Noninvasive assessment of central and peripheral arterial pressure (waveforms): implications of calibration methods

Impact of a cuff-based device calibration method on the agreement between invasive and noninvasive aortic and brachial pressure

INTRODUCTION

Brachial cuff-based methods are increasingly used to estimate aortic systolic blood pressure (aoSBP). However, there are several unresolved issues.

AIMS

to determine to what extent the scheme used to calibrate brachial records (1) can affect noninvasive obtained aoSBP levels, and consequently, the level of agreement with the aoSBP recorded invasively, and (2) how different ways of calibrating ultimately impact the relationship between aoSBP and cardiac properties.

METHODS

brachial and aortic blood pressure (BP) was simultaneously obtained by invasive (catheterisation) and noninvasive (brachial oscillometric-device) methods (89 subjects). aoSBP was noninvasive obtained using three calibration schemes: 'SD': diastolic and systolic brachial BP, 'C': diastolic and calculated brachial mean BP (bMBP), 'Osc': diastolic and oscillometry-derived bMBP. Agreement between invasive and noninvasive aoSBP, and associations between BP and echocardiographic-derived parameters were analysed.

CONCLUSIONS

'C' and 'SD' schemes generated aoSBP levels lower than those recorded invasively (mean errors: 6.9 and 10.1 mmHg); the opposite was found when considering 'Osc'(mean error: -11.4 mmHg). As individuals had higher invasive aoSBP, the three calibration schemes increasingly underestimated aoSBP levels; and viceversa. The 'range' of invasive aoSBP in which the calibration schemes reach the lowest error level (-5-5 mmHg) is different: 'C': 103-131 mmHg; 'Osc': 159-201 mmHg; 'SD':101-124 mmHg. The calibration methods allowed reaching levels of association between aoSBP and cardiac characteristics, somewhat lower, but very similar to those obtained when considering invasive aoSBP. There is no evidence of a clear superiority of one calibration method over another when considering the association between aoSBP and cardiac characteristics.

Value and Variability of Pulse Shape Indicator for Estimating Mean Arterial Pressure in the Radial and Femoral Arteries

BACKGROUND

The form factor (FF) is a pulse shape indicator that corresponds to the fraction of pulse pressure added to diastolic blood pressure to estimate the time-averaged mean arterial pressure (MAP). Our invasive study assessed the FF value and variability at the radial and femoral artery levels and evaluated the recommended fixed FF value of 0.33.

METHODS AND RESULTS

Hemodynamically stable patients were prospectively included in 2 intensive care units. FF was documented at baseline and during dynamic maneuvers. A total of 632 patients (64±16 years of age, 66% men, MAP=81±14 mm Hg) were included. Among them, 355 (56%) had a radial catheter and 277 (44%) had a femoral catheter. The FF was 0.34±0.06. In multiple linear regression, FF was influenced by biological sex (P<0.0001) and heart rate (P=0.04) but not by height, weight, or catheter location. The radial FF was 0.35±0.06, whereas the femoral FF was 0.34±0.05 (P=0.08). Both radial and femoral FF were higher in women than in men (P<0.05). When using the 0.33 FF value to estimate MAP, the error was -0.4±4.0 mm Hg and -0.1±2.9 mm Hg at the radial and femoral level, respectively, and the MAP estimate still demonstrated high accuracy and good precision even after changes in norepinephrine dose, increase in positive end-expiratory pressure level, fluid administration, or prone positioning (n=218).

CONCLUSIONS

Despite higher FF in women and despite interindividual variability in FF, using a fixed FF value of 0.33 yielded accurate and precise estimations of MAP. This finding has potential implications for blood pressure monitoring devices and the study of pulse wave amplification.

Central-to-peripheral blood pressure amplification: role of the recording site, technology, analysis approach, and calibration scheme in invasive and non-invasive data agreement

Background

Systolic blood pressure amplification (SBPA) and pulse pressure amplification (PPA) can independently predict cardiovascular damage and mortality. A wide range of methods are used for the non-invasive estimation of SBPA and PPA. The most accurate non-invasive method for obtaining SBPA and/or PPA remains unknown.

Aim

This study aims to evaluate the agreement between the SBPA and PPA values that are invasively and non-invasively obtained using different (1) measurement sites (radial, brachial, carotid), (2) measuring techniques (tonometry, oscillometry/plethysmography, ultrasound), (3) pulse waveform analysis approaches, and (4) calibration methods [systo-diastolic vs. approaches using brachial diastolic and mean blood pressure (BP)], with the latter calculated using different equations or measured by oscillometry.

Methods

Invasive aortic and brachial pressure (catheterism) and non-invasive aortic and peripheral (brachial, radial) BP were simultaneously obtained from 34 subjects using different methodologies, analysis methods, measuring sites, and calibration methods. SBPA and PPA were quantified. Concordance correlation and the Bland-Altman analysis were performed.

Results

(1) In general, SBPA and PPA levels obtained with non-invasive approaches were not associated with those recorded invasively. (2) The different non-invasive approaches led to (extremely) dissimilar results. In general, non-invasive measurements underestimated SBPA and PPA; the higher the invasive SBPA (or PPA), the greater the underestimation. (3) None of the calibration schemes, which considered non-invasive brachial BP to estimate SBPA or PPA, were better than the others. (4) SBPA and PPA levels obtained from radial artery waveform analysis (tonometry) (5) and common carotid artery ultrasound recordings and brachial artery waveform analysis, respectively, minimized the mean errors.

Conclusions

Overall, the findings showed that (i) SBPA and PPA indices are not "synonymous" and (ii) non-invasive approaches would fail to accurately determine invasive SBPA or PPA levels, regardless of the recording site, analysis, and calibration methods. Non-invasive measurements generally underestimated SBPA and PPA, and the higher the invasive SBPA or PPA, the higher the underestimation. There was not a calibration scheme better than the others. Consequently, our study emphasizes the strong need to be critical of measurement techniques, to have methodological transparency, and to have expert consensus for non-invasive assessment of SBPA and PPA.

Unveiling the gothic aortic arch and cardiac mechanics: insights from young patients after arterial switch operation for d-transposition of the great arteries

The arterial switch operation (ASO) has become the standard surgical treatment for patients with d-transposition of the great arteries. While ASO has significantly improved survival rates, a subset of patients develop a unique anatomical anomaly known as the gothic aortic arch (GAA). Understanding cardiac mechanics in this population is crucial, as altered mechanics can have profound consequences for cardiac function and exercise capacity. The GAA has been associated with changes in ventricular function, hemodynamics, and exercise capacity. Studies have shown a correlation between the GAA and decreased ascending aorta distensibility, loss of systolic wave amplitude across the aortic arch, and adverse cardiovascular outcomes. Various imaging techniques, including echocardiography, cardiac magnetic resonance imaging, and cardiac computed tomography, play a crucial role in assessing cardiac mechanics and evaluating the GAA anomaly. Despite significant advancements, gaps in knowledge regarding the prognostic implications and underlying mechanisms of the GAA anomaly remain. This review aims to explore the implications of the GAA anomaly on cardiac mechanics and its impact on clinical outcomes in young patients after ASO. Advancements in imaging techniques, such as computational modeling, offer promising avenues to enhance our understanding of cardiac mechanics and improve clinical management.

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.

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.

Central blood pressure estimation in type 1 diabetes: impact and implications of peripheral calibration method

OBJECTIVE

Peripheral blood pressure (BP) waveforms are used for noninvasive central BP estimation. Central BP could assist in cardiovascular risk assessment in patients with type 1 diabetes mellitus (T1DM). However, correct calibration of peripheral BP waveforms is important to accurately estimate central BP. We examined differences in central BP estimated by radial artery tonometry depending on which brachial BP (SBP/DBP vs. MAP/DBP) is used for calibration of the radial waveforms, for the first time in T1DM.

METHODS

A cross-sectional study in T1DM patients without known cardiovascular disease. Radial artery BP waveforms were acquired using applanation tonometry ( SphygmoCor ) for the estimation of central SBP, central pulse pressure (PP) and central augmentation pressure, using either brachial SBP/DBP or MAP/DBP for the calibration of the radial pressure waveforms.

RESULTS

Fifty-four patients (age: 46 ± 9.5 years; T1DM duration: 27 ± 8.8 years) were evaluated. Central BP parameters were significantly higher when brachial MAP/DBP-calibration was used compared with brachial SBP/DBP-calibration (7.5 ± 5.04, 7.5 ± 5.04 and 1.5 ± 1.36 mmHg higher central SBP, central PP and central augmentation pressure, respectively, P  < 0.001).

CONCLUSION

In patients with T1DM, there are significant differences in central BP values estimated with radial artery tonometry, depending on the method used for calibration of the radial waveforms. Brachial MAP/DBP-calibration resulted in consistently higher central BP as compared to using brachial SBP/DBP, leading to patient re-stratification. Hence, the accuracy of noninvasive estimation of central BP by radial tonometry is dependent on calibration approach, and this problem must be resolved in validation studies using an invasive reference standard to determine which method best estimates true central BP.

Importance of central BP assessment in ISH of the young. Which devices are best suited for practical use?

Isolated systolic hypertension (ISH), defined as brachial systolic blood pressure (bSBP) ≥140 mmHg and diastolic blood pressure (DBP) <90 mmHg, is highly prevalent among young subjects and in the elderly. The prognostic significance of ISH in young individuals remains the object of large debate which might be solved, at least in part, if considering the prognostic role of central BP. For any given value of pBP, the cardiovascular (CV) risk is better defined by central BP (cBP). Young individuals with ISH have long been considered at low CV risk, given the assumption that a "spurious hypertension" phenotype characterized by elevated peripheral (brachial) BP (pBP), normal cBP, and elevated BP amplification was often found in this population. However, this remains to be proven, because many other studies found no differences in BP amplification between ISH and sisto-diastolic hypertension. Despite numerous attempts, methodologies for cBP assessment by non-invasive devices are currently not standardized. As a result, different devices could provide different cBP values despite using the same biological signals. Devices providing accurate estimates of BP amplification as a dimensionless ratio between amplitudes of central and peripheral arterial waveforms might be well suited for clinical purposes in young individuals with ISH. There is urgent need of well-designed prospective studies aiming at longitudinally evaluating the amount of CV risk associated with elevated cBP in young subjects with ISH and their related incremental prognostic value.

New Method to Estimate Central Systolic Blood Pressure From Peripheral Pressure: A Proof of Concept and Validation Study

Objective: The non-invasive estimation of central systolic blood pressure (cSBP) is increasingly performed using new devices based on various pulse acquisition techniques and mathematical analyses. These devices are most often calibrated assuming that mean (MBP) and diastolic (DBP) BP are essentially unchanged when pressure wave travels from aorta to peripheral artery, an assumption which is evidence-based. We tested a new empirical formula for the direct central blood pressure estimation of cSBP using MBP and DBP only (DCBP = MBP²/DBP).

Methods and Results: First, we performed a post-hoc analysis of our prospective invasive high-fidelity aortic pressure database (n = 139, age 49 ± 12 years, 78% men). The cSBP was 146.0 ± 31.1 mmHg. The error between aortic DCBP and cSBP was −0.9 ± 7.4 mmHg, and there was no bias across the cSBP range (82.5–204.0 mmHg). Second, we analyzed 64 patients from two studies of the literature in whom invasive high-fidelity pressures were simultaneously obtained in the aorta and brachial artery. The weighed mean error between brachial DCBP and cSBP was 1.1 mmHg. Finally, 30 intensive care unit patients equipped with fluid-filled catheter in the radial artery were prospectively studied. The cSBP (115.7 ± 18.2 mmHg) was estimated by carotid tonometry. The error between radial DCBP and cSBP was −0.4 ± 5.8 mmHg, and there was no bias across the range.

Conclusion: Our study shows that cSBP could be reliably estimated from MBP and DBP only, provided BP measurement errors are minimized. DCBP may have implications for assessing cardiovascular risk associated with cSBP on large BP databases, a point that deserves further studies.

Pulse Wave Calibration and Implications for Blood Pressure Measurement: Systematic Review and Meta-Analysis

[Figure: see text].

Age-specific association between invasively measured central blood pressure and left ventricular mass index

Background: The impact of age on the association between central aortic hemodynamics and left ventricular (LV) remodeling has not been well elucidated. We compared the relationship between measurements of central blood pressure (CBP) and LV mass index (LVMI) according to their ages (<50 years versus ≥50 years). Methods: A total of 305 consecutive subjects (64.4 ± 10.9 years, 60.7% males) who underwent invasive coronary angiography (ICA) for the evaluation of coronary artery disease were prospectively enrolled. Just before ICA, CBP was measured at the aortic root using a pig-tail catheter, and CBP indices, including aortic systolic blood pressure (aSBP), aortic pulse pressure (aPP), aortic fractional pulse pressure (=aPP/mean aortic pressure), and aortic pulsatility index (=aPP/diastolic aortic pressure), were recorded. All subjects underwent transthoracic echocardiography, and LVMI was measured on the same day of ICA. Results: In simple linear correlation analyses, LVMI was associated with all CBP indices in subjects aged <50 years (n = 29) (P < .05 for each), but not in those aged ≥50 years (n = 276) (P > .05 for each). In the younger age group (≤50 years), multivariable analysis showed that aSBP (β = 0.457, P= .021) and aPP (β = 0.610, P= .006) had a significant association with LVMI after adjusting for possible confounding factors. The results remained consistent even when analyzed in a 1:1 propensity score-matched cohort. In conclusion, invasively measured aPP showed the closest association with LVMI in subjects aged <50 years, but not those aged ≥50 years. Conclusion: Aortic pulsatile hemodynamic status appears to have a greater effect on LV remodeling in younger people than in older people.

Personalization of electro-mechanical models of the pressure-overloaded left ventricle: fitting of Windkessel-type afterload models

Computer models of left ventricular (LV) electro-mechanics (EM) show promise as a tool for assessing the impact of increased afterload upon LV performance. However, the identification of unique afterload model parameters and the personalization of EM LV models remains challenging due to significant clinical input uncertainties. Here, we personalized a virtual cohort of N = 17 EM LV models under pressure overload conditions. A global-local optimizer was developed to uniquely identify parameters of a three-element Windkessel (Wk3) afterload model. The sensitivity of Wk3 parameters to input uncertainty and of the EM LV model to Wk3 parameter uncertainty was analysed. The optimizer uniquely identified Wk3 parameters, and outputs of the personalized EM LV models showed close agreement with clinical data in all cases. Sensitivity analysis revealed a strong dependence of Wk3 parameters on input uncertainty. However, this had limited impact on outputs of EM LV models. A unique identification of Wk3 parameters from clinical data appears feasible, but it is sensitive to input uncertainty, thus depending on accurate invasive measurements. By contrast, the EM LV model outputs were less sensitive, with errors of less than 8.14% for input data errors of 10%, which is within the bounds of clinical data uncertainty. This article is part of the theme issue 'Uncertainty quantification in cardiac and cardiovascular modelling and simulation'.

Radiofrequency-based wall tracking for noninvasive assessment of local carotid pulse pressure: comparison with applanation tonometry and association with organ damage

OBJECTIVES

Central pulse pressure (PP) has been suggested a better predictor of cardiovascular risk than brachial PP, and its routine noninvasive assessment can be useful for risk stratification. The present study evaluated the capability of a radiofrequency-based carotid wall tracking to estimate central PP from distension curves, comparing the values of carotid PP as obtained by wall tracking with those provided by applanation tonometry. Furthermore, the associations of carotid PP with intermediate markers of cardiovascular risk, like carotid intima-media thickness (IMT) and left ventricular mass (LVM), were assessed.

METHODS

Carotid PP was measured by wall tracking and applanation tonometry during the same session in 346 individuals (healthy controls, patients with hypertension and diabetes). IMT was measured in all individuals and LVM was measured in 253.

RESULTS

Carotid PP values as measured by wall tracking and applanation tonometry were highly correlated [r = 0.87; slope 0.90 (0.85-0.95); P < 0.0001; mean difference = 3.1 ± 6.8 mmHg], and were independently determined by the same variables (age, heart rate, triglycerides, blood pressure-lowering therapy). Carotid IMT and LVM correlated more strongly with carotid PP (r = 0.44 and 0.50; P < 0.0001 for both) than with brachial PP (r = 0.34 and 0.42; P < 0.0001 for both). Patients with carotid PP at least 50 mmHg had higher IMT, LVM, and prevalence of LV hypertrophy than those with PP less than 50 mmHg (P = 0.0001 to <0.0001).

CONCLUSIONS

Local carotid PP as estimated by wall tracking is comparable to that obtained by applanation tonometry, and it shows a better association with target organ damage than brachial blood pressure. Assessment of carotid PP during routine ultrasound examination of extracranial carotid tree may provide additional information for individual risk stratification.

Blunted Cardiac Output from Overtraining Is Related to Increased Arterial Stiffness

PURPOSE

Moderate overtraining has been characterized by decreased exercising HR and recently decreased exercising stroke volume (SV), independent of alterations to blood volume. The aim of this study was to assess changes in arterial stiffness and central hemodynamics, and their relationship to exercising SV, after 3 wk of overload training.

METHODS

Twenty-six cyclists and triathletes completed 3 wk of either regular training (CON; n = 13) or overload training (OL; n = 13). Testing took place before (PRE) and after regular or overload training (POST). Resting measures included brachial blood pressure, HR, carotid-femoral pulse wave velocity (PWV) to assess arterial stiffness, and carotid pulse wave analysis to assess wave reflections and central hemodynamics. An incremental cycle test was used to assess peak power, maximal HR, and maximal lactate to assess overtraining status. Cardiac output (Q˙), SV, and HR were assessed using cardiac impedance.

