Noninvasive studies of central aortic pressure

Estimation of central blood pressure waveform from femoral blood pressure waveform by blind sources separation

Background

Central blood pressure (cBP) is a better indicator of cardiovascular morbidity and mortality than peripheral BP (pBP). However, direct cBP measurement requires invasive techniques and indirect cBP measurement is based on rigid and empirical transfer functions applied to pBP. Thus, development of a personalized and well-validated method for non-invasive derivation of cBP from pBP is necessary to facilitate the clinical routine. The purpose of the present study was to develop a novel blind source separation tool to separate a single recording of pBP into their pressure waveforms composing its dynamics, to identify the compounds that lead to pressure waveform distortion at the periphery, and to estimate the cBP. The approach is patient-specific and extracts the underlying blind pressure waveforms in pBP without additional brachial cuff calibration or any a priori assumption on the arterial model.

Methods

The intra-arterial femoral BPfe and intra-aortic pressure BPao were anonymized digital recordings from previous routine cardiac catheterizations of eight patients at the German Heart Centre Berlin. The underlying pressure waveforms in BPfe were extracted by the single-channel independent component analysis (SCICA). The accuracy of the SCICA model to estimate the whole cBP waveform was evaluated by the mean absolute error (MAE), the root mean square error (RMSE), the relative RMSE (RRMSE), and the intraclass correlation coefficient (ICC). The agreement between the intra-aortic and estimated parameters including systolic (SBP), diastolic (DBP), mean arterial pressure (MAP), and pulse pressure (PP) was evaluated by the regression and Bland-Altman analyses.

Results

The SCICA tool estimated the cBP waveform non-invasively from the intra-arterial BPfe with an MAE of 0.159 ± 1.629, an RMSE of 5.153 ± 0.957 mmHg, an RRMSE of 5.424 ± 1.304%, and an ICC of 0.94, as well as two waveforms contributing to morphological distortion at the femoral artery. The regression analysis showed a strong linear trend between the estimated and intra-aortic SBP, DBP, MAP, and PP with high coefficient of determination R2 of 0.98, 0.99, 0.99, and 0.97 respectively. The Bland-Altman plots demonstrated good agreement between estimated and intra-aortic parameters with a mean error and a standard deviation of difference of -0.54 ± 2.42 mmHg [95% confidence interval (CI): -5.28 to 4.20] for SBP, -1.97 ± 1.62 mmHg (95% CI: -5.14 to 1.20) for DBP, -1.49 ± 1.40 mmHg (95% CI: -4.25 to 1.26) for MAP, and 1.43 ± 2.79 mmHg (95% CI: -4.03 to 6.90) for PP.

Conclusions

The SCICA approach is a powerful tool that identifies sources contributing to morphological distortion at peripheral arteries and estimates cBP.

Reconstruction of central arterial pressure waveform based on CBi-SAN network from radial pressure waveform

The central arterial pressure (CAP) is an important physiological indicator of the human cardiovascular system which represents one of the greatest threats to human health. Accurate non-invasive detection and reconstruction of CAP waveforms are crucial for the reliable treatment of cardiovascular system diseases. However, the traditional methods are reconstructed with relatively low accuracy, and some deep learning neural network models also have difficulty in extracting features, as a result, these methods have potential for further advancement. In this study, we proposed a novel model (CBi-SAN) to implement an end-to-end relationship from radial artery pressure (RAP) waveform to CAP waveform, which consisted of the convolutional neural network (CNN), the bidirectional long-short-time memory network (BiLSTM), and the self-attention mechanism to improve the performance of CAP reconstruction. The data on invasive measurements of CAP and RAP waveform were used in 62 patients before and after medication to develop and validate the performance of CBi-SAN model for reconstructing CAP waveform. We compared it with traditional methods and deep learning models in mean absolute error (MAE), root mean square error (RMSE), and Spearman correlation coefficient (SCC). Study results indicated the CBi-SAN model performed great performance on CAP waveform reconstruction (MAE: 2.23 ± 0.11 mmHg, RMSE: 2.21 ± 0.07 mmHg), concurrently, the best reconstruction effect was obtained in the central artery systolic pressure (CASP) and the central artery diastolic pressure(CADP) (RMSECASP: 2.94 ± 0.48 mmHg, RMSECADP: 1.96 ± 0.06 mmHg). These results implied the performance of the CAP reconstruction based on CBi-SAN model was superior to the existing methods, hopped to be effectively applied to clinical practice in the future.

Central Aortic Blood Pressure Waveform Estimation with a Temporal Convolutional Network

A novel temporal convolutional network (TCN) model is utilized to reconstruct the central aortic blood pressure (aBP) waveform from the radial blood pressure waveform. The method does not need manual feature extraction as traditional transfer function approaches. The data acquired by the SphygmoCor CVMS device in 1,032 participants as a measured database and a public database of 4,374 virtual healthy subjects were used to compare the accuracy and computational cost of the TCN model with the published convolutional neural network and bi-directional long short-term memory (CNN-BiLSTM) model. The TCN model was compared with CNN-BiLSTM in the root mean square error (RMSE). The TCN model generally outperformed the existing CNN-BiLSTM model in terms of accuracy and computational cost. For the measured and public databases, the RMSE of the waveform using the TCN model was 0.55 ± 0.40 mmHg and 0.84 ± 0.29 mmHg, respectively. The training time of the TCN model was 9.63 min and 25.51 min for the entire training set; the average test time was around 1.79 ms and 8.58 ms per test pulse signal from the measured and public databases, respectively. The TCN model is accurate and fast for processing long input signals, and provides a novel method for measuring the aBP waveform. This method may contribute to the early monitoring and prevention of cardiovascular disease.

Oscillometric pulse wave analysis for detecting low flow arteriovenous fistula

BACKGROUND

Pulse wave analysis may be useful to assess fistula function. We aimed to prospectively evaluate if convenient oscillometric devices are applicable to detect flow below 500 ml/min in a real life clinical setting.

METHODS

Pulse waves were recorded ambilaterally with the vicorder® device at the brachial artery in 53 patients on haemodialysis with native fistula. Primary variables consisted of the mean slope between the systolic maximum and the diacrotic notch (Slope2), the sum of the mean slopes in the four characteristic sections of pulse waves (Slope∑) and the amplitude of relative volumetric change in the measuring cuff at the upper arm (AMP). Fistula flow was measured with the use of duplex sonography using a standardized approach.

RESULTS

Parameter values above or below the median indicated measurement at the non-fistula side, with sensitivities/specificities of 0.79/0.79 (p < 0.001) for Slope 2, 0.64/0.64 (p = 0.003) for Slope∑ and 0.81/0.81 (p < 0.001) for AMP if measurements at the fistula and non-fistula arm were considered. ROC-analyses of parameter values measured at the fistula to detect low flow demonstrated AUCs (with CI) of 0.652 (0.437-0.866, p = 0.167) for Slope2, 0.732 (0.566-0.899, p = 0.006) for Slope∑ and 0.775 (0.56-0.991, p = 0.012) for AMP. The point with maximal youden's index was regarded as optimal cut-off, which corresponded to sensitivities and specificities of 0.8/0.56 for slope2, 0.86/ 0.56 for Slope∑ and 0.93/0.78 for AMP.

