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Blood pressure (BP) is a key contributor to the lifetime risk of preclinical organ damage and cardiovascular disease. Traditional clinic-based BP readings are typically measured infrequently and under standardized/resting conditions and therefore do not capture BP values during normal everyday activity. Therefore, current hypertension guidelines emphasize the importance of incorporating out-of-office BP measurement into strategies for hypertension diagnosis and management. However, conventional home and ambulatory BP monitoring devices use the upper-arm cuff oscillometric method and only provide intermittent BP readings under static conditions or in a limited number of situations. New innovations include technologies for BP estimation based on processing of sensor signals supported by artificial intelligence tools, technologies for remote monitoring, reporting and storage of BP data, and technologies for BP data interpretation and patient interaction designed to improve hypertension management ("digital therapeutics"). The number and volume of data relating to new devices/technologies is increasing rapidly and will continue to grow. This International Society of Hypertension position paper describes the new devices/technologies, presents evidence relating to new BP measurement techniques and related indices, highlights standard for the validation of new devices/technologies, discusses the reliability and utility of novel BP monitoring devices, the association of these metrics with clinical outcomes, and the use of digital therapeutics. It also highlights the challenges and evidence gaps that need to be overcome before these new technologies can be considered as a user-friendly and accurate source of novel BP data to inform clinical hypertension management strategies., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Measuring blood pressure (BP) and investigating arterial hemodynamics are essential in understanding cardiovascular disease and assessing cardiovascular risk. Several methods are used to measure BP in the doctor's office, at home, or over 24 h under ambulatory conditions. Similarly, several noninvasive methods have been introduced for assessing arterial structure and function; these methods differ for the large arteries, the small ones, and the capillaries. Consequently, when studying arterial hemodynamics, the clinician is faced with a multitude of assessment methods whose technical details, advantages, and limitations are sometimes unclear. Moreover, the conditions and procedures for their optimal implementation, and/or the reference normality values for the parameters they yield are not always taken into sufficient consideration. Therefore, a practice guideline summarizing the main methods and their use in clinical practice is needed. This expert group position paper was developed by an international group of scientists after a two-day meeting during which each of the most used methods and techniques for blood pressure measurement and arterial function and structure evaluation were presented and discussed, focusing on their advantages, limitations, indications, normal values, and their pragmatic clinical application., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc.)

There is little quantitative clinical data available to support blood pressure measurement accuracy during cuff inflation. In this study of 35 male and 5 female lightly anaesthetized subjects aged 64.1 ± 9.6 years, we evaluate and compare the performance of both the oscillometric ratio and gradient methods during cuff deflation and cuff inflation with reference to intra-arterial measurements. We show that the oscillometric waveform envelopes (OWE), which are key to both methods, exhibit significant variability in both shape and smoothness leading to at least 15% error in the determination of mean pressure (MP). We confirm the observation from our previous studies that K1 Korotkoff sounds underestimate systolic blood pressure (SBP) and note that this underestimation is increased during cuff inflation. The estimation of diastolic blood pressure (DBP) is generally accurate for both the ratio and the gradient method, with the latter showing a significant increase during inflation. Since the gradient method estimates SBP and DBP from points of maximum gradient on each OWE recorded, it may offer significant benefits over the ratio method. However, we have shown that the ratio method can be optimized for any data set to achieve either a minimum mean error (ME) of close to 0 mmHg or minimum root mean square error (RMSE) with standard deviation (SD) of <5.0 mmHg. We conclude that whilst cuff inflation may offer some advantages, these are neither significant nor substantial, leaving as the only benefit, the potential for more rapid measurement and less patient discomfort., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Most non-invasive blood pressure (BP) measurements are carried out using instruments which implement either the Ratio or the Maximum Gradient oscillometric method, mostly during cuff deflation, but more rarely during cuff inflation. Yet, there is little published literature on the relative advantages and accuracy of these two methods. In this study of 40 lightly sedated individuals aged 64.1 ± 9.6 years, we evaluate and compare the performance of the oscillometric ratio (K) and gradient (Grad) methods for the non-invasive estimation of mean pressure, SBP and DBP with reference to invasive intra-arterial values. There was no significant difference between intra-arterial estimates of mean pressure made via Korotkoff sounds (MP-OWE) or the gradient method (MP-Grad). However, 17.7% of MP-OWE and 15% of MP-Grad were in error by more than 10 mmHg. SBP-K and SBP-Grad underestimated SBP by 14 and 18 mmHg, whilst accurately estimating DBP with mean errors of 0.4 ± 5.0 and 1.7 ± 6.1 mmHg, respectively. Relative to the reference standard SBP-K, SBP-Grad and DBP-Grad were estimated with a mean error of -4.5 ± 6.6 and 1.4 ± 5.6 mmHg, respectively, noting that using the full range of recommended ratios introduces errors of 12 and 7 mmHg in SBP and DBP, respectively. We also show that it is possible to find ratios which minimize the root mean square error (RMSE) and the mean error for any particular individual cohort. We developed linear models for estimating SBP and SBP-K from a range of demographic and non-invasive OWE variables with resulting mean errors of 0.15 ± 5.6 and 0.3 ± 5.7 mmHg, acceptable according to the Universal standard., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Conventional sphygmomanometry with cuff deflation is used to calibrate all noninvasive BP (NIBP) instruments and the International Standard makes no mention of calibrating methods specifically for NIBP instruments, which estimate systolic and diastolic pressure during cuff inflation rather than cuff deflation. There is however increasing interest in inflation-based NIBP (iNIBP) instruments on the basis of shorter measurement time, reduction in maximal inflation pressure and improvement in patient comfort and outcomes. However, we have previously demonstrated that SBP estimates based on the occurrence of the first K1 Korotkoff sounds during cuff deflation can underestimate intra-arterial SBP (IA-SBP) by an average of 14 ± 10 mmHg. In this study, we compare the dynamics of intra-arterial blood pressure (IABP) measurements with sequential measurement of Korotkoff sounds during both cuff inflation and cuff deflation in the same individual. In 40 individuals aged 64.1 ± 9.6 years (range 36-86 years), the overall dynamic responses below the cuff were similar, but the underestimation error was significantly larger during inflation than deflation, increasing from 14 ± 10 to 19 ± 12 mmHg ( P  < 0.0001). No statistical models were found which could compensate for this error as were found for cuff deflation. The statistically significant BP differences between inflation and deflation protocols reported in this study suggest different behaviour of the arterial and venous vasculature between arterial opening and closing which warrant further investigation, particularly for iNIBP devices reporting estimates during cuff inflation. In addition, measuring Korotkoff sounds during cuff inflation represents significant technical difficulties because of increasing pump motor noise., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Cardiovascular disease is the number 1 cause of death globally, with elevated blood pressure (BP) being the single largest risk factor. Hence, BP is an important physiological parameter used as an indicator of cardiovascular health. Noninvasive cuff-based automated monitoring is now the dominant method for BP measurement and irrespective of whether the oscillometric or the auscultatory method is used, all are calibrated according to the Universal Standard (ISO 81060-2:2019), which requires two trained operators to listen to Korotkoff K1 sounds for SBP and K4/K5 sounds for DBP. Hence, Korotkoff sounds are fundamental to the calibration of all NIBP devices. In this study of 40 lightly sedated patients, aged 64.1 ± 9.6 years, we compare SBP and DBP recorded directly by intra-arterial fluid filled catheters to values recorded from the onset (SBP-K) and cessation (DBP-K) of Korotkoff sounds. We demonstrate that whilst DBP-K measurements are in good agreement, with a mean difference of -0.3 ± 5.2 mmHg, SBP-K underestimates true intra-arterial SBP (IA-SBP) by an average of 14 ± 9.6 mmHg. The underestimation arises from delays in the re-opening of the brachial artery following deflation of the brachial cuff to below SBP. The reasons for this delay are not known but appear related to the difference between SBP and the pressure under the cuff as blood first begins to flow, as the cuff deflates. Linear models are presented that can correct the underestimation in SBP resulting in estimates with a mean difference of 0.2 ± 7.1 mmHg with respect to intra-arterial SBP., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Background: There is intense effort to develop cuffless blood pressure (BP) measuring devices, and several are already on the market claiming that they provide accurate measurements. These devices are heterogeneous in measurement principle, intended use, functions, and calibration, and have special accuracy issues requiring different validation than classic cuff BP monitors. To date, there are no generally accepted protocols for their validation to ensure adequate accuracy for clinical use., Objective: This statement by the European Society of Hypertension (ESH) Working Group on BP Monitoring and Cardiovascular Variability recommends procedures for validating intermittent cuffless BP devices (providing measurements every >30 sec and usually 30-60 min, or upon user initiation), which are most common., Validation Procedures: Six validation tests are defined for evaluating different aspects of intermittent cuffless devices: static test (absolute BP accuracy); device position test (hydrostatic pressure effect robustness); treatment test (BP decrease accuracy); awake/asleep test (BP change accuracy); exercise test (BP increase accuracy); and recalibration test (cuff calibration stability over time). Not all these tests are required for a given device. The necessary tests depend on whether the device requires individual user calibration, measures automatically or manually, and takes measurements in more than one position., Conclusion: The validation of cuffless BP devices is complex and needs to be tailored according to their functions and calibration. These ESH recommendations present specific, clinically meaningful, and pragmatic validation procedures for different types of intermittent cuffless devices to ensure that only accurate devices will be used in the evaluation and management of hypertension., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

Noninvasive blood pressure (NIBP) devices are calibrated against validated auscultation sphygmomanometers using Korotkoff sounds. This study aimed to investigate the timing of Korotkoff sounds in relation to pulse appearance in the brachial artery and values of intra-arterial blood pressure. Experiments were carried out on 15 participants, (14 males, 64.3 ± 10.4 years; one female, 86 yo), undergoing coronary angiography. A conventional occluding cuff, with a microphone for Korotkoff sounds, was placed on the upper arm (on the brachial artery). Intra-arterial blood pressure (IABP) was measured below the cuff with a fluid-filled catheter inserted via the radial artery and an external transducer. Finger photoplethysmography was used to measure brachial pulse wave velocity (PWV). Korotkoff sounds were processed electronically and custom algorithms identified the cuff pressure (CP) at which the first and last Korotkoff sounds were heard. PWV and max slope of the IABP pressure pulse were recorded to estimate arterial stiffness. The brachial artery closed at a CP of 132.0 ± 17.1 mmHg. Systolic and diastolic blood pressure (SBP and DBP) were 147.6 ± 14.3 and 72.7 ± 10.1 mmHg; mean pressure (MP, 100.1 ± 10.4 mmHg) was similar to MP derived from the peak of the oscillogram (98.5 ± 13.6 mmHg). Difference between IABP and CP recorded at first and last occurrence of Korotkoff sounds were, SBP: 19.0 ± 8.3 (range 2-29) mmHg, DBP: 4.0 ± 4.3 (range 2-12) mmHg. SBP derived from the onset of Korotkoff sounds can underestimate IABP by up to 19 mmHg. Since Korotkoff sounds are the recommended method mandated by the universal standard for the validation of blood pressure measuring devices, these errors are propagated through to all NIBP measurement devices irrespective of whether they use auscultatory or oscillometric methods.

Objective: Development and testing of cuffless blood pressure (BP) devices requires methods to increase and decrease BP. This is also required by cuffless BP validation standards. Pharmacological interventions, whilst successful, are not always feasible for all subpopulations or research settings. Non-pharmacological approaches for increasing BP are available, however, methods for decreasing BP are not well described. This study investigates the hyperemic response following bilateral leg-cuff ischemia as a method for acute BP lowering., Design and Method: Participants (n=8, 24±8 years, 6 female) had their BP measured by continuous (finger, Peňáz technique) and intermittent (brachial cuff, oscillometric) methods before, