American Society of Hypertension position paper: central blood pressure waveforms in health and disease

Central blood pressure and peripheral augmentation index following acute submaximal arm versus leg exercise

BACKGROUND

Aerobic exercises like running and cycling may lower cardiovascular disease (CVD) risk through favorable effects on central blood pressure and vascular function. Arm ergometry is a popular exercise modality used in rehabilitation settings, but little is known regarding the central hemodynamic and vascular effects of this form of exercise.

PURPOSE

To compare the acute effects of leg versus arm exercise on central blood pressure and vascular function.

METHODS

Twenty-one participants (n = 11 female, Age 21 ± 3, BMI 24.5 ± 3.2 kg/m2) completed two visits to the Human Performance Laboratory. Central systolic blood pressure (cSBP), central diastolic blood pressure (cDBP), and peripheral augmentation index (pAIx) were measured using a brachial oscillometric blood pressure cuff with measures being taken before and after 20 min of acute moderate-intensity (submaximal) arm or leg cycling exercise.

RESULTS

There was a condition-by-time interaction for pAIx (p = 0.011). pAIx slightly increased following arm exercise but significantly decreased following leg exercise. There was a condition-by-time interaction for cDBP (p = 0.011). cDBP significantly decreased following arm exercise but increased immediately following leg exercise. There was no condition-by-time interaction for cSBP (p = 0.721). There were similar acute increases in cSBP immediately post-exercise for both conditions.

CONCLUSION

Arm exercise increased pAlx and decreased cDBP compared to leg exercise. As an increase in pAIx may increase left ventricular work and a reduction in cDBP may reduce coronary perfusion pressure, these findings suggest that a single bout of arm exercise may not have the same favorable acute effect on central hemodynamic load as a single bout of leg exercise.

A Review of Noninvasive Methodologies to Estimate the Blood Pressure Waveform

Accurate estimation of blood pressure (BP) waveforms is critical for ensuring the safety and proper care of patients in intensive care units (ICUs) and for intraoperative hemodynamic monitoring. Normal cuff-based BP measurements can only provide systolic blood pressure (SBP) and diastolic blood pressure (DBP). Alternatively, the BP waveform can be used to estimate a variety of other physiological parameters and provides additional information about the patient's health. As a result, various techniques are being proposed for accurately estimating the BP waveforms. The purpose of this review is to summarize the current state of knowledge regarding the BP waveform, three methodologies (pressure-based, ultrasound-based, and deep-learning-based) used in noninvasive BP waveform estimation research and the feasibility of employing these strategies at home as well as in ICUs. Additionally, this article will discuss the physical concepts underlying both invasive and noninvasive BP waveform measurements. We will review historical BP waveform measurements, standard clinical procedures, and more recent innovations in noninvasive BP waveform monitoring. Although the technique has not been validated, it is expected that precise, noninvasive BP waveform estimation will be available in the near future due to its enormous potential.

Central Blood Pressure and Subclinical Atherosclerotic Risk in Young Hispanic American Women

Background

The incidence of younger women being hospitalized from cardiovascular disease (CVD) events is on the rise. Hispanic women are generally thought to have higher CVD risk factor burden than non-Hispanic White (NHW) women yet Hispanic Americans have lower mortality from CVD. Traditional measures of CVD may not accurately capture CVD risk in Hispanic Americans. Hence, the purpose of this study was to assess the impact of ethnicity on vascular reactivity and central hemodynamic load to gain insight into subclinical CVD risk in young women.

Methods

Brachial flow-mediated dilation (FMD), low-flow mediated constriction (L-FMC), carotid-femoral pulse wave velocity (cfPWV), and pulse wave analysis (from synthesized aortic pressure waveforms) were measured in 25 Hispanic women and 31 NHW women aged between 18-35 years. FMD and L-FMC were combined to provide an index of total vessel reactivity.

Results

NHW and Hispanic women did not differ in age or traditional CVD risk factors (P>.05 for all). Compared with NHW women, Hispanic women had greater vascular reactivity (8.7±4.1 vs 11.7±4.1 %, P=.011), lower central pulse pressure (28±5 vs 24±3 mm Hg, P=.001) and lower pressure from wave reflections (12±2 vs 10±1 mm Hg, P=.001). There were no differences in cfPWV between NHW women and Hispanic women (5.4±0.7 vs 5.3±0.7 m/s, P=.73).

Conclusion

Young Hispanic women have greater vascular reactivity and lower central pulsatile hemodynamic load compared with NHW women, suggesting lower subclinical CVD risk.

Associations between remnant lipoprotein cholesterol and central systolic blood pressure in a Chinese community-based population: a cross-sectional study

Background

The lipid profile is reportedly related to peripheral blood pressure or pulse wave velocity. However, no studies have investigated the associations between lipid parameters, especially remnant lipoprotein cholesterol (RLP-C), and central systolic blood pressure (cSBP).

Methods

This study used baseline data of a community-based cohort in Beijing, China. Participants who had been treated with anti-hypertensive or lipid-lowering agents were excluded. RLP-C is equal to total cholesterol (TC) minus the sum of low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C). An Omron HEM-9000AI device was used to measure non-invasive cSBP. The associations between blood lipid profile and non-invasive cSBP were evaluated using multivariable regression models.

Results

The 5173 included participants were 55.0 ± 8.5 years old; 35.7% (1845) of participants were men. Increased cSBP was significantly associated with increased TC, LDL-C, non-high-density lipoprotein cholesterol (non-HDL-C), triglyceride (TG), and RLP-C but with decreased HDL-C, even after adjusting for possible covariates. When simultaneously entering individual pairs of RLP-C and other blood lipid parameters into the multivariable regression model, RLP-C remained significantly associated with cSBP, even after adjusting for other lipids. Compared with participants who had RLP-C levels in the first quartile (Q1), cSBP for those with RLP-C in Q4 was increased to 4.57 (95% confidence interval [CI]: 3.08–6.06) mmHg after adjusting for LDL-C, 4.50 (95%CI: 2.98–6.02) mmHg after adjusting for TC, 3.91 (95%CI: 1.92–5.89) mmHg after adjusting for TG, 5.15 (95%CI: 3.67–6.63) mmHg after adjusting for HDL-C, and 4.10 (95%CI: 2.36–5.84) mmHg after adjusting for non-HDL-C.

Conclusions

Increased blood RLP-C level was significantly associated with higher cSBP in a Chinese population, independently of other lipids, which indicates its importance in individual cardiovascular risk assessment.

Screening System for Cardiac Problems through Non-Invasive Identification of Blood Pressure Waveform

This paper presents the initial development of a non-invasive system for identification of the pulse pressure waveform to be used for screening cardiac problems. The system employs a tonometric method using an off-the-shelf force sensor and custom-designed electronic circuits. Initial results on the use of the system are presented.

Estimation of wave reflection in aorta from radial pulse waveform by artificial neural network: a numerical study

BACKGROUND AND OBJECTIVE

Wave reflection in aorta has been shown to have incremental value for predicting cardiovascular events. However, its estimation by wave separation analysis (WSA) is complex.

METHODS

In this study, a novel method was proposed based on a cascade artificial neural network (ANN) for wave reflection estimation by the frequency features of radial pressure waveform alone. The simulation database of 4000 samples was generated by a 55-segment transmission line model of human arterial tree and was used for evaluating the ANN with 10-fold cross validation for the estimation of reflection magnitude (RM_ANN) and reflection index (RI_ANN) of wave reflection in aorta. RM and RI also were estimated by the WSA with a triangle waveform of aortic flow (RM_WSA and RI_WSA) and with a real aortic flow waveform (RM_Ref and RI_Ref) as reference values.