RESULTS

Resting arterial stiffness was unaltered in CON but increased with OL after increased training (CON -0.1 ± 0.6 m·s vs OL +0.5 ± 0.8 m·s, P = 0.04). Resting blood pressure and central hemodynamics, including aortic pressures, augmentation index, and subendocardial viability ratio, did not change (all P > 0.05). Maximal SV (CON +3 mL vs OL -9 mL, P = 0.04), HR (CON -2 ± 4 bpm vs OL -9 ± 3 bpm, P < 0.001), and Q˙ (CON +0.32 L·min vs OL -1.75 L·min, P = 0.01) decreased with OL from PRE to POST. A significant inverse relationship existed between changes in PWV and maximal Q˙ (r = -0.44, P = 0.04) and changes in PWV and peak power (r = -0.48, P = 0.01), and trended for SV and PWV (r = -0.41, P = 0.055).

CONCLUSIONS

Overload training results in increased resting arterial stiffness and reduced SV during exercise, with no changes to resting central hemodynamics.

Multiscale mathematical modeling vs. the generalized transfer function approach for aortic pressure estimation: a comparison with invasive data

We aimed to evaluate the performance of a mathematical model and currently available non-invasive techniques (generalized transfer function (GTF) method and brachial pressure) in the estimation of aortic pressure. We also aimed to investigate error dependence on brachial pressure errors, aorta-to-brachial pressure changes and demographic/clinical conditions. Sixty-two patients referred for invasive hemodynamic evaluation were consecutively recruited. Simultaneously, the registration of the aortic pressure using a fluid-filled catheter, brachial pressure and radial tonometric waveform was recorded. Accordingly, the GTF device and mathematical model were set. Radial invasive pressure was recorded soon after aortic measurement. The average invasive aortic pressure was 141.3 ± 20.2/76 ± 12.2 mm Hg. The simultaneous brachial pressure was 144 ± 17.8/81.5 ± 11.7 mm Hg. The GTF-based and model-based aortic pressure estimates were 133.1 ± 17.3/82.4 ± 12 and 137 ± 21.6/72.2 ± 16.7 mm Hg, respectively. The Bland-Altman plots showed a marked tendency to pressure overestimation for increasing absolute values, with the exclusion of mathematical model diastolic estimations. The systolic pressure was increased from the aortic to radial locations (7.5 ± 19 mm Hg), while the diastolic pressure was decreased (3.8 ± 9.8 mm Hg). The brachial pressure underestimated the systolic and overestimated diastolic intra-arterial radial pressure. GTF errors were independently correlated with the variability in pulse pressure amplification and with the brachial error. Errors of the mathematical model were related to only demographic and clinical conditions. Neither a multiscale mathematical model nor a generalized transfer function device substantially outperformed the oscillometric brachial pressure in the estimation of aortic pressure. Mathematical modeling should be improved by including further patient-specific conditions, while the variability in pulse pressure amplification may hamper the performance of the GTF method in patients at the risk of coronary artery disease.

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.

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.

Relationships between serum free fatty acid and pulse pressure amplification in overweight/obese men: insights from exercise training and dietary modification

Pulse pressure amplification (i.e., the ratio of peripheral to central pulse pressure) is a strong predictor of cardiovascular events. Circulating free fatty acid, which is a major cause of insulin resistance, has been reported to favorably be associated with pulse pressure amplification in the arm (from the aorta to brachial artery). We hypothesized that this paradoxical relationship depended on an evaluating site of pulse pressure amplification and investigated whether serum free fatty acid level is related to pulse pressure amplification in the arm or trunk (from the aorta to femoral artery) in overweight/obese men. In a cross-sectional study, 85 men participated, and regression analyses revealed that serum free fatty acid level was significantly and independently associated with pulse pressure amplification in the arm but not the trunk. In a longitudinal study, 33 men completed a 12-week lifestyle intervention that involved both exercise training and dietary modification. The lifestyle intervention-induced change in serum free fatty acid level was significantly correlated to that in pulse pressure amplification in the arm but not the trunk. These results support our hypothesis and suggest that pulse pressure amplification should be measured in the trunk instead of the arm in overweight/obese men to simplify its interpretation.

Relationships between serum free fatty acid and pulse pressure amplification in overweight/obese men: insights from exercise training and dietary modification

Pulse pressure amplification (i.e., the ratio of peripheral to central pulse pressure) is a strong predictor of cardiovascular events. Circulating free fatty acid, which is a major cause of insulin resistance, has been reported to favorably be associated with pulse pressure amplification in the arm (from the aorta to brachial artery). We hypothesized that this paradoxical relationship depended on an evaluating site of pulse pressure amplification and investigated whether serum free fatty acid level is related to pulse pressure amplification in the arm or trunk (from the aorta to femoral artery) in overweight/obese men. In a cross-sectional study, 85 men participated, and regression analyses revealed that serum free fatty acid level was significantly and independently associated with pulse pressure amplification in the arm but not the trunk. In a longitudinal study, 33 men completed a 12-week lifestyle intervention that involved both exercise training and dietary modification. The lifestyle intervention-induced change in serum free fatty acid level was significantly correlated to that in pulse pressure amplification in the arm but not the trunk. These results support our hypothesis and suggest that pulse pressure amplification should be measured in the trunk instead of the arm in overweight/obese men to simplify its interpretation.

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.

Influence of carotid atherosclerotic plaques on pulse wave assessment with arterial tonometry

OBJECTIVE

Aortic stiffness and central pressure measurements have become increasingly important for the overall estimation of cardiovascular risk. The aim of this study is to verify whether the presence of stenosis in the carotid arteries due to atherosclerotic plaques may induce a bias in the measurement of carotid-femoral pulse wave velocity (PWV) and in the analysis of central pulse waveform variables assessed by carotid tonometry.

METHODS

Eighty-four patients (age: 67.1 ± 12.4 years) undergoing screening for carotid atherosclerosis were enrolled, divided into three groups according to carotid ultrasound findings (NASCET criteria): 28 patients without significant stenosis, 30 patients with bilateral plaques, and 26 patients with right or left monolateral stenosis. PWV and other variables derived from the central pulse waveform analysis (central blood pressure, augmentation index and forward and backward waves) were measured at both right and left carotid arteries by a validated PulsePen tonometer. A repeatability study was performed in 28 young healthy patients (age: 25.4 ± 2.9 years).

RESULTS

A high degree of correlation was found between bilateral measurements in all groups, and particularly in groups with monolateral carotid stenosis, with no significant difference attributable to lateralized stenosis. Right-left differences in asymmetric groups were 0.35 ± 5.12 mmHg (R = 0.960) for central blood pressure, -2.12 ± 7.39% (R = 0.743) for augmentation index, 0.64 ± 1.56 m/s (R = 0.947) for PWV, 0.08 ± 8.48 mmHg for forward wave (R = 0.742) and 0.35 ± 2.35 mmHg for backward wave (R = 0.907).

CONCLUSION

Measurement of PWV and of variables derived from the central pulse waveform analysis by carotid tonometry is not biased by the presence of local atherosclerotic plaques.

Central Hemodynamics for Management of Arteriosclerotic Diseases

Arteriosclerosis, particularly aortosclerosis, is the most critical risk factor associated with cardiovascular, cerebrovascular, and renal diseases. The pulsatile hemodynamics in the central aorta consists of blood pressure, flow, and stiffness and substantially differs from the peripheral hemodynamics in muscular arteries. Arteriosclerotic changes with age appear earlier in the elastic aorta, and age-dependent increases in central pulse pressure are more marked than those apparent from brachial pressure measurement. Central pressure can be affected by lifestyle habits, metabolic disorders, and endocrine and inflammatory diseases in a manner different from brachial pressure. Central pulse pressure widening due to aortic stiffening increases left ventricular afterload in systole and reduces coronary artery flow in diastole, predisposing aortosclerotic patients to myocardial hypertrophy and ischemia. The widened pulse pressure is also transmitted deep into low-impedance organs such as the brain and kidney, causing microvascular damage responsible for lacunar stroke and albuminuria. In addition, aortic stiffening increases aortic blood flow reversal, which can lead to retrograde embolic stroke and renal function deterioration. Central pressure has been shown to predict cardiovascular events in most previous studies and potentially serves as a surrogate marker for intervention. Quantitative and comprehensive evaluation of central hemodynamics is now available through various noninvasive pressure/flow measurement modalities. This review will focus on the clinical usefulness and mechanistic rationale of central hemodynamic measurements for cardiovascular risk management.

Comparison of Central Blood Pressure Estimated by a Cuff-Based Device With Radial Tonometry

BACKGROUND

New techniques that measure central blood pressure (BP) using an upper arm cuff-based approach require performance assessment. The aim of this study was to compare a cuff-based device (CuffCBP) to estimate central BP indices (systolic BP (SBP), diastolic BP (DBP), pulse pressure (PP), augmentation pressure (AP), augmentation index (AIx)) with noninvasive radial tonometry (TonCBP).

METHODS

Consecutive CuffCBP (SphygmoCor Xcel) and TonCBP (SphygmoCor 8.1) duplicate recordings were measured in 182 people with treated hypertension (aged 61±7 years, 48% male). Agreement between methods was assessed using standard calibration with brachial SBP and DBP (measured with the Xcel device), as well as with brachial mean arterial pressure (MAP; 40% form factor method) and DBP.

RESULTS

The mean difference ± SD for central SBP (cSBP), central DBP (cDBP), and central PP (cPP) between methods were -0.89±3.48mm Hg (intra-class correlation (ICC) 0.977; 95% confidence interval (CI) 0.973-0.982), -0.50±1.54mm Hg (ICC 0.992, 95% CI 0.987-0.993), and -0.42±3.57mm Hg (ICC 0.966, 95% CI 0.958-0.972), indicating good agreement. Wider limits of agreement were observed for central AP (cAP) and central AIx (cAIx) (-0.91±5.31mm Hg; ICC 0.802; 95% CI 0.756-0.839, -0.99±10.91%; ICC 0.749; 95% CI 0.691-0.796). Re-calibration with brachial MAP and DBP resulted in an overestimation of cSBP with CuffCBP compared with TonCBP (8.58±19.06mm Hg, ICC 0.164, 95% CI -0.029 to 0.321).

CONCLUSION

cSBP, cDBP, and cPP derived from CuffCBP are substantially equivalent to TonCBP, although the level of agreement is dependent on calibration method. Further validity testing of CuffCBP by comparison with invasively measured central BP will be required.

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.

Prognostic significance of mechanical biomarkers derived from pulse wave analysis for predicting long-term cardiovascular mortality in two population-based cohorts

BACKGROUND

Numerous mechanical biomarkers derived from pulse wave analysis (PWA) have been proposed to predict cardiovascular outcomes. However, whether these biomarkers carry independent prognostic value and clinical utility beyond traditional cardiovascular risk factors hasn't been systematically evaluated. We aimed to investigate the additive utility of PWA-derived biomarkers in two independent population-based cohorts.

METHODS

PWA on central arterial pressure waveforms obtained from subjects without a prior history of cardiovascular diseases of two studies was conducted based on the wave transmission and reservoir-wave theory: firstly in the Kinmen study (1272 individuals, a median follow-up of 19.8years); and then in the Cardiovascular Disease Risk Factors Two-Township Study (2221 individuals, median follow-up of 10years). The incremental value of the biomarkers was evaluated by net reclassification index (NRI).

RESULTS

In multivariate Cox analyses accounting for age, gender, body mass index, systolic blood pressure, fasting glucose, high-density- and low-density-lipoprotein cholesterol, and smoking, only systolic (SC) and diastolic rate constant (DC) of reservoir pressure could independently and consistently predict cardiovascular mortality in both cohorts and the combined cohort (SC: hazard ratio 1.18 [95% confidence interval 1.08-1.28, p<0.001; DC: 1.18 [1.09-1.28], p<0.001]. Risk prediction estimates in traditional risk prediction models were significantly more accurate when incorporating peak of reservoir pressure (NRI=0.049, p=0.0361), SC (NRI=0.043, p=0.0236) and DC (NRI=0.054, p=0.047).