CONCLUSION

Functional surveillance with oscillometry is a promising clinical application to detect a low fistula flow. Among all investigated pulse wave parameters AMP revealed the highest diagnostic accuracy.

Association between the reflection magnitude and blood pressure in a multiethnic cohort: the Healthy Life in an Urban Setting study

AIMS

Reflection magnitude (RM), the ratio of the amplitudes of the backward and forward central arterial pressure waves, has been shown to predict cardiovascular events. However, the association with blood pressure (BP) and hypertension is unclear.

METHODS

We assessed RM in 10 195 individuals of Dutch, South-Asian Surinamese, African Surinamese, Ghanaian, Turkish and Moroccan origin aged between 18 and 70 years (54.2% female) participating in the Healthy Life in an Urban Setting study. To determine RM, central arterial pressure and flow were reconstructed from finger BP. Hypertension was defined based on office-BP and medication. Associations with BP, hypertension, and hypertensive organ damage were assessed using linear regression models with correction for relevant covariates.

RESULTS

Mean RM was 62.5% (standard deviation [SD] 8.0) in men and 63.8% (SD 8.1) in women. RM was lowest in Dutch and highest in South-Asian and African participants. RM increased linearly with 1.35 (95% confidence interval [CI] 1.23-1.46) for every 10 mmHg increase in systolic BP from 120 mmHg onwards, while the relation with diastolic BP was nonlinear. RM was 2.40 (95% CI 2.04-2.76) higher in hypertensive men and 3.82 (95% CI 3.46-4.19) higher in hypertensive women compared to normotensive men and women. In hypertensive men and women with ECG-based left ventricular hypertrophy or albuminuria RM was 1.64 (95% CI 1.09-2.20) and 0.94 (95% CI 0.37-1.52) higher compared to hypertensive participants without hypertensive organ damage.

CONCLUSION

RM is associated with BP, hypertension and hypertensive organ damage, and may in part explain disparities in hypertension associated cardiovascular risk.

Association between the reflection magnitude and blood pressure in a multiethnic cohort: the Healthy Life in an Urban Setting study

Aims:

Reflection magnitude (RM), the ratio of the amplitudes of the backward and forward central arterial pressure waves, has been shown to predict cardiovascular events. However, the association with blood pressure (BP) and hypertension is unclear.

Methods:

We assessed RM in 10 195 individuals of Dutch, South-Asian Surinamese, African Surinamese, Ghanaian, Turkish and Moroccan origin aged between 18 and 70 years (54.2% female) participating in the Healthy Life in an Urban Setting study. To determine RM, central arterial pressure and flow were reconstructed from finger BP. Hypertension was defined based on office-BP and medication. Associations with BP, hypertension, and hypertensive organ damage were assessed using linear regression models with correction for relevant covariates.

Results:

Mean RM was 62.5% (standard deviation [SD] 8.0) in men and 63.8% (SD 8.1) in women. RM was lowest in Dutch and highest in South-Asian and African participants. RM increased linearly with 1.35 (95% confidence interval [CI] 1.23–1.46) for every 10 mmHg increase in systolic BP from 120 mmHg onwards, while the relation with diastolic BP was nonlinear. RM was 2.40 (95% CI 2.04–2.76) higher in hypertensive men and 3.82 (95% CI 3.46–4.19) higher in hypertensive women compared to normotensive men and women. In hypertensive men and women with ECG-based left ventricular hypertrophy or albuminuria RM was 1.64 (95% CI 1.09–2.20) and 0.94 (95% CI 0.37–1.52) higher compared to hypertensive participants without hypertensive organ damage.

Conclusion:

RM is associated with BP, hypertension and hypertensive organ damage, and may in part explain disparities in hypertension associated cardiovascular risk.

Vascular Aging and Arterial Stiffness

O envelhecimento biológico é reflexo da interação entre genética, idade cronológica e fatores externos; é a base para novos conceitos em envelhecimento vascular, cuja progressão é determinada pela diferença entre idade biológica e cronológica. Do ponto de vista estrutural, os efeitos do envelhecimento vascular são mais evidentes na camada média das grandes artérias elásticas e resultam em aumento da rigidez arterial, da dilatação do lúmen e da espessura da parede. Esses efeitos são descritos no continuum de envelhecimento cardiovascular (proposto por Dzau em 2010) em que as etapas progressivas de lesões da microvasculatura de coração, rins e cérebro, têm início a partir do processo de envelhecimento. O aumento da rigidez arterial pode ser verificado de forma não invasiva por vários métodos. Os eventos cardiovasculares têm sido tradicionalmente previstos utilizando escores que combinam fatores de risco convencionais para aterosclerose. No continuum cardiovascular clássico (Dzau, 2006), é desafiador avaliar o peso exato da contribuição de cada fator de risco; entretanto, por refletir o dano precoce e cumulativo desses fatores de riscos cardiovascular, a rigidez arterial reflete o verdadeiro dano à parede arterial. Este artigo fornece uma visão geral dos mecanismos da fisiopatogenia, alterações estruturais das artérias e consequências hemodinâmicas do envelhecimento arterial; métodos não invasivos para a avaliação da rigidez arterial e da medida central da pressão arterial; o continuum de envelhecimento cardiovascular, e aplicação do conceito de rigidez arterial na estratificação de risco cardiovascular.

Factors That May Impact the Noninvasive Measurement of Central Blood Pressure Compared to Invasive Measurement: The MATCHY Study

Calibration affects central blood pressure (BP) estimation accuracy. Factors influencing the accuracy of noninvasive central BP measurement, type of calibration method implemented (systolic/diastolic BP or mean/diastolic BP), and type of BP measurement device used (devices using the transfer function method, directly measurement from the carotid artery, and the transfer function-like method), were investigated. Fifty participants (aged 62.4 ± 8.9 years) without overt heart diseases were recruited. Invasive aortic and radial BP was measured. Simultaneously, noninvasive central BP was measured using three types of devices. The mean invasive aortic BP was 127 ± 19/95 ± 14 mmHg. Noninvasive central BP tended to be slightly lower than invasive BP, though without statistical significance. The type of calibration method did not significantly influence the noninvasive cSBP measurements (p ≥ 0.24). Results from cuff-based devices were significantly lower than invasive measurements (p = 0.04). Multiple regression analyses showed that gender was significantly correlated with the accuracy of noninvasive cSBP measurement. In conclusion, noninvasive cSBP measurements are comparable to invasive measurements but might underestimate true cSBP. The type of device may affect the accuracy of measurement. Either of the two calibration methods is acceptable.