RESULTS

The results showed the correlation coefficient and mean difference between RM_ANN and RM_Ref (R² = 0.92, mean ± standard deviation (SD) = 0.0 ± 0.02) and those between RI_ANN and RI_Ref (R² = 0.91, mean ± SD = 0.0 ± 0.01) were better than those between RM_WSA and RM_Ref (R² = 0.51, mean ± SD = 0.01 ± 0.07) and those between RI_WSA and RI_Ref (R² = 0.50, mean ± SD = 0.0 ± 0.02). As the sample diversity in the simulation database was increased but the total number of samples keeps constant, the advantage of the ANN, though decreased slightly, became more significant than those of WSA (RM_ANN VS. RM_Ref and RI_ANN VS. RI_Ref: R² = 0.88 and 0.88, mean ± SD = 0.0 ± 0.05 and 0.0 ± 0.05; RM_WSA VS. RM_Ref and RI_WSA VS. RI_Ref: R² = 0.24 and 0.24, mean ± SD = 0.07 ± 0.24 and 0.02 ± 0.08, respectively). In addition, the ANN can achieve better results than the traditional method WSA even only two hidden neurons are used.

CONCLUSIONS

ANN is a potential method for the estimation of wave reflection in aorta by a single radial pulse waveform, but further validation of this method in clinic trials is needed.

Acute Effects of High-Level PM2.5 Exposure on Central Blood Pressure

Central aortic blood pressure (BP) has been increasingly recognized as having a closer relationship with cardiovascular risks than peripheral BP. However, the effects of particulate matter pollution on central aortic BP have not been clearly demonstrated. In this study, we assessed the association between short-term ambient fine particulate matter (with an aerodynamic diameter ≤2.5 μm; PM_2.5) exposure and central aortic BP in a Chinese community-based population. A total of 4715 visits were in our final analysis, including 2151 visits at the baseline and 2564 visits at the follow-up. Central aortic systolic BP (cSBP) was measured noninvasively using the method of radial artery tonometry with Omron HEM-9000AI machine. Data from air pollution monitoring stations were used to estimate daily PM_2.5 exposure. Generalized additive mixed models with clinical and meteorologic covariates adjusted were used to examine the association between PM_2.5 exposure and cSBP. The relationships between PM_2.5 exposure and cSBP were nonlinear, and significant increments of cSBP were observed when the PM_2.5 exposure concentration was above 100 μg/cm³. An interquartile range increase (80.25 μg/m³) in daily PM_2.5 on the day of cSBP measurement (lag 0 day) was associated with 2.54 mm Hg (95% CI, 0.92-4.16) elevation in cSBP. The associations of PM_2.5 with cSBP were not modified by age, sex, body mass index, medications, and comorbid diseases except for cardiovascular disease. Our findings demonstrated that short-term exposure to high concentration of ambient PM_2.5 above 100 μg/cm³ was associated with significant increases in central aortic BP in a Chinese community-based population.

Augmentation index in the assessment of wave reflections and systolic loading

BACKGROUND

Augmentation index (AI_x) is used to quantify the augmented systolic aortic pressure that impedes ventricular ejection. Its use as an index of wave reflections is questionable. We hypothesize that AI_x is quantitatively different from the reflection coefficient under varied physiological conditions.

METHODS

42 datasets of aortic pressure and flow waveforms were obtained during induced hypertension (methoxamine infusion) and vasodilation (nitroprusside infusion) in our mongrel dog experiments (n = 5) and from Mendeley data during various interventions (vasoconstrictors, vasodilators, pacing, stimulation, hemorrhage and hemodilution). Wave reflections and principal components of reflection coefficients were computed for comparison to AI_x and heart rate normalized AI_x. RESULTS: Principal reflection coefficient, Γ₁, increased in hypertension and decreased in vasodilation, hemorrhage and hemodilution. AI_x followed the trend in many cases but was consistently lower than Γ₁ in almost all the subjects. The Bland-Altman analysis also showed that both AI_x and normalized AI_x underestimated Γ₁. The relationship between augmentation index and reflection coefficient was explained by a linear regression model (r² = 0.23, p < 0.01) in which AI_x followed directional changes in Γ₁ and the normalization of AI_x resulted in a linear model that explained less variation in the relationship between AI_x and Γ₁.

CONCLUSION

AI_x is a reasonable clinical trend indicator, albeit not an accurate surrogate measure of the amount of wave reflections.

