, P < 0.0001), body mass index (r = +0.132, P = 0.018), GGT (r = +0.271, P < 0.0001), daytime augmentation index adjusted for heart rate (AIx@75) (r = +0.140, P=0.014), 24-h pulse wave velocity (PWV) (r = +0.143, P = 0.014) and daytime PWV (r = +0.158, P = 0.007). From the 25th to 75th quartile of serum GGT, MBPS increased significantly (Ptrend < 0.0001). In multivariate linear regression analysis, MBPS was independently associated with age (P = 0.002), dipping status (P < 0.0001) and logGGT (P < 0.0001). In conclusion, MBPS is independently associated serum GGT activity in essential hypertensive patients. This is the first study in the literature to demonstrate an independent and a dose-response relationship between the two novel cardiovascular risk factors, MBPS and serum GGT, in this patient population.

Morning surge in blood pressure is associated with reactivity of the sympathetic nervous system

BACKGROUND

An exaggerated morning surge in blood pressure (BP) closely relates to target organ damage and cardiovascular risk, but whether the causative mechanism involves greater reactivity of the sympathetic nervous system (SNS) is unknown. We determined whether the response of the SNS to a cold pressor test predicted the BP morning surge.

METHODS

Ambulatory BP recordings were obtained from 14 men and 19 women (age = 41±4 years), and the amplitude (day-night difference), rate of rise (RoR), rate by amplitude product (BPPower), and morning BP surge (MBPS; post-awake minus pre-awake) of morning mean arterial pressure (MAP) were determined. The reactivity of the SNS to CPT was assessed by recording of muscle sympathetic nerve activity (MSNA).

RESULTS

CPT induced a marked increase in MAP and all parameters of MSNA, including burst amplitude. Log-normalized BPPower positively correlated with the overall average CPT-induced increases in total MSNA (r = 0.38; P = 0.04) and burst amplitude (r = 0.43; P = 0.02) but was not related to the increase in MSNA frequency. Furthermore, a strong positive linear trend in the CPT-induced changes in burst amplitude across tertiles of BPPower and RoR was observed. BPPower and RoR were not related to CPT-induced hemodynamic changes. The MBPS did not correlate with any of the CPT-induced changes in vascular or MSNA variables.

CONCLUSIONS

These results suggest that the central nervous system mechanisms influencing the increase in MSNA burst amplitude during arousal may also be fundamental in determining the rate and power of BP rise during the morning period.

Race, plasma renin activity, and morning blood pressure surge--results from the Dietary Approaches to Stop Hypertension trial

BACKGROUND

The association of preawake (difference between pre- and postwaking blood pressure (BP)) and sleep-through surge (difference between sleeping nadir and postwaking BP) with cardiovascular events is unclear. Examination of factors associated with surge may provide novel insights. We examined the association of race, which associates with nocturnal dipping, and plasma renin activity (PRA) with preawake and sleep-through surge among individuals on a controlled diet.

METHODS

We performed a post hoc analysis of 323 subjects from the Dietary Approaches to Stop Hypertension trial who had available 24-hour BP data and who ingested a control diet during a 3-week run-in period. Linear regression models were fit to estimate the association of race and PRA with preawake and sleep-through surge.

RESULTS

Of the 323 individuals, 55% were black, 53% were men, and the average age was 45 years. After controlling for other factors, black race was associated with a 3.2mm Hg lower preawake and a 3.7mm Hg lower sleep-through surge compared with nonblacks. In nonblacks, higher PRA was associated with greater preawake surge only. There was no association of PRA with either preawake or sleep-through surge in blacks. Additional adjustment for dipping status resulted in attenuation of the race-surge associations.

CONCLUSIONS

Black race is associated with lower preawake and sleep-through surge compared with nonblacks, but the effect is partially attenuated by dipping status. Higher PRA appears to be associated with a higher preawake surge in nonblacks only. Further research should address if morning surge is definitively associated with clinical outcomes in racial subgroups, independent of dipping.

