Pulse pressure amplification, pressure waveform calibration and clinical applications

Validation of a Suprasystolic Cuff System for Static and Dynamic Representation of the Central Pressure Waveform

BACKGROUND

Noninvasive pulse waveform analysis is valuable for central cardiovascular assessment, yet controversies persist over its validity in peripheral measurements. Our objective was to compare waveform features from a cuff system with suprasystolic blood pressure hold with an invasive aortic measurement.

METHODS AND RESULTS

This study analyzed data from 88 subjects undergoing concurrent aortic catheterization and brachial pulse waveform acquisition using a suprasystolic blood pressure cuff system. Oscillometric blood pressure (BP) was compared with invasive aortic systolic BP and diastolic BP. Association between cuff and catheter waveform features was performed on a set of 15 parameters inclusive of magnitudes, time intervals, pressure-time integrals, and slopes of the pulsations. The evaluation covered both static (subject-averaged values) and dynamic (breathing-induced fluctuations) behaviors. Peripheral BP values from the cuff device were higher than catheter values (systolic BP-residual, 6.5 mm Hg; diastolic BP-residual, 12.4 mm Hg). Physiological correction for pressure amplification in the arterial system improved systolic BP prediction (r2=0.83). Dynamic calibration generated noninvasive BP fluctuations that reflect those invasively measured (systolic BP Pearson R=0.73, P<0.001; diastolic BP Pearson R=0.53, P<0.001). Static and dynamic analyses revealed a set of parameters with strong associations between catheter and cuff (Pearson R>0.5, P<0.001), encompassing magnitudes, timings, and pressure-time integrals but not slope-based parameters.

CONCLUSIONS

This study demonstrated that the device and methods for peripheral waveform measurements presented here can be used for noninvasive estimation of central BP and a subset of aortic waveform features. These results serve as a benchmark for central cardiovascular assessment using suprasystolic BP cuff-based devices and contribute to preserving system dynamics in noninvasive measurements.

A Pneumatic Low-Pass Filter for High-Fidelity Cuff-Based Pulse Waveform Acquisition

Cuff-based pulse waveform acquisition (CBPWA) devices are reliable solutions for non-invasive cardiovascular diagnostics. However, poor signal resolution has limited clinical applications. This study aims to demonstrate the improved signal quality of CBPWA devices by implementing passive pneumatic low-pass filters (pLPF). Conventionally, pressure sensor output resolution is a percentage of the operating range. Therefore, measurement of small pressure changes in a large range must sacrifice signal resolution to accommodate for the large mean pressures. We design a pLPF to obtain the running mean pressure and combine it with a high-resolution differential pressure sensor for isolating the signal's pulsatile component. Thirty-one volunteers participated in a device proof-of-concept study at Caltech. Volunteers were measured at rest in the supine position on the left arm. The filtering behavior is mathematically modeled and experimentally verified, showing good agreement between measured and predicted cutoff frequencies. In the human study, the device successfully captured high-fidelity pulse waveform measurements for all volunteers: a blood pressure (BP) reading was followed by inflate-and-hold acquisition in diastolic BP (DBP), mean arterial pressure (MAP), and supra systolic BP (sSBP). The study demonstrated the reliability and high signal resolution of pLPF for CBPWA. Considering the widespread use of the brachial cuff, a system for high-resolution CBPWA motivates the clinical implementation of non-invasive pulse waveform analysis (PWA).

Non-Invasive Estimation of Central Systolic Blood Pressure by Radial Tonometry: A Simplified Approach

BACKROUND

Central systolic blood pressure (cSBP) provides valuable clinical and physiological information. A recent invasive study showed that cSBP can be reliably estimated from mean (MBP) and diastolic (DBP) blood pressure. In this non-invasive study, we compared cSBP calculated using a Direct Central Blood Pressure estimation (DCBP = MBP2/DBP) with cSBP estimated by radial tonometry.

METHODS

Consecutive patients referred for cardiovascular assessment and prevention were prospectively included. Using applanation tonometry with SphygmoCor device, cSBP was estimated using an inbuilt generalized transfer function derived from radial pressure waveform, which was calibrated to oscillometric brachial SBP and DBP. The time-averaged MBP was calculated from the radial pulse waveform. The minimum acceptable error (DCBP-cSBP) was set at ≤5 (mean) and ≤8 mmHg (SD).

RESULTS

We included 160 patients (58 years, 54%men). The cSBP was 123.1 ± 18.3 mmHg (range 86-181 mmHg). The (DCBP-cSBP) error was -1.4 ± 4.9 mmHg. There was a linear relationship between cSBP and DCBP (R2 = 0.93). Forty-seven patients (29%) had cSBP values ≥ 130 mmHg, and a DCBP value > 126 mmHg exhibited a sensitivity of 91.5% and specificity of 94.7% in discriminating this threshold (Youden index = 0.86; AUC = 0.965).

CONCLUSIONS

Using the DCBP formula, radial tonometry allows for the robust estimation of cSBP without the need for a generalized transfer function. This finding may have implications for risk stratification.

Agreement between distal and forearm radial arterial pressures in patients undergoing prone spinal surgery: a prospective, self-controlled, observational study

OBJECTIVE

To test agreement and interchangeability between distal (dRA) and forearm radial arterial (RA) pressures (AP) during general anesthesia (GA) for prone spinal surgery.

METHODS

This prospective observational study involved 40 patients scheduled for GA spinal surgery. The right dRA and left forearm RA were cannulated in all patients to continuously measure invasive blood pressures (IBP). We compared the agreement and trending ability of systolic AP (SAP), diastolic AP (DAP), and mean AP (MAP) at each site 15 minutes after tracheal intubation, start of surgery, 30 and 60 minutes after the start of surgery, and after skin suturing.

RESULTS

Paired BP values (n = 184) (37 cases) were analyzed. The bias (standard deviation), limits of agreement, and percentage error were: SAP: 0.19 (3.03), -5.75 to 6.12, and 5.04%; DAP: -0.06 (1.75), -3.50 to 3.38, and 5.10%; and MAP: 0.08 (1.52), -2.90 to 3.05, and 3.54%, respectively. The linear regression coefficients of determination were 0.981, 0.982, and 0.988 for SAPs, DAPs, and MAPs, respectively; four-quadrant plot concordance rates were 95.11%, 92.03%, and 92.66%, respectively.

CONCLUSION

All arterial BPs showed good agreement and trending capabilities for both the dRA and RA. The dRA may be substituted for the RA in IBP monitoring.

Direct estimation of central aortic pressure from measured or quantified mean and diastolic brachial blood pressure: agreement with invasive records

Background

Recently it has been proposed a new approach to estimate aortic systolic blood pressure (aoSBP) without the need for specific devices, operator-dependent techniques and/or complex wave propagation models/algorithms. The approach proposes aoSBP can be quantified from brachial diastolic and mean blood pressure (bDBP, bMBP) as: aoSBP = bMBP2/bDBP. It remains to be assessed to what extent the method and/or equation used to obtain the bMBP levels considered in aoSBP calculation may affect the estimated aoSBP, and consequently the agreement with aoSBP invasively recorded.

Methods

Brachial and aortic pressure were simultaneously obtained invasively (catheterization) and non-invasively (brachial oscillometry) in 89 subjects. aoSBP was quantified in seven different ways, using measured (oscillometry-derived) and calculated (six equations) mean blood pressure (MBP) levels. The agreement between invasive and estimated aoSBP was analyzed (Concordance correlation coefficient; Bland-Altman Test).

Conclusions

The ability of the equation "aoSBP = MBP2/DBP" to (accurately) estimate (error <5 mmHg) invasive aoSBP depends on the method and equation considered to determine bMBP, and on the aoSBP levels (proportional error). Oscillometric bMBP and/or approaches that consider adjustments for heart rate or a form factor ∼40% (instead of the usual 33%) would be the best way to obtain the bMBP levels to be used to calculate aoSBP.

Brachial Blood Pressure Invasively and Non-Invasively Obtained Using Oscillometry and Applanation Tonometry: Impact of Mean Blood Pressure Equations and Calibration Schemes on Agreement Levels

The use of oscillometric methods to determine brachial blood pressure (bBP) can lead to a systematic underestimation of the invasively measured systolic (bSBP) and pulse (bPP) pressure levels, together with a significant overestimation of diastolic pressure (bDBP). Similarly, the agreement between brachial mean blood pressure (bMBP), invasively and non-invasively measured, can be affected by inaccurate estimations/assumptions. Despite several methodologies that can be applied to estimate bMBP non-invasively, there is no consensus on which approach leads to the most accurate estimation. Aims: to evaluate the association and agreement between: (1) non-invasive (oscillometry) and invasive bBP; (2) invasive bMBP, and bMBP (i) measured by oscillometry and (ii) calculated using six different equations; and (3) bSBP and bPP invasively and non-invasively obtained by applanation tonometry and employing different calibration methods. To this end, invasive aortic blood pressure and bBP (catheterization), and non-invasive bBP (oscillometry [Mobil-O-Graph] and brachial artery applanation tonometry [SphygmoCor]) were simultaneously obtained (34 subjects, 193 records). bMBP was calculated using different approaches. Results: (i) the agreement between invasive bBP and their respective non-invasive measurements (oscillometry) showed dependence on bBP levels (proportional error); (ii) among the different approaches used to obtain bMBP, the equation that includes a form factor equal to 33% (bMBP = bDBP + bPP/3) showed the best association with the invasive bMBP; (iii) the best approach to estimate invasive bSBP and bPP from tonometry recordings is based on the calibration scheme that employs oscillometric bMBP. On the contrary, the worst association between invasive and applanation tonometry-derived bBP levels was observed when the brachial pulse waveform was calibrated to bMBP quantified as bMBP = bDBP + bPP/3. Our study strongly emphasizes the need for methodological transparency and consensus for non-invasive bMBP assessment.

Aortic systolic and pulse pressure invasively and non-invasively obtained: Comparative analysis of recording techniques, arterial sites of measurement, waveform analysis algorithms and calibration methods

Background: The non-invasive estimation of aortic systolic (aoSBP) and pulse pressure (aoPP) is achieved by a great variety of devices, which differ markedly in the: 1) principles of recording (applied technology), 2) arterial recording site, 3) model and mathematical analysis applied to signals, and/or 4) calibration scheme. The most reliable non-invasive procedure to obtain aoSBP and aoPP is not well established. Aim: To evaluate the agreement between aoSBP and aoPP values invasively and non-invasively obtained using different: 1) recording techniques (tonometry, oscilometry/plethysmography, ultrasound), 2) recording sites [radial, brachial (BA) and carotid artery (CCA)], 3) waveform analysis algorithms (e.g., direct analysis of the CCA pulse waveform vs. peripheral waveform analysis using general transfer functions, N-point moving average filters, etc.), 4) calibration schemes (systolic-diastolic calibration vs. methods using BA diastolic and mean blood pressure (bMBP); the latter calculated using different equations vs. measured directly by oscillometry, and 5) different equations to estimate bMBP (i.e., using a form factor of 33% ("033"), 41.2% ("0412") or 33% corrected for heart rate ("033HR"). Methods: The invasive aortic (aoBP) and brachial pressure (bBP) (catheterization), and the non-invasive aoBP and bBP were simultaneously obtained in 34 subjects. Non-invasive aoBP levels were obtained using different techniques, analysis methods, recording sites, and calibration schemes. Results: 1) Overall, non-invasive approaches yielded lower aoSBP and aoPP levels than those recorded invasively. 2) aoSBP and aoPP determinations based on CCA recordings, followed by BA recordings, were those that yielded values closest to those recorded invasively. 3) The "033HR" and "0412" calibration schemes ensured the lowest mean error, and the "033" method determined aoBP levels furthest from those recorded invasively. 4) Most of the non-invasive approaches considered overestimated and underestimated aoSBP at low (i.e., 80 mmHg) and high (i.e., 180 mmHg) invasive aoSBP values, respectively. 5) The higher the invasively measured aoPP, the higher the level of underestimation provided by the non-invasive methods. Conclusion: The recording method and site, the mathematical method/model used to quantify aoSBP and aoPP, and to calibrate waveforms, are essential when estimating aoBP. Our study strongly emphasizes the need for methodological transparency and consensus for the non-invasive aoBP assessment.

Mean arterial pressure estimated by brachial pulse wave analysis and comparison with currently used algorithms

OBJECTIVE

Mean arterial pressure (MAP) is usually calculated by adding one-third of pulse pressure (PP) to DBP. This formula assumes that the average value of pulse waveform is constant in all individuals and coincides with 33.3% of PP amplitude (MAP = DBP + PP × 0.333). Other formulas were lately proposed to improve the MAP estimation, adding to DBP an established percentage of PP: MAP = DBP + PP × 0.40; MAP = DBP + PP × 0.412; MAP = DBP + PP × 0.333 + 5 mmHg.