N-Point Moving Average: A Special Generalized Transfer Function Method for Estimation of Central Aortic Blood Pressure

OBJECTIVE

N-point moving average (NPMA) is a simplified method of central aortic systolic pressure (CASP) estimation in comparison with the generalized transfer function (GTF). The fundamental difference or similarity between the methods is not established. This study investigates theoretical properties of NPMA relative to GTF and explores the integer and fractional denominator for the averaging process in the NPMA.

METHODS

Convolution of a specified square wave and the radial (or brachial) blood pressure waveform constituted the NPMA . A single uniform tube model-based TF (MTF) was employed to investigate potential physiological meaning of NPMA. In experimental analysis, invasive, simultaneously recorded aortic and radial pressure waveforms were obtained in 62 subjects under control conditions and following nitroglycerin administration. CASP was estimated by NPMA (), GTF ( ), and MTF (CASP _MTF) from radial waveforms by tenfold cross validation.

RESULTS

Theoretical analysis showed that NPMA was an inversed constant TF. Its spectrum matched that of MTF in low frequency (<4 Hz for radial and <5 Hz for brachial) by optimizing reflection coefficient and propagation time. Experiment results showed the NPMA optimized fractional denominator of K = 4.4 significantly decreased the mean difference between CASP_NPMA and measured CASP to 0.0 ± 4.7 mmHg from -1.8 ± 4.6 mmHg for integer denominator of K = 4. CASP_NPMA correlated with CASP_MTF and CASP _GTF (r² = 0.99 and 0.97, mean difference: -0.3 ± 1.8 and 0.5 ± 2.7 mmHg).

CONCLUSION

This study demonstrated that NPMA is similar in nature to the GTF.

The Role of Central Blood Pressure Monitoring in the Management of Hypertension

PURPOSE OF REVIEW

Central blood pressure is a novel predictor of cardiovascular risk that can be measured in the clinical setting using currently available technology. This paper will review current available methods of central blood pressure monitoring as well as its impact in cardiac and renal disease.

RECENT FINDINGS

Both aortic and carotid systolic blood pressure are independently associated with cardiovascular mortality and serious cardiac events. Furthermore, studies show that systolic aortic blood pressure has been shown to be superior predictor of cardiovascular as compared to brachial blood pressure. Inhibitors of the renin angiotensin axis may have a beneficial effect on central blood pressure; however, long term studies evaluating the impact of lowering central blood pressure on clinical outcomes are lacking. Central blood pressure is a good predictor of cardiovascular risk. As more studies emerge demonstrating the value of central blood pressure as a therapeutic target, it is possible that targeting central blood pressure may become an important part of the armamentarium to lower cardiovascular risk.

Estimation of aortic systolic blood pressure from radial systolic and diastolic blood pressures alone using artificial neural networks

BACKGROUND

Current aortic SBP estimation methods require recording of a peripheral pressure waveform, a step with no consensus on method. This study investigates the possibility of aortic SBP estimation from radial SBP and DBP using artificial neural networks (ANN) with [ANNSBP.DBP.heart rate (HR)] and without HR (ANNSBP.DBP).

METHODS

Ten-fold cross validation was applied to invasive, simultaneously recorded aortic and radial pressure during rest and nitroglycerin infusion (n = 62 patients). The results of the ANN models were compared with an ANN model using additional waveform features (ANNwaveform), to an N-point moving average method (NPMA) and to existing, validated generalized transfer function (GTF).

RESULTS

Estimated aortic SBP for all methods was on average less than 1 mmHg away from measured aortic SBP with the exception of NPMA (difference 2.0 ± 3.5 mmHg, P = 0.62). Variability of the difference was significantly greater in ANNSBP.DBP.HR and ANNSBP.DBP (both SD of ± 5.9 mmHg, P < 0.001 compared with GTF, ± 4.0 mmHg, P < 0.001). Inclusion of waveform features decreased the variability (ANNwaveform ± 3.9 mmHg, P = 0.264). Estimated aortic SBP in all models was correlated with measured SBP, with ANN models providing statistically similar results to the GTF method, only the NPMA being statistically different (P = 0.031).