Effects of acute and long-term slow breathing exercise on muscle sympathetic nerve activity in untreated male patients with hypertension

OBJECTIVE

Acute slow breathing (SLOWB) affects sympathetic cardiovascular regulation, but its long-term effects are unknown. Using device-guided breathing we explored short-term and long-term SLOWB effects on blood pressure (BP), heart rate (HR) and muscle sympathetic nerve activity (MSNA) in essential hypertension.

METHODS

We measured BP, HR and MSNA in 10 hypertensive individuals at rest, during laboratory stressors, before and after acute SLOWB, and 8 weeks after SLOWB exercise. Twelve matched hypertensive controls underwent a similar protocol excluding SLOWB intervention. Office and 24-h BP were obtained at baseline and at follow-up.

RESULTS

Acute SLOWB had no influence on BP, HR, but decreased MSNA (P < 0.01). BP, HR, MSNA responses to handgrip were comparable before and after acute SLOWB. Acute SLOWB tended to reduce SBP (P = 0.09), HR (P = 0.08), but not MSNA (P = 0.20) responses to mental stress. Long-term SLOWB decreased office SBP (P < 0.001), DBP (P < 0.01), HR (P = 0.004), but not 24-h BP. Resting MSNA was unchanged after long-term SLOWB (P = 0.68). Long-term SLOWB did not influence BP, HR or MSNA responses to handgrip and cold pressor, but reduced SBP (P = 0.03), HR (P = 0.03) responses to mental stress without MSNA changes. In controls BP, HR, MSNA responses to laboratory stressors remained unchanged at baseline and at follow-up.

CONCLUSION

In essential hypertension, MSNA is reduced during acute SLOWB, but remains unaltered following long-term SLOWB. Long-term SLOWB reduces office, but not ambulatory BP and HR. SLOWB attenuates cardiovascular response to mental stress, but not physical stressors. These findings may be indicative of beneficial SLOWB effects on stress reduction in essential hypertension.

Morning blood pressure surge is associated with arterial stiffness and sympathetic baroreflex sensitivity in hypertensive seniors

Morning blood pressure (BP) surge is considered to be an independent risk factor for cardiovascular diseases. We tested the hypothesis that increased large-artery stiffness and impaired sympathetic baroreflex sensitivity (BRS) contribute to augmented morning surge in elderly hypertensive subjects. Morning surge was assessed as morning systolic BP averaged for 2 h just after waking up minus minimal sleeping systolic BP by using ambulatory BP monitoring (ABPM) in 40 untreated hypertensive [68 ± 1 (SE) yr] and 30 normotensive (68 ± 1 yr) subjects. Beat-by-beat finger BP and muscle sympathetic nerve activity (MSNA) were recorded in the supine position and at 60° upright tilt. We assessed arterial stiffness with carotid-to-femoral pulse wave velocity (cfPWV) and sympathetic BRS during spontaneous breathing. Awake and asleep ABPM-BPs and morning surge were higher in hypertensive than normotensive subjects (all P < 0.001). cfPWV was higher (P = 0.002) and sympathetic BRS was lower (P = 0.096) in hypertensive than normotensive subjects. Hypertensive subjects with morning surge ≥35 mmHg (median value) had higher cfPWV (11.9 ± 0.5 vs. 9.9 ± 0.4 m/s, P = 0.002) and lower sympathetic BRS (supine: -2.71 ± 0.25 vs. -3.73 ± 0.29, P = 0.011; upright: -2.62 ± 0.22 vs. -3.51 ± 0.35 bursts·100 beats(-1)·mmHg(-1), P = 0.052) than those with morning surge <35 mmHg. MSNA indices were similar between groups (all P > 0.05), while upright total peripheral resistance was higher in hypertensive subjects with greater morning surge than those with lesser morning surge (P = 0.050). Morning surge was correlated positively with cfPWV (r = 0.59, P < 0.001) and negatively with sympathetic BRS (r = 0.51, P < 0.001) in hypertensive subjects only. Thus, morning BP surge is associated with arterial stiffness and sympathetic BRS, as well as vasoreactivity during orthostasis in hypertensive seniors.