METHODS

The current study evaluated the integral of brachial pulse waveform recorded by applanation tonometry in 1526 patients belonging to three distinct cohorts: normotensive or hypertensive elderly, hypertensive adults, and normotensive adults.

RESULTS

The percentage of PP to be added to DBP to obtain MAP was extremely variable among individuals, ranging from 23 to 58% (mean: 42.2 ± 5.5%), higher in women (42.9 ± 5.6%) than men (41.2 ± 5.1%, P < 0.001), lower in the elderly cohort (40.9 ± 5.3%) than in the general population cohort (42.8 ± 6.0%, P < 0.001) and in the hypertensive patients (42.4 ± 4.8%, P < 0.001). This percentage was significantly associated with DBP (β = 0.357, P < 0.001) and sex (β = 0.203, P < 0.001) and significantly increased after mental stress test in 19 healthy volunteers (from 39.9 ± 3.2 at baseline, to 43.0 ± 4.0, P < 0.0001). The average difference between MAP values estimated by formulas, compared with MAP assessed on the brachial tonometric curve, was (mean ± 1.96 × SD): -5.0 ± 6.7 mmHg when MAP = DBP + PP × 0333; -1.2 ± 6.1 mmHg when MAP = DBP + PP × 0.40; -0.6 ± 6.1 mmHg when MAP = DBP + PP × 0.412; -0.4 ± 6.7 mmHg when MAP = DBP + PP × 0.333 + 5.

CONCLUSION

Due to high interindividual and intraindividual variability of pulse waveform, the estimation of MAP based on fixed formulas derived from SBP and DBP is unreliable. Conversely, a more accurate estimation of MAP should be based on the pulse waveform analysis.

Association Between Central-Peripheral Blood Pressure Amplification and Structural and Functional Cardiac Properties in Children, Adolescents, and Adults: Impact of the Amplification Parameter, Recording System and Calibration Scheme

INTRODUCTION

Systolic blood pressure (SBPA) and pulse pressure amplification (PPA) were quantified using different methodological and calibration approaches to analyze (1) the association and agreement between different SBPA and PPA parameters and (2) the association between these SBPA and PPA parameters and left ventricle (LV) and atrium (LA) structural and functional characteristics.

METHODS

In 269 healthy subjects, LV and LA parameters were echocardiography-derived. SBPA and PPA parameters were quantified using: (1) different equations (n = 9), (2) methodological approaches (n = 3): brachial sub-diastolic (Mobil-O-Graph®) and supra-systolic oscillometry (Arteriograph®) and aortic diameter waveform re-calibration (RCD; ultrasonography), and (3) using three different calibration schemes: systo-diastolic (SD), calculated mean (CM) and oscillometric mean (OscM).

RESULTS

SBPA and PPA parameters obtained with different equations, techniques, and calibration schemes show a highly variable association level (negative, non-significant, and/or positive) among them. The association between SBPA and PPA with cardiac parameters were highly variable (negative, non-significant, or positive associations). Differences in BPA parameter data between approaches were more sensitive to the calibration method than to the device used. Both, SBPA and PPA obtained with brachial sub-diastolic technique and calibrated to CM or OscM showed higher levels of association with LV and LA structural characteristics.

CONCLUSIONS

Our data show that many of the parameters that assume to quantify the same phenomenon of BPA are not related to each other in the different age groups. Both, SBPA and PPA obtained with brachial sub-diastolic technique and calibrated to CM or OscM showed higher levels of association with LV and LA structural characteristics.

Association of pulse wave velocity and pressure wave reflection with the ankle-brachial pressure index in Japanese men not suffering from peripheral artery disease

BACKGROUND AND AIMS

We examined the cross-sectional and longitudinal association of arterial stiffness and pressure wave reflection with the ankle-brachial pressure index (ABI) in middle-aged Japanese subjects free of peripheral artery disease (PAD).

METHODS

ABI, brachial-ankle pulse wave velocity (baPWV) and radial augmentation index (rAI) were measured annually during the 9-year observation period in 3066 men (42 ± 9 years old) with ABI ≥1.00 at baseline of the study period, and not taking any antihypertensive medication.

RESULTS

In the cross-sectional assessments, mediation analysis demonstrated that baPWV showed both direct and indirect (via the rAI) associations with ABI, and rAI showed both direct and indirect (via the heart-arm difference of systolic blood pressure) associations with the ankle-arm difference of systolic blood pressure, both at study baseline and end of study period. Mixed model linear regression analysis of the repeated-measurement data obtained over the 9-year observation period demonstrated that annual increase of baPWV (estimate = 0.73 × 10^-4, p < 0.01) and rAI (estimate = 0.33 × 10^-3, <0.01) was associated with ABI. When baPWV and rAI were entered into the same model, only baPWV showed a significant longitudinal association with ABI.

CONCLUSION

In middle-aged Japanese men free of PAD, arterial stiffness may contribute to ABI directly and via pressure wave reflection. Pressure wave reflection may contribute to ABI directly and, at least in part, via attenuation of peripheral pulse pressure amplification.

Vitamin K2 Status and Arterial Stiffness Among Untreated Migraine Patients: A Case-Control Study

OBJECTIVE

We aimed to examine arterial stiffness and vitamin K2 status in migraine subjects by comparison to controls.

BACKGROUND

Migraine is a primary headache disorder that has been associated with an increased risk of cardiovascular events. Mechanisms underlying this increased risk, however, remain unclear. Vitamin K2 deficiency emerged as a cardiovascular risk factor, but vitamin K2 status has never been explored in migraine subjects.

DESIGN AND METHODS

This is a case-control, single-center, observational study that includes a cohort of subjects with migraine and their age- and sex-matched controls. Arterial stiffness was measured using carotid-femoral pulse wave velocity (cfPWV). Dephosphorylated-uncarboxylated matrix-Gla-protein (dp-ucMGP) was used as a marker for vitamin K2 status. A propensity-matched scoring method was used.

