Estimation of central systolic blood pressure using an oscillometric blood pressure monitor

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Accuracy of cuff blood pressure and systolic blood pressure amplification

Automated cuff measured blood pressure (BP) is the global standard used for diagnosing hypertension, but there are concerns regarding the accuracy of the method. Individual variability in systolic BP (SBP) amplification from central (aorta) to peripheral (brachial) arteries could be related to the accuracy of cuff BP, but this has never been determined and was the aim of this study. Automated cuff BP and invasive brachial BP were recorded in 795 participants (74% male, aged 64 ± 11 years) receiving coronary angiography at five independent research sites (using seven different automated cuff BP devices). SBP amplification was recorded invasively by catheter and defined as brachial SBP minus aortic SBP. Compared with invasive brachial SBP, cuff SBP was significantly underestimated (130 ± 18 mmHg vs. 138 ± 22 mmHg, p < 0.001). The level of SBP amplification varied significantly among individuals (mean ± SD, 7.3 ± 9.1 mmHg) and was similar to level of difference between cuff and invasive brachial SBP (mean difference -7.6 ± 11.9 mmHg). SBP amplification explained most of the variance in accuracy of cuff SBP (R2 = 19%). The accuracy of cuff SBP was greatest among participants with the lowest SBP amplification (ptrend < 0.001). After cuff BP values were corrected for SBP amplification, there was a significant improvement in the mean difference from the intra-arterial standard (p < 0.0001) and in the accuracy of hypertension classification according to 2017 ACC/AHA guideline thresholds (p = 0.005). The level of SBP amplification is a critical factor associated with the accuracy of conventional automated cuff measured 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.

Low central blood pressure and sympathetic activity predispose for the development of intradialytic hypotension

Intradialytic hypotension (IDH) may lead to a poor life quality and was associated with cardiovascular mortality in patients under hemodialysis. This study investigated the autonomic nerve and cardiovascular function in the IDH episodes.In this case-control study, 70 end stage renal disease patients (198 visits) were recruited. Pulse wave analysis and heart rate variability were evaluated before hemodialysis. Two definitions of IDH were confirmed by medical records. IDH-f indicated a drop of systolic blood pressure or mean arterial pressure, accompanied with symptoms; IDH-n indicated a low nadir systolic pressure during the hemodialysis. All parameters were evaluated for the possible predisposing factors under each definition.A total of 24 IDH-f and 37 IDH-n were noted in 177 visits. For both definitions, central pulse pressure seemed to be a consistent predisposing factor. Furthermore, lower sympathetic activity (odds ratio [OR] 0.55; 95% confidence interval [CI] 0.35-0.87), lower pulse pressure (OR 0.95; 95% CI 0.92-0.98), and higher augmentation index (OR 17.36; 95% CI 1.48-204.10) were the possible predisposing factors for IDH-f. On the contrary, lower mean arterial pressure (OR 0.87; 95% CI 0.78-0.98) was identified as the possible factor for IDH-n.It was suggested that the lower central pulse pressure and sympathetic activity might be involved in the development of IDH.

Identifying Isolated Systolic Hypertension From Upper-Arm Cuff Blood Pressure Compared With Invasive Measurements

Isolated systolic hypertension (ISH) is the most common form of hypertension and is highly prevalent in older people. We recently showed differences between upper-arm cuff and invasive blood pressure (BP) become greater with increasing age, which could influence correct identification of ISH. This study sought to determine the difference between identification of ISH by cuff BP compared with invasive BP. Cuff BP and invasive aortic BP were measured in 1695 subjects (median 64 years, interquartile range [55-72], 68% male) from the INSPECT (Invasive Blood Pressure Consortium) database. Data were recorded during coronary angiography among 29 studies, using 21 different cuff BP devices. ISH was defined as ≥130/<80 mm Hg using cuff BP compared with invasive aortic BP as the reference. The prevalence of ISH was 24% (n=407) according to cuff BP but 38% (n=642) according to invasive aortic BP. There was fair agreement (Cohen κ, 0.36) and 72% concordance between cuff and invasive aortic BP for identifying ISH. Among the 28% of subjects (n=471) with misclassification of ISH status by cuff BP, 20% (n=96) of the difference was due to lower cuff systolic BP compared with invasive aortic systolic BP (mean, -16.4 mm Hg [95% CI, -18.7 to -14.1]), whereas 49% (n=231) was from higher cuff diastolic BP compared with invasive aortic diastolic BP (+14.2 mm Hg [95% CI, 11.5-16.9]). In conclusion, compared with invasive BP, cuff BP fails to identify ISH in a sizeable portion of older people and demonstrates the need to improve cuff BP measurements.

Learning-Based Model for Central Blood Pressure Estimation using Feature Extracted from ECG and PPG signals

Pre-detection of hypertension mostly considers the measurement of Brachial Artery Blood Pressure (BABP). Although being a standard vital, it is still considered a poor alternative for Central Blood Pressure (CBP). However, CBP is measured invasively during the process of cardiac catheterization (Cath). Though cuff-less techniques to estimate BABP are widely employed, CBP estimation has not been explored yet. Moreover, to best of our knowledge intermittent CBP estimation has not been proposed earlier. Therefore, we present a cuff-less and beat-by-beat CBP estimation technique using linear regression analysis on features extracted from continuous Electrocardiogram (ECG) and Photoplethysmograph (PPG) signals. Unlike for BABP estimation, 30 supplementary features to conventional pulse transit time such as ST-interval, Psystolic peak interval, etc., were extracted to enhance CBP accuracy. This extraction was done using Haar wavelet along with modulus maxima. Feature selection has been done using the wrapper technique and reduced using principal component analysis. Segregation of each beat was achieved with the help of constraints developed based on iteration and backtracing. This model estimates Systolic CBP with a validation error of 0.109±2.37 mmHg and Diastolic CBP with an error of 0.031±2.102 mmHg for 33 Cath lab patients.

Vascular Aging and Central Aortic Blood Pressure: From Pathophysiology to Treatment

Large conductive arteries undergo to structural modifications by aging, eventually leading to increased vascular stiffness. As consequence, cardiovascular hemodynamic changes by increasing central blood pressure which may be also associated to the remodelling of peripheral resistance arteries that contribute to increase further the central vascular stiffness and blood pressure. These modifications resemble the ones that has been shown in essential hypertension, thus a condition of "early vascular aging" has been described in hypertensive patients. Since hypertension related target organs, particularly the heart, face aortic blood pressure rather than brachial blood pressure, it has been recently suggested that central blood pressure and other parameters of large arteries' stiffness, including pulse wave velocity (PWV), may better correlate with subclinical organ damage and might be useful to assess the cardiovascular risk of patients beyond the traditional risk factors. Different devices have been validated to measure central blood pressure and PWV, and are currently available for clinical use. The increasing application of these tools in clinical practice could improve the management of hypertensive patients by better defining the cardiovascular risk and address the antihypertensive therapy.

Central blood pressure for the management of hypertension: Is it a practical clinical tool in current practice?

Since noninvasive central blood pressure (BP) measuring devices are readily available, central BP has gained growing attention regarding its clinical application in the management of hypertension. The disagreement between central and peripheral BP has long been recognized. Some previous studies showed that noninvasive central BP may be better than the conventional brachial BP in association with target organ damages and long-term cardiovascular outcomes. Recent studies further suggest that the central BP strategy for confirming a diagnosis of hypertension may be more cost-effective than the conventional strategy, and guidance of hypertension management with central BP may result in less use of medications to achieve BP control. Despite the use of central BP being promising, more randomized controlled studies comparing central BP-guided therapeutic strategies with conventional care for cardiovascular events reduction are required because noninvasive central and brachial BP measures are conveniently available. In this brief review, the rationale supporting the utility of central BP in clinical practice and relating challenges are summarized.

2019 Consensus of the Taiwan Hypertension Society and Taiwan Society of Cardiology on the Clinical Application of Central Blood Pressure in the Management of Hypertension

The Taiwan Society of Cardiology (TSOC) and the Taiwan Hypertension Society (THS) have appointed a joint consensus group for the 2019 Consensus of the TSOC and THS on the Clinical Application of Central blood pressure (BP) in the Management of Hypertension with the aim of formulating a management consensus on the clinical application of central BP in the management of hypertension. This consensus document focuses on the clinical application of central BP in the care of patients with hypertension. The major determinants of central BP are increased arterial stiffness and wave reflection, which are also the dominant hemodynamic manifestations of vascular aging. Central BP can be measured noninvasively using various techniques, including with convenient cuff-based oscillometric central BP monitors. Noninvasive central BP is better than conventional brachial BP to assess target organ damage and long-term cardiovascular outcomes. Based on the analysis of long-term events, a central BP threshold of 130/90 mmHg for defining hypertension has been proposed. Recent studies have suggested that a central BP strategy to confirm a diagnosis of hypertension may be more cost-effective than conventional strategies, and that guiding hypertension management with central BP may result in the use of fewer medications to achieve BP control. Although noninvasive measurements of brachial BP are inaccurate and central BP has been shown to carry superior prognostic value beyond brachial BP, the use of central BP should be justified in studies comparing central BP-guided therapeutic strategies with conventional care for cardiovascular events.

Estimation of Cardiovascular Risk Predictors from Non-Invasively Measured Diametric Pulse Volume Waveforms via Multiple Measurement Information Fusion

This paper presents a novel multiple measurement information fusion approach to the estimation of cardiovascular risk predictors from non-invasive pulse volume waveforms measured at the body's diametric (arm and ankle) locations. Leveraging the fact that diametric pulse volume waveforms originate from the common central pulse waveform, the approach estimates cardiovascular risk predictors in three steps by: (1) deriving lumped-parameter models of the central-diametric arterial lines from diametric pulse volume waveforms, (2) estimating central blood pressure waveform by analyzing the diametric pulse volume waveforms using the derived arterial line models, and (3) estimating cardiovascular risk predictors (including central systolic and pulse pressures, pulse pressure amplification, and pulse transit time) from the arterial line models and central blood pressure waveform in conjunction with the diametric pulse volume waveforms. Experimental results obtained from 164 human subjects with a wide blood pressure range (systolic 144 mmHg and diastolic 103 mmHg) showed that the approach could estimate cardiovascular risk predictors accurately (r ≥ 0.78). Further analysis showed that the approach outperformed a generalized transfer function regardless of the degree of pulse pressure amplification. The approach may be integrated with already available medical devices to enable convenient out-of-clinic cardiovascular risk prediction.