CONCLUSIONS

Of all PWA-derived biomarkers, SC and DC were consistently identified as valuable parameters for incremental cardiovascular risk prediction in two large prospective cohorts.

Selective Heart Rate Reduction With Ivabradine Increases Central Blood Pressure in Stable Coronary Artery Disease

Abstract—

Heart rate (HR) lowering by β-blockade was shown to be beneficial after myocardial infarction. In contrast, HR lowering with ivabradine was found to confer no benefits in 2 prospective randomized trials in patients with coronary artery disease. We hypothesized that this inefficacy could be in part related to ivabradine’s effect on central (aortic) pressure. Our study included 46 patients with chronic stable coronary artery disease who were randomly allocated to placebo (n=23) or ivabradine (n=23) in a single-blinded fashion for 6 months. Concomitant baseline medication was continued unchanged throughout the study except for β-blockers, which were stopped during the study period. Central blood pressure and stroke volume were measured directly by left heart catheterization at baseline and after 6 months. For the determination of resting HR at baseline and at follow-up, 24-hour ECG monitoring was performed. Patients on ivabradine showed an increase of 11 mm Hg in central systolic pressure from 129±22 mm Hg to 140±26 mm Hg ( P =0.02) and in stroke volume by 86±21.8 to 107.2±30.0 mL ( P =0.002). In the placebo group, central systolic pressure and stroke volume remained unchanged. Estimates of myocardial oxygen consumption (HR×systolic pressure and time-tension index) remained unchanged with ivabradine.The decrease in HR from baseline to follow-up correlated with the concomitant increase in central systolic pressure ( r =−0.41, P =0.009) and in stroke volume ( r =−0.61, P <0.001). In conclusion, the decrease in HR with ivabradine was associated with an increase in central systolic pressure, which may have antagonized possible benefits of HR lowering in coronary artery disease patients.

Clinical Trials—URL:

http://www.clinicaltrials.gov . Unique identifier NCT01039389.

Assessment of systolic aortic pressure and its association to all cause mortality critically depends on waveform calibration

BACKGROUND

The aim of this study is the prospective investigation of the association of brachial SBP (bSBP) and aortic SBP (aSBP) to all-cause mortality, with special emphasis on different calibration methods for central pressure estimates, in particular, brachial systolic and diastolic, as well as brachial mean and diastolic pressures.

METHOD

One hundred and fifty-nine patients were enrolled in a longitudinal, prospective study of arterial stiffness and cardiovascular risk in a chronic kidney disease stages 2-4 cohort. Office measurements of bSBP and aSBP were assessed by a validated oscillometric device. Prognostic factors of survival were identified by use of Cox proportional-hazards regression models.

RESULTS

After a mean follow-up duration of 42 months (range 30-50 months), 13 patients died. In univariate Cox analysis, bSBP and aSBP calibrated using bSBP and bDBP did not significantly predict mortality, only aSBP assessed using measured mean and diastolic pressure calibration was significantly associated with mortality (hazard ratio 1.027, P = 0.008). This remained significant in multivariate analysis after adjustment for age, sex, and anthropometric measures. More important, adding bSBP to the multivariate model (hazard ratio 0.91, P = 0.003) lead to a significantly increased prognostic power of aortic systolic pressure (hazard ratio 1.097, P < 0.001) and indicated that differences between bSBP and aSBP are of potential interest.

CONCLUSION

Within our cohort, only aSBP assessed with measured mean and diastolic pressure independently predicted mortality and provided additional prognostic value on top of bSBP readings. Therefore, the method of calibration plays an important role for predictive power of aSBP.

Association of Central Versus Brachial Blood Pressure With Target-Organ Damage: Systematic Review and Meta-Analysis

Accumulating evidence suggests that central blood pressure (BP) may reflect the hemodynamic stress on target organs more accurately than brachial BP. A systematic review assessing the relationship of central versus brachial BP with preclinical target-organ damage was performed. Meta-analysis of cross-sectional data showed that central compared with brachial systolic BP was more closely associated with (1) left ventricular mass index (12 studies, n=6431; weighted age [SD], 49.9 [13.1] years; 51% hypertensives): pooled correlation coefficients r=0.30; 95% confidence interval (CI), 0.23-0.37 versus r=0.26; 95% CI, 0.19-0.33, respectively; P<0.01 for difference; (2) carotid intima-media thickness (7 studies, n=6136; weighted age, 55.6 [13.2] years; 48% hypertensives): r=0.27; 95% CI, 0.19-0.34 versus r=0.23; 95% CI, 0.16-0.30, respectively; P<0.01 for difference; (3) pulse-wave velocity (14 studies, n=3699; weighted age, 53.9 [13.3] years; 53% hypertensives): r=0.42; 95% CI, 0.37-0.47 versus r=0.39; 95% CI, 0.33-0.45, respectively; P<0.01 for difference. Four studies assessing urine albumin excretion (n=3718; weighted age, 56.4 [5] years; 69% hypertensives) reported similar correlations (P=not significant) with central (r=0.22; 95% CI, 0.14-0.29) and brachial systolic BP (r=0.22; 95% CI, 0.12-0.32). Similar findings were observed for central compared with brachial pulse pressure in terms of relationship with target-organ damage. Metaregression analyses did not reveal any significant effect of age. In conclusion, central compared with brachial BP seems to be more strongly associated with most of the investigated indices of preclinical organ damage.

Evaluation of a brachial cuff and suprasystolic waveform algorithm method to noninvasively derive central blood pressure

BACKGROUND

Central blood pressure (BP) can be estimated noninvasively by analyzing brachial artery waveforms. In this study, our aim was to assess the validity of a brachial cuff-based (suprasystolic) technique for estimating central BP (CBPestimated) by comparison with invasive aortic BP (CBPinvasive).