RESULTS

A total of 146 patients (73 matched pairs) were included in this study, of whom 89% were women with a mean age of 31.9 ± 8.4 years. Compared with controls, migraine patients had statistically significantly higher mean cfPWV (7.2 ± 1.1 vs 6.4 ± 0.8 m/s, 95% confidence interval (CI) of mean difference [0.45, 1.08], P < .001), as well as higher dp-ucMGP (454.3 ± 116.7 pmol/L vs 379.8 ± 126.6 pmol/L, 95% CI of mean difference [34.63, 114.31], P < .001). Higher cfPWV was associated with higher dp-ucMGP concentrations only in the migraine with aura (MWA) group. Moreover, migraine subjects had a higher frequency of vitamin K2 deficiency (dp-ucMGP ≥ 500 pmol/L) compared to controls, but this association was not statistically significant (23/73 [31.5%] vs 16/73 [21.9%], P = .193).

CONCLUSIONS

Individuals with migraine have worse indices of arterial stiffness as compared with their age- and sex-matched control subjects. This increase in arterial stiffness is associated with an increase in markers of vitamin K2 deficiency in the MWA group.

Impact of Methodological and Calibration Approach on the Association of Central and Peripheral Systolic Blood Pressure with Cardiac Structure and Function in Children, Adolescents and Adults

INTRODUCTION

Peripheral and aortic systolic blood pressure (pSBP and aoSBP) were measured using different methodological and calibration approaches to analyze the association and agreement between pSBP and/or aoSBP, and the association of pSBP and aoSBP with left ventricle (LV) and atrium (LA) structural-functional characteristics.

METHODS

In healthy subjects (n = 269, age: 9-85 years; n = 147, age < 24 years) LV and LA parameters were echocardiography-derived. pSBP and aoSBP were obtained by brachial sub-diastolic (Mobil-O-Graph^®) and supra-systolic oscillometry (Arteriograph^®) and aortic diameter waveform re-calibration (RCD; ultrasonography), using three calibration schemes: systo-diastolic (SD), calculated mean (CM), and oscillometric mean (OscM).

RESULTS

Always pSBP and aoSBP were positively associated; aoSBP obtained with the Mobil-O-Graph^® and calibrated to CM or OscM were the ones that showed the lowest levels of association with the remaining forms of aoSBP and pSBP. Bland-Altman related mean errors varied noticeably (e.g. - 27, - 23, - 17, - 12 or 8 mmHg when aoSBP obtained with MOG (OscM) was compared with data from other methodological and calibration schemes). The aoSBP data obtained with Mobil-O-Graph^® (calibration: CM and OscM) showed the highest levels of association with cardiac structural characteristics. aoSBP values obtained calibrating to OscM were higher than those obtained calibrating to SD or CM.

CONCLUSIONS

aoSBP obtained with Mobil-O-Graph^® and calibrated to CM or OscM showed (1) lower association with other forms of aoSBP and pSBP determination and (2) higher levels of association with LV and LA structural characteristics. Differences in aoSBP data between approaches were more sensitive to the calibration method than to the device used.

The association of smoothness index of central blood pressure with ambulatory carotid femoral pulse wave velocity after 20-week treatment with losartan in combination with amlodipine versus hydrochlorothiazide

Supplemental Digital Content is available in the text

The aim of this study was to identify associations between the smoothness index of central SBP (CSBP) and changes of ambulatory carotid femoral pulse wave velocity in response to 20-week treatments with losartan and amlodipine vs. losartan and hydrochlorthiazide combinations.

Carotid pulse wave analysis: left or right, does it matter?

INTRODUCTION

Pulse wave analysis (PWA) over the carotid artery is one of the available methodological options to obtain central arterial pressures and other important hemodynamic parameters. However, limited data exist relating the PWA estimates of one carotid artery over the contralateral one as the majority of the available data rely on measures over the right carotid artery.

OBJECTIVE

To evaluate the agreement of the PWA estimates between the right carotid artery and the left carotid artery.

PATIENTS AND METHODS

A cross-sectional study of 38 patients, with a mean age of 28.85±1.70 years, was carried out. Brachial blood pressure was evaluated using a sphygmomanometer. Subsequently, PWA was obtained randomly over the left or the right carotid arteries with the Complior Analyse. All the evaluations were performed by the same experienced operator.

RESULTS

The overall mean differences observed by comparing the obtained parameters in each carotid territory were -1.50±8.06 mmHg for central systolic blood pressure (SBP), -1.63±7.98 mmHg for central pulse pressure, -3.37±27.80% for the augmentation index, and 1.50±8.06 mmHg for the SBP amplification, and were not statistically significant for all the parameters. The Bland-Altman analysis showed distinct correlations and concordance levels for different parameters: central SBP and central pulse pressure showed a very strong agreement (intraclass correlation of 0.926 and 0.886, respectively). In contrast, the concordance for the augmentation index and the SBP amplification was moderate (intraclass correlations between 0.5 and 0.8).

CONCLUSION

PWA provides similar measures of central blood pressure, whether measured over the right or the left carotid arteries, even though the morphological features of the pulse waves showed moderate agreement. The advantages of PWA over each arterial territory and the requirements that should mediate the choice of one of the both sides require further investigation.

Changes of Arterial Pulse Waveform Characteristics with Gestational Age during Normal Pregnancy

Arterial pulse waveform analysis has been widely used to reflect physiological changes in the cardiovascular system. This study aimed to comprehensively investigate the changes of waveform characteristics of both photoplethysmographic (PPG) and radial pulses with gestational age during normal pregnancy. PPG and radial pulses were simultaneously recorded from 130 healthy pregnant women at seven gestational time points. After normalizing the arterial pulse waveforms, the abscissa of notch point, the total pulse area and the reflection index were extracted and compared between different measurement points and between the PPG and radial pulses using post-hoc multiple comparisons with Bonferrioni correction. The results showed that the effect of gestational age on all the three waveform characteristics was significant (all p < 0.001) after adjusting for maternal age, heart rate and blood pressures. All the three waveform characteristics demonstrated similar changing trends with gestational age, and they were all significantly different between the measurements from gestational week 12–15 and the others (all p < 0.05, except for the PPG total pulse area between the first and second measurement points). In conclusion, this study has comprehensively quantified similar changes of both PPG and radial pulse waveform characteristics with gestational age.

Aortic systolic pressure derived with different calibration methods: associations to brachial systolic pressure in the general population

BACKGROUND

There is increasing evidence that the method of calibration directly influences the association between brachial systolic blood pressure (bSBP) and estimated aortic systolic blood pressure (aSBP) and subsequently affects prognostic and diagnostic differentiation power of the latter.

OBJECTIVE

The aim of this study was to investigate associations between different methods of systolic pressure assessment in a large cohort and its comparison with recently published evidence.