The association between brain-derived neurotrophic factor and central pulse pressure after an oral glucose tolerance test

BACKGROUND

Arterial stiffening blunts postprandial vasodilatation. We hypothesized that brain-derived neurotrophic factor (BDNF) may modulate postprandial central pulse pressure, a surrogate marker for arterial stiffening.

METHODS

A total of 82 non-diabetic subjects received a 75-g oral glucose tolerance test (OGTT) after overnight fasting. Serum BDNF concentrations were determined at 0, 30, and 120min to calculate the area under the curve (AUC). Brachial and central blood pressures were measured using a noninvasive central blood pressure monitor before blood withdrawals at 0 and 120min.

RESULTS

With the median AUC of BDNF of 45(ng/ml)∗h as the cutoff value, the central pulse pressure after glucose intake was significantly higher in the subjects with a low BDNF than in those with a high BDNF (63±16 vs. 53±11mmHg, P=0.003), while the brachial pulse pressure was not significantly different between the 2 groups (P=0.099). In a multivariate linear regression model, a lower AUC of BDNF was an independent predictor of a higher central pulse pressure after oral glucose intake (linear regression coefficient-0.202, 95% confidence interval-0.340 to -0.065, P=0.004).

CONCLUSION

After oral glucose challenge, a lower serum BDNF response is significantly associated with a higher central pulse pressure.

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.

Hemodynamic Determinants of the Short-Term Blood Pressure Variability: Differential Roles of Arterial Stiffness and Wave Reflection

BACKGROUND

A high 24-hour ambulatory diastolic (DBP) but not systolic (SBP) blood pressure variability (BPV) is significantly predictive of long-term cardiovascular mortality in untreated hypertensive subjects, independent of office or 24-hour SBP. The present study was aimed to investigate hemodynamic factors that are independently associated with systolic and diastolic BPV from the 24-hour ambulatory blood pressure monitoring (ABPM).

METHODS

A cohort of 624 normotensive and 633 untreated hypertensive participants with baseline ABPM was drawn from a community-based survey. BPV was assessed by the read-to-read average real variability of the 24-hour SBP and DBP (ARVs and ARVd, respectively). Hemodynamic variables including total peripheral resistance (TPR), carotid-femoral pulse wave velocity (cf-PWV), and amplitudes of the decomposed forward (Pf) and backward (Pb) carotid pressure waves were analyzed.

RESULTS

In multivariable analyses, hemodynamic variables independently associated with 24-hour SBP were 24-hour heart rate (HR), TPR, cf-PWV, Pf, and Pb (model r2 = 0.535). Hemodynamic factors independently associated with ARV were 24-hour HR, Pf, and Pb for ARVs, and 24-hour HR, cf-PWV, Pf, and Pb for ARVd (model R2 = 0.345 and 0.220, respectively). Addition of 24-hour SBP to the ARV models only slightly improved variance explained by the models (R2 = 0.383 and 0.224, respectively). Pb accounted for >50% of total variance of ARVs and ARVd, whereas cf-PWV was a minor determinant of ARVd (<5% of total variance).

CONCLUSIONS

ARVd was associated with fewer hemodynamic variables than to 24-hour SBP. Among those hemodynamic variables wave reflection but not arterial stiffness had the dominant independent association with ARV.

Investigation of Viscoelasticity in the Relationship Between Carotid Artery Blood Pressure and Distal Pulse Volume Waveforms

We investigated the relationship between carotid artery blood pressure (BP) and distal pulse volume waveforms (PVRs) via subject-specific mathematical modeling. We conceived three physical models to define the relationship: a tube-load model augmented with a gain (TLG), Voigt (TLV), and standard linear solid (TLS) models. We compared these models using PVRs measured via BP cuffs at an upper arm and an ankle as well as carotid artery tonometry waveform collected from 133 subjects. At both upper arm and ankle, PVR was related to carotid artery tonometry by TLV and TLS models better than by TLG model; when root-mean-squared over all the subjects, the systolic and diastolic BP errors between measured carotid artery tonometry waveform and the one estimated from distal PVR reduced from 4.3 mmHg and 4.6 mmHg (TLG) to 1.1 mmHg and 1.0 mmHg (TLS) for the upper arm (p < 0.0167), and from 2.1 mmHg and 1.7 mmHg (TLG) to 2.1 mmHg and 1.5 mmHg (TLV) for the ankle. Further, TLV and TLS models exhibited superior Akaike's Information Criterion (AIC) in both locations than TLG model. However, the difference between TLG versus TLV and TLS models associated with the ankle was not large. Therefore, the relationship of central arterial BP to arm PVR arises from both wave reflection and viscoelasticity while the relationship to ankle PVR mainly arises from wave reflection. These findings may imply that an effective subject-specific transfer function for estimating accurate central arterial BP from an arm PVR should account for the impact of viscoelasticity.

Vascular aging and hypertension: Implications for the clinical application of central blood pressure

Vascular aging may be responsible for the high residual lifetime risk for hypertension in the middle-aged and elderly individuals. Increased arterial stiffness and wave reflection has been recognized as the dominant hemodynamic manifestations of vascular aging, and both are major determinants of central blood pressure (BP) and independent predictors for incident hypertension. Because central BP is strongly linearly associated with age, it can be regarded as an integrated marker for vascular aging. Central BP can be measured noninvasively using various techniques, including the convenient cuff-based oscillometric central BP monitors. Noninvasive central BP is likely better than the conventional brachial BP in association with target organ damages and long term cardiovascular outcomes. Based on the analysis of the long-term events of derivation and validation cohorts, the central BP threshold of 130/90mmHg for defining hypertension has been proposed. Recent studies suggest that the central BP strategy for confirming a diagnosis of hypertension may be more cost-effective than the conventional brachial BP strategy, and guidance of hypertension management with central BP may result in less use of medications to achieve BP control. Vascular aging-related hypertension is expected to become the dominant phenotype in many countries, especially in the Asian regions. Although noninvasive measurement of brachial BP is inaccurate and central BP has been shown to carry superior prognostic value beyond brachial BP, the use of central BP should be justified by studies comparing central blood pressure-guided therapeutic strategies with classic guidelines-guided strategies for preventing cardiovascular events. Future randomized control trials are required to support that the diagnosis and monitoring of vascular aging-related hypertension is best managed with the central BP strategy.

Is Noninvasive Brachial Systolic Blood Pressure an Accurate Estimate of Central Aortic Systolic Blood Pressure?

OBJECTIVES

Noninvasive brachial systolic blood pressure (nSBP-B) usually approaches invasive central systolic blood pressure (iSBP-C) with a high correlation. Whether nSBP-B is an accurate estimate of iSBP-C remained to be investigated. Thus, this study aimed to compare the errors of nSBP-B and noninvasive central systolic blood pressure (nSBP-C) with different techniques in estimating iSBP-C.

METHODS

Simultaneous invasive high-fidelity central aortic pressure waveforms and the noninvasive left brachial pulse volume recording (PVR) waveform were recorded in a Generation group ( N = 40) and a Validation group ( N = 100). The accuracy of the noninvasive estimates of iSBP-C obtained from analysis of the calibrated PVR waveform using the generalized transfer function (GTF), pulse waveform analysis (PWA), and N-point moving average (NPMA) methods was examined in the Validation group by calculating the mean absolute error (MAE).

RESULTS

In Generation group, the MAE was 4.6±4.1mm Hg between nSBP-B and invasive brachial SBP, and 6.8±5.5mm Hg between nSBP-B and iSBP-C. In comparison, the MAE of between iSBP-C and nSBP-C with PWA, NPMA, and GTF were 5.5±4.5, 5.8±4.9, and 5.9±5.0mm Hg, respectively. In Validation group, the MAE of nSBP-B (6.9±4.6mm Hg) for estimating iSBP-C was significantly greater than that of PWA (5.0±3.4mm Hg) and NPMA (6.1±4.4mm Hg), and GTF (6.1±4.9mm Hg). The percentage of absolute band error ≤5mm Hg was 62% for nSBP-B, 69% for GTF, 83% for PWA, and 69% for NPMA.

CONCLUSIONS

The accuracy of nSBP-B was inferior to the n SBP-C measures in estimating iSBP-C.

Practical Suitability of a Stand-Alone Oscillometric Central Blood Pressure Monitor: A Review of the Microlife WatchBP Office Central

Accumulating evidence indicates that central blood pressure (CBP) is a better cardiovascular risk predictor than brachial blood pressure (BP). Although more additional benefits of CBP-based treatment above usual hypertension treatment are to be demonstrated, the demand for implementing CBP assessment in general clinical practice is increasing. For this, the measurement procedure must be noninvasive, easy to perform, and cost- and time-efficient. Therefore, oscillometric devices with the possibility to assess CBP seem the best option. Recently, such an oscillometric BP monitor, the Microlife WatchBP Office Central, was developed, which demonstrated its high accuracy in a validation study against invasive BP measurement. Calibration errors of this device are limited because the procedure is automated, standardized, and performed at the same place of and within 30 s from pulse wave assessment. The transformation from the peripheral pulse wave to CBP is done by means of an individual-based pulse wave analysis according to a theory of arterial compliance and wave reflections. In addition, the device has demonstrated to enable a more reliable diagnosis of hypertension by CBP than by peripheral BP, with a lower frequency of over- and underdiagnosis. Altogether, the available clinical evidence suggests that the Microlife WatchBP Office Central fulfills the criteria for general clinical use.

Cost-effectiveness of noninvasive central blood pressure monitoring in the diagnosis of hypertension

BACKGROUND

Central blood pressure (CBP) betters conventional clinical BP (cuff BP) in predicting cardiovascular outcomes. Noninvasive CBP monitoring has emerged as a new technology for management of hypertension. This study aimed to analyze the cost-effectiveness of noninvasive CBP compared to cuff BP monitoring for confirming a diagnosis of hypertension.

METHODS

Lifetime costs and quality-adjusted life years (QALYs) were estimated for CBP and cuff BP monitoring using a cohort Markov model. We applied model calibration and probabilistic sensitivity analysis on populations representative of the general population, in 10-year age brackets, from age 35 years to over 75 years of age.

RESULTS

The CBP strategy was more cost-effective than cuff BP for men and women across all age subgroups, with mean incremental cost-effectiveness ratios ranging from £226 to £2,750 per QALY gained. The cost-effectiveness was mainly driven by improved patient outcomes, represented by the QALY gains (0.09-0.88), at an acceptable incremental cost (£116-£371). Deterministic and probabilistic sensitivity analyses demonstrated the consistency and robustness of the cost-effectiveness of the CBP strategy.

CONCLUSIONS

Early evidence on the diagnostic accuracy of noninvasive CBP monitoring suggests significant improvements in the confirmation of suspected hypertension, compared to cuff BP. This paper suggests that the long-term benefits of improved diagnostic performance justify the supplementary purchase costs of new, noninvasive CBP monitors. The results highlight the potential value of CBP, and hence the value of further research to confirm the diagnostic and prognostic role of CBP for the management of hypertension.

Wave reflections, arterial stiffness, and orthostatic hypotension

BACKGROUND

The effect of wave reflections on blood pressure change associated with posture remains unclear. We therefore applied a wave separation technique to investigate the relations of the backward pressure wave amplitude with orthostatic pressure changes and orthostatic hypotension (OH).

METHODS

We analyzed data from 613 subjects who had participated in our hemodynamic studies. Measurements of brachial systolic (SBP) and diastolic blood pressures (DBP), carotid-femoral pulse wave velocity (cf-PWV), and backward pressure wave amplitude from a decomposed carotid pressure wave (Pb) were obtained at supine position. SBP and DBP were measured again 3 minutes after standing. OH was defined as a fall of ≥20 mm Hg in SBP and/or ≥10 mm Hg in DBP.

RESULTS

Subjects with OH (n = 100) were characterized with significantly higher supine SBP and DBP and significantly lower standing SBP and DBP when compared with subjects without OH. Subjects with OH were also characterized with significantly higher cf-PWV and Pb. cf-PWV and Pb separately were significantly associated with the orthostatic SBP change in univariable and multivariable analyses. Also, cf-PWV and Pb separately were significant predictors of OH in univariable and multivariable analyses. cf-PWV predicted OH in the younger but less so in the older subgroup, whereas Pb demonstrated similar prediction in both subgroups. In a final multivariable model, both cf-PWV and Pb were significant independent predictors of OH.

CONCLUSIONS

Wave reflections are an independent determinant of orthostatic SBP change and OH in both younger and older subjects.

Validation of the integration of technology that measures additional "vascular" indices into an ambulatory blood pressure monitoring system

BACKGROUND

The objective of this study was to validate the novel integration of oscillometric (Vasotens(®)) technology into a BPLab(®) ambulatory blood pressure (BP) monitoring system to measure central BP, the aortic augmentation index, and pulse wave velocity (PWV) compared with the recommended and widely accepted tonometric method.

METHODS

The ARTERY Society guidelines for comparison of PWV measurement techniques were used as the basis for recruitment of 99 individuals (mean age 44±19 years, 52 males). The standard for comparison was the conventional "classic" SphygmoCor device.

RESULTS

Accordance of the two methods was satisfactory (r=0.98, mean difference of 2.9±3.5 mmHg for central systolic BP; r=0.98, mean difference of -1.1±2.3 mmHg for central diastolic BP; r=0.83, mean difference of -2.6%±13% for aortic augmentation index; r=0.85, mean difference of 0.69±1.4 for PWV).

CONCLUSION

The performance of Vasotens algorithms using an oscillometric ambulatory BP monitoring system is feasible for accurate diagnosis, risk assessment, and evaluation of the effects of antihypertensive drugs.

Invasive validation of arteriograph estimates of central blood pressure in patients with type 2 diabetes

BACKGROUND

Central blood pressure (BP) has attracted increasing interest because of a potential superiority over brachial BP in predicting cardiovascular morbidity and mortality. Several devices estimating central BP noninvasively are now available. The aim of our study was to determine the validity of the Arteriograph, a brachial cuff-based, oscillometric device, in patients with type 2 diabetes.

METHODS

We measured central BP invasively and compared it with the Arteriograph-estimated values in 22 type 2 diabetic patients referred to elective coronary angiography.

RESULTS

The difference (invasively measured BP minus Arteriograph-estimated BP) in central systolic BP (SBP) was 4.4±8.7 mm Hg (P = 0.03). The limits of agreement were ±17.1 mm Hg.

CONCLUSIONS

Compared with invasively measured central SBP, we found a systematic underestimation by the Arteriograph. However, the limits of agreement were similar to the previous Arteriograph validation study and to the invasive validation studies of other brachial cuff-based, oscillometric devices. A limitation in our study was the large number of patients (n = 14 of 36) in which the Arteriograph was unable to analyze the pressure curves. In a research setting, the Arteriograph seems applicable in patients with type 2 diabetes.

CLINICAL TRAIL REGISTRATION

ClinicalTrials.gov ID NCT01538290.

Application of the N-Point Moving Average Method for Brachial Pressure Waveform–Derived Estimation of Central Aortic Systolic Pressure

The N-point moving average (NPMA) is a mathematical low-pass filter that can smooth peaked noninvasively acquired radial pressure waveforms to estimate central aortic systolic pressure using a common denominator of N/4 (where N=the acquisition sampling frequency). The present study investigated whether the NPMA method can be applied to brachial pressure waveforms. In the derivation group, simultaneously recorded invasive high-fidelity brachial and central aortic pressure waveforms from 40 subjects were analyzed to identify the best common denominator. In the validation group, the NPMA method with the obtained common denominator was applied on noninvasive brachial pressure waveforms of 100 subjects. Validity was tested by comparing the noninvasive with the simultaneously recorded invasive central aortic systolic pressure. Noninvasive brachial pressure waveforms were calibrated to the cuff systolic and diastolic blood pressures. In the derivation study, an optimal denominator of N/6 was identified for NPMA to derive central aortic systolic pressure. The mean difference between the invasively/noninvasively estimated (N/6) and invasively measured central aortic systolic pressure was 0.1±3.5 and −0.6±7.6 mm Hg in the derivation and validation study, respectively. It satisfied the Association for the Advancement of Medical Instrumentation standard of 5±8 mm Hg. In conclusion, this method for estimating central aortic systolic pressure using either invasive or noninvasive brachial pressure waves requires a common denominator of N/6. By integrating the NPMA method into the ordinary oscillometric blood pressure determining process, convenient noninvasive central aortic systolic pressure values could be obtained with acceptable accuracy.

Diagnostic performance of a stand-alone central blood pressure monitor: application of central blood pressure in the diagnosis of high blood pressure

BACKGROUND

Oscillometric central blood pressure (CBP) monitors have emerged as a new technology for blood pressure (BP) measurements. With a newly proposed diagnostic threshold for CBP, we investigated the diagnostic performance of a novel CBP monitor.

METHODS

We recruited a consecutive series of 138 subjects (aged 30-93 years) without previous use of antihypertensive agents for simultaneous invasive and noninvasive measurements of BP in a catheterization laboratory. With the cutoff (CBP ≥130/90 mm Hg) for high blood pressure (HBP), the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the novel CBP monitor were calculated with reference to the measured CBP. In comparison, the diagnostic performance of the conventional cuff BP was also evaluated.

RESULTS

The noninvasive CBP for detecting HBP in a sample with a prevalence of 52% showed a sensitivity of 93% (95% confidence interval (CI) = 91-95), specificity of 95% (95% CI = 94-97), PPV of 96% (95% CI = 94-97), and NPV of 93% (95% CI = 90-95). In contrast, with cuff BP and the traditional HBP criterion (cuff BP ≥140/90 mm Hg), the sensitivity, specificity, PPV, and NPV were 49% (95% CI = 44-53), 94% (95% CI = 92-96), 90% (95% CI = 86-93), and 63% (95% CI 59-66), respectively.

CONCLUSIONS

A stand-alone oscillometric CBP monitor may provide CBP values with acceptable diagnostic accuracy. However, with reference to invasively measured CBP, cuff BP had low sensitivity and NPV, which could render possible management inaccessible to a considerable proportion of HBP patients, who may be identifiable through noninvasive CBP measurements from the CBP monitor.

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

OBJECTIVES

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Associations of serum uric acid levels with arterial wave reflections and central systolic blood pressure

BACKGROUND

Uric acid may be involved in the pathogenesis of hypertension. We investigated the roles of four major hemodynamic parameters of blood pressure, including arterial stiffness, wave reflections, cardiac output (CO), and total peripheral resistance (TPR), in the association between uric acid and central systolic blood pressure (SBP-c).

METHODS

A sample of 1303 normotensive and untreated hypertensive Taiwanese participants (595 women, aged 30-79 years) was drawn from a community-based survey. Study subjects' baseline characteristics, biochemical parameters, carotid-femoral pulse wave velocity (cf-PWV), amplitude of the backward pressure wave decomposed from a calibrated tonometry-derived carotid pressure waveform (Pb), CO, TPR, and SBP-c were analyzed.

RESULTS

In multi-variate analyses adjusted for age, waist circumference, body mass index, creatinine, total cholesterol, smoking, and heart rate, uric acid significantly correlated with Pb and cf-PWV in men, and Pb and TPR in women. The correlation between uric acid and Pb remained significant in men and women when cf-PWV was further adjusted. In the final multi-variate prediction model (model r(2)=0.839) for SBP-c, the significant independent variables included uric acid (partial r(2)=0.005), Pb (partial r(2)=0.651), cf-PWV (partial r(2)=0.005), CO (partial r(2)=0.062), TPR (partial r(2)=0.021), with adjustment for age, sex, waist circumference, body mass index, creatinine, total cholesterol, smoking, and heart rate.

CONCLUSIONS

Uric acid was significantly independently associated with wave reflections, which is the dominant determinant of SBP-c. Uric acid was also significantly associated with SBP-c independently of the major hemodynamic parameters.

The barriers to clinical application of non-invasively obtained central blood pressure

With the demonstration of superior prognostic value of central blood pressure (CBP) beyond traditionally used brachial BP, there have been increasing interest in the development of novel devices reporting parameters of CBP. The emerging devices for non-invasive estimation of CBP, based on either tonometry-based or cuff-based techniques, were evaluated with various validation studies. Therefore, the research community and clinicians have been faced with challenges regarding the conduction and interpretation of the validation studies for the non-invasively obtained CBP. We summarize here the barriers to the clinical application of the CBP concept, which provide research opportunities to further the subsequent translation.

