Pressure wave reflection assessed from the peripheral pulse: is a transfer function necessary?

Non-contact quantification of aortic stenosis and mitral regurgitation using carotid waveforms from skin displacements

Objective. Early diagnosis of heart problems is essential for improving patient prognosis.Approach. We created a non-contact imaging system that calculates the vessel-induced deformation of the skin to estimate the carotid artery pressure displacement waveforms. We present a clinical study of the system in patients (n= 27) with no underlying condition, aortic stenosis (AS), or mitral regurgitation (MR).Main results. Displacement waveforms were compared to aortic catheter pressures in the same patients. The morphologies of the pressure and displacement waveforms were found to be similar, and pulse wave analysis metrics, such as our modified reflection indices (RI) and waveform duration proportions, showed no significant differences. Compared with the control group, AS patients displayed a greater proportion of time to peak (p= 0.026 andp= 0.047 for catheter and displacement, respectively), whereas augmentation index (AIx)was greater for the displacement waveform only (p= 0.030). The modified RI for MR (p= 0.047 andp= 0.004 for catheter and displacement, respectively) was lower than in the controls. AS and MR were also significantly different for the proportion of time to peak (p= 0.018 for the catheter measurements), RI (p= 0.045 andp= 0.002 for the catheter and displacement, respectively), and AIx (p= 0.005 for the displacement waveform).Significance. These findings demonstrate the ability of our system to provide insights into cardiac conditions and support further development as a diagnostic/telehealth-based screening tool.

Estimation of Central Systolic Blood Pressure from Peripheral Pressure Waves using a Novel Second Systolic Pressure-Based Method in Normal and Heritable Hypercholesterolemic Rabbits

AIM

Central systolic blood pressure (cSBP) was closely related to hypertension-related organ damage rather than peripheral systolic blood pressure (pSBP). We aimed to estimate cSBP from pSBP without generalized transfer function in normal and Kurosawa and Kusanagi-hypercholesterolemic (KHC) rabbits aged 12 months.

METHODS

Two catheter-tip transducers were advanced into the ascending aorta (AA) and distal end of the right brachial artery (Br) through the right common carotid and right radial arteries, respectively, under pentobarbital anesthesia. Pressure waves in response to the intravenous administration of angiotensin II and sodium nitroprusside were simultaneously recorded in AA and Br under regular cardiac pacing.

RESULTS

The first (pSBP) and second peaks (pSBP2) of the brachial blood pressure and their average (pSBPm) were significantly correlated with cSBP, despite Murgo's wave pattern of central pressure waves in both rabbit groups. In Bland-Altman plot and its modification as a function of the peripheral augmentation index (pAI) analyses, the differences between pSBP and cSBP decreased, and those between pSBP2 and cSBP increased significantly in their average- or pAI-dependent manner, with undeniable mean biases in both rabbit groups. When the same analyses for SBPm were performed instead, the mean bias was around zero, with reduced variance in the two rabbit groups. The observed pressure or pAI-dependent systematic biases for pSBP and pSBP2 disappeared, representing the precise feature of pSBPm as a cSBP estimate.

CONCLUSIONS

We conclude that pSBPm could be more precise than pSBP2 as a cSBP estimate, irrespective of blood pressure levels, pAI, or the presence of atherosclerosis.

The Diastolic Oscillation Amplitude Used as an Arterial Aging Indicator

Introduction

The compliance of the distal arteries depends on their vasoconstrictor tone and distensibility and is sensitive to endothelial function and aging. C2, a component of the Windkessel model, is a measure of distal arterial compliance, and establishes the magnitude of the pressure rise during early diastole. It is calculated from the diastolic portion of the radial pulse wave using sophisticated analyses. C2 is used as a cardiovascular risk indicator since it decreases with aging, high blood pressure, and diabetes. Here, we propose an alternative method to assess the distal arteries distensibility by measuring the amplitude of the oscillation that occurs at the beginning of diastole.

Methods

Peripheral pulse wave was evaluated noninvasively by applanation tonometry in 511 individuals (264 women) aged between 13 and 70 years. Diastolic amplitude (DA) was measured as the peak-to-peak amplitude of the diastolic oscillation. Radial augmentation index (RAIx) and pulse wave velocity (PWV) were also calculated.

Results

DA decreased approximately 2% per decade of life between 16 and 70 years from 19% to 7%, and was higher in men than in women (p<0.0001). Linear regression analysis identified RAIx as the strongest predictor of AD (p<0.0001), followed by age and height. Sex modified the age-related decrease in DA (p< 0.001). By applying the method to measure DA from previously published data, we found a strong linear correlation with C2.

Conclusion

DA decreased linearly with age in a reciprocal manner to the increase in radial augmentation index, was greater in men than women, and was independent of blood pressure and heart rate, as previously reported for C2. We propose that measuring DA could provide an alternative index to evaluate distal arterial compliance and aging.

Central and brachial pulse pressure predicts cardiovascular and renal events in treated hypertensive patients

PURPOSES

Central blood pressure is a stronger predictor of cardiovascular prognosis rather than brachial blood pressure. The reflection wave reaches the abdominal aorta sooner than ascending aorta. Thus, the contribution of central pulse pressure (cPP) to renal events may differ from that of cardiovascular events.

METHODS

The subanalysis of the ABC-J II study was performed. Subjects were 3434 treated hypertensive patients with a mean follow-up of 4.7 years. Left ventricular hypertrophy, an index of cardiovascular risk, correlated with cPP better than central systolic blood pressure in this cohort. The contribution of brachial pulse pressure (bPP) and cPP to cardiovascular and renal events was analysed.

RESULTS

Cox proportional-hazard analysis revealed that sex (p < 0.001), height (p < 0.05), history of cardiovascular diseases (p < 0.001), number of antihypertensive drugs (p < 0.05), and cPP (p < 0.05) contributed to cardiovascular events. However, Cox proportional-hazard analysis disclosed that baseline serum creatinine (p < 0.001) and bPP (p < 0.05) predicted renal events. After adjusting for the history of cardiovascular diseases, Cox regression demonstrated only sex as a significant predictor of cardiovascular events. After adjusting for baseline serum creatinine, no parameters were shown to predict renal events.

CONCLUSIONS

The present findings support our previous data that the absence of cardiovascular or renal diseases is an important determinant for event-free survival, and suggest that cPP and bPP contribute to cardiovascular and renal events in treated hypertensive patients.

Modulation of Arterial Stiffness Gradient by Acute Administration of Nitroglycerin

Background: Physiologically, the aorta is less stiff than peripheral conductive arteries, creating an arterial stiffness gradient, protecting microcirculation from high pulsatile pressure. However, the pharmacological manipulation of arterial stiffness gradient has not been thoroughly investigated. We hypothesized that acute administration of nitroglycerin (NTG) may alter the arterial stiffness gradient through a more significant effect on the regional stiffness of medium-sized muscular arteries, as measured by pulse wave velocity (PWV). The aim of this study was to examine the differential impact of NTG on regional stiffness, and arterial stiffness gradient as measured by the aortic-brachial PWV ratio (AB-PWV ratio) and aortic-femoral PWV ratio (AF-PWV ratio).