METHODS

Eighty-four simultaneous CBPestimated (Pulsecor R7.0) and CBPinvasive measures were recorded in 47 patients (aged 63±10 years, 62% male) undergoing coronary angiography. Measures were captured at baseline and acutely following intravenous glyceryl trinitrate (GTN; 100-200 μg). Mean CBPinvasive systolic BP (SBP) and diastolic BP (DBP) were compared with CBPestimated SBP and DBP calibrated with brachial SBP and DBP recorded from the Pulsecor device. To test validity of the central BP algorithm, measures of CBPestimated SBP were also compared with CBPinvasive SBP following recalibration with invasive mean arterial pressure (MAP) and DBP.

RESULTS

At baseline, mean difference ± standard deviation between CBPestimated SBP and CBPinvasive SBP was -7±9mm Hg (intraclass correlation coefficient (ICC) = 0.86; P < 0.001) with similar underestimation post-GTN (-6±9mm Hg; ICC = 0.90; P < 0.001). Recalibration of CBPestimated SBP with invasive MAP and DBP resulted in closer mean difference to CBPinvasive SBP (-2±7mm Hg; ICC = 0.95; P < 0.001) at baseline but not post-GTN (-6±7mm Hg; ICC = 0.95; P < 0.001).

CONCLUSIONS

The Pulsecor algorithm to derive central BP has acceptable validity when calibrated with invasive pressures. However, accuracy is compromised when noninvasive brachial cuff BP calibration is used.

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.

Brachial vs. central systolic pressure and pulse wave transmission indicators: a critical analysis

This critique is intended to provide background for the reader to evaluate the relative clinical utilities of brachial cuff systolic blood pressure (SBP) and its derivatives, including pulse pressure, central systolic pressure, central augmentation index (AI), and pulse pressure amplification (PPA). The critical question is whether the newer indicators add sufficient information to justify replacing or augmenting brachial cuff blood pressure (BP) data in research and patient care. Historical context, pathophysiology of variations in pulse wave transmission and reflection, issues related to measurement and model errors, statistical limitations, and clinical correlations are presented, along with new comparative data. Based on this overview, there is no compelling scientific or practical reason to replace cuff SBP with any of the newer indicators in the vast majority of clinical situations. Supplemental value for central SBP may exist in defining patients with exaggerated PPA ("spurious systolic hypertension"), managing cardiac and aortic diseases, and in studies of cardiovascular drugs, but there are no current standards for these possibilities.

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.

Arterial wave reflections and ventricular-vascular interaction in patients with left ventricular systolic dysfunction

Central aortic pressure waveform (AoPW) is the summation of a forward-traveling wave generated by the left ventricle and a backward-traveling wave caused by the reflection of the forward wave. The aim of this study was to evaluate the effect of ventricular-vascular coupling on the morphology of AoPW in chronic heart failure patients with different degrees of left ventricular systolic dysfunction (LVSD) using pulse wave analysis (PWA). PWA of AoPW and left ventricular (LV) function were evaluated by applanation tonometry in 26 control subjects, in 12 patients with left ventricular ejection fraction (LVEF) ≤ 30%, and in 14 patients with LVEF > 30%. Augmentation pressure, augmentation index, wasted energy, and ejection duration were lower in patients with LVEF ≤ 30% than in those with LVEF > 30% and in control subjects. Furthermore, augmentation index showed an inverse correlation with Doppler mitral E-wave amplitude (r = -0.40; P = 0.04) and E/A ratio (r = -0.42; P = 0.03) and a direct correlation with deceleration time of mitral E-waves (r = 0.39; P = 0.04). In patients with severe LVSD (LVEF ≤ 30%), aortic wave reflections negatively interfere with LV function and induce a shortening of ejection duration. In contrast, AoPW is similar in patients with moderate LVSD (LVEF > 30%) and in control subjects.

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.

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.

Carotid arterial intima–media thickness and arterial stiffness in pre-eclampsia: analysis with a radiofrequency ultrasound technique

OBJECTIVE

Whether arterial elasticity is reduced in preeclampsia has been investigated only rarely. This study aimed to characterize in vivo the carotid arterial intima–media thickness (IMT) and mechanical properties in women with pre-eclampsia by employing a radiofrequency ultrasound technique.

METHODS

We included 22 late-onset pre-eclamptic pregnant women and 28 normotensive pregnant women who were matched for age (29 ± 6 vs. 27 ± 3, P=0.09) and gestational age (36.0 ± 3.2 vs. 35.8 ± 2.4 weeks, P=0.802). All women were nulliparous with singleton pregnancy. The pre-eclamptic women had a significantly higher arterial pressure than did the normotensive women (P<0.0001). All women underwent right common carotid arterial measurements with an ultrasound machine equipped with automatic Quality IMT (QIMT) and Quality Arterial Stiffness (QAS) capability. At follow-up examination 18 months after parturition, measurements were repeated in 10 of the pre-eclamptic women and 11 of the normotensive women.

RESULTS

In pre-eclamptic compared with normotensive pregnancy, carotid arterial IMT (459 ± 95 vs. 351 ± 85 μm, P=0.0001), internal diameter (7.8 ± 0.5 vs. 7.2 ± 0.4 mm, P<0.0001), pulse wave velocity (7.1 ± 1.7 vs. 6.0 ± 1.5 m/s, P=0.007), augmentation index (7.9 ± 9.2 vs. −5.0 ± 5.6%, P<0.0001) and arterial wall tension (55.0 ± 6.5 vs. 38.6 ± 4.9 mmHg/cm, P<0.0001) were significantly greater, and the distensibility coefficient (0.020 ± 0.009 vs. 0.029 ± 0.011 1/kPa, P=0.006) was significantly smaller, remaining so after adjusting for body mass index and carotid arterial pressure. Eighteen months after parturition, carotid arterial internal diameter, pressure and wall tension remained greater in the pre-eclamptic group.

CONCLUSION

Carotid arterial remodeling, including changes in arterial internal diameter and wall thickness, and arterial stiffening occur in pre-eclampsia but this may reverse, to some extent, postpartum. QIMT and QAS techniques together could provide a comprehensive assessment of carotid arterial remodeling.

Self-reported sitting time is associated with higher pressure from wave reflections independent of physical activity levels in healthy young adults

BACKGROUND

Time spent in sedentary pursuits such as sitting (SIT) is associated with an increased risk of cardiovascular disease independent of physical activity (PA). The purpose of this study was to examine the associations of PA and SIT with central hemodynamic burden in young adults.

METHODS

Aortic pressure waveforms were obtained using radial applanation tonometry and a generalized transfer function in 70 young healthy men (n = 41) and women (n = 29) (mean age = 23±1 years; body mass index = 24±1kg/m(2)). A wave separation technique that uses a physiologic pseudoaortic flow waveform was used to derive incident/forward wave pressure (Pf) and reflected/backward wave pressure (Pb). Levels of PA (metabolic equivalent, minutes per week) and SIT (sitting time per day) were obtained by self-report using the International Physical Activity Questionnaire.

RESULTS

A negative correlation existed between PA and Pf (r = -0.30; P < 0.05) and Pb (r = -0.36; P < 0.05). A positive correlation existed between SIT and Pf (r = 0.39; P < 0.05) and Pb (r = 0.44; P < 0.05). According to results from multiple regression, after adjusting for potential confounders (age, sex, height, heart rate, mean pressure) and PA, associations between SIT and Pf (P < 0.05) and SIT and Pb (P < 0.05) remained.

CONCLUSIONS

SIT is associated with higher forward wave pressure and backward wave pressure, 2 novel hemodynamic correlates of cardiovascular disease risk and target organ damage, in young apparently healthy men and women. This association is independent of PA.

Comparison of the SphygmoCor and Omron devices in the estimation of pressure amplification against the invasive catheter measurement

BACKGROUND

We previously tested the accuracy of the SphygmoCor and Omron HEM-9000AI devices in the estimation of central blood pressure. In the present study, we investigated these two devices in the estimation of central-to-brachial pressure amplification against the invasive catheter measurement.

METHODS

In 33 individuals undergoing cardiac catheterization, we measured central blood pressure simultaneously by the invasive catheter and each of the two noninvasive devices and brachial blood pressure by the invasive catheter and an automated oscillometric blood pressure monitor of the Omron device. Pressure amplification was calculated as central-to-brachial systolic pressure difference and pulse pressure difference and ratio. The agreement between each of these two noninvasive devices and the invasive catheter was evaluated using the Student's t-test, intraclass correlation analysis, and the Bland-Altman method.

RESULTS

The mean central-to-brachial systolic pressure difference and pulse pressure difference and ratio estimated by Omron were significantly lower than those measured by the catheter (P < 0.001), whereas no difference was observed for SphygmoCor (P ≥ 0.07). Nonetheless, the intraclass correlation coefficients for systolic pressure difference and pulse pressure difference and ratio between the noninvasive and invasive catheter measurements were similar for the two devices, being 0.11 (P = 0.56), 0.38 (P = 0.03), and 0.40 (P = 0.02), respectively, for SphygmoCor, and 0.15 (P = 0.41), 0.23 (P = 0.20), and 0.53 (P = 0.002), respectively, for Omron.

CONCLUSION

If the invasive catheter measurement would be considered as standard, the two noninvasive devices have similar accuracy in the estimation of pressure amplification, but apparently require device-specific criteria for diagnosis. Pulse pressure ratio seems to be a more consistent measure of central-to-brachial pressure amplification.

Inaccuracy in determining mean arterial pressure with oscillometric blood pressure techniques

OBJECTIVE

Accurate determination of MAP is important in the calibration of pressure waveforms for calculating central blood pressure (BP). Currently, a precise, individualized measurement of mean arterial pressure (MAP) can be obtained only with intra-arterial measurements of BP or with applanation tonometry. We conducted a study of whether easy-to-use oscillometric devices, validated for systolic and diastolic BP measurements (BHS protocol), give accurate determinations of MAP.

METHODS

We compared measurements of MAP made with the WatchBP Office oscillometric monitor in 102 subjects with values of MAP assessed by pulse-wave analysis (PWA) (SphygmoCor).

RESULTS

The mean (± SD) oscillometric MAP assessed with the WatchBP Office monitor was 97 ± 12.5 mm Hg, which was equivalent to 23.6 ± 9.1% of the pulse pressure (PP) above diastolic blood pressure (DBP). The MAP as assessed through PWA was 106 ± 14.6 mm Hg (P < 0.01), or 37.7 ± 3.9% of the PP above DBP. In simultaneous measurements made on both arms with the WatchBP Office monitor we observed individual differences in pressure in the left vs. the right arm.

CONCLUSIONS

The MAP displayed by the WatchBP Office monitor is too imprecise to be used for calibrations. We suggest that devices for measuring BP not display MAP unless their accuracy is tested.

Brachial artery tonometry and the Popeye phenomenon: explanation of anomalies in generating central from upper limb pressure waveforms

BACKGROUND

Noninvasive applanation tonometry studies of the brachial and radial artery pressure waves show that the arterial pulse is substantially amplified between the brachial and radial sites. Brachial tonometry waveforms have also been used to calibrate carotid tonometry waves as a measure of central pressure in major clinical trials. These trials assume identity of mean and of DBP in calculation of central (carotid) SBP. None of these trials showed superiority of central over brachial pressure in predicting outcome, but all showed equivalence of SBP and pulse pressure at brachial and carotid sites!

METHOD

We tested this method by measuring pressure waves at brachial, radial and carotid sites by applanation tonometry in 100 patients, with attention to any subtle difference between brachial and radial waveforms, and with both calibrated to cuff SBP and DBP.

RESULTS

The results confirmed no proximal and strong distal amplification in the arm. However, this was accompanied by blunting of the brachial compared with radial waveform with brachial pressure 2.7 mmHg higher during most of the cardiac cycle. Form factor of the ensemble-averaged brachial wave [39.1 standard deviation (SD) 4.9%] was similar to the carotid (40.2 SD 4.1%) but different to the radial wave (34.8 SD 3.7%; P < 0.01).

CONCLUSIONS

All findings were explained by inability to applanate the brachial artery, and resulting systematic error in generating brachial waveforms. In estimation of central pressure with applanation tonometry, the radial pressure wave, which can be accurately applanated, should be used, and calibrated to the brachial cuff.