Measurement accuracy of a stand-alone oscillometric central blood pressure monitor: a validation report for Microlife WatchBP Office Central

BACKGROUND

The superiority of prognostic value of blood pressure (BP) measured at central aorta (CBP) over conventional brachial BP measured by cuff-based BP monitors has reignited the development of new noninvasive techniques for estimating CBP. The present study validated the accuracy of CBP measured by a newly developed stand-alone CBP monitor.

METHODS

The CBP monitor provided readings of brachial systolic BP (SBP), brachial diastolic BP (DBP), central SBP, and central pulse pressure (PP). Brachial PP and central DBP were calculated from the relevant readings. The accuracy of the brachial and central SBP, PP, and DBP was validated against the simultaneously recorded invasively measured central aortic SBP, PP, and DBP, according to the invasive standard requirements for the noninvasive brachial BP monitors from the Association for the Advancement of Medical Instrumentation (AAMI) in 85 subjects (255 measurements; age range, 30-93 years).

RESULTS

The mean differences of cuff BP with reference to the invasively measured central SBP, PP, and DBP were -2.6 ± 9.0, -8.6 ± 11.2, and 6.1 ± 7.0 mm Hg, respectively, with the former two being obviously underestimated at high CBP and overestimated at low CBP. In contrast, the corresponding differences for the central SBP, PP, and DBP measured by the CBP monitor were -0.6 ± 5.5, -0.4 ± 7.0, and -0.2 ± 6.5 mm Hg, respectively, without obvious systematic bias. The distribution of measurement errors for central SBP, PP, and DBP surpassed the AAMI criteria.

CONCLUSION

Central SBP, PP, and DBP can be measured accurately by a stand-alone automatic BP monitor.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

BACKGROUND AND OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Measurement of central systolic blood pressure by pulse volume plethysmography with a noninvasive blood pressure monitor

BACKGROUND

Central systolic blood pressure (SBP) can be estimated by an oscillometric method developed from a pulse volume plethysmography (PVP) device. The present study applied this novel method to a noninvasive blood pressure monitor (NBPM).

METHODS

We enrolled 50 patients (37 men, age range 30-84 years) referred for cardiac catheterization. Invasive right brachial and central aortic pressures (using a dual-sensor pressure catheter), and noninvasive left brachial SBP and diastolic blood pressure (DBP), and PVP waveform (using a customized NBPM) were simultaneously recorded. Central SBP was estimated by analysis of the PVP waveform calibrated to the noninvasive SBP and DBP, using both the original (CSBP-O) and the newly generated (CSBP-N) regression equations. The reproducibility of the invasive central SBP by CSBP-O and CSBP-N was examined using the concordance correlation coefficient.

RESULTS

Overall, the invasive central aortic SBP ranged 86-176 with a mean of 124 ± 21 mm Hg. The mean differences between the estimated and the invasive central SBP were -1.3 ± 6.7 mm Hg for CSBP-O and 0.0 ± 6.2 mm Hg for CSBP-N, respectively. The concordance correlation coefficients for CSBP-O and CSBP-N were 0.94 (95% confidence interval (CI): 0.93-0.94) and 0.95 (95% CI: 0.95-0.96), and both were significantly better than that for the noninvasive brachial SBP (0.87, 0.84-0.91) indicated by non-overlapping CIs.

CONCLUSIONS

The PVP method for noninvasive estimation of central SBP can be applied to a commonly used NBPM. Whether the NBPM-derived central SBP is superior to the noninvasive brachial SBP in the prediction of cardiovascular risks remains to be investigated.

Validity and reliability of central blood pressure estimated by upper arm oscillometric cuff pressure

BACKGROUND

Noninvasive central blood pressure (BP) independently predicts mortality, but current methods are operator-dependent, requiring skill to obtain quality recordings. The aims of this study were first, to determine the validity of an automatic, upper arm oscillometric cuff method for estimating central BP (O(CBP)) by comparison with the noninvasive reference standard of radial tonometry (T(CBP)). Second, we determined the intratest and intertest reliability of O(CBP).

METHODS

To assess validity, central BP was estimated by O(CBP) (Pulsecor R6.5B monitor) and compared with T(CBP) (SphygmoCor) in 47 participants free from cardiovascular disease (aged 57 ± 9 years) in supine, seated, and standing positions. Brachial mean arterial pressure (MAP) and diastolic BP (DBP) from the O(CBP) device were used to calibrate in both devices. Duplicate measures were recorded in each position on the same day to assess intratest reliability, and participants returned within 10 ± 7 days for repeat measurements to assess intertest reliability.

RESULTS

There was a strong intraclass correlation (ICC = 0.987, P < 0.001) and small mean difference (1.2 ± 2.2 mm Hg) for central systolic BP (SBP) determined by O(CBP) compared with T(CBP). Ninety-six percent of all comparisons (n = 495 acceptable recordings) were within 5 mm Hg. With respect to reliability, there were strong correlations but higher limits of agreement for the intratest (ICC = 0.975, P < 0.001, mean difference 0.6 ± 4.5 mm Hg) and intertest (ICC = 0.895, P < 0.001, mean difference 4.3 ± 8.0 mm Hg) comparisons.