PARTICIPANTS AND METHODS

During a public health campaign, cardiovascular hemodynamic data were assessed using a validated oscillometric device in a pharmacy setting. The device measures bSBP, mean arterial pressure, and diastolic blood pressure (DBP), and records brachial waveforms at the DBP level. aSBP1 was derived using bSBP and DBP and aSBP2 using measured mean arterial pressure and DBP for waveform calibration. In addition to pressures, age, sex, and anthropometric data were recorded. Regression analysis was carried out to investigate associations.

RESULTS

A total of 7409 (5133/2276, female/male) individuals with a median age of 54 years were sampled. aSBPs differed significantly from bSBP (126.0 mmHg) for aSBP1 (117.0 mmHg) and aSBP2 (127.5 mmHg, both P<0.0001). Regression analysis showed that aSBP2 (R=0.853) is significantly less associated with bSBP than aSBP1 (R=0.937) (Williams' test, P<0.001 for comparison). Subgroup analysis showed the major influence of sex and heart rate. The association between bSBP, aSBP1 (R=0.83), and aSBP2 (R=0.66), respectively, reduced significantly for borderline hypertensives (P<0.001 for comparison).

CONCLUSION

In contrast to aSBP1, the association between bSBP and aSBP2 is significantly less dominant and therefore aSBP2 may have potential prognostic superiority over bSBP.

Pulse wave analysis reproducibility with the Complior Analyse device: a methodological study

INTRODUCTION

The aim of this study was to assess the interobserver and intraobserver reproducibility, as well as the temporal variability of the new Complior Analyse assessing central arterial hemodynamic parameters through carotid pulse wave analysis (PWA).

PATIENTS AND METHODS

Eighty-seven (60% men) participants, with a mean age of 34.26±16.58 years, were enrolled in a cross-sectional study. All patients were subjected to sequential measures of carotid PWA by two experienced operators. In a group of 27 patients, PWA was also determined 1 month after the first evaluation to address the temporal stability of the PWA estimations with the device.

RESULTS

The analysis of concordance revealed a very good agreement for paired PWA values, regarding both intraobserver variability and interobserver variability and also the temporal variability. Intraclass correlation coefficients above 0.9 were calculated for central systolic blood pressure, central pulse pressure, and the augmentation index, in all three conditions. Small mean differences for intraobserver, interobserver, and temporal reproducibility were also observed for the three major parameters: -0.5 mmHg [limits of agreement (LOA): 9.1;8.1], 0.1 mmHg (LOA: 6.6;6.8), and -0.3 mmHg (LOA: 10.2;9.6), respectively, for central systolic blood pressure; 0.4 mmHg (LOA: 6.2;6.9), 1.0 mmHg (LOA: 6.0;8.1), and -0.4 mmHg (LOA: 6.7;6.1), respectively, for central pulse pressure; and 0.8% (LOA: 14.0;15.5), 0.1% (LOA: 15.6;15.9), and -0.1% (LOA: 16.2;16.1), respectively, for the augmentation index. The observed correlations were independent of sex, age, arterial pressure, heart rate, and BMI.

CONCLUSION

The data demonstrated an excellent reproducibility of the Complior Analyse for the assessment of central hemodynamic parameters, when used in ideal conditions and by experienced observers. The results demonstrates that this device is suitable for the inclusion in integrated clinical follow-up programs, particularly regarding central arterial pressure estimations.

Central Blood Pressure Monitoring via a Standard Automatic Arm Cuff

Current oscillometric devices for monitoring central blood pressure (BP) maintain the cuff pressure at a constant level to acquire a pulse volume plethysmography (PVP) waveform and calibrate it to brachial BP levels estimated with population average methods. A physiologic method was developed to further advance central BP measurement. A patient-specific method was applied to estimate brachial BP levels from a cuff pressure waveform obtained during conventional deflation via a nonlinear arterial compliance model. A physiologically-inspired method was then employed to extract the PVP waveform from the same waveform via ensemble averaging and calibrate it to the brachial BP levels. A method based on a wave reflection model was thereafter employed to define a variable transfer function, which was applied to the calibrated waveform to derive central BP. This method was evaluated against invasive central BP measurements from patients. The method yielded central systolic, diastolic, and pulse pressure bias and precision errors of -0.6 to 2.6 and 6.8 to 9.0 mmHg. The conventional oscillometric method produced similar bias errors but precision errors of 8.2 to 12.5 mmHg (p ≤ 0.01). The new method can derive central BP more reliably than some current non-invasive devices and in the same way as traditional cuff BP.

Validity of the augmentation index and pulse pressure amplification as determined by the SphygmoCor XCEL device: a comparison with invasive measurements

Augmentation index (AIx) and pulse pressure (PP) amplification can be determined by the SphygmoCor XCEL device in an operator-independent manner. This study aimed to examine its validity against invasive measurements. Simultaneous recordings of central aortic pressure waveforms were performed with oscillometric and high-fidelity invasive methods in 35 patients who underwent coronary arteriography. Brachial blood pressure was also recorded using the two methods. AIx for the aortic pressure waveform was defined as the ratio of augmentation pressure to PP. PP amplification was defined as the ratio of brachial PP to aortic PP. The differences between the invasive and oscillometric measurements were -7.7±12.7% for AIx and 0.17±0.14 for PP amplification (mean±s.d.). Strong correlations between the invasive and oscillometric measurements were found in both indices (AIx: r=0.75; PP amplification: r=0.80; both P<0.001). The Bland-Altman plot showed a proportional bias of PP amplification, but not of AIx (AIx: r=-0.21, P=0.23; PP amplification: r=-0.61; P<0.001). In conclusion, estimated AIx may be reliable considering the high correlation between the invasive and noninvasive values and the lack of proportional bias against invasive assessment. However, a substantial underestimation and a large scatter of estimated AIx were also observed. Further studies using the device to investigate associations with target organ damage or prognoses are needed to clarify its clinical validity.

Assessing the blood pressure waveform of the carotid artery using an ultrasound image processing method

PURPOSE

The aim of this study was to introduce and implement a noninvasive method to derive the carotid artery pressure waveform directly by processing diagnostic sonograms of the carotid artery.

METHODS

Ultrasound image sequences of 20 healthy male subjects (age, 36±9 years) were recorded during three cardiac cycles. The internal diameter and blood velocity waveforms were extracted from consecutive sonograms over the cardiac cycles by using custom analysis programs written in MATLAB. Finally, the application of a mathematical equation resulted in time changes of the arterial pressure. The resulting pressures were calibrated using the mean and the diastolic pressure of the radial artery.

RESULTS

A good correlation was found between the mean carotid blood pressure obtained from the ultrasound image processing and the mean radial blood pressure obtained using a standard digital sphygmomanometer (R=0.91). The mean absolute difference between the carotid calibrated pulse pressures and those measured clinically was -1.333±6.548 mm Hg.

CONCLUSION

The results of this study suggest that consecutive sonograms of the carotid artery can be used for estimating a blood pressure waveform. We believe that our results promote a noninvasive technique for clinical applications that overcomes the reproducibility problems of common carotid artery tonometry with technical and anatomical causes.

A Simple Adaptive Transfer Function for Deriving the Central Blood Pressure Waveform from a Radial Blood Pressure Waveform

Generalized transfer functions (GTFs) are available to compute the more relevant central blood pressure (BP) waveform from a more easily measured radial BP waveform. However, GTFs are population averages and therefore may not adapt to variations in pulse pressure (PP) amplification (ratio of radial to central PP). A simple adaptive transfer function (ATF) was developed. First, the transfer function is defined in terms of the wave travel time and reflection coefficient parameters of an arterial model. Then, the parameters are estimated from the radial BP waveform by exploiting the observation that central BP waveforms exhibit exponential diastolic decays. The ATF was assessed using the original data that helped popularize the GTF. These data included radial BP waveforms and invasive reference central BP waveforms from cardiac catheterization patients. The data were divided into low, middle, and high PP amplification groups. The ATF estimated central BP with greater accuracy than GTFs in the low PP amplification group (e.g., central systolic BP and PP root-mean-square-errors of 3.3 and 4.2 mm Hg versus 6.2 and 7.1 mm Hg; p ≤ 0.05) while showing similar accuracy in the higher PP amplification groups. The ATF may permit more accurate, non-invasive central BP monitoring in elderly and hypertensive patients.

Importance of Calibration Method in Central Blood Pressure for Cardiac Structural Abnormalities

BACKGROUND

Central blood pressure (CBP) independently predicts cardiovascular risk, but calibration methods may affect accuracy of central systolic blood pressure (CSBP). Standard central systolic blood pressure (Stan-CSBP) from peripheral waveforms is usually derived with calibration using brachial SBP and diastolic BP (DBP). However, calibration using oscillometric mean arterial pressure (MAP) and DBP (MAP-CSBP) is purported to provide more accurate representation of true invasive CSBP. This study sought to determine which derived CSBP could more accurately discriminate cardiac structural abnormalities.

METHODS

A total of 349 community-based patients with risk factors (71±5years, 161 males) had CSBP measured by brachial oscillometry (Mobil-O-Graph, IEM GmbH, Stolberg, Germany) using 2 calibration methods: MAP-CSBP and Stan-CSBP. Left ventricular hypertrophy (LVH) and left atrial dilatation (LAD) were measured based on standard guidelines.

RESULTS

MAP-CSBP was higher than Stan-CSBP (149±20 vs. 128±15mm Hg, P < 0.0001). Although they were modestly correlated (rho = 0.74, P < 0.001), the Bland-Altman plot demonstrated a large bias (21mm Hg) and limits of agreement (24mm Hg). In receiver operating characteristic (ROC) curve analyses, MAP-CSBP significantly better discriminated LVH compared with Stan-CSBP (area under the curve (AUC) 0.66 vs. 0.59, P = 0.0063) and brachial SBP (0.62, P = 0.027). Continuous net reclassification improvement (NRI) (P < 0.001) and integrated discrimination improvement (IDI) (P < 0.001) corroborated superior discrimination of LVH by MAP-CSBP. Similarly, MAP-CSBP better distinguished LAD than Stan-CSBP (AUC 0.63 vs. 0.56, P = 0.005) and conventional brachial SBP (0.58, P = 0.006), whereas Stan-CSBP provided no better discrimination than conventional brachial BP (P = 0.09).

CONCLUSIONS

CSBP is calibration dependent and when oscillometric MAP and DBP are used, the derived CSBP is a better discriminator for cardiac structural abnormalities.

Cardiorespiratory interactions: Noncontact assessment using laser Doppler vibrometry

The application of a noncontact physiological recording technique, based on the method of laser Doppler vibrometry (LDV), is described. The effectiveness of the LDV method as a physiological recording modality lies in the ability to detect very small movements of the skin, associated with internal mechanophysiological activities. The method is validated for a range of cardiovascular variables, extracted from the contour of the carotid pulse waveform as a function of phase of the respiration cycle. Data were obtained from 32 young healthy participants, while resting and breathing spontaneously. Individual beats were assigned to four segments, corresponding with inspiration and expiration peaks and transitional periods. Measures relating to cardiac and vascular dynamics are shown to agree with the pattern of effects seen in the substantial body of literature based on human and animal experiments, and with selected signals recorded simultaneously with conventional sensors. These effects include changes in heart rate, systolic time intervals, and stroke volume. There was also some evidence for vascular adjustments over the respiration cycle. The effectiveness of custom algorithmic approaches for extracting the key signal features was confirmed. The advantages of the LDV method are discussed in terms of the metrological properties and utility in psychophysiological research. Although used here within a suite of conventional sensors and electrodes, the LDV method can be used on a stand-alone, noncontact basis, with no requirement for skin preparation, and can be used in harsh environments including the MR scanner.

Hemodynamic Correlates of Abnormal Aortic Root Dimension in an Adult Population: The Strong Heart Study

Background

We evaluated the relationship of aortic root dimension (ARD) with flow output and both peripheral and central blood pressure, using multivariable equations predicting ideal sex‐specific ARD at a given age and body height.

Methods and Results

We measured echocardiographic diastolic ARD at the sinuses of Valsalva in 3160 adults (aged 42±16 years, 61% women) from the fourth examination of the Strong Heart Study who were free of prevalent coronary heart disease, and we compared measured data with the theoretical predicted value to calculate a z score. Central blood pressure was estimated by applanation tonometry of the radial artery in 2319 participants. ARD z scores were divided into tertiles representing small, normal, and large ARD. Participants with large ARD exhibited greater prevalence of central obesity and higher levels of inflammatory markers and lipids (0.05<P<0.0001). Stroke volume, heart rate, and both cuff and central diastolic blood pressure were progressively greater from small to large ARD (all P<0.0001). Pulse pressure was higher in small ARD (P<0.0001). In multivariable analysis, ARD z score was related positively to stroke volume, either cuff or central diastolic blood pressure, and negatively to pulse pressure. Large ARD was also independently correlated to higher waist circumference and percentages of neutrophils and plasminogen activator inhibitor‐1 (all P<0.01).

Conclusions

Aortic root dilatation is associated with high diastolic blood pressure, high stroke volume, central fat distribution, and inflammatory status. In contrast, at a given diastolic blood pressure and stroke volume, aortic root dilatation is associated with lower pulse pressure and systolic blood pressure.

Clinical Use of Pulse Wave Analysis: Proceedings From a Symposium Sponsored by North American Artery

The use of pulse wave analysis may guide the provider in making choices about blood pressure treatment in prehypertensive or hypertensive patients. However, there is little clinical guidance on how to interpret and use pulse wave analysis data in the management of these patients. A panel of clinical researchers and clinicians who study and clinically use pulse wave analysis was assembled to discuss strategies for using pulse wave analysis in the clinical encounter. This manuscript presents an approach to the clinical application of pulse waveform analysis, how to interpret central pressure waveforms, and how to use existing knowledge about the pharmacodynamic effect of antihypertensive drug classes in combination with brachial and central pressure profiles in clinical practice. The discussion was supplemented by case-based examples provided by panel members, which the authors hope will provoke discussion on how to understand and incorporate pulse wave analysis into clinical practice.

A region-matching method for pulse transit time estimation: potential for improving the accuracy in determining carotid femoral pulse wave velocity

Carotid femoral pulse wave velocity (cfPWV) is the 'gold standard' for assessment of arterial stiffness. The reliability of cfPWV measurement depends on the estimation of pulse transit time (PTT). This study aimed to validate a region-matching method for determining PTT and cfPWV against the existing 'foot-to-foot' methods. A cohort of 81 subjects (33 males and 48 females) aged 25-80 (45.1±15.7 years) were studied. PTTs were estimated by the region matching and 'foot-to-foot' methods ('diastole minimum', 'maximum first derivative', 'maximum second derivative' and 'tangent intersection' methods) with manual identification as the reference method and were subsequently used to calculate cfPWV. In a subgroup of 30 individuals, the measurements were repeated after 1 h. There were excellent correlations between cfPWV obtained by the reference method and all the estimated methods (r>0.9, P<0.001 for all), except the diastole minimum method (r=0.793, P<0.001). The region-matching method yielded cfPWV with a better accuracy (mean difference=-0.161 m s(-1), limits of agreement: -0.79 to 0.46 m s(-1)) and repeatability (mean difference=-0.228 m s(-1), intraclass correlation coefficient=0.957) comparing with the 'foot-to-foot' methods. These results demonstrate that the proposed region-matching method is more accurate and suitable for PTT estimation and cfPWV measurement.

Pulse pressure waveform estimation using distension profiling with contactless optical probe

The pulse pressure waveform has, for long, been known as a fundamental biomedical signal and its analysis is recognized as a non-invasive, simple, and resourceful technique for the assessment of arterial vessels condition observed in several diseases. In the current paper, waveforms from non-invasive optical probe that measures carotid artery distension profiles are compared with the waveforms of the pulse pressure acquired by intra-arterial catheter invasive measurement in the ascending aorta. Measurements were performed in a study population of 16 patients who had undergone cardiac catheterization. The hemodynamic parameters: area under the curve (AUC), the area during systole (AS) and the area during diastole (AD), their ratio (AD/AS) and the ejection time index (ETI), from invasive and non-invasive measurements were compared. The results show that the pressure waveforms obtained by the two methods are similar, with 13% of mean value of the root mean square error (RMSE). Moreover, the correlation coefficient demonstrates the strong correlation. The comparison between the AUCs allows the assessment of the differences between the phases of the cardiac cycle. In the systolic period the waveforms are almost equal, evidencing greatest clinical relevance during this period. Slight differences are found in diastole, probably due to the structural arterial differences. The optical probe has lower variability than the invasive system (13% vs 16%). This study validates the capability of acquiring the arterial pulse waveform with a non-invasive method, using a non-contact optical probe at the carotid site with residual differences from the aortic invasive measurements.

Associations between bicycling and carotid arterial stiffness in adolescents: The European Youth Hearts Study

The aim of the study was to investigate the associations between bicycling and carotid arterial stiffness, independent of objectively measured moderate-and-vigorous physical activity. This cross-sectional study included 375 adolescents (age 15.7 ± 0.4 years) from the Danish site of the European Youth Heart Study. Total frequency of bicycle usage was assessed by self-report, and carotid arterial stiffness was assessed using B-mode ultrasound. After adjusting for pubertal status, body height, and objectively measured physical activity and other personal lifestyle and demographic factors, boys using their bicycle every day of the week displayed a higher carotid arterial compliance {standard beta 0.47 [95% confidence interval (CI) 0.07-0.87]} and distension [standard beta 0.38 (95% CI -0.04 to 0.81)]. Boys using their bicycle every day of the week furthermore displayed a lower Young's elastic modulus [standard beta -0.48 (95% CI -0.91 to -0.06)]. Similar trends were observed when investigating the association between commuter bicycling and carotid arterial stiffness. These associations were not observed in girls. Our observations suggest that increasing bicycling in adolescence may be beneficial to carotid arterial health among boys.

Pulse wave analysis with two tonometric devices: a comparison study

Pulse wave analysis is a pivotal tool to estimate central haemodynamic parameters. Available commercial devices use applanation tonometry and have been validated against invasive catheterism. We previously observed differences on a radial second systolic peak (rSPB2) between two commonly used devices: SphygmoCor (AtCor, Australia) and PulsePen (DiaTecne, Italy). The aim of our study was to further quantify differences in radial and carotid signals from the two devices.We measured radial and carotid waveforms in 38 patients with minimal changes between systolic, diastolic blood pressure and heart rate.rSBP2, mean pressure, form factor and augmentation index were different with SphygmoCor providing lower values (mean differences: 2.2 ± 3.8 mmHg; 1.5 ± 1.7 mmHg; 3.2 ± 3.5%; 4.2 ± 8.4%, respectively). Carotid augmentation index and form factor were similar. However carotid systolic pressure (cSBP) from PulsePen was higher than cSBP from SphygmoCor (2.7 ± 4.4 mmHg, p < 0.001). For both carotid and radial signals, harmonics moduli were similar across the spectrum with the exception of the 1st harmonic.PulsePen and SphygmoCor sensors are not equivalent and provide different wave shapes despite similar harmonics content with more discrepancy on radial derived parameters than on carotid derived parameters. Further studies are required to compare invasive pressure parameters to indices derived from these two devices.

