Sympathetic nervous system activity and unattended blood pressure measurement

Background/Introduction

Sympathetic nervous system activation plays a crucial role in the pathophysiology and variability of hypertension. It has been hypothesized that measurement of unattended blood pressure (BP) may provide additional information to conventionally attended BP measurement, as it can lead to the limitation of the white coat effect.

Purpose

The aim of this study was to demonstrate the relationship of sympathetic nervous system activation and BP measurement variations with and without medical supervision.

Methods

We studied 103 untreated hypertensive patients, who underwent muscle sympathetic nerve activity (MSNA) estimation by microneurography. Both unattended (patient alone in the room, an oscillometric device programmed to perform 3 BP measurements at 1-minute intervals, after 5 minutes of rest) and attended BP measurements were conducted in all participants, with the same device, on the same day of MSNA recording in random order. Patients were divided into two groups based on the difference between attended and unattended BP. In group A, patients had unattended BP greater than attended BP (n=31) and in group B, patients had unattended BP lower than attended BP (n=72). The two groups were compared regarding the median value of MSNA recordings in our population (median MSNA = 63 bursts per 100 heartbeats).

Results

The two groups did not differ as regards both attended SBP levels (group A: 142.3±15.4 mmHg, group B: 145.6±13.7 mmHg, p=0.29) and attended DBP levels (group A: 89.2±9.8 mmHg, group B: 91.2±11.5 mmHg, p=0.25). A difference was observed concerning unattended SBP levels (group A: 152±16.3 mmHg, group B: 142.5±13.8 mmHg, p=0.03) and unattended DBP levels (group A: 94.4±10.3 mmHg, group B: 85.2±11.8 mmHg, p<0.01). Higher levels of MSNA were recorded in patients in group A when compared to group B, although this difference was not statistically significant (66.8±15.6 vs. 61.6±14.8 bursts per 100 heartbeats, p=0.11). Higher percentage of patients in group A had MSNA levels greater than the median value of MSNA compared to group B (68% vs 46% respectively).

Conclusions

In the present study, we found that the majority of patients who exhibit higher BP during the unattended measurement also record high MSNA values, suggesting a more stimulated sympathetic nervous system. On the contrary, most of the patients who can calm down during the unattended measurement exhibit lower levels of MSNA. More patients are needed to fully determine the clinical significance of this observation.

Funding Acknowledgement

Type of funding sources: None.

Effect of blood pressure reduction on cardiovascular outcomes in patients with different baseline cardiovascular risk: systematic review and meta-analysis of randomized trials

Background/Introduction

Blood pressure (BP) lowering is accompanied by a reduction on cardiovascular (CV) outcomes and death in hypertensive patients. There is no data on the effect of lowering BP in patients stratified according to their baseline CV risk as indicated by SCORE 2.

Purpose

The aim of this meta-analysis was to demonstrate the impact of BP-lowering treatment on the occurrence of CV events in these previously reported patients.

Methods

A systematic review in electronic databases (Pubmed and CENTRAL, years: 1966 to 9/2021) was conducted to identify randomized trials that study the effect of BP-lowering treatment against placebo or less aggressive BP reduction on 6 fatal or non-fatal CV outcomes and all-cause death. Selected studies reported outcomes in patients without a history of previous CV disease. In each study, baseline cardiovascular risk was estimated using SCORE-2. Risk ratios (RR) were calculated together with their 95% confidence interval (CI) under the random-effects model.

Results

The analysis was composed of 54 studies, of which 12 trials included patients with low-to-moderate CV risk, (n=21,192 patients), 13 trials with high CV risk patients (n=66,886) and 29 trials with very high CV risk patients (n=79,061). For a standard SBP/DBP reduction of 10/5 mmHg, the relative risk of the combined outcome of major CV events (i.e., myocardial infarction, stroke, and heart failure) was decreased by 27% (95% CI, 22–35%) in the category of very high-risk patients. This reduction was significantly greater (p=0.02) compared to high-risk trials (0.90 [95% CI, 0.77–1.04]). CV death showed a significant reduction in the high-risk group of patients compared to the low-moderate risk group (p=0.005), as well as in the very high-risk group compared to the low-moderate risk group (p=0.001). The same pattern was observed for all-cause death in the very high-risk group compared to the high-risk group (p=0.045).

Conclusions

With the present meta-analysis, we observed that the greatest benefit from BP lowering in primary prevention in the occurrence of CV events and mortality is observed in patients at higher baseline cardiovascular risk, as calculated by the SCORE-2.

Funding Acknowledgement

Type of funding sources: None.

Parameters indicating development of hypertension in three-year follow-up study of subjects with high normal blood pressure

Funding Acknowledgements

Type of funding sources: None.

Background/Introduction

The clinical importance of a hypertensive response to exercise (HRE) in subjects with high normal blood pressure (BP) is not fully elucidated, while sympathetic overactivity followed by arterial stiffening are linked with development of hypertension (HTN).

Purpose

The aim of this study was to assess the relation of HRE with sympathetic drive as assessed by muscle sympathetic nerve activity (MSNA) and arterial stiffness in subjects with high normal BP who developed hypertension in a 3 year follow up.

Methods

100 subjects with high normal office BP [systolic BP=130-139 mmHg and diastolic BP=85-89 mmHg] underwent a treadmill exercise stress test. Arterial stiffness was evaluated based on carotid to femoral pulse wave velocity (PWV). Sympathetic drive was assessed by MSNA levels. Follow up was every 6 months for 3 years, where BP was measured at both office (OffBP) and ambulatory blood pressure monitoring (ABPM). All participants offered lifestyle advises. Endpoint was development of HTN diagnosed either from OffBP or from ABPM. Then they were divided into Group I: those developed HTN and Group II: those remained normotensive.

Results

Mean age 54±8 years, 42 males, baseline offBP: 132/82 mmHg, ABPM: 122/76 mmHg). Out of them, 50 subjects developed HRE (BP ³210mmHg in men and ³190 mmHg in women) and 40 HTN. Group I developed higher HRE (75% vs. 13%, p=0.026), higher levels of PWV (8.35 vs 7.5 m/sec, p=0.043) and MSNA levels (37 vs. 31 bursts, p=0.04), while did not differ at their metabolic profile. Echocardiographically left ventricular mass index did not differ statistically as E/A ratio of mitral valve inflow (0.92 vs 1.05, p=0.034). Those who developed HTN was related to night systolic BP from ABPM (116 vs 112 mmHg, p<0.04), as also to intermediate stage intervals of 3 min (160 vs 147 mmHg, p=0.068) and 6 min (181 vs 164, p=0.035) of Bruce protocol. A novel metric, the SBP/MET-slope [(peak SBP—resting SBP)/(peak MET-1)] found to add crucial information. Regarding those who developed HTN, SBP/MET-slope was higher in all stages till peak exercise (stage 1: 6.25 vs 4.25, stage 2: 7.6 vs 5.3, peak: 7.22 vs 5.1, p=0.035). It was noticed that they performed a higher exercise capacity (10 vs 11.5 METs) and additionally differ significantly in their maximal heart rate (HR) at peak exercise (154 vs 164, p=0.001).

Conclusion

In subjects with high normal BP, a HRE, the intermediate BP intervals along with the SBP/MET-slope, identifies a state of systemic vascular resistance, arterial stiffening and sympathetic overdrive, as reflected by increased PWV and MSNA levels respectively. Additionally, exercise capacity demonstrates cardiovascular functional tolerance. These findings suggest that exercise testing provides determining clinical information regarding the overall cardiovascular status, proving its superior prognostic value as a hypertension screening tool, that alarms the physician to warn the patient to take action.

Effect of the Mediterranean diet on blood pressure in adults with and without hypertension: a systematic review and meta-analysis of randomized controlled trials

Background

It is unclear whether the Mediterranean diet (MedDiet) has a favorable effect on blood pressure (BP) levels because among randomized controlled trials (RCTs) investigating the MedDiet-mediated BP reduction there are significant methodological and clinical differences.

Purpose

The purpose of this study was to comprehensively assess the MedDiet BP-effect compared to the usual diet or another dietary intervention (e.g. low-fat diet) in adults with and without hypertension, accounting for different confounders.

Methods

We systematically searched Medline and the Cochrane Collaboration Library databases and identified 35 RCTs (13,943 participants). Random-effects model was used to calculate the mean attained systolic BP (SBP) and diastolic BP (DBP) differences during follow-up. Subgroup and meta-regression analyses were also conducted.

Results

Compared to the usual diet and all other active intervention diets the MedDiet reduced SBP and DBP (difference in means: −1.5 mm Hg; 95% CI: −2.8, −0.1; P=0.035, and −0.9 mm Hg; 95% CI: −1.5, −0.3; P=0.002, respectively). Compared only to the usual diet the MedDiet reduced SBP and DBP, while compared to all other active intervention diets or only to the low-fat diet the MedDiet did not reduce SBP and DBP. The MedDiet reduced DBP levels to a higher extent in trials with a mean baseline SBP ≥130 mm Hg, while both SBP and DBP were reduced more in trials with a mean follow-up period ≥16 weeks. The quality of evidence was rated as moderate for both outcomes according to the grading of recommendations, assessment, development and evaluation (GRADE) approach.

Conclusions

The adoption of the MedDiet was accompanied by a relatively small, but yet significant BP reduction, while higher baseline SBP levels and longer follow-up duration enhanced the BP-lowering effect of the intervention

Funding Acknowledgement

Type of funding sources: None.

Dietary approaches to stop hypertension (DASH) diet and blood pressure reduction in adults with and without hypertension: a systematic review and meta-analysis of randomized controlled trials

Background

The dietary approaches to stop hypertension (DASH) diet is recognized as an effective dietary intervention to reduce blood pressure (BP). However, among randomized controlled trials (RCTs) investigating the DASH diet mediated BP reduction,there are significant methodological and clinical differences.

Purpose

The purpose of this study was to comprehensively assess the effect of the DASH diet on BP levels in adults with and without hypertension, accounting for underlying methodological and clinical confounders.

Methods

We systematically searched Medline and the Cochrane Collaboration Library databases and identified 30 RCTs (n=5,545 participants) that investigated the BP effects of the DASH diet compared to a control diet in hypertensive and non-hypertensive adults. Both random-effects and fixed-effect models were used to calculate the mean attained systolic BP (SBP) and diastolic BP (DBP) differences during follow-up. Subgroup and meta-regression analyses were also conducted.

Results

The DASH diet reduced SBP and DBP significantly more compared to the control diet (difference in means: −3.2 mm Hg; 95% CI: −4.2, −2.3; P<0.001, and −2.5 mm Hg; 95% CI: −3.5, −1.5; P<0.001, respectively). Hypertension status did not modify the effect on BP reduction. The DASH diet compared to the control diet reduced SBP levels to a higher extent in trials with sodium intake >2,400 mg/day compared to trials with sodium intake ≤2,400 mg/day, while both SBP and DBP were reducedmore in trials with mean age <50 years compared to trials of older participants. The quality of evidence was rated as moderate forboth outcomes according to the Grading of Recommendations, Assessment, Development and Evaluation approach.

Conclusion

The adoption of the DASH diet was accompanied by significant BP reduction in adults with and without hypertension, while higher daily sodium intake and younger age enhanced the BP-lowering effect of the intervention. This meta-analysis was registered in the International Prospective Register of Systematic Reviews as CRD42019128120.

Funding Acknowledgement

Type of funding source: None

Improving Melt Strength of Polylactic Acid

Melt strength of polylactic acid (PLA) was improved through various modifications including grafting, crosslinking, chain extension, blending, plasticizing and nucleation. The results showed that melt strength was increased, to varying degrees, by crosslinking, chain extension and blending. In addition, melt strain (detected by velocity) was increased by chain extension, blending with elastomer, and plasticizing, but was decreased by crosslinking. The molecular weights, thermal properties and viscosity of the modified PLAs were also studied to investigate the causes of the observed variations in melt strength. Viscosity results generally corresponded with that of melt strength, but not with that of melt strain. With the exception of plasticizing and nucleation, the modifications had no significant effect on the thermal properties of PLA. The molecular weight (in particular the extremely large molecules representing by Mz) and the polydispersity of PLA were significantly increased after crosslinking and chain extension, which accounts for the observed increase in melt strength.