CONCLUSION

These findings indicate that use of radial SBP, DBP, and HR alone can provide aortic SBP estimation comparable with the GTF, albeit with slightly greater variance. Pending noninvasive validation, the technique provides plausible aortic SBP estimation without waveform analysis.

Joint Effect of Non-invasive Central Systolic Blood Pressure and Peripheral Systolic Blood Pressure on Incident Hypertension in a Chinese Community-based Population

Central blood pressure level is not always consistent with peripheral blood pressure level, and especially their joint effect on incident hypertension is not well established. A total of 1607 non-hypertensive subjects from an atherosclerosis cohort in Beijing, China were included. Central systolic blood pressure (cSBP) was obtained using Omron HEM-9000AI machine and peripheral systolic blood pressure (pSBP) was measured using Omron HEM-7117 electronic sphygmomanometer, separately. Hypertension was defined as BP ≥ 140/90 mmHg or self-reported hypertension or taking any antihypertension drugs at the follow-up survey. After a median follow-up of 2.3 years, incident hypertension was 13.1%. Every 1 standard deviation increase of cSBP and pSBP was associated with 1.98 (95%CI: 1.69-2.33) and 2.84 (95%CI: 2.30-3.52) times of incident hypertension after adjustment for confounders. Moreover, hypertension risk in single pSBP ≥ 120 mmHg group, single cSBP ≥ 120 mmHg group, and both pSBP and cSBP ≥ 120 mmHg group was 2.83 (95%CI: 0.98-8.16), 3.28 (95%CI: 1.24-8.70), and 11.47 (95%CI: 4.97-26.46) times higher than both pSBP and cSBP < 120 mmHg group, respectively. The joint effect of cSBP and pSBP is superior to either cSBP or pSBP to predict incident hypertension in a Chinese community-based population. Screening of central blood pressure should be considered in non-hypertensive population for the purpose of primary intervention, especially for subjects with pSBP ≥ 120 mmHg.

Effect of CPAP, Weight Loss, or CPAP Plus Weight Loss on Central Hemodynamics and Arterial Stiffness

Obesity and obstructive sleep apnea tend to coexist. Little is known about the effects of obstructive sleep apnea, obesity, or their treatment on central aortic pressures and large artery stiffness. We randomized 139 adults with obesity (body mass index >30 kg/m2) and moderate-to-severe obstructive sleep apnea to (1) continuous positive airway pressure (CPAP) therapy (n=45), (2) weight loss (WL) therapy (n=48), or (3) combined CPAP and WL (n=46) for 24 weeks. We assessed the effect of these interventions on central pressures and carotid-femoral pulse wave velocity (a measure of large artery stiffness), measured with arterial tonometry. Central systolic pressure was reduced significantly only in the combination arm (-7.4 mm Hg; 95% confidence interval, -12.5 to -2.4 mm Hg; P=0.004), without significant reductions detected in either the WL-only (-2.3 mm Hg; 95% confidence interval, -7.5 to 3.0; P=0.39) or the CPAP-only (-3.1 mm Hg; 95% confidence interval, -8.3 to 2.0; P=0.23) arms. However, none of these interventions significantly changed central pulse pressure, pulse pressure amplification, or the central augmentation index. The change in mean arterial pressure (P=0.008) and heart rate (P=0.027) induced by the interventions was significant predictors of the change in carotid-femoral pulse wave velocity. However, after adjustment for mean arterial pressure and heart rate, no significant changes in carotid-femoral pulse wave velocity were observed in any group. In obese subjects with obstructive sleep apnea, combination therapy with WL and CPAP is effective in reducing central systolic pressure. However, this effect is largely mediated by changes in mean, rather than central pulse pressure. WL and CPAP, alone or in combination, did not reduce large artery stiffness in this population.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00371293.

Automated oscillometric blood pressure and pulse-wave acquisition for evaluation of vascular stiffness in atherosclerosis

OBJECTIVE

Evaluation of diagnostic accuracy of an oscillometry-based device (VascAssist) combining fully automated ankle-brachial index (ABI) and pulse-wave velocity (PWV) assessment for detection of peripheral arterial disease (PAD).