Arterial compliance across the spectrum of ankle-brachial index: the Multiethnic Study of Atherosclerosis

OBJECTIVE

A low ankle-brachial index is associated with cardiovascular disease and reduced arterial compliance. A high ankle-brachial index is also associated with an increased risk of cardiovascular events. We tested the hypothesis that subjects with a high ankle-brachial index demonstrate a lower arterial compliance. In addition, we assessed whether pulse pressure amplification is increased among subjects with a high ankle-brachial index.

METHODS

We studied 6814 adults enrolled in the Multiethnic Study of Atherosclerosis who were, by definition, free of clinical cardiovascular disease at baseline. Differences in total arterial compliance (ratio of stroke volume to pulse pressure), aortic and carotid distensibility (measured with magnetic resonance imaging and duplex ultrasound, respectively) were compared across ankle-brachial index subclasses (≤0.90, 0.91-1.29; ≥1.30) with analyses adjusted for cardiovascular risk factors and subclinical atherosclerosis.

RESULTS

Peripheral arterial disease was detected in 230 (3.4%) and high ABI in 648 (9.6%) of subjects. Those with high ankle-brachial index demonstrated greater aortic/radial pulse pressure amplification than those with a normal ankle-brachial index. In adjusted models aortic and carotid distensibility as well as total arterial compliance, were lowest among those with ankle-brachial index≤0.9 (p<0.01 vs. all), but were not reduced in subjects with an ankle-brachial index≥1.3.

CONCLUSION

Lower aortic, carotid and total arterial compliance is not present in subjects free of overt cardiovascular disease and with a high ankle-brachial index. However, increased pulse pressure amplification contributes to a greater ankle-brachial index in the general population and may allow better characterization of individuals with this phenotype.

Effects of antihypertensive drugs on central blood pressure in humans: a preliminary observation

BACKGROUND

Central blood pressure (BP) is considered a better predictor of cardiovascular events than brachial BP. Modifications of central, beyond brachial BP, can be assessed by pressure amplification, a potential new cardiovascular risk factor. Comparison between drugs' effect on central hemodynamics has been poorly studied. Our aim was to assess the hemodynamic effect of a 12-week treatment with amlodipine 5mg, or candesartan 8mg, or indapamide sustained-release 1.5mg, in comparison with placebo.

METHODS

We analyzed 145 out-patients with essential hypertension in primary prevention enrolled in the Natrilix SR Versus Candesartan and Amlodipine in the Reduction of Systolic Blood Pressure in Hypertensive Patients (X-CELLENT) study, a multicenter, randomized, double-blinded, placebo-controlled trial. Arterial stiffness, central BP, pressure amplification, and wave reflection were measured by applanation tonometry.

RESULTS

Baseline characteristics of patients were homogeneous between groups. After treatment, we found that active drugs produced similar reduction of both central and peripheral BPs, with no significant interdrug differences (all P < 0.05; excluded peripheral pulse pressure, compared with placebo). Second, amlodipine (1.9% ± 15.3%), candesartan (3.0% ± 14.6%) and indapamide (4.1% ± 14.4%) all increased pulse pressure amplification, but only indapamide was statistically different from placebo (P = 0.02). Finally, no significant changes were observed on pulse wave velocity, heart rate, and augmentation index.

CONCLUSIONS

The 3 antihypertensive drugs similarly reduced peripheral and central BP, as compared with placebo, but a significant increase in pulse pressure amplification was obtained only with indapamide, independently of arterial stiffness modifications.

REGISTRATION NUMBER

3283161 by BIOPHARMA.

[Pressure wave shape comparison between two non-invasive tonometric devices]

BACKGROUND AND AIM

Pulse wave analysis is a pivotal instrument to estimate central hemodynamic parameters. Applanation tonometry on radial and/or carotid arteries is usually used to detect pressure waveforms. Available commercial devices have been validated against invasive catheterism, showing a good agreement of harmonics pattern. In a previous investigation, we observed differences on radial second systolic peak (rSPB2) between two commonly used devices: SphygmoCor (AtCor, Australia) and PulsePen (Diatecne, Italy). The aim of our study was to further quantify differences on radial and carotid signals from the two devices.

METHODS

We measured radial and carotid pressure waveforms in 38 patients where systolic, diastolic blood pressure and heart rate presented minimal changes between measurements. Waveforms were digitally extracted for off-line analysis.

RESULTS

Radial rSBP2, mean arterial pressure, form factor and augmentation index were different with SphygmoCor providing lower values. Carotid augmentation index and form factor were similar. However, carotid systolic pressure (cSBP) from PulsePen was higher that cSBP from SphygmoCor (2.7 ± 4.4 mmHg, P<0.001).

CONCLUSION

PulsePen and SphygmoCor sensors are not equivalent and provide different wave shapes. These differences on wave shape have important consequences on parameters computed from these waveforms with more discrepancy on radial derived parameters such as rSBP2 and mean arterial pressure than on carotid derived parameters. Further studies are required to compare invasive pressure parameters to indices derived from these two devices.

Does it make sense to measure only the brachial blood pressure?

The significant reduction in cardiovascular mortality in the second half of the 20th century, due to an effective battle against high blood pressure, may be considered one of the greatest medical success stories of the past century. However, several epidemiological and clinical studies have recently highlighted that the single acquisition of blood pressure values at brachial level is inadequate to accurately predict the cardiovascular risk of patients with high blood pressure values. Furthermore, some studies suggest the importance of central systolic blood pressure and central pulse pressure (central systolic blood pressure - diastolic blood pressure) as cardiovascular prognostic factors. Central systolic blood pressure and central pulse pressure are able to evaluate the real pressure load imposed on the left ventricle much better than peripheral systolic blood pressure and peripheral pulse pressure. Moreover, the disappearance of the blood pressure amplification phenomenon (i.e. the difference between peripheral and central systolic blood pressure) is a significant predictor of all-cause (including cardiovascular) mortality, independent of age and other standard confounding factors. Thus, the measurement of central arterial pressure provides more precise information on the cardiovascular risk than brachial artery blood pressure measurement.