Noninvasive estimation of aortic pressure waveform based on simplified Kalman filter and dual peripheral artery pressure waveforms

BACKGROUND AND OBJECTIVE

Aortic pressure (P_a) is important for the diagnosis of cardiovascular disease. However, its direct measurement is invasive, not risk-free, and relatively costly. In this paper, a new simplified Kalman filter (SKF) algorithm is employed for the reconstruction of the P_a waveform using dual peripheral artery pressure waveforms.

METHODS

P_a waveforms obtained in a previous study were collected from 25 patients. Simultaneously, radial and femoral pressure waveforms were generated from two simulation experiments, using transfer functions. In the first, the transfer function is a known finite impulse response; and in the second, it is derived from a tube-load model. To analyze the performance of the proposed SKF algorithm, variable amounts of noise were added to the observed output signal, to give a range of signal-to-noise ratios (SNRs). Additionally, central aortic, brachial and femoral pressure waveforms were simultaneously collected from 2 Sprague-Dawley rats and the measured and reconstructed P_a waveforms were compared.

RESULTS

The proposed SKF algorithm outperforms canonical correlation analysis (CCA), which is the current state-of-the-art blind system identification method for the non-invasive estimation of central aortic blood pressure. It is also shown that the proposed SKF algorithm is more noise-tolerant than the CCA algorithm over a wide range of SNRs.

CONCLUSION

The simulations and animal experiments illustrate that the proposed SKF algorithm is accurate and stable in the face of low SNRs. Improved methods for estimating central blood pressure as a measure of cardiac load adds to their value as a prognostic and diagnostic tool.

Carotid Pulse Wave Analysis: Future Direction of Hemodynamic and Cardiovascular Risk Assessment

Evaluation of the hemodynamic function of the cardiovascular system via measurement of the mechanical properties of the large arteries may provide a substantial improvement over present techniques. Practitioners are familiar with the problem of low reproducibility of conventional sphygmomanometry, which exhibits reasonable accuracy but low precision owing to its marked variability over time and in different circumstances (e.g., the white coat effect). Arterial wall stiffness is a consequence of atherosclerosis developing over time; thus, it has little short-term variability and is thus preferable to be used as a prognostic marker. In particular, arterial stiffness can be evaluated at the carotid artery using noninvasive approaches based on wearable sensor technologies for pulse wave analysis. These enable the assessment of central pressures and pulse waveform parameters that are expected to replace peripheral blood pressure measurement using the inflatable cuff. In this study, we discuss this simple and inexpensive technique, which has been shown to be reliable with the clinical and epidemiological evidence for its use as a biomarker of cardiovascular risk.

Radiation effects on atherosclerosis in atomic bomb survivors: a cross-sectional study using structural equation modeling

Past reports indicated that total-body irradiation at low to moderate doses could be responsible for cardiovascular disease risks, but the mechanism remains unclear. The purpose of this study was to investigate the association between radiation exposure and atherosclerosis, an underlying pathology of cardiovascular diseases, in the Japanese atomic bomb survivors. We performed a cross-sectional study measuring 14 clinical-physiological atherosclerosis indicators during clinical exams from 2010 to 2014 in 3274 participants of the Adult Health Study cohort. Multivariable analyses were performed by using a structural equation model with latent factors representing underlying atherosclerotic pathologies: (1) arterial stiffness, (2) calcification, and (3) plaque　as measured with indicators chosen a priori on the basis of clinical-physiological knowledge. Radiation was linearly associated with calcification (standardized coefficient per Gy 0.15, 95 % confidence interval: CI [0.070, 0.23]) and plaque (0.11, 95 % CI [0.029, 0.20]), small associations that were comparable to about 2 years of aging per Gy of radiation exposure, but not with arterial stiffness (0.036, 95 % CI [− 0.025, 0.095]). The model fitted better and had narrower confidence intervals than separate ordinary regression models explaining individual indicators independently. The associations were less evident when the dose range was restricted to a maximum of 2 or 1 Gy. By combining individual clinical-physiological indicators that are correlated because of common, underlying atherosclerotic pathologies, we found a small, but significant association of radiation with atherosclerosis.

On-line parameter identification of the lumped arterial system model: A simulation study

A lumped model of the arterial system has been used in constructing a hybrid mock loop due to its real-time response. However, the parameters of the model are always from a general case and not adapted to a specific patient. In this study, we focused on on-line parameter identification of the lumped model of the arterial system that could be used for a specific patient. A five-element lumped arterial model is adopted in this study, in which the five parameters are to be determined. The aortic flow rate and the venous pressure are chosen as the inputs of the model, and aortic pressure as the output. An iterative optimization based on the established state space equations of the five-element model is used to seek the best parameter values by minimizing the difference between the model prediction and the previously obtained aortic pressure. The method is validated using simulated data from a complete numerical cardiovascular model. Results show that the method can track the dynamic variation of the parameters very well. Finally, a sensitivity analysis of the model parameters is conducted to interpret the effect of parameter changes. The good performance of the identification demonstrates the potential application of this method to customize a hybrid mock loop for a specific patient or clinically monitor the arterial vessel characteristics in real time.

Pulse Wave Analysis and Pulse Wave Velocity for Fistula Assessment

BACKGROUND/AIMS

Pulse wave analysis (PWA) and pulse wave velocity (PWV) provide information about arterial stiffness and elasticity, which is mainly used for cardiovascular risk stratification. In the presented prospective observational pilot study, we examined the hypothesis that radiocephalic fistula (RCF)-related changes of haemodynamics and blood vessel morphology including high as well as low flow can be seen in specific changes of pulse wave (PW) morphology.

METHODS

Fifty-six patients with RCF underwent local ambilateral peripheral PWA and PWV measurement with the SphygmoCor® device. Given that the output parameters of the SphygmoCor® are not relevant for the study objectives, we defined new suitable parameters for PWA in direct proximity to fistulas and established an appropriate analysing algorithm. Duplex sonography served as reference method.

RESULTS

Marked changes of peripheral PW morphology when considering interarm differences of slope and areas between the fistula and non-fistula arms were observed in the Arteria radialis, A. brachialis and arterialized Vena cephalica. The sum of the slope differences was found to correlate with an increased flow, while in patients with fistula failure no changes in PW morphology were seen. Moreover, PWV was significantly reduced in the fistula arm.

CONCLUSION

Beside duplex sonography, ambilateral peripheral PWA and PWV measurements are potential new clinical applications to characterize and monitor RCF function, especially in terms of high and low flow.

Central rather than brachial pressures are stronger predictors of cardiovascular outcomes: A longitudinal prospective study in a Chinese population

The purpose of this study was to assess the association of blood pressure (BP) measurements with the risk of cardiovascular disease (CVD) and examine whether central systolic BP (CSBP) predicts CVD better than brachial BP measurements (SBP and pulse pressure [PP]). Based on a cross-sectional study conducted in 2009-2010 with follow-up in 2016-2017 among 35- to 64-year-old subjects in China, we evaluated the performance of non-invasively predicted CSBP over brachial BP measurements on the first CVD events. Each BP measurement, individually and jointly with another BP measurement, was entered into the multivariate Cox proportional-hazards models, to examine the predictability of central and brachial BP measurements. Mean age of participants (n = 8710) was 50.1 years at baseline. After a median follow-up of 6.36 years, 187 CVD events occurred. CSBP was a stronger predictor for CVD than brachial BP measurements (CSBP, 1-standard deviation increment HR = 1.49, 95%CI: 1.31-1.70). With CSBP and SBP entering into models jointly, the HR for CSBP and SBP was 1.28 (1.04-1.58) and 1.22 (0.98-1.50), respectively. With CSBP and PP entering into models jointly, the HR for CSBP and PP was 1.51 (1.28-1.78) and 0.98 (0.83-1.15), respectively. For subgroup analysis, the association of CSBP with CVD was stronger than brachial BP measurements in women, those with hypertension and obesity. In the middle-aged Chinese population, noninvasively estimated CSBP may offer advantages over brachial BP measurements to predict CVD events, especially for participants with higher risk. These findings suggest prospective assessment of CSBP as a prevention and treatment target in further trials.

Measurement of arterial stiffness and vascular aging in community pharmacies-The ASINPHAR@2action project

The ASINPHAR@2action project aims at raising awareness to arterial stiffness (AS) and early vascular aging (EVA) through a community pharmacy-based intervention. This preliminary analysis is focused on the analysis of the proportion of participants with increased AS and the identification of its main determinants. We performed an observational cross-sectional study of participants enrolled in 11 community pharmacies in Portugal, between April and November 2017. Blood pressure (BP) and arterial function parameters were measured with a validated device. Clinical and demographic information was gathered, as well as the estimation of global cardiovascular risk, health-related quality of life, and dietary profile. Cholesterol and glycaemia were taken from a recent laboratory bulletin. The cohort includes 658 participants with a mean age of 57.3 ± 16.3 years, 66% women. Brachial BP was 126.6 ± 16.4 mm Hg and 79.9 ± 11.5 mm Hg, and central BP was 115.8 ± 15.4 mm Hg and 81.2 ± 11.6 mm Hg, respectively, for systolic and diastolic BP. Mean pulse wave velocity (PWV) was 8.5 ± 2.3 m/s, and the augmentation index was 23.6 ± 15.6%. The proportion of participants with increased AS was 19.8%. The overall best-fitting model for AS included age, gender, aortic PP, visceral fat, HDL cholesterol, AIx@75, total vascular resistance, hypertension, and diabetes, corresponding to an AUC of 0.910 (CI: 0.883, 0.937; P < 0.001) in the ROC curve analysis. The preliminary results of this pioneering large-scale study measuring arterial function in community pharmacies provide the grounds for the operationalization of subclinical target organ damage screening in pharmacies, as a strategy to improve cardiovascular risk monitoring and to promote adherence to treatment.

Myocardial preload alters central pressure augmentation through changes in the forward wave

OBJECTIVE

Augmentation index (AIx) is often used to quantify the contribution of wave reflection to central pulse pressure. Recent studies have challenged this view by showing how contractility-induced changes in the forward pressure wave can markedly impact AIx. We hypothesized that changes in preload will also affect AIx through changes in the forward wave and studied this in two experiments.

METHODS

Noninvasively obtained aortic pressure was used to study central haemodynamics and wave morphology. In the first experiment, we examined the effects of head-up tilt with and without unilateral thigh cuff in 12 young healthy volunteers (mean age 26 years, 50% men). In the second experiment, we examined the effects of active standing in 31 middle-aged patients (mean age 57 years, 65% men) before and after phlebotomy.

RESULTS

Head-up tilt or active standing significantly decreased AIx [-17.7 ± 10.4 percentage point (pp) in the young population, -4.7 ± 12.3 pp in the middle-aged population, both P < 0.05]. The fall in AIx was associated with increases in HR, diastolic pressure and systemic vascular resistance and a decrease in stroke volume (all P < 0.05). Inflation of a unilateral thigh cuff reduced the decrease in AIx by 10.7 pp, whereas 500 ml of blood loss augmented the fall in AIx by 5.9 pp (both P < 0.05). The changes in AIx were related to a preload-induced change in forward pressure wave shape (earlier peaking and steeper downstroke).

CONCLUSION

Next to inotropic and chronotropic effects, preload emerges as another myocardial factor that obscures the relation between wave reflection and AIx.

Gestational hypertensive disorders show unique patterns of circulatory deterioration with ongoing pregnancy

A combined assessment of heart, arteries, veins, and body fluid content throughout pregnancy has not yet been reported. We hypothesized that a gradual aggravation of circulatory dysfunction exists from the latent to the clinical phase of gestational hypertensive disease (GHD), and that pathways are unique for preeclampsia with early onset < 34 wk (EPE) and late onset ≥ 34 wk (LPE), and gestational hypertension (GH). Women with singleton pregnancy and no known diseases were invited for a prospective, observational study and had standardized sphygmomanometric blood pressure measurement, bioimpedance body water spectrum analysis, impedance cardiography for cardiac and arterial assessment, and combined Doppler-ECG of hepatic and renal interlobar veins and uterine arteries. Outcome was categorized as uncomplicated (UP, n = 1,700), EPE ( n = 87), LPE ( n = 218), or GH ( n = 188). A linear mixed model for repeated measurements, corrected for age, parity, and body mass index, was employed in SAS 9.4 to analyze trimestral changes within and between groups. From the first to the third trimester, body water increased in all groups, and an increasing number of abnormal parameters relative to UP occurred in all GHD. First-trimester blood pressure and peripheral resistance were higher in GHD than UP, together with increased uterine flow resistance and extracellular water in EPE, and with lower heart rate and aorta flow velocity in LPE. An overall gestational rise of body water volumes coexists with a gradual worsening of cardiovascular dysfunction in GHD, of which pathophysiological pathways are unique for EPE, LPE, and GH, respectively.

Impaired aortic distensibility and elevated central blood pressure in Turner Syndrome: a cardiovascular magnetic resonance study

BACKGROUND

Women with Turner Syndrome have an increased risk for aortic dissection. Arterial stiffening is a risk factor for aortic dilatation and dissection. Here we investigate if arterial stiffening can be observed in Turner Syndrome patients and is an initial step in the development of aortic dilatation and subsequent dissection.

METHODS

Fifty-seven women with Turner Syndrome (48 years [29-66]) and thirty-six age- and sex-matched controls (49 years [26-68]) were included. Distensibility, blood pressure, carotid-femoral pulse wave velocity (PWV), the augmentation index (Aix) and central blood pressure were determined using cardiovascular magnetic resonance, a 24-h blood pressure measurement and applanation tonometry. Aortic distensibility was determined at three locations: ascending aorta, transverse aortic arch, and descending aorta.

RESULTS

Mean aortic distensibility in the descending aorta was significantly lower in Turner Syndrome compared to healthy controls (P = 0.02), however, this was due to a much lower distensibility among Turner Syndrome with coarctation, while Turner Syndrome without coarctation had similar distensibility as controls. Both the mean heart rate adjusted Aix (31.4% vs. 24.4%; P = 0.02) and central diastolic blood pressure (78.8 mmHg vs. 73.7 mmHg; P = 0.02) were higher in Turner Syndrome compared to controls, and these indices correlated significantly with ambulatory night-time diastolic blood pressure. The presence of aortic coarctation (r = - 0.44, P = 0.005) and a higher central systolic blood pressure (r = - 0.34, P = 0.03), age and presence of diabetes were inversely correlated with aortic distensibility in TS.

CONCLUSION

Aortic wall function in the descending aorta is impaired in Turner Syndrome with lower distensibility among those with coarctation of the aorta, and among all Turner Syndrome higher Aix, and elevated central diastolic blood pressure when compared to sex- and age-matched controls.

TRIAL REGISTRATION

The study was registered at ClinicalTrials.gov ( #NCT01678274 ) on September 3, 2012.

Noradrenaline modifies arterial reflection phenomena and left ventricular efficiency in septic shock patients: A prospective observational study

PURPOSE

To determine whether noradrenaline alters the arterial pressure reflection phenomena in septic shock patients and the effects on left ventricular (LV) efficiency.

MATERIAL AND METHODS

Thirty-seven septic shock patients with a planned change in noradrenaline dose. Timing and magnitude (Reflection Magnitude and Augmentation Index) of arterial reflections were evaluated. Total, steady, and oscillatory LV power (also expressed as fraction of the total power), subendocardial viability ratio (SEVR), energy efficiency and transmission ratios were used as a marker of LV efficiency.

RESULTS

An incremental change in noradrenaline increased Reflection Magnitude [0.28(0.09) to 0.31(0.1], Augmentation Index [-6.4(23.6) to 4.8(20.7)%], and LV total power [0.79(IQR:0.47-1) to 0.98(IQR:0.57-1.27)W], all p < 0.001; whereas decreased arrival time of reflected waves [from 95(87 to 121) to 83(79 to 101)ms; p < 0.001]. Variables of LV performance showed a decreased efficiency: oscillatory fraction and energy efficiency ratio increased [20.9(5.7) to 22.8(4.9)%, and 8.2(1.7) to 10.1(2) mW.min.litre^-1; p < 0.001, respectively]; and energy transmission ratio and SEVR decreased [73.8(9.9) to 72(9.8)% and 146(IQR:113-188) to 143(IQR:109-172)%, p = 0.003 and p = 0.041, respectively].

CONCLUSIONS

Noradrenaline increased reflection phenomena, increasing LV workload and worsening LV performance in septic shock patients. These conditions could explain the detrimental effects during long-term use of noradrenaline.

Associations of plasma homocysteine levels with peripheral systolic blood pressure and noninvasive central systolic blood pressure in a community-based Chinese population

Previous studies indicated that homocysteine (Hcy) is associated with higher peripheral systolic blood pressure (pSBP). There have been few data on the relationship between Hcy and central SBP (cSBP). A total of 4,364 Chinese subjects from the Shijingshan community in Beijing were included. cSBP and pSBP were measured with an Omron HEM-9000AI device. Subjects were 57.20 ± 8.9 years old, 37.9% were male. The median of Hcy was 11.96 μmol/L. The mean of cSBP and pSBP was 129.94 ± 18.03 mmHg and 133.25 ± 18.58 mmHg. lnHcy was associated with cSBP (adjusted β = 2.17, SE = 0.80, P = 0.007) and pSBP (adjusted β = 2.42, SE = 0.75, P = 0.001). With increasing Hcy, there were enhanced correlations of Hcy with pSBP and cSBP (p for trend between quartiles <0.01). Using Q1 for reference, the Q4 was associated with cSBP (adjusted β = 1.77, SE = 0.89, P = 0.047) and pSBP (adjusted β = 2.15, SE = 0.84, P = 0.011). The correlations were more significant in non-obese subjects than in obese subjects (cSBP: β = 4.30 vs 0.46, pSBP: β = 5.04 vs 1.18, P for interaction <0.001). Our study showed that Hcy was associated with higher cSBP and pSBP, especially in non-obese subjects.

Early Detection System of Vascular Disease and Its Application Prospect

Markers of imaging, structure, and function reflecting vascular damage, integrating a long time accumulation effect of traditional and unrecognized cardiovascular risk factors, can be regarded as surrogate endpoints of target organ damage before the occurrence of clinical events. Prevention of cardiovascular disease requires risk stratification and treatment of traditional risk factors, such as smoking, hypertension, hyperlipidemia, and diabetes. However, traditional risk stratification is not sufficient to provide accurate assessment of future cardiovascular events. Therefore, vascular injury related parameters obtained by ultrasound or other noninvasive devices, as a surrogate parameter of subclinical cardiovascular disease, can improve cardiovascular risk assessment and optimize the preventive treatment strategy. Thus, we will summarize the research progress and clinical application of early assessment technology of vascular diseases in the present review.

Arterial Compliance Measurement in Overweight and Hypertensive Children

OBJECTIVES

To investigate the pulse wave velocity (PWV) and augmentation index (Alx), measures of arterial stiffness, in relation to hypertension and obesity, the main risk factors for cardiovascular diseases.

METHODS

Two groups of pediatric patients, 31 children and adolescents with hypertension and 85 with overweight, were analysed and compared to the control group (50 healthy individuals). Subjects were sampled by opportunity sampling at the Department of Pediatrics, Maribor. In each patient, blood pressure, anthropometrical parameters and PWV measurements using the applanation tonometry technique were performed.

RESULTS

There was a significant correlation between PWV and age (r = 0.461, p = 0.001) in the control group, whereas no correlation was obtained between PWV and body mass index (BMI) or central mean arterial pressure (CMAP). In the hypertensive group, PWV only correlated with CMAP (r = 0.496, p = 0.005). A significant correlation was found in the overweight group between PWV and both age and BMI (r = 0.484, p < 0.001 and r = 0.347, p = 0.001, respectively). Alx results were not taken into consideration.

CONCLUSIONS

The results of this pilot study show that overweight and hypertensive children and adolescents are associated with less compliant arteries than their healthy peers, which could be used for screening of patients with expected early cardiovascular risk.

Role of heart rate in the relation between regional body fat and subendocardial viability ratio in women

Subendocardial viability ratio (SEVR) is a measure of left ventricular function, specifically; it is an index of myocardial perfusion relative to left ventricular workload. Women have lower SEVR than men, partly due to a faster resting heart rate that reduces diastolic time (i.e., time for myocardial perfusion). It is unclear if body fat relates to SEVR, thus the purpose of this study was to examine the relation between body fat and SEVR in women. Twenty-eight middle-aged (31-45 years) and 31 older (60-80 years) women were examined. Radial artery applanation tonometry was used to calculate SEVR from a synthesized central aortic pressure wave. Dual-energy X-ray absorptiometry was used to assess body composition including fat in the trunk, legs, android and gynoid regions. Body fat was not related (P>.05) with SEVR in older women. In middle-aged women, all measures of regional fat were correlated with heart rate (range, r=.49-.59, P≤.01) and SEVR (range, r=.43-.53, P≤.01). Android-to-gynoid ratio was identified as the strongest predictor (r(2) =-.26, P<.01) of SEVR among measures of regional fat. Middle-aged women with lower android-to-gynoid fat ratio had higher SEVR (1.96±0.33 vs 1.66±0.20, P=.009) than women with higher fat ratio, even after adjusting for age, height, daily physical activity, and aortic mean pressure (P=.02). Adjusting for heart rate or diastolic time abolished the difference in SEVR between groups (1.80±0.09 vs 1.82±0.09, P=.56). These results suggest that middle-aged women with a greater distribution of fat in the abdomen have poorer left ventricular function that is dependent on the negative influence of heart rate on diastolic time.

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.

Arterial pressure: agreement between a brachial cuff-based device and radial tonometry

Objectives:

Aortic (central) blood pressure (BP) differs from brachial BP and may be a superior predictor of cardiovascular events. However, its measurement is currently restricted to research settings, owing to a moderate level of operator dependency. We tested a new noninvasive device in a large UK cohort. The device estimates central BP using measurements obtained with an upper arm cuff inflated to suprasystolic pressure. We compared these estimates with those obtained using radial tonometry as well as with invasively acquired measurements of aortic BP in a limited number of individuals.

Methods:

Consecutive cuff-based and tonometry-based estimates of the pressure waveform and the central BP were obtained from 1107 individuals (70 ± 6 years). Short-term and long-term reproducibility studies were performed on 28 individuals. Simultaneous cuff-based and invasively measured pressure traces were acquired and compared in an additional six individuals (65 ± 20 years).

Results:

Central systolic BP, as estimated by the cuff-based device, was found to be highly reproducible (coefficient of variation 4 and 8% for short and long-term reproducibility, respectively) and was comparable to that estimated by tonometry (average difference 3 ± 6 mmHg, intraclass correlation coefficient = 0.91). The cuff-based pressure waveforms were similar to those acquired invasively (cross-correlation coefficient 0.93), and the difference in the estimated central systolic BP was −5 ± 8 mmHg (P = 0.2).

Conclusion:

Cuff-based devices show promise to simplify the measurement of central BP, whilst maintaining a similar fidelity to tonometry. This could lead to improved adoption of estimates of central BP in clinical practice.

Central blood pressure: current evidence and clinical importance

Pressure measured with a cuff and sphygmomanometer in the brachial artery is accepted as an important predictor of future cardiovascular risk. However, systolic pressure varies throughout the arterial tree, such that aortic (central) systolic pressure is actually lower than corresponding brachial values, although this difference is highly variable between individuals. Emerging evidence now suggests that central pressure is better related to future cardiovascular events than is brachial pressure. Moreover, anti-hypertensive drugs can exert differential effects on brachial and central pressure. Therefore, basing treatment decisions on central, rather than brachial pressure, is likely to have important implications for the future diagnosis and management of hypertension. Such a paradigm shift will, however, require further, direct evidence that selectively targeting central pressure, brings added benefit, over and above that already provided by brachial artery pressure.

Cerebrovascular time constant in patients suffering from hydrocephalus

OBJECTIVES

We studied possible link between cerebrospinal fluid (CSF) compensation and indices describing pulsatile inflow of cerebral arterial blood.

METHODS

A total of 50 infusion tests performed in patients with symptoms of normal pressure hydrocephalus (NPH) were examined retrospectively. Waveforms of CSF pressure, noninvasive arterial blood pressure (ABP), and transcranial Doppler (TCD) cerebral blood flow velocity (CBFV) were used to estimate relative changes in cerebral arterial compliance (Ca) and cerebrovascular resistance (CVR). Product of Ca and CVR, called cerebral arterial time constant (τ, unit: seconds), was calculated at the baseline and plateau phase of the test and compared with CSF compensatory parameters such as resistance to CSF outflow, elasticity, slope of amplitude-pressure line, and pulse amplitude of CSF pressure.

RESULTS

Neither of CSF compensatory parameters correlated with hemodynamic indices. However, the change in cerebral perfusion pressure (CPP) provoked change in τ (R  =  0.33; P  =  0.017) secondary to a change in CVR (R  =  0.81; P < 0.0001). Changes in CVR and Ca had a reciprocal character (R  =  -0.64; P < 0.0001) with magnitude of variation in CVR (68%) prevailing over magnitude of changes in Ca (49%).

DISCUSSION

Hemodynamics of pulsatile inflow of cerebral arterial blood assessed by cerebral arterial time constant is not directly linked to dynamics of CSF circulation and pressure-volume compensation but is sensitive to changes in CPP during infusion test.

Differential associations of central and brachial blood pressure with carotid atherosclerosis and microvascular complications in patients with type 2 diabetes

Background

We examined the relationship between central blood pressure (BP), brachial BP with carotid atherosclerosis and microvascular complications in type 2 diabetes mellitus (T2DM).

Methods

We recruited 201 patients who were evaluated for central BP, brachial BP, carotid ultrasonography, brachial-ankle pulse wave velocity (baPWV), ankle-brachial index (ABI) and microvascular complications. Central BP were calculated using a radial automated tonometric system.

Results

Agreement between central BP and brachial BP was very strong (concordance correlation coefficient between central and brachial SBP = 0.889, between central and brachial PP = 0.816). Central pulse pressure (PP) was correlated with mean carotid intima-media thickness (CIMT), baPWV and ABI, whereas brachial PP was borderline significantly correlated with CIMT. The prevalence of nephropathy(DN) and retinopathy(DR) according to the brachial PP tertiles increased, the prevalences of microvascular complications were not different across central PP tertiles. In multivariate analysis, the relative risks (RRs) for the presence of DR were 1.2 and 4.6 for the brachial PP tertiles 2 and 3 when compared with the first tertile. Also, the RRs for the presence of DN were 1.02 and 3 for the brachial PP tertiles 2 and 3 when compared with the first tertile.

Conclusions

Agreement of central BP and brachial BP was very strong. Nonetheless, this study showed that higher brachial PP levels are associated with increased probability for the presence of microvascular complications such as DR/DN. However, there are no associations with central SBP and central PP with microvascular complications. Central BP levels than brachial BP are correlated with surrogate marker of macrovascular complications.

Assessment of central blood pressure in patients with type 2 diabetes: a comparison between SphygmoCor and invasively measured values

BACKGROUND

The SphygmoCor is used for noninvasive assessment of ascending aortic blood pressure (BP). However, the validity of the SphygmoCor transfer function has not been tested in an exclusively type 2 diabetic patient sample. Calibration with systolic (SBP) and diastolic (DBP) brachial BP has previously been associated with substantial imprecision of central BP estimates. We hypothesized that different noninvasive calibration strategies might improve the accuracy of the estimated ascending aortic BPs.

METHODS

In 34 patients with type 2 diabetes we estimated ascending aortic SBP and DBP using the SphygmoCor device and compared these data with invasively recorded data. The validity of the transfer function was assessed by calibrating with invasively recorded DBP and mean BP (MBP). The influence of noninvasive calibration strategies was assessed by calibrating with brachial oscillometric SBP+DBP vs. DBP+MBP using a form factor (ff) of 0.33 and 0.40, respectively.

RESULTS

When calibrating with invasive BP, the difference between estimated and invasively measured ascending aortic SBP and DBP was -2.3±5.6/1.0±0.9 mm Hg. When calibrating with oscillometric brachial BPs, the differences were -9.6±8.1/14.1±6.2 mm Hg (calibration with SBP and DBP), -8.3±11.7/13.9±6.1 mm Hg (DBP and MBP; ff = 0.33), and 1.9±12.2/14.1±6.2 mm Hg (DBP and MBP; ff = 0.40), respectively. Calibration with the average of 3 brachial BPs did not improve accuracy.

CONCLUSIONS

The SphygmoCor transfer function seems valid in patients with type 2 diabetes. Noninvasive calibration with DBP and MBP (ff = 0.40) enables accurate estimation of mean ascending aortic SBP at the group level. However, the wide limits of agreement indicate limited accuracy in the individual patient.

CLINICAL TRIALS REGISTRATION

Clinical Trials No. NCT01538290.

The peroxisome proliferator activated receptor-γ pioglitazone improves vascular function and decreases disease activity in patients with rheumatoid arthritis

Background

Rheumatoid arthritis (RA) is associated with heightened mortality due to atherosclerotic cardiovascular disease (CVD). Inflammatory pathways in RA negatively affect vascular physiology and promote metabolic disturbances that contribute to CVD. We hypothesized that the peroxisome proliferator activated receptor‐γ (PPAR‐γ) pioglitazone could promote potent vasculoprotective and anti‐inflammatory effects in RA.

Methods and Results

One hundred forty‐three non‐diabetic adult RA patients (76.2% female, age 55.2±12.1 [mean±SD]) on stable RA standard of care treatment were enrolled in a randomized, double‐blind placebo controlled crossover trial of 45 mg daily pioglitazone versus placebo, with a 3‐month duration/arm and a 2‐month washout period. Pulse wave velocity of the aorta (PWV), brachial artery flow mediated dilatation (FMD), nitroglycerin mediated dilatation (NMD), microvascular endothelial function (reactive hyperemia index [RHI]), and circulating biomarkers of inflammation, insulin resistance, and atherosclerosis risk all were quantified. RA disease activity was assessed with the 28‐Joint Count Disease Activity Score (DAS‐28) C‐reactive protein (CRP) and the Short Form (36) Health Survey quality of life questionnaire. When added to standard of care RA treatment, pioglitazone significantly decreased pulse wave velocity (ie, aortic stiffness) (P=0.01), while FMD and RHI remained unchanged when compared to treatment with placebo. Further, pioglitazone significantly reduced RA disease activity (P=0.02) and CRP levels (P=0.001), while improving lipid profiles. The drug was well tolerated.

Conclusions

Addition of pioglitazone to RA standard of care significantly improves aortic elasticity and decreases inflammation and disease activity with minimal safety issues. The clinical implications of these findings remain to be established.

Clinical Trial Registration

URL: ClinicalTrials.gov Unique Identifier: NCT00554853.

Derivation and validation of diagnostic thresholds for central blood pressure measurements based on long-term cardiovascular risks

OBJECTIVES

This study sought to derive and validate outcome-driven thresholds of central blood pressure (CBP) for diagnosing hypertension.

BACKGROUND

Current guidelines for managing patients with hypertension mainly rely on blood pressure (BP) measured at brachial arteries (cuff BP). However, BP measured at the central aorta (central BP [CBP]) may be a better prognostic factor for predicting future cardiovascular events than cuff BP.

METHODS

In a derivation cohort (1,272 individuals and a median follow-up of 15 years), we determined diagnostic thresholds for CBP by using current guideline-endorsed cutoffs for cuff BP with a bootstrapping (resampling by drawing randomly with replacement) and an approximation method. To evaluate the discriminatory power in predicting cardiovascular outcomes, the derived thresholds were tested in a validation cohort (2,501 individuals with median follow-up of 10 years).

RESULTS

The 2 analyses yielded similar diagnostic thresholds for CBP. After rounding, systolic/diastolic threshold was 110/80 mm Hg for optimal BP and 130/90 mm Hg for hypertension. Compared with optimal BP, the risk of cardiovascular mortality increased significantly in subjects with hypertension (hazard ratio: 3.08, 95% confidence interval: 1.05 to 9.05). Of the multivariate Cox proportional hazards model, incorporation of a dichotomous variable by defining hypertension as CBP ≥ 130/90 mm Hg was associated with the largest contribution to the predictive power.

CONCLUSIONS

CBP of 130/90 mm Hg was determined to be the cutoff limit for normality and was characterized by a greater discriminatory power for long-term events in our validation cohort. This report represents an important step toward the application of the CBP concept in clinical practice.

Estimation of central aortic pressure waveform features derived from the brachial cuff volume displacement waveform

There is increasing interest in non-invasive estimation of central aortic waveform parameters in the clinical setting. However, controversy has arisen around radial tonometric based systems due to the requirement of a trained operator or lack of ease of use, especially in the clinical environment. A recently developed device utilizes a novel algorithm for brachial cuff based assessment of aortic pressure values and waveform (SphygmoCor XCEL, AtCor Medical). The cuff was inflated to 10 mmHg below an individual's diastolic blood pressure and the brachial volume displacement waveform recorded. The aortic waveform was derived using proprietary digital signal processing and transfer function applied to the recorded waveform. The aortic waveform was also estimated using a validated technique (radial tonometry based assessment, SphygmoCor, AtCor Medical). Measurements were taken in triplicate with each device in 30 people (17 female) aged 22 to 79 years of age. An average for each device for each individual was calculated, and the results from the two devices were compared using regression and Bland-Altman analysis. A high correlation was found between the devices for measures of aortic systolic (R(2)=0.99) and diastolic (R(2)=0.98) pressure. Augmentation index and subendocardial viability ratio both had a between device R(2) value of 0.82. The difference between devices for measured aortic systolic pressure was 0.5±1.8 mmHg, and for augmentation index, 1.8±7.0%. The brachial cuff based approach, with an individualized sub-diastolic cuff pressure, provides an operator independent method of assessing not only systolic pressure, but also aortic waveform features, comparable to existing validated tonometric-based methods.

Basis of monitoring central blood pressure and hemodynamic parameters by peripheral arterial pulse waveform analyses

In hypertension clinics, central blood pressure (CBP) should be estimated, instead of directly measured, by the "signal processing" of a noninvasive peripheral pressure waveform. This paper deals with the data obtained in our three separate studies focusing on a major estimation method, i.e., radial artery late systolic shoulder pressure (rSBP2)-based CBP estimation. Study 1: Using a wave separation analysis of precise animal data of pressure wave transmission along the upper-limb arteries, we first demonstrate that pulse pressure amplification is largely attributable to local wave reflection alone. Study 2: A frequency component analysis of simultaneously recorded human central and radial artery pressure waveforms showed a predominance of lower (1st+2nd) harmonic components in determining the central augmentation peak amplitude. The features of a central pressure waveform, including its phase property, may contribute to the less-altered transmission of augmentation peak pressure to rSBP2. Study 3: Comparisons of noninvasive rSBP2 with direct or estimated central systolic blood pressure (cSBP) revealed broad agreement but also augmentation-dependent biases. Based on the features of the biases as well as the counterbalanced relationship between pulse pressure amplification and the transmission-induced alterations of augmentation peak amplitude observed in Study 2, we propose an improved cSBP estimate, SBPm, the simple arithmetic mean of rSBP2 and peripheral systolic blood pressure.

Measurement of central aortic pulse pressure: noninvasive brachial cuff-based estimation by a transfer function vs. a novel pulse wave analysis method

BACKGROUND

The prognostic value of central aortic pulse pressure (PP-C) may have been underestimated due to its measurement inaccuracy. We aimed to investigate the accuracy of noninvasive brachial cuff-based estimation of PP-C by a generalized transfer function (GTF) or a novel pulse wave analysis (PWA) approach to directly estimate PP-C.

METHODS

Invasive high-fidelity right brachial and central aortic pressure tracings, and left brachial pulse volume plethysmography (PVP) waveforms from an oscillometric blood pressure (BP) monitor were all digitized simultaneously in 40 patients during cardiac catheterization. An aortic-to-brachial GTF and a PWA multivariate prediction model using the PVP waveforms calibrated to brachial cuff systolic BP (SBP) and diastolic BP(DBP) were constructed. Accuracy of the two methods was examined in another 100 patients against invasively measured PP-C.

RESULTS

The error of cuff PP in estimating PP-C was 1.8 ± 12.4 mm Hg. Application of the GTF on noninvasively calibrated PVP waveforms produced reconstructed aortic pressure waves and PP-C estimates with errors of -3.4 ± 11.6 mm Hg (PP-C = reconstructed aortic SBP - aortic DBP) and -2.3 ± 11.4 mm Hg (PP-C = reconstructed aortic SBP - cuff DBP), respectively. The observed systematic errors were proportional to the magnitudes of PP-C. In contrast, the error of the PWA prediction model was 3.0 ± 7.1 mm Hg without obvious proportional systematic error.

CONCLUSIONS

Large random and systematic errors are introduced into the PP-C estimates when PP-C is calculated as the difference between the estimated central SBP and central or cuff DBP. The accuracy can be improved substantially with the novel PWA approach.

Aortic function quantified: the heart's essential cushion

Arterial compliance is mainly determined by the elasticity of proximal large-conduit arteries of which the aorta is the largest contributor. Compliance forms an important part of the cardiac load and plays a role in organ (especially coronary) perfusion. To follow local changes in aortic compliance, as in aging, noninvasive determination of compliance distribution would be of great value. Our goal is to determine regional aortic compliance noninvasively in the human. In seven healthy individuals at six locations, aortic blood flow and systolic/diastolic area (ΔA) was measured with MRI. Simultaneously brachial pulse pressure (ΔP) was measured with standard cuff. With a transfer function we derived ΔP at the same aortic locations as the MRI measurements. Regional aortic compliance was calculated with two approaches, the pulse pressure method, and local area compliance (ΔA/ΔP) times segment length, called area compliance method. For comparison, pulse wave velocity (PWV) from local flows at two locations was determined, and compliance was derived from PWV. Both approaches show that compliance is largest in the proximal aorta and decreases toward the distal aorta. Similar results were found with PWV-derived compliance. Of total arterial compliance, ascending to distal arch (segments 1-3) contributes 40% (of which 15% is in head and arms), descending aorta (segments 4 and 5) 25%, and "hip, pelvic and leg arteries" 20%. Pulse pressure method includes compliance of side branches and is therefore larger than the area compliance method. Regional aortic compliance can be obtained noninvasively. Therefore, this technique allows following changes in local compliance with age and cardiovascular diseases.

Measurement accuracy of non-invasively obtained central blood pressure by applanation tonometry: a systematic review and meta-analysis

BACKGROUND AND OBJECTIVES

Non-invasive methods based on applanation tonometry have been proposed to estimate central blood pressure. However, the accuracy of these methods hasn't been systematically examined.

METHODS

We performed a systematic review and meta-analysis of studies comparing estimated and invasively measured central BP.

RESULTS

Sufficient data were available in 22 studies for meta-analysis (857 subjects and 1167 measurements). Acquired arterial pressure waveforms in these studies were directly measured, calibrated to match invasive aortic mean BP and diastolic BP or calibrated to match brachial BP measured with a sphygmomanometer, cuff BP. Of the former 2 conditions, the errors of estimated central BP were small with a mean and standard deviation of difference -1.1 ± 4.1mm Hg (95% limits of agreement -9.1-6.9 mm Hg) for central systolic BP; -0.5 ± 2.1mm Hg (-4.6-3.6mm Hg) for central diastolic BP; and -0.8 ± 5.1mm Hg (-10.8-9.2mm Hg) for central pulse pressure. However, the errors inflated to -8.2 ± 10.3mm Hg (-28.4-12.0mm Hg) for central systolic BP, 7.6 ± 8.7 mm Hg (-9.5-24.6mm Hg) for central diastolic BP, and -12.2 ± 10.4mm Hg (-32.5-8.1mm Hg) for central pulse pressure, when calibrated to cuff BP. The findings were still evident in subgroup analysis conducted with different central BP estimating methods and validated cuff BP monitors.

CONCLUSION

Present tonometry-based central BP estimating methods are acceptable in theory, with small errors. However, based on current available evidence, there is substantial room for improvement in measurement accuracy of central BP when cuff BP is used to calibrate the peripheral waveforms.