Methods: In 93 subjects (age: 61 years, men: 67%, chronic kidney disease [CKD]: 41%), aortic, brachial, and femoral stiffnesses were determined by cf-PWV, carotid-radial (cr-PWV), and femoral-dorsalis pedis artery (fp-PWV) PWVs, respectively. The measurements were repeated 5 min after the sublingual administration of NTG (0.4 mg). The AB-PWV and AF-PWV ratios were obtained by dividing cf-PWV by cr-PWV or fp-PWV, respectively. The central pulse wave profile was determined by radial artery tonometry through the generalized transfer function.

Results: At baseline, cf-PWV, cr-PWV, and fp-PWV were 12.12 ± 3.36, 9.51 ± 1.81, and 9.71 ± 1.89 m/s, respectively. After the administration of NTG, there was a significant reduction in cr-PWV of 0.86 ± 1.27 m/s (p < 0.001) and fp-PWV of 1.12 ± 1.74 m/s (p < 0.001), without any significant changes in cf-PWV (p = 0.928), leading to a significant increase in the AB-PWV ratio (1.30 ± 0.39 vs. 1.42 ± 0.46; p = 0.001) and AF-PWV ratio (1.38 ± 0.47 vs. 1.56 ± 0.53; p = 0.001). There was a significant correlation between changes in the AF-PWV ratio and changes in the timing of wave reflection (r = 0.289; p = 0.042) and the amplitude of the heart rate-adjusted augmented pressure (r = − 0.467; p < 0.001).

Conclusion: This study shows that acute administration of NTG reduces PWV of muscular arteries (brachial and femoral) without modifying aortic PWV. This results in an unfavorable profile of AB-PWV and AF-PWV ratios, which could lead to higher pulse pressure transmission into the microcirculation.

Pulse sharpness as a quantitative index of vascular aging

The aim of this study was to develop a robust algorithm to quantify pulse sharpness that can complement the limitations of radial augmentation index (rAIx) and explore the role of this quantitative sharpness index in reflecting vascular aging or arterial stiffness. The pulse sharpness index (PSI) was developed by combining the end point angle and virtual height, and 528 radial pulses were analyzed. The PSI could be uniformly applied to various waveform morphologies, even those with no or vague tidal waves, unlike the rAIx. Significant sex differences were identified in the rAIx and PSI (P < 0.01 for both), and significant age-dependent decreases in the PSI were observed (P < 0.01). In addition, the PSI and age were correlated (r = - 0.550) at least as strong as the rAIx and age (r = 0.532), and the PSI had a significant negative correlation with arterial stiffness (r = - 0.700). Furthermore, the multiple linear regression model for arterial stiffness using the PSI, age, sex and heart rate showed the excellent performance (cross-validated R2 = 0.701), and the PSI was found to have the greatest influence on arterial stiffness. This study confirmed that the PSI could be a quantitative index of vascular aging and has potential for use in inferring arterial stiffness with an advantage over the rAIx.

Transfer-function-free technique for the noninvasive determination of the human arterial pressure waveform

The estimation of central aortic blood pressure is a cardinal measurement, carrying effective physiological, and prognostic data beyond routine peripheral blood pressure. Transfer function-based devices effectively estimate aortic systolic and diastolic blood pressure from peripheral pressure waveforms, but the reconstructed pressure waveform seems to preserve features of the peripheral waveform. We sought to develop a new method for converting the local diameter distension waveform into a pressure waveform, through an exponential function whose parameters depend on the local wave speed. The proposed method was then tested at the common carotid artery. Diameter and blood velocity waveforms were acquired via ultrasound at the right common carotid artery while simultaneously recording pressure at the left common carotid artery via tonometer in 203 people (122 men, 50 ± 18 years). The wave speed was noninvasively estimated via the lnDU-loop method and then used to define the exponential function to convert the diameter into pressure. Noninvasive systolic and mean pressures estimated by the new technique were 3.8 ± 21.8 (p = 0.015) and 2.3 ± 9.6 mmHg (p = 0.011) higher than those obtained using tonometery. However, differences were much reduced and not significant in people >35 years (0.6 ± 18.7 and 0.8 ± 8.3 mmHg, respectively). This proof of concept study demonstrated that local wave speed, estimated from noninvasive local measurement of diameter and flow velocity, can be used to determine an exponential function that describes the relationship between local pressure and diameter. This pressure-diameter function can then be used for the noninvasive estimation of local arterial pressure.

Self-Adhesive, Stretchable, Biocompatible, and Conductive Nonvolatile Eutectogels as Wearable Conformal Strain and Pressure Sensors and Biopotential Electrodes for Precise Health Monitoring

Conductive stretchable hydrogels and ionogels consisting of ionic liquids can have interesting application as wearable strain and pressure sensors and bioelectrodes due to their soft nature and high conductivity. However, hydrogels have a severe stability problem because of water evaporation, whereas ionogels are not biocompatible or even toxic. Here, we demonstrate self-adhesive, stretchable, nonvolatile, and biocompatible eutectogels that can always form conformal contact to skin even during body movement along with their application as wearable strain and pressure sensors and biopotential electrodes for precise health monitoring. The eutectogels consist of a deep eutectic solvent that has high conductivity, waterborne polyurethane that is an elastomer, and tannic acid that is an adhesive. They can have an elongation at a break of 178%, ionic conductivity of 0.22 mS/cm, and adhesion force of 12.5 N/m to skin. They can be used as conformal strain sensors to accurately monitor joint movement and breath. They can be even used as pressure sensors with a piezoresistive sensitivity of 284.4 kPa^-1 to precisely detect subtle physical movements like arterial pulses, which can provide vital cardiovascular information. Moreover, the eutectogels can be used as nonvolatile conformal electrodes to monitor epidermal physiological signals, such as electrocardiogram (ECG) and electromyogram (EMG).

Sex modification of the association of the radial augmentation index and incident hypertension in a Chinese community-based population

BACKGROUND

Arterial stiffness, as assessed by aortic ultrasound and pulse wave velocity, is associated with incident hypertension. However, there is still no consensus on whether the augmentation index (AI) affects new onset of hypertension. This study investigated the relationship of radial AI (rAI) and incident hypertension in a Chinese community-based population without hypertension at baseline.

METHOD

A total of 1,615 Chinese non-hypertensive participants from an atherosclerosis cohort in Beijing, China were included in our analysis. Baseline rAI normalized to heart rate of 75 beats/min (rAIp75) was obtained using HEM-9000AI. New-onset hypertension was defined as blood pressure ≥ 140/90 mmHg or self-reported hypertension or taking anti-hypertensive medications at the follow up survey. Multivariate regression models were used to evaluate the impact of rAIp75 on the risk of new-onset hypertension.

RESULTS

After a mean 2.35-year follow-up, 213 (13.19%) participants developed incident hypertension. No significant relation between rAIp75 and incident hypertension was observed in the whole population after adjustment for possible confounders (adjusted odds ratio (OR) and 95% confidence interval (CI): 1.09 [0.95-1.27];P = 0.2260). However, rAIp75 was significantly associated with incident hypertension in women, but not in men (adjusted OR and 95% CI: 1.29 [1.06-1.56],P = 0.0113 for women; 0.91 [0.72-1.15],P = 0.4244 for men; P for interaction = 0.0133).

