Factors Associated with Baroreflex Sensitivity: Association with Morning Blood Pressure

Race differences in ambulatory blood pressure monitoring parameters

BACKGROUND

Mean systolic and diastolic blood pressure (SBP and DBP) on ambulatory blood pressure (BP) monitoring (ABPM) are higher among Black compared with White adults. With 48 to 72 BP measurements obtained over 24 h, ABPM can generate parameters other than mean BP that are associated with increased risk for cardiovascular events. There are few data on race differences in ABPM parameters other than mean BP.

METHODS

To estimate differences between White and Black participants in ABPM parameters, we used pooled data from five US-based studies in which participants completed ABPM (n = 2580). We calculated measures of SBP and DBP level, including mean, load, peak, and measures of SBP and DBP variability, including average real variability (ARV) and peak increase.

RESULTS

There were 1513 (58.6%) Black and 1067 (41.4%) White participants with mean ages of 56.1 and 49.0 years, respectively. After multivariable adjustment, asleep SBP and DBP load were 5.7% (95% CI: 3.5-7.9%) and 2.7% (95% CI: 1.1-4.3%) higher, respectively, among Black compared with White participants. Black compared with White participants also had higher awake DBP ARV (0.3 [95%CI: 0.0-0.6] mmHg) and peak increase in DBP (0.4 [95% CI: 0.0-0.8] mmHg). There was no evidence of Black:White differences in awake measures of SBP level, asleep peak SBP or DBP, awake and asleep measures of SBP variability or asleep measures of DBP variability after multivariable adjustment.

CONCLUSION

Asleep SBP load, awake DBP ARV and peak increase in awake DBP were higher in Black compared to White participants, independent of mean BP on ABPM.

Acute social jetlag augments morning blood pressure surge: a randomized crossover trial

Although social jetlag (SJL) is generally considered a chronic condition, even acute SJL may have unfavorable effects on the cardiovascular system. We focused on the acute effects of SJL on morning blood pressure (BP) surge. This randomized crossover trial recruited 20 healthy men. In the SJL trial, participants delayed their bedtime by three hours on Friday and Saturday nights. Participants in the control (CON) trial implemented the same sleep-wake timing as on weekdays. Pre- and post-intervention measurements were performed to evaluate resting cardiovascular variables on Friday and Monday mornings, respectively. The ambulatory BP was automatically measured during the sleep and awake periods for 2 h after the participant woke up at night before pre- and post-intervention measurements. SJL (average mid-sleep time on weekends - average mid-sleep time on weekdays) occurred only in the SJL trial (SJL: 181 ± 24 min vs. CON: 8 ± 47 min). Carotid-femoral pulse wave velocity (cfPWV) and morning BP surge on Monday in the SJL trial were significantly higher than those on Friday in the SJL trial (cfPWV: P = 0.001, morning BP surge: P < 0.001), and those on Monday in the CON trial (cfPWV: P = 0.007; morning BP surge: P < 0.001). Furthermore, a significant positive correlation was found between ΔcfPWV and Δmorning BP surge (R = 0.587, P = 0.004). These results suggest that even acute SJL augments morning BP surge. This phenomenon may correspond to increased central arterial stiffness.State the details of Clinical Trials: Name: Effect of acute social jetlag on risk factors of lifestyle-related diseases. URL: https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000053204 . Unique identifier: UMIN000046639. Registration date: 17/01/2022.

Altered baroreflex sensitivity at rest and during Valsalva maneuver in healthy male offspring of hypertensive patients

INTRODUCTION

A family history of hypertension puts young adults at a higher risk of developing hypertension, that too, at an earlier age than their parents. Recent studies suggest that the baroreflex mechanism, which takes care of the short-term regulation of blood pressure (BP), also plays a role in the long-term regulation of BP. Studies have reported decreased baroreflex sensitivity (BRS) in hypertensives. Reduced BRS is shown to herald the future occurrence of cardiovascular diseases (CVD) and helps in risk stratification AIM: To assess BRS at rest and during the Valsalva maneuver among apparently healthy male offspring (age 18-35 years) of hypertensive patients.

METHODS

We recruited 37 participants whose parents (either/both) were hypertensive in the study group and whose parents (both) were not hypertensive in the control group. We measured basic anthropometric parameters (height, weight, waist circumference), cardiovascular parameters (heart rate and BP), short-term heart rate variability, and BRS (at rest and during Valsalva).