SUBJECTS AND METHODS

110 consecutive subjects including symptomatic PAD patients (n = 41) and healthy PAD-free participants (n = 69) were recruited. All subjects underwent standard manual Doppler-based ABI (sABI) and oscillometry-based automated ABI (aABI) measurements (VascAssist). Oscillometry by the VascAssist included central and peripheral PWV assessment. Additionally, arterial stiffness (AS) was evaluated by flow-mediated vasodilation (FMD) of the brachial artery in all patients. All symptomatic PAD patients underwent catheter angiography for endovascular intervention and post-interventional acquisition of sABI, aABI, PWV and FMD.

RESULTS

Sensitivity, specificity, PPV and NPV of aABI for detecting PAD was 73%, 100%, 100%, and 86% as compared to 80%, 96%, 92%, and 89% for sABI. Pearson-correlation for diabetics was r = 0.81; (P < .001) and for non-diabetics r = 0.77; (P < .001). Bland-Altman-analysis revealed a difference (95% CI) for diabetics of 0.09 (-0.22-0.4] and non-diabetics 0.022 [-0.25-0.295]. Weak correlation exists for FMD/AS analysis (pre-interventional R = 0.386, P = .043; post-interventional R = -0.06; P = .76) and significant increase of pre-/post-interventional PWV analysis (P < .001).

CONCLUSION

Combined automatic ABI and PWV acquisition with the VascAssist device showed excellent diagnostic accuracy for detection of PAD. Compared to FMD, AS analysis may serve as an investigator-independent (screening) tool for determination of functional vascular damage in atherosclerosis.

Pyridostigmine bromide versus fludrocortisone in the treatment of orthostatic hypotension in Parkinson's disease - a randomized controlled trial

BACKGROUND AND PURPOSE

Evidence for effective treatment options for orthostatic hypotension (OH) in Parkinson's disease (PD) is scarce. Elevation of cholinergic tone with pyridostigmine bromide has been reported as a way to improve blood pressure (bp) regulation in neurogenic hypotension without causing supine hypertension.

METHODS

This was a double-centre, double-blind, randomized, active-control, crossover, phase II non-inferiority trial of pyridostigmine bromide for OH in PD (clinicaltrials.gov NCT01993680). Patients with confirmed OH were randomized to 14 days 3 × 60 mg/day pyridostigmine bromide or 1 × 0.2 mg/day fludrocortisone before crossover. Outcome was measured by peripheral and central bp monitoring during the Schellong manoeuvre and questionnaires.

RESULTS

Thirteen participants were enrolled between April 2013 and April 2015 with nine participants completing each trial arm. Repeated measures comparison showed a significant 37% improvement with fludrocortisone for the primary outcome diastolic bp drop on orthostatic challenge (baseline 22.9 ± 13.6 vs. pyridostigmine bromide 22.1 ± 17.0 vs. fludrocortisone 14.0 ± 12.6 mmHg; P = 0.04), whilst pyridostigmine bromide had no effect. Fludrocortisone caused an 11% peripheral systolic supine bp rise (baseline 128.4 ± 12.8 vs. pyridostigmine bromide 130.4 ± 18.3 vs. fludrocortisone 143.2 ± 10.1 mmHg; P = 0.01) but no central mean arterial supine bp rise (baseline 107.2 ± 7.8 vs. pyridostigmine bromide 97.0 ± 12.0 vs. fludrocortisone 107.3 ± 6.3 mmHg; P = 0.047). Subjective OH severity, motor score and quality of life remained unchanged by both study interventions.

CONCLUSIONS

Pyridostigmine bromide is inferior to fludrocortisone in the treatment of OH in PD. This trial provides first objective evidence of the efficacy of 0.2 mg/day fludrocortisone for OH in PD, causing minor peripheral but no central supine hypertension. In addition to peripheral bp, future trials should include central bp measurements, known to correlate more closely with cardiovascular risk.