CONCLUSIONS

Sex modified the effect of the rAI on incident hypertension in a Chinese, community-based, non-hypertensive population. Screening of the rAI could be considered in women with a high risk of hypertension for the purpose of primary intervention.

Influence of noninvasive central blood pressure devices for afterload monitoring with aortic velocity-pressure Loop in anesthetized patients

BACKGROUND

Global afterload angle (GALA) is a parameter derived from velocity-pressure loop (VP Loop), for continuous assessment of cardiac afterload in the operating room. It has been validated with invasive measure of central pressure. The aim of this study was to evaluate the feasibility of noninvasive VP Loop obtained with central pressure measured with two different noninvasive tonometers.

METHODS

A prospective, observational, monocentric study was conducted in 51 patients under general anesthesia. Invasive central pressure (cPINV) was measured with a fulfilled intravascular catheter, and noninvasive central pressure signals were obtained with two applanation tonometry devices: radial artery tonometry (cPSHYG: Sphygmocor tonometer) and carotid tonometry (cPCOMP: Complior tonometer). Three VP Loops were built: VP LoopINV, VP LoopSPHYG and VP LoopCOMP. Patients were separated according to cardiovascular risk factors.

RESULTS

In the 51 patients under general anesthesia, cPSHYG was adequately obtained in 48 patients (89%) but, compared to cPINV, SBP was underestimated (-4 ± 6 mmHg, P < 0.0001), augmentation index (AIXSPHYG) and a GALASPHYG were overestimated (+13 ± 19%, P = 0.0077 and +4 ± 8°, P = 0.0024, respectively) with large limit of agreement (LOA) (-21 to 47% and -13 to 21° for AIXSPHYG and GALASPHYG, respectively). With the Complior, the failure rate of measurement for cPCOMP was 41%. SBP was similar (3 ± 17 mmHg, P = 0.32), AIXCOMP was underestimated (-11 ± 19%, P = 0.0046) and GALACOMP was similar but with large LOA (-50 to 26% and -20 to 18° for AIXCOMP and GALACOMP, respectively).

CONCLUSION

In anesthetized patient, the reliability of noninvasive central pressure monitoring by tonometry seems too limited to monitor cardiac afterload with VP Loop.

A systematic review of invasive, high-fidelity pressure studies documenting the amplification of blood pressure from the aorta to the brachial and radial arteries

It is commonly accepted that systolic blood pressure (SBP) is significantly higher in the brachial/radial artery than in the aorta while mean (MBP) and diastolic (DBP) pressures remain unchanged. This may have implications for outcome studies and for non-invasive devices calibration. We performed a systematic review of invasive high-fidelity pressure studies documenting BP in the aorta and brachial/radial artery. We selected articles published prior to July 2015. Pressure amplification (Amp = peripheral minus central pressure) was calculated (weighted mean). The six studies retained (n = 294, 76.5% male, mean age 63.5 years) mainly involved patients with suspected coronary artery disease (CAD). In two studies at the aortic/brachial level (n = 64), MBP and DBP were unchanged (MPAmp = 0.1 mmHg, DPAmp = -1.3 mmHg), while SBP increased (SPAmp = 4.2 mmHg; relative amplification = 3.1%). In four studies in which MBP was not documented (n = 230), brachial DBP remained unchanged and SBP increased (SPAmp = 6.6 mmHg; 4.9%). One of these four studies also reported radial SBP and DBP, not MBP (n = 12). Few high-fidelity pressure studies were found, and they have been performed mainly in elderly male patients with suspected CAD. Counter to expectations, the mean amplification of SBP from the aorta to brachial artery was < 5%. Further studies on SPAmp phenotypes (positive, null, negative) are advocated. Non-invasive device calibration assumptions were confirmed, namely unchanged MBP and DBP from the aorta to the brachial artery. Data did not allow for firm conclusions on the amount of BP changes from the aorta to the radial artery, and from the aorta to the brachial/radial arteries in other populations.

Arterial stiffness and pressure wave reflection in the development of isolated diastolic hypertension

OBJECTIVES

This prospective study was conducted to clarify the significance of augmented pressure wave reflection without accompanying increased arterial stiffness in the development of isolated diastolic hypertension (IDHT).

METHODS

A total of 3022 Japanese men without hypertension at the start of this study were included in the analyses. The blood pressure, brachial--ankle pulse wave velocity (brachial-ankle PWV), and radial augmentation index (rAI) were measured annually from year 2007 through year 2015.

RESULTS

At the end of the study period, 129 participants were diagnosed as having systolic/diastolic hypertension (SDHT), 112 as having isolated systolic hypertension (ISHT), and 74 as having IDHT. Both the brachial--ankle PWV and rAI showed significant individual odds ratios for new onset of SDHT and new onset of ISHT. However, only rAI, but not the brachial--ankle PWV, showed a significant odds ratio (1.44, P < 0.01) for new onset of IDHT. This association was significant in participants without elevated brachial--ankle PWV values at the start of the study, but not in those with elevated brachial--ankle PWV at the start of the study. Generalized estimating equation analyses demonstrated a significant longitudinal association of the rAI, but not brachial--ankle PWV, with the development of IDHT.

CONCLUSION

Although increased arterial stiffness and augmented pressure wave reflection present concomitantly may be associated with the development of SDHT and ISHT, augmented pressure wave reflection alone, which may be related to isolated peripheral vascular damage, in the absence of accompanying increase of the arterial stiffness, may be a significant factor in the development of IDHT.

Measurement, Analysis and Interpretation of Pressure/Flow Waves in Blood Vessels

The optimal performance of the cardiovascular system, as well as the break-down of this performance with disease, both involve complex biomechanical interactions between the heart, conduit vascular networks and microvascular beds. ‘Wave analysis’ refers to a group of techniques that provide valuable insight into these interactions by scrutinizing the shape of blood pressure and flow/velocity waveforms. The aim of this review paper is to provide a comprehensive introduction to wave analysis, with a focus on key concepts and practical application rather than mathematical derivations. We begin with an overview of invasive and non-invasive measurement techniques that can be used to obtain the signals required for wave analysis. We then review the most widely used wave analysis techniques—pulse wave analysis, wave separation and wave intensity analysis—and associated methods for estimating local wave speed or characteristic impedance that are required for decomposing waveforms into forward and backward wave components. This is followed by a discussion of the biomechanical phenomena that generate waves and the processes that modulate wave amplitude, both of which are critical for interpreting measured wave patterns. Finally, we provide a brief update on several emerging techniques/concepts in the wave analysis field, namely wave potential and the reservoir-excess pressure approach.

Impact of simultaneous measurement of central blood pressure with the SphygmoCor Xcel during MRI acquisition to better estimate aortic distensibility

OBJECTIVES

Aortic distensibility estimation of local aortic stiffness is based on local aortic strains and central pulse pressure (cPP) measurements. Most MRI studies used either brachial PP (bPP) despite differences with cPP, or direct cPP estimates obtained after MRI examination, assuming no major pressure variations. We evaluated the feasibility of assessment of cPP with a specific device fitted with a 6 m long hose (study1) and looked at the influence of using such cPP within the magnet instead of bPP on aortic distensibility in a control population (study 2).

METHODS

Brachial and central pressures values were recorded with the SphygmoCor XCEL system fitted with 2 and 6 m long tubing randomly assigned on arms. A 6 m long tubing was used in the second study to measure aortic distensibility with MRI. Aortic distensibility was calculated using either bPP (bAD) or cPP (cAD).

RESULTS

Study1, performed on 38 patients (mean age: 43 ± 17 years), showed no statistical difference between bPP and cPP measured with 2 or 6 m long tubing (0.41 ± 4.45 and 0.78 ± 3.18 mmHg, respectively, both P = ns). In study 2, cAD provided statistically higher values than bAD (1.87 ± 1.43 10 · mmHg, P < 0.001) especially in younger individuals (3.28 ± 0.86 10 · mmHg). The correlation between age and aortic distensibility was stronger with cAD (r = -0.92; P < 0,001) than with bAD (r = -0.88; P < 0.001).

CONCLUSION

cPP can be estimated with reasonable accuracy during MRI acquisition using a 6 m long tube. Using either cPP or bPP greatly influences aortic distensibility values, especially in young individuals in whom an accurate detection of early or accelerated vascular aging can be of major importance.

Magnetic-Assisted Transparent and Flexible Percolative Composite for Highly Sensitive Piezoresistive Sensor via Hot Embossing Technology

A highly transparent and flexible percolative composite with magnetic reduced graphene oxide@nickel nanowire (mGN) fillers in EcoFlex matrix is proposed as a sensing layer to fabricate high-performance flexible piezoresistive sensors. Large excluded volume and alignment of mGN fillers contribute to low percolation threshold (0.27 vol %) of mGN-EcoFlex composites, leading to high electrical conductivity of 0.003 S m^-1, optical transmittance of 71.8%, and low Young's modulus of 122.8 kPa. Large-scale microdome templates for sensors are prepared by hot embossing technology cost-effectively and COMSOL Multiphysics is utilized to optimize the sensor performances. Piezoresistive sensors fabricated experimentally show superior average sensitivity of 1302.1 kPa^-1 with a low device-to-device variation of 3.74%, which provides a new way to achieve transparent, highly sensitive, and large-scale electronic skin.

Innovative multi-site photoplethysmography measurement and analysis demonstrating increased arterial stiffness in paediatric heart transplant recipients

OBJECTIVE

It has been documented that heart transplantation in children is often complicated by arterial hypertension and increased arterial stiffness. We use innovative multi-site photoplethysmography (MPPG) pulse measurement and analysis technology to assess changes in arterial stiffness in paediatric heart transplant recipients (HTRs) in comparison with healthy control (HC) children.

APPROACH

A group of 20 HTRs (median age 13.5 years, eight male) were compared to an overall age- and gender-matched group of 161 HCs (median age 11.6 years, 74 male). Peripheral pulse was recorded bilaterally using MPPG at the ear lobe, index finger and great toe sites, along with an electrocardiogram cardiac timing reference. Segmental pulse arrival times between peripheral sites (finger-ear, PATf-e; toe-finger, PATt-f; and toe-ear PATt-e) were calculated as arterial stiffness measures, and differences between subject groups were tested using multivariate analysis. Normalised ear, finger and toe pulse shapes were also studied and compared between groups.

MAIN RESULTS

After correction for heart rate and diastolic and mean arterial blood pressures, the HTR group was found to have significantly lower segmental PATt-e and PATt-f measurements, with median values of 150 ms versus 172 ms in the HC group (p  =  0.02), and 104 ms versus 118 ms in the HC group (p  =  0.01), respectively, consistent with increased arterial stiffness in the patient group. The normalised ear, finger and toe sites showed only a mild elongation in each pulse rise time for the transplant group.

SIGNIFICANCE

This study shows that innovative and easy-to-do MPPG gives further evidence for increased arterial stiffness in children who have undergone successful cardiac transplantation.

Arterial reservoir characteristics and central-to-peripheral blood pressure amplification in the human upper limb

BACKGROUND

Arterial reservoir characteristics are related to blood pressure (BP) and independently predict cardiovascular events. It is unknown if arterial reservoir characteristics are modified from the central-to-peripheral large arteries and whether there is a contributory role to BP amplification. The aim of this study was to assess central-to-peripheral changes in arterial reservoir characteristics and determine associations with BP.

METHODS

Reservoir pressure (RP) and excess pressure (XSP) were derived from intra-arterial BP waveforms among 51 participants (aged 63 ± 13 years, 63% men) undergoing clinically indicated cardiac angiography. BP waveforms were recorded in the ascending aorta, brachial (mid-humerus) and radial (wrist) arteries via catheter pull-back.

RESULTS

There was no significant difference in RP between arterial sites (54 ± 15, 53 ± 15 and 52 ± 17 mmHg for the aorta, brachial and radial artery, respectively; P = 0.68). Conversely, XSP increased stepwise from the aorta to the brachial and radial arteries (24 ± 11, 42 ± 14 and 53 ± 16 mmHg; P < 0.001), as did SBP (134 ± 18, 141 ± 16 and 146 ± 19 mmHg; P = 0.004). There were highly significant associations between RP and SBP at all arterial sites (r = 0.821, 0.649 and 0.708; P < 0.001 for all), but the strength of associations between peak XSP and SBP increased significantly from the aorta to the radial artery (r = 0.121 and 0.508; z = 3.04; P = 0.004).

CONCLUSION

Arterial reservoir characteristics are modified through the large arteries of the upper limb. Although RP remains relatively constant, XSP increases significantly and is highly related to BP (SBP and pulse pressure) amplification. These data provide a new understanding on arterial reservoir characteristics and large-artery BP physiology.

Velocity-pressure loops for continuous assessment of ventricular afterload: influence of pressure measurement site

VPloop, the graphical representation of pressure versus velocity, and its characteristic angles, GALA and β, can be used to monitor cardiac afterload during anesthesia. Ideally VPloop should be measured from pressure and velocity obtained at the same arterial location but standard of care usually provide either radial or femoral pressure waveforms. The purpose of this study was to look at the influence of arterial sites and the use of a transfer function (TF) on VPloop and its related angles. Invasive pressure signals were recorded in 25 patients undergoing neuroradiology intervention under general anesthesia with transesophageal flow velocity monitoring. Pressures were recorded in the descending thoracic aorta, abdominal aorta, femoral and radial arteries. We compared GALA and β from VPloops generated from each location and in high and low risk patients. GALA was similar in the central locations (55°[49-63], 52°[47-61] and 54°[45-62] from descending thoracic to femoral artery, median[interquartile], p = 0.10), while there was a difference in β angle (16°[4-27] to 8°[3-15], p < 0.0001). GALA and β obtained from radial waveforms were different (39°[31-47] compared to 46°[36-54] and 6°[2-14] compared to 16°[4-27] for GALA and β angles respectively, p < 0.001) which was corrected by the use of a TF (45°[32-55] and 17°[5-28], p = ns). GALA and β are underestimated when measured with a radial catheter. Using pressure waveforms from femoral locations alters VPloops, GALA and β in a smaller extend. The use of a TF on radial pressure allows to correctly plot VPloops and their characteristic angles for routine clinical use.

Radial Pulse and Electrocardiography Modulation by Mild Thermal Stresses Applied to Feet: An Exploratory Study with Randomized, Crossover Design

OBJECTIVE

To investigate the changes in radial pulse induced by thermal stresses (TSs).

METHODS

Sixty subjects were enrolled. Using an open-label, 2×2 crossover randomization design, both feet of each subject were immersed in 15 °C water for cold stress (CS) and in 40 °C water for heat stress (HS) for 5 min each. Radial pulse, respiration and electrocardiogram (ECG) signals were recorded before, during and immediately after the TSs.

RESULTS

The analysis of heart rate variability revealed that CS increased the low-frequency (LF) and high-frequency (HF) components (P <0.05) and that HS reduced the LF and HF components (P <0.01). Both TSs reduced the normalized LF, increased the normalized HF, and reduced the LF/HF ratio. The differences in the ECG signals were more dominant during the TS sessions, but those in the radial pulse signals became more dominant immediately after the TS sessions. CS decreased the pulse depth (P <0.01) and increased the radial augmentation index (P <0.1), and HS increased the pulse pressure (P <0.1) and subendocardial viability ratio (P <0.01). There were no significant differences in pulse rate during the three time sequences of each TS. The respiration rate was increased (P <0.1), and the pulse rate per respiration (P/R ratio) was significantly decreased (P <0.05) with CS. The HF region (10-30 Hz) of the pulse spectral density was suppressed during both TSs.

CONCLUSIONS

CS induced vasoconstriction and sympathetic reactions, and HS induced vasodilation and parasympathetic reactions. Based on definitions used in pulse diagnosis, we made the novel discoveries that the pulse became slower (decreased P/R ratio), more floating and tenser under CS and that the HF region of the spectral power decreased significantly under both TSs.

Surface-Embedded Stretchable Electrodes by Direct Printing and their Uses to Fabricate Ultrathin Vibration Sensors and Circuits for 3D Structures

Printing is one of the easy and quick ways to make a stretchable wearable electronics. Conventional printing methods deposit conductive materials "on" or "inside" a rubber substrate. The conductors made by such printing methods cannot be used as device electrodes because of the large surface topology, poor stretchability, or weak adhesion between the substrate and the conducting material. Here, a method is presented by which conductive materials are printed in the way of being surface-embedded in the rubber substrate; hence, the conductors can be widely used as device electrodes and circuits. The printing process involves a direct printing of a metal precursor solution in a block-copolymer rubber substrate and chemical reduction of the precursor into metal nanoparticles. The electrical conductivity and sensitivity to the mechanical deformation can be controlled by adjusting the number of printing operations. The fabrication of highly sensitive vibration sensors is thus presented, which can detect weak pulses and sound waves. In addition, this work takes advantage of the viscoelasticity of the composite conductor to fabricate highly conductive stretchable circuits for complicated 3D structures. The printed electrodes are also used to fabricate a stretchable electrochemiluminescence display.

Diastolic Augmentation Index Improves Radial Augmentation Index in Assessing Arterial Stiffness

Arterial stiffness is an important risk factor for cardiovascular events. Radial augmentation index (AI_r) can be more conveniently measured compared with carotid-femoral pulse wave velocity (cfPWV). However, the performance of AI_r in assessing arterial stiffness is limited. This study proposes a novel index AI_rd, a combination of AI_r and diastolic augmentation index (AI_d) with a weight α, to achieve better performance over AI_r in assessing arterial stiffness. 120 subjects (43 ± 21 years old) were enrolled. The best-fit α is determined by the best correlation coefficient between AI_rd and cfPWV. The performance of the method was tested using the 12-fold cross validation method. AI_rd (r = 0.68, P < 0.001) shows a stronger correlation with cfPWV and a narrower prediction interval than AI_r (r = 0.61, P < 0.001), AI_d (r = −0.17, P = 0.06), the central augmentation index (AI_c) (r = 0.61, P < 0.001) or AI_c normalized for heart rate of 75 bpm (r = 0.65, P < 0.001). Compared with AI_r (age, P < 0.001; gender, P < 0.001; heart rate, P < 0.001; diastolic blood pressure, P < 0.001; weight, P = 0.001), AI_rd has fewer confounding factors (age, P < 0.001; gender, P < 0.001). In conclusion, AI_rd derives performance improvement in assessing arterial stiffness, with a stronger correlation with cfPWV and fewer confounding factors.

Traditional Chinese medicine wrist pulse-taking is associated with pulse waveform analysis and hemodynamics in hypertension

BACKGROUND

Pulse wave analysis (PWA) quantifies the phenomenon of pulse waveform propagation in patients with cardiovascular diseases, whereas pulse image analysis (PIA) is a subjective examination in traditional Chinese medicine.

OBJECTIVE

This study evaluated the association of PIA with PWA and hemodynamics in patients with hypertension.

DESIGN, SETTING, PARTICIPANTS AND INTERVENTIONS

This observational, cross-sectional study enrolled 45 patients (26 men, (55.2 ± 10.3) years, systolic blood pressure (155 ± 28) mmHg, diastolic blood pressure (93 ± 17) mmHg) for assessment of clinical and laboratorial data.

MAIN OUTCOME MEASURES

Primary outcomes comprised: pattern differentiation based on an automated method; PIA at the radial artery using the 'simultaneous pressing' method for identification of factors such as strength (strong/weak), depth (superficial/deep), and speed (fast/moderate/slow); and PWA at the same artery using a noninvasive system.

RESULTS

Significant multivariate main effects were observed for depth (λ=0.648, F5,29 =3.149, P=0.022, η(2) =0.352), strength (λ=0.608, F5,29 =3.736, P=0.010, η(2) =0.392), and speed (λ=0.535, F5,29 =5.302, P=0.002, η(2) =0.465). General effects comprised high values of PWA and blood pressure for superficial, strong, and fast pulse images. A strong pulse was found for pulse pressure ≥ 62.5 mmHg and systolic blood pressure ≥ 149.5 mmHg, whereas a superficial pulse was found for heart rate ≥ 58.25 beats/min; a fast pulse was found for heart rate ≥ 69.6 beats/min and pulse wave velocity ≥ 9.185 m/s.

CONCLUSION

Associations were explained by LaPlace's law, arterial remodeling in hypertension, alongside the traditional criterion for classifying speed in pulse images. PIA is associated with PWA and hemodynamics in patients with hypertension. Systolic and pulse pressures, heart rate, and pulse wave velocity are quantitative variables that have information to describe the qualitative pulse images such as strength, depth and speed.

Reduction of Central Blood Pressure in Response to Oral Glucose Loading Is Blunted in Patients With Diabetes Mellitus

BACKGROUND

Recent studies have shown that arterial stiffness is reduced after meal intake. We evaluated the acute response of central hemodynamics to glucose loading and the variation in their responses among normal glucose tolerance (NGT), impaired glucose tolerance (IGT), and diabetes mellitus (DM).

METHODS

The study enrolled 85 patients with known or suspected coronary artery disease who underwent a 75-g oral glucose tolerance test. Central hemodynamic measurements were assessed using radial applanation tonometry at fasting, 60, and 120 minutes after glucose loading.

RESULTS

Glucose loading decreased the augmentation index normalized to a heart rate of 75 bpm (AIx@75) (81.6±13.9 to 74.5±14.1%, P < 0.01) and central systolic blood pressure (SBP) (115±22 to 109±21mm Hg, P < 0.01) at 120 minutes without a significant change in brachial SBP (126±25 to 125±25mm Hg, P = 0.93). Glucose loading decreased central SBP in NGT and IGT groups but did not affect the DM group. Change in AIx@75 at 120 minutes after glucose loading was blunted in IGT and DM groups compared with the NGT group (-5.7±4.4 vs. -3.6±4.1 vs. -9.3±6.2%, P < 0.01). Multivariate logistic regression analysis identified DM as an independent factor associated with the presence of blunted response of AIx to glucose loading.

CONCLUSIONS

Oral glucose loading decreased central SBP and AIx@75 without a significant change in brachial SBP, and these central hemodynamic responses were blunted in patients with DM.

Associations and clinical relevance of aortic-brachial artery stiffness mismatch, aortic reservoir function, and central pressure augmentation

Central augmentation pressure (AP) and index (AIx) predict cardiovascular events and mortality, but underlying physiological mechanisms remain disputed. While traditionally believed to relate to wave reflections arising from proximal arterial impedance (and stiffness) mismatching, recent evidence suggests aortic reservoir function may be a more dominant contributor to AP and AIx. Our aim was therefore to determine relationships among aortic-brachial stiffness mismatching, AP, AIx, aortic reservoir function, and end-organ disease. Aortic (aPWV) and brachial (bPWV) pulse wave velocity were measured in 359 individuals (aged 61 ± 9, 49% male). Central AP, AIx, and aortic reservoir indexes were derived from radial tonometry. Participants were stratified by positive (bPWV > aPWV), negligible (bPWV ≈ aPWV), or negative stiffness mismatch (bPWV < aPWV). Left-ventricular mass index (LVMI) was measured by two-dimensional-echocardiography. Central AP and AIx were higher with negative stiffness mismatch vs. negligible or positive stiffness mismatch (11 ± 6 vs. 10 ± 6 vs. 8 ± 6 mmHg, P < 0.001 and 24 ± 10 vs. 24 ± 11 vs. 21 ± 13%, P = 0.042). Stiffness mismatch (bPWV-aPWV) was negatively associated with AP (r = -0.18, P = 0.001) but not AIx (r = -0.06, P = 0.27). Aortic reservoir pressure strongly correlated to AP (r = 0.81, P < 0.001) and AIx (r = 0.62, P < 0.001) independent of age, sex, heart rate, mean arterial pressure, and height (standardized β = 0.61 and 0.12, P ≤ 0.001). Aortic reservoir pressure independently predicted abnormal LVMI (β = 0.13, P = 0.024). Positive aortic-brachial stiffness mismatch does not result in higher AP or AIx. Aortic reservoir function, rather than discrete wave reflection from proximal arterial stiffness mismatching, provides a better model description of AP and AIx and also has clinical relevance as evidenced by an independent association of aortic reservoir pressure with LVMI.

Noninvasive calculation of the aortic blood pressure waveform from the flow velocity waveform: a proof of concept

Estimation of aortic and left ventricular (LV) pressure usually requires measurements that are difficult to acquire during the imaging required to obtain concurrent LV dimensions essential for determination of LV mechanical properties. We describe a novel method for deriving aortic pressure from the aortic flow velocity. The target pressure waveform is divided into an early systolic upstroke, determined by the water hammer equation, and a diastolic decay equal to that in the peripheral arterial tree, interposed by a late systolic portion described by a second-order polynomial constrained by conditions of continuity and conservation of mean arterial pressure. Pulse wave velocity (PWV, which can be obtained through imaging), mean arterial pressure, diastolic pressure, and diastolic decay are required inputs for the algorithm. The algorithm was tested using 1) pressure data derived theoretically from prespecified flow waveforms and properties of the arterial tree using a single-tube 1-D model of the arterial tree, and 2) experimental data acquired from a pressure/Doppler flow velocity transducer placed in the ascending aorta in 18 patients (mean ± SD: age 63 ± 11 yr, aortic BP 136 ± 23/73 ± 13 mmHg) at the time of cardiac catheterization. For experimental data, PWV was calculated from measured pressures/flows, and mean and diastolic pressures and diastolic decay were taken from measured pressure (i.e., were assumed to be known). Pressure reconstructed from measured flow agreed well with theoretical pressure: mean ± SD root mean square (RMS) error 0.7 ± 0.1 mmHg. Similarly, for experimental data, pressure reconstructed from measured flow agreed well with measured pressure (mean RMS error 2.4 ± 1.0 mmHg). First systolic shoulder and systolic peak pressures were also accurately rendered (mean ± SD difference 1.4 ± 2.0 mmHg for peak systolic pressure). This is the first noninvasive derivation of aortic pressure based on fluid dynamics (flow and wave speed) in the aorta itself.

Paradoxical normoxia-dependent selective actions of inorganic nitrite in human muscular conduit arteries and related selective actions on central blood pressures

BACKGROUND

Inorganic nitrite dilates small resistance arterioles via hypoxia-facilitated reduction to vasodilating nitric oxide. The effects of nitrite in human conduit arteries have not been investigated. In contrast to nitrite, organic nitrates are established selective dilators of conduit arteries.

METHODS AND RESULTS

We examined the effects of local and systemic administration of sodium nitrite on the radial artery (a muscular conduit artery), forearm resistance vessels (forearm blood flow), and systemic hemodynamics in healthy male volunteers (n=43). Intrabrachial sodium nitrite (8.7 μmol/min) increased radial artery diameter by a median of 28.0% (25th and 75th percentiles, 25.7% and 40.1%; P<0.001). Nitrite (0.087-87 μmol/min) displayed conduit artery selectivity similar to that of glyceryl trinitrate (0.013-4.4 nmol/min) over resistance arterioles. Nitrite dose-dependently increased local cGMP production at the dose of 2.6 μmol/min by 1.1 pmol·min(-1)·100 mL(-1) tissue (95% confidence interval, 0.5-1.8). Nitrite-induced radial artery dilation was enhanced by administration of acetazolamide (oral or intra-arterial) and oral raloxifene (P=0.0248, P<0.0001, and P=0.0006, respectively) but was inhibited under hypoxia (P<0.0001) and hyperoxia (P=0.0006) compared with normoxia. Systemic intravenous administration of sodium nitrite (8.7 μmol/min) dilated the radial artery by 10.7% (95% confidence interval, 6.8-14.7) and reduced central systolic blood pressure by 11.6 mm Hg (95% confidence interval, 2.4-20.7), augmentation index, and pulse wave velocity without changing peripheral blood pressure.

CONCLUSIONS

Nitrite selectively dilates conduit arteries at supraphysiological and near-physiological concentrations via a normoxia-dependent mechanism that is associated with cGMP production and is enhanced by acetazolamide and raloxifene. The selective central blood pressure-lowering effects of nitrite have therapeutic potential to reduce cardiovascular events.

Evaluation of 24-Hour Arterial Stiffness Indices and Central Hemodynamics in Healthy Normotensive Subjects versus Treated or Untreated Hypertensive Patients: A Feasibility Study

Objective. Central blood pressure (BP) and vascular indices estimated noninvasively over the 24 hours were compared between normotensive volunteers and hypertensive patients by a pulse wave analysis of ambulatory blood pressure recordings. Methods. Digitalized waveforms obtained during each brachial oscillometric BP measurement were stored in the device memory and analyzed by the validated Vasotens technology. Averages for the 24 hours and for the awake and asleep subperiods were computed. Results. 142 normotensives and 661 hypertensives were evaluated. 24-hour central BP, pulse wave velocity (PWV), and augmentation index (AI) were significantly higher in the hypertensive group than in the normotensive group (119.3 versus 105.6 mmHg for systolic BP, 75.6 versus 72.3 mmHg for diastolic BP, 10.3 versus 10.0 m/sec for aortic PWV, −9.7 versus −40.7% for peripheral AI, and 24.7 versus 11.0% for aortic AI), whereas reflected wave transit time (RWTT) was significantly lower in hypertensive patients (126.6 versus 139.0 ms). After adjusting for confounding factors a statistically significant between-group difference was still observed for central BP, RWTT, and peripheral AI. All estimates displayed a typical circadian rhythm. Conclusions. Noninvasive assessment of 24-hour arterial stiffness and central hemodynamics in daily life dynamic conditions may help in assessing the arterial function impairment in hypertensive patients.

A new tonometric device for radial augmentation index and subendocardial viability ratio: potential use in health screening

Augmentation index (AIx) and subendocardial viability ratio (SEVR) are widely accepted indices of wave reflection and myocardial oxygen demand relative to supply. This study aimed to validate a new tonometric device (IIM-2010A) for obtaining AIx and SEVR from radial artery. A total of 68 outpatients (32 men and 36 women) aged 20 to 76 years (44.7±16.6 years) recruited from a health screening center participated in the study. AIx was obtained from radial pressure using the HEM-9000AI and IIM-2010A devices, while SEVR was measured from carotid pressure with the tonometric method and from radial pressure by the IIM-2010A device. In a subgroup of 24 patients, the measurements of AIx and SEVR were repeated after an interval of 10 minutes. The correlation of radial AIx between the IIM-2010A and HEM-9000AI devices was highly significant (r=0.956, P<.01). Radial SEVR determined from IIM-2010A was also highly related to carotid SEVR (r=0.864, P<.01), although the value was about 13.1% lower. There was no statistically significant difference between the repeated measurements of both indices. The lower coefficient of variation (2.9% vs 4.3% for AIx, 3.3% vs 4.1% for SEVR) and higher intraclass correlation coefficient (0.96 vs 0.91 for AIx, 0.93 vs 0.86 for SEVR) of IIM-2010A confirmed better short-term reproducibility, compared with the HEM-9000AI device and carotid tonometry. The new tonometric device IIM-2010A is effective and reproducible in calculating radial AIx and SEVR and has potential use in health screening.

Ivabradine therapy to unmask heart rate-independent effects of β-blockers on pulse wave reflections

BACKGROUND

Prior studies suggest that β-blockers lead to increased pulse wave reflections, thereby negating the blood pressure lowering effects on cardiovascular mortality. Parts of these effects may be induced by the heart rate reduction under β-blockade. The aim of this study was to unmask heart rate-independent effects of β-blockade on pulse wave reflections by switching therapy from β-blockers to ivabradine, an I f channel inhibitor without impact on systemic hemodynamics.

METHODS

14 male patients (age 61 ± 3 years, LVEF 62 ± 1 %) with arterial hypertension and coronary artery disease (CAD) under chronic β-blocker therapy at moderate dosage and additional renin-angiotensin system-blocking therapy were included. We determined radial augmentation index (rAI) by radial applanation tonometry in patients under β-blockade both at rest and during early recovery after exercise. β-Blockers were then replaced by ivabradine. Six weeks later, patients were re-tested at rest and after exercise under ivabradine therapy.

RESULTS

Mean heart rate (68 ± 3 vs. 63 ± 3 bpm; p = ns) and resting mean arterial pressure (98 ± 2 vs. 98 ± 2 mmHg; p = ns) were not different between β-blocker or ivabradine therapy, respectively. The rAI remained unchanged after switching therapy from β-blocker to ivabradine (86 ± 2 vs. 84 ± 4 %; p = ns). Post exercise, the rAI revealed an identical decrease in both groups (-7.2 ± 2.4 vs. -5.4 ± 2.5 %, p = ns). The increase in heart rate between resting conditions and early recovery post exercise was inversely correlated with the decrease of rAI under β-blockade (r = -0.70; p < 0.01) and showed a trend towards correlation under ivabradine (r = -0.52; p = 0.07).

CONCLUSION

In men at the age of 60 years and CAD, β-blockade does not exert heart rate-independent, pleiotropic effects on peripheral pulse wave reflections, both at rest or after exercise. Our results fit well within recent studies, demonstrating the fundamental influence of heart rate on rAI.

Meta-analysis of the comparative effects of different classes of antihypertensive agents on brachial and central systolic blood pressure, and augmentation index

AIMS

Brachial systolic blood pressure (bSBP) exceeds aortic pressure by a variable amount, and estimated central systolic blood pressure (cSBP) may be a better indicator of cardiovascular risk than bSBP. We undertook a systematic review and meta-analysis to compare the effect of single and multiple antihypertensive agents on bSBP, cSBP and augmentation index (AIx).

METHODS

A random effects meta-analysis was performed on 24 randomized controlled trials of antihypertensives with measurements of bSBP, cSBP and/or AIx. Separate analyses were performed for drug comparisons with or without placebo, and drug combinations.

RESULTS

In the placebo vs. drug meta-analysis, antihypertensive therapy reduced bSBP more than cSBP and there was no statistically significant evidence of heterogeneity by drug class, although the number of individual studies was small. In placebo-adjusted drug vs. drug comparison, treatment with β-blockers, omapatrilat and thiazide diuretics lowered cSBP significantly less than bSBP (i.e. central to brachial amplification decreased), whereas other monotherapies lowered cSBP and bSBP to similar extents. Sample sizes were too small and effect estimates insufficiently precise to allow firm conclusions to be made regarding comparisons between individual drug classes. Antihypertensive combinations that included β-blockers decreased central to brachial amplification. β-Blockers increased AIx, whereas all other antihypertensive agents reduced AIx to similar extents.

CONCLUSIONS

A reduction in central to brachial amplification by some classes of antihypertensive drug will result in lesser reductions in cSBP despite achievement of target bSBP. This effect could contribute to differences in outcomes in randomized clinical trials when β-blocker- and/or diuretic-based antihypertensive therapy are compared with other regimens.

Heart rate affects endothelial function in essential hypertension

Increased heart rate (HR) is a risk factor for cardiovascular morbidity and mortality in the general population and in some clinical conditions. Endothelial dysfunction is an adverse prognostic factor for cardiovascular events. The aim of the study was to evaluate the effect of HR on central hemodynamic parameters and endothelial function in hypertension. We evaluated forearm blood flow (FBF) response to intra-arterial infusion of acetylcholine (ACh) and sodium nitroprusside (SNP) in 30 patients with HR ≤60 min(-1) and 30 with HR ≥80 min(-1). The FBF was measured by strain-gauge plethysmography. Transesophageal atrial pacing was used to increase the HR. Radial artery applanation tonometry and pulse wave analysis were used to derive central aortic pressures and correlate hemodynamic indices. The FBF response to ACh is lower in hypertensives with HR ≤60 min(-1) than in those with HR ≥80 min(-1) (10.6 ± 4.2 vs. 13.6 ± 5.1 ml × 100 ml(-1) of tissue × min(-1), P < 0.001). Vascular resistance decreases to 9.3 ± 2.8 U in patients with lower HR versus 7.2 ± 2.1 U in those with higher HR (P = 0.002). The FBF response to SNP is similar in both groups. Central systolic and pulse pressure are higher in bradycardic patients than in those with HR ≥80 min(-1) (140 ± 8 vs. 131 ± 8 mmHg, P = 0.0001 and 49 ± 10 vs. 39 ± 11 mmHg, P = 0.0001). All central hemodynamic parameters decrease during incremental atrial pacing. Augmentation index is the strongest predictor of endothelial dysfunction at multivariate analysis. These findings demonstrate that low HR affects endothelium-dependent vasodilation in hypertension. Increased central aortic pressure and hemodynamic correlates seem to be the underlying mechanisms by which bradycardia interferes with endothelium-dependent reactivity.

Does the augmentation index of pulse waves truly increase with progression of atherosclerosis? An experimental study with hypercholesterolemic rabbits

BACKGROUND

Recently, the central augmentation index (AIx) has been reported to show a nonlinear correlation with age. We investigated whether the AIx of the central artery changes with the progression of atherosclerosis in Kurosawa and Kusanagi-hypercholesterolemic (KHC) rabbits.

METHODS

We simultaneously recorded pressure and flow waves in the ascending aorta in normal and KHC rabbits aged 10-12, 22-24, and 34-36 months, under pentobarbital anesthesia.

RESULTS

The systolic, diastolic, and mean arterial pressures and total peripheral vascular resistance were significantly higher in KHC rabbits than in their age-matched controls. The systolic pressure of the KHC rabbits increased with age. Additionally, the AIx of the KHC rabbits was significantly higher than that of their age-matched controls, although the AIx did not show a significant age-dependent increase in either of the two rabbit groups. However, the development of atherosclerotic lesions progressed markedly in KHC rabbits, and the early and late (pulse pressure [PP]) systolic waves increased progressively in amplitude with age in the KHC rabbits. On the other hand, no significant differences were seen in the normal and KHC rabbits' cardiac output (CO), stroke volume (SV), or heart rate (HR) at any age, nor did the two strains show significant age-related changes in these variables. Aortic compliance (SV/PP) was significantly lower in the 22-24- and 34-36-month-old KHC rabbits than in their age-matched controls, and decreased with age in the KHC rabbits.

CONCLUSIONS

Although the progression of atherosclerosis stiffened the aortic wall, it did not affect the AIx. This was partly the result of the decreased distensibility of the wall, in which the pressure waves used to determine AIx were measured.

Central systolic augmentation indexes and urinary sodium in a white population

BACKGROUND

The association between cardiovascular health and salt intake remains controversial. The objective of our study was to assess the association between arterial stiffness and urinary sodium, both cross-sectionally and prospectively.

METHODS

In 630 participants (mean age 40.6 years; 51% women), randomly recruited from a Flemish population, we measured sodium and creatinine in 24-hour urine samples at baseline and follow-up (median, 9.7 years) and the carotid and aortic augmentation indexes (AIs) standardized to heart rate at follow-up only.

RESULTS

From baseline to follow-up, the urinary sodium concentration decreased (117.1 vs. 105.2 mmol/L; P < 0.0001), whereas 24-hour urinary sodium did not change significantly (166.5 vs. 171.5 mmol/L; P = 0.12). In multivariable-adjusted longitudinal analyses, a 40 mmol/L (~1 SD) increase in the urinary sodium concentration was independently and inversely associated with the carotid AI (effect size, -1.38 ± 0.66%; P = 0.04) and aortic AI (-1.54 ± 0.72%; P = 0.02). In cross-sectional analyses of follow-up data, these estimates were -1.26 ± 0.70% (P = 0.07) and -1.52 ± 0.76% (P = 0.04), respectively. In the longitudinal and cross-sectional analyses, the carotid and aortic AIs were unrelated to the 24-hour urinary excretion of sodium.

CONCLUSIONS

Our study showed an inverse association between the central arterial AIs and the urinary sodium concentration. Further research is required to consolidate our findings, to unravel the underlying mechanism, and to establish the role of renal vasodilatation in the maintenance of sodium balance.

Acupuncture Effects on the Pulse Spectrum of Radial Pressure Pulse in Dyspepsia

This study is to investigate the influences of acupuncture for dyspepsia on the Radial Pressure Pulse (RPP) between the Chun, Guan and Chy positions of the right/left wrist. Two series of experiments were designed; for the first series, 30 patients with dyspepsia (Group P) and 30 normal subjects (Group N) were seated to undergo the measurements of pulse pressure waveforms from radial artery by sphygmograph. The parameters of RPP included the spectral energy of 0–10 Hz (SE0–10Hz), 10–50 Hz (SE10–50Hz) and 13–50 Hz (SE13–50Hz). For the second series, acupuncture was administered at the right and left Tsu San Li (St-36) points for the same 30 dyspepsia patients, and then their pulse pressure waveforms were re-examined. The results showed that the SE0–10Hz at Right Guan (RB) (p < 0.05), the SE10–50Hz at RB (p < 0.01), and the SE13–50Hz at RB (p < 0.01) and Left Guan (LB) (p < 0.05) of Group P were significantly greater than that of Group N. After the acupuncture, there were significant decreases in the SE0–10Hz only at RB (p < 0.01), in the SE10–50Hz at RB (p < 0.01), Right Chy (RC) (p < 0.05) and LB (p < 0.05), and in the SE13–50Hz RB (p < 0.01), RC (p < 0.05) and LB (p < 0.01). We concluded that the pulse-frequency spectrum at RB was a more effective characteristic for dyspepsia patients, and the acupuncture had an effect on SE10–50Hz and SE13–50Hz more obviously than that on SE0–10Hz.