RESULTS

We found that BRS at rest and BRS during the Valsalva maneuver were reduced among healthy male offspring of hypertensive parents than in healthy male offspring of non-hypertensive parents. Further, HRV indices and Valsalva ratio showed a sympathovagal imbalance in the form of decreased vagal and increased sympathetic activity.

CONCLUSION

The reduced BRS and sympathovagal imbalance in male offspring of hypertensive parents reveal the early risk of developing hypertension in the future.

Stress and the baroreflex

The stress response to emotions elicits the release of glucocorticoids from the adrenal cortex, epinephrine from the adrenal medulla, and norepinephrine from the sympathetic nerves. The baroreflex adapts to buffer these responses to ensure that perfusion to the organs meets the demands while maintaining blood pressure within a within a narrow range. While stressor-evoked autonomic cardiovascular responses may be adaptive for the short-term, the recurrent exaggerated cardiovascular stress reactions can be maladaptive in the long-term. Prolonged stress or loss of the baroreflex's buffering capacity can predispose episodes of heightened sympathetic activity during stress leading to hypertension, tachycardia, and ventricular wall motion abnormalities. This review discusses 1) how the baroreflex responds to acute and chronic stressors, 2) how lesions in the neuronal pathways of the baroreflex alter the ability to respond or counteract the stress response, and 3) the techniques to assess baroreflex sensitivity and stress responses. Evidence suggests that loss of baroreflex sensitivity may predispose heightened autonomic responses to stress and at least in part explain the association between stress, mortality and cardiovascular diseases.

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.

Oral oestrogen reverses ovariectomy-induced morning surge hypertension in growth-restricted mice

Perinatal growth restriction (GR) is associated with heightened sympathetic tone and hypertension. We have previously shown that naturally occurring neonatal GR programmes hypertension in male but not female mice. We therefore hypothesized that intact ovarian function or post-ovariectomy (OVX) oestrogen administration protects GR female mice from hypertension. Utilizing a non-interventional model that categorizes mice with weanling weights below the tenth percentile as GR, control and GR adult mice were studied at three distinct time points: baseline, post-OVX and post-OVX with oral oestrogen replacement. OVX elicited hypertension in GR mice that was significantly exacerbated by psychomotor arousal (systolic blood pressure at light to dark transition: control 122 ± 2; GR 119 ± 2; control-OVX 116 ± 3; GR-OVX 126 ± 3 mmHg). Oestrogen partially normalized the rising blood pressure surge seen in GR-OVX mice (23 ± 7% reduction). GR mice had left ventricular hypertrophy, and GR-OVX mice in particular had exaggerated bradycardic responses to sympathetic blockade. For GR mice, a baseline increase in baroreceptor reflex sensitivity and high frequency spectral power support a vagal compensatory mechanism, and that compensation was lost following OVX. For GR mice, the OVX-induced parasympathetic withdrawal was partially restored by oestrogen (40 ± 25% increase in high frequency spectral power, P<0.05). In conclusion, GR alters cardiac morphology and cardiovascular regulation. The haemodynamic consequences of GR are attenuated in ovarian-sufficient or oestrogen-replete females. Further investigations are needed to define the role of hormone replacement therapy targeted towards young women with oestrogen deficiency and additional cardiovascular risk factors, including perinatal GR, cardiac hypertrophy and morning surge hypertension.

Effects of Celiprolol and Bisoprolol on Blood Pressure, Vascular Stiffness, and Baroreflex Sensitivity

BACKGROUND

We tested the hypothesis that celiprolol and bisoprolol have differential effects on blood pressure (BP), flow-mediated dilation (FMD), and vascular stiffness.

METHODS

We analyzed 102 hypertensives (mean age: 59±14 years) who were being treated other than beta-blockers. They were randomized to receive add-on treatment with either celiprolol 100-200mg (C group) or bisoprolol 2.5-5mg (B group), and followed up for 3 months. In addition to clinic, home, and ambulatory BP monitoring, the FMD, radial augmentation index (AI), brachial-ankle pulse wave velocity (baPWV), urine albumin-to-creatinine ratio, and baroreflex sensitivity (BRS) were measured at baseline and at the end of the study.