CONCLUSIONS

Estimation of central SBP using cuff oscillometry is comparable to radial tonometry and has good reproducibility. As a noninvasive, relatively operator-independent method, O(CBP) may be as useful as T(CBP) for estimating central BP in clinical practice.

Quantification of the calibration error in the transfer function-derived central aortic blood pressures

BACKGROUND

The accuracy of the central aortic systolic (SBP-C) and pulse (PP-C) blood pressures estimated noninvasively by a generalized transfer function technique has been questioned. The purpose of the present study was to quantify precisely the impact of the input errors (differences between the oscillometric (SBP-O, DBP-O, PP-O) and invasive (SBP-B, DBP-B, PP-B) brachial systolic, diastolic, and pulse blood pressures) on the output errors (differences between the estimated and invasively measured SBP-C and PP-C).

METHODS

Invasive high-fidelity right brachial and central aortic pressure waveforms, and SBP-O, DBP-O, and PP-O (=SBP-O - DBP-O) were obtained simultaneously in 40 patients during cardiac catheterization. A generalized transfer function was applied on the individual brachial pressure waveform to derive predicted SBP-C and PP-C.

RESULTS

Observed input errors were -2.3 ± 5.8 mm Hg from SBP-O, 8.1 ± 5.3 mm Hg from DBP-O, and -10.4 ± 7.1 mm Hg from PP-O, respectively. The output errors were -2.2 ± 6.4 mm Hg and -10.3 ± 8.0 mm Hg for SBP-C and PP-C, respectively, when the brachial pressure waveforms were recalibrated using SBP-O and DBP-O. The outputs were determined by the inputs according to the Equation (1): SBP-C error = 0.97 × SBP-O error + 0.03 (r = 0.88, P < 0.01); and the Equation (2): PP-C error = 0.96 × PP-O error - 0.30 (r = 0.86, P < 0.01).

CONCLUSIONS

Noninvasive application of the generalized transfer function techniques produces estimates of SBP-C and PP-C with errors equivalent to those of the oscillometric blood pressure monitor in the estimation of SBP-B and PP-B. The output errors can be predicted from input errors of SBP-O and DBP-O.

Measurement Accuracy of Non-invasively Obtained Central Blood Pressure: A Systematic Review and Meta-analysis

BACKGROUND

Blood pressures determined at different sites vary considerably. Non-invasive methods are available to estimate central aortic blood pressure, the blood pressure at the origin of all arterial pulses. These methods obtain estimated central blood pressure by calibration and/or mathematical calculations for peripheral pulse waveforms. However, the accuracy of these methods has not been systematically examined.

OBJECTIVES

The review aimed to synthesise the best evidence on the accuracy of non-invasive measurement methods for central blood pressure.

INCLUSION CRITERIA

Types of participantsStudies with adult patients receiving invasive and non-invasive measurements of central blood pressure were considered.

PHENOMENA OF INTEREST

Studies were considered for inclusion if the focus was accuracy of non-invasive central BP estimating methods compared to invasively obtained corresponding values.

TYPES OF STUDIES

Studies examining agreement between measurements using non-invasive central blood pressure estimating methods compared to invasive corresponding values were considered.

TYPES OF OUTCOMES

This review included the means and standard deviation of differences between estimated and invasively measured central blood pressure.

SEARCH STRATEGY

The search sought to identify any relevant published or unpublished studies with a three-step search strategy.

METHODOLOGICAL QUALITY

Two independent reviewers assessed methodological quality of studies by a critical appraisal tool modified from Cochrane Diagnostic Test Accuracy Working Group.

DATA COLLECTION

We used an original form to extract from included studies all study characteristics possibly related to agreement.

DATA SYNTHESIS

Inverse variance weighted approach and DerSimonian-Laird weights for the random effects model, which incorporates a between-study variance, were used to obtain pooled estimates of systematic and random error from individual study estimates of the mean and standard deviation of differences between the paired measurements. Heterogeneity was assessed using Cochran Q. All analyses were performed in Microsoft Excel 2003.

RESULTS

Twenty eight studies were eligible for inclusion and critically appraised in this review. Appropriate data for agreement were extracted from papers or authors in 20 studies, which were further included in meta-analysis. Acquired peripheral waveforms in these studies were directly measured, calibrated to match invasively obtained aortic mean blood pressure and diastolic blood pressure, or calibrated using brachial blood pressure measured by sphygomomanometer, the cuff blood pressure. Estimated central blood pressure of the studies using the last totally non-invasively methods (real world practices) were subject to meta-analysis separately from studies with the former two invasive methods (theoretical practice). Of the invasive methods, mean difference of the estimated central blood pressure was small (-1.2 ± 4.2mmHg for central systolic blood pressure, -0.6 ± 2.1mmHg for central diastolic blood pressure, and -1.1 ± 5.3 mmHg for central pulse pressure). However, the errors of the non-invasive method inflated considerably (-8.1 ± 10.7mmHg for central systolic blood pressure, 8.8 ± 9.5mmHg for central diastolic blood pressure, and -11.8 ± 13.3 mmHg for central pulse pressure). The findings were similar in subgroup analysis by different central blood pressure methods and by validated cuff monitors.

CONCLUSIONS

Current central blood pressure estimating methods are acceptable in theory with small systematic and random error. However, the error of these methods was evident when cuff blood pressure was used for calibration and probably made them clinically inapplicable.