RESULTS

Compared to the baseline values, home and 24-hour BP were significantly lowered in the third month in both groups (all Ps < 0.05). Pulse rate (PR) and baPWV were reduced (P < 0.001), and BRS was increased significantly only in the B group (P = 0.02). Radial AI was unchanged in the C group but was significantly increased in the B group (P < 0.001). Central BP was significantly reduced in the C group (P = 0.003) but was unchanged in the B group. FMD was significantly increased in both groups (both P < 0.01).

CONCLUSION

Bisoprolol achieved the greater reduction of PR and improved BRS and vascular stiffness, whereas, celiprolol reduced the central BP level. In treated hypertensive patients, add-on use of celiprolol may be favorable in uncomplicated stage of hypertension. On the other hand, bisoprolol may be useful in hypertensives with cardiac or vascular diseases who have advanced atherosclerotic changes and sympathetic nervous system activation.

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.

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.

A bedtime dose of ARB was better than a morning dose in improving baroreflex sensitivity and urinary albumin excretion--the J-TOP study

The hypothesis that the bedtime dosing of angiotensin receptor blocker (ARB) is superior to morning dose in improving baroreflex sensitivity (BRS) and urinary albumin/creatinine ratio (UACR) was tested in this study. Baroreflex sensitivity was measured at baseline and at 6th month (N = 109) and was found to increase in the bedtime-dose group (P = .004), but not in the morning-dose group. The correlations between the change in BRS and the change in UACR were insignificant in the morning-dose group (r = 0.17, P = .26), but were significant in the bedtime-dose group (r = -0.29, P = .04). In conclusion, the improvement of BRS could be one of the mechanisms by which bedtime dosing of ARB confers renal protection.

Diurnal Variation in the Mechanical and Neural Components of the Baroreflex

Diminished baroreflex sensitivity in the morning negatively influences morning coronary blood flow and blood pressure control in hypertensive patients. Our aim was to determine the contribution of the mechanical and neural components of the cardiac baroreflex to diurnal variation in blood pressure control. In 12 healthy participants, we used the modified Oxford method to quantify baroreflex sensitivity for rising (G up ) and falling (G down ) pressures in the morning (7:00 am ) and afternoon (4:00 pm ). Beat-to-beat blood pressure, R-R intervals, and carotid artery diameter measurements were recorded. Integrated sensitivity was determined by plotting R-R intervals against systolic blood pressure. The mechanical component was carotid artery diameter plotted against systolic blood pressure, and the neural component was R-R intervals plotted against carotid artery diameter. Linear mixed models were used to compare the integrated, mechanical, and neural sensitivities between morning and afternoon. We found significant diurnal variation in integrated sensitivity, with an attenuated response in the morning (G up =13.0±0.6; G down =6.3±0.4 ms/mm Hg) when compared with the afternoon (G up =15.1±0.6; G down =12.6±0.4 ms/mm Hg). For rising pressures, the diminished integrated sensitivity in the morning was caused by a reduction in mechanical sensitivity, whereas for falling pressures it was caused by a reduction in neural sensitivity. Our findings explicate the mechanisms underlying diurnal variation in baroreflex function. Pharmacological and lifestyle interventions targeted specifically at the diminished component of the cardiac baroreflex in the morning may lead to better management of hypertension.

Maximum value of home blood pressure: a novel indicator of target organ damage in hypertension

The maximum office systolic blood pressure (SBP) has been shown to be a strong predictor of cardiovascular events, independently of the mean SBP level. However, the clinical implications of maximum home SBP have never been reported. We investigated the association between the maximum home SBP and target organ damage (TOD). We assessed the left ventricular mass index (LVMI) and carotid intima-media thickness (IMT) using ultrasonography and the urinary albumin/creatinine ratio (UACR) as measures of TOD in 356 never-treated hypertensive subjects. Home BP was taken in triplicate in the morning and evening, respectively, for 14 consecutive days with a memory-equipped device. The maximum home SBP was defined as the maximum mean triplicate BP reading in the 14-day period for each individual and was significantly correlated with LVMI (r=0.51, P<0.001), carotid IMT (r=0.40, P<0.001), and UACR (r=0.29, P<0.001). The correlation coefficients with LVMI and carotid IMT were significantly larger for the maximum home SBP than the mean home SBP. In multivariate regression analyses, the maximum home SBP was independently associated with LVMI and carotid IMT, regardless of the mean home BP level. In the prediction of left ventricular hypertrophy and carotid atherosclerosis, the goodness-of-fit of the model was significantly improved when the maximum home SBP was added to the sum of the mean office and home BPs (P=0.002 and P<0.001, respectively). These findings indicate that assessment of the maximum home SBP, in addition to the mean home SBP, might increase the predictive value of hypertensive TOD in the heart and artery.

Autonomic nervous system adjustment (ANSA) in patients with hypertension treated with enalapril

BACKGROUND AND AIM

Reduced baroreflex sensitivity (BRS), decreased heart rate variability (HRV) and increased blood pressure (BP) variability have serious consequences for target organ damage in patients with hypertension, beside the BP level. The study was aimed to evaluate acute and long-term effects of enalapril, on BRS and HRV in individuals with prehypertension and mild essential hypertension.

METHODOLOGY

We enrolled in the study 85 patients (male 53%, age 42-67) with prehypertension and mild hypertension (systolic blood pressure ≥120 mmHg or diastolic blood pressure ≥80 mmHg). All patients were tested before, 30 minutes after first oral enalapril dose and three weeks after monotherapy with enalapril. The methodology included: beat to beat HRV analysis, BRS measurements with sequence technique, ECG with short term and 24-hour HRV analysis, 24-hour ambulatory blood pressure monitoring with systolic and diastolic BP variability analysis. Patients were divided into groups with sympathetic or vagal predominance based on Autonomic Nervous System Adjustment (ANSA) method.

RESULTS

1) 30 min after initial dose enalapril significantly and effectively reduced systolic BP with shift towards the parasympathetic predominance as reflected in decreased heart rate and low frequency (LF) to high frequency (HF) ratio (LF/HF ratio); 2) chronic enalapril therapy effectively reduced BP, including both systolic BP, diastolic BP and pulls pressure, had positively influence on dipping status, but did not significantly change BP variability; 3) in the whole patient group chronic enalapril therapy did not significantly change HRV, but it significantly decreased LF(nu) in the patient with high basal sympathetic activity, and significantly increased LF(nu) in patients with high basal vagal activity; enalapril also significantly decreased HF (nu) in patients with high basal parasympathetic activity; 4) despite initial, transit changes in maximal and minimal slope of BRS enalapril did not significantly affect sensitivity of spontaneous baroreflex activation.

CONCLUSION

Initial enalapril dose significantly reduced systolic BP and had beneficial effects on autonomic tone and baroreflex sensitivity. Chronic enalapril therapy effectively reduced BP without significant influence on BRS, but had significant autonomic effects on HRV when initial autonomic profile in each patient was analyzed by ANSA. Analyzed by ANSA method chronic enalapril therapy managed to retrieve disturbed sympathovagal balance and established autonomic equilibrium.

Cilnidipine inhibits the sympathetic nerve activity and improves baroreflex sensitivity in patients with hypertension

N-type calcium channel blocker, cilnidipine, is reported not to increase the heart rate in spite of the strong depressor effect. However, it has not been determined whether cilnidipine has the sympatho-inhibitory effects or not. Moreover, the effect of cilnidipine on the baroreflex control has not been determined. The aim of this study was to determine the effect of cilnidipine on sympathetic and parasympathetic nerve activity, and baroreflex sensitivity. We studied five hypertensive patients treated with 10 mg cilnidipine (10-mg group) and five hypertensive patients treated with 20 mg cilnidipine (20-mg group). Before the treatment and 6 months after the treatment, we measured the blood pressure, spontaneous baroreflex sensitivity (BRS), heart rate variability (HRV), and blood pressure variability (BPV). After 6 months, systolic blood pressure (SBP) and the low-frequency component of systolic BPV expressed in normalized units (LFnuSBP), as the parameter of sympathetic nerve activity, was significantly decreased in both groups, and the suppressive effects were stronger in the 20-mg group than in the 10-mg group. The high-frequency component of HRV expressed in normalized units, as the parameter of parasympathetic nerve activity, and BRS were significantly increased in 20-mg group, but not significant in 10-mg group. These results suggest that 6 months treatment with cilnidipine for hypertension has the sympatho-inhibtory effect, and that high-dose cilnidipine improves the parasympathetic nerve activity and baroreflex control in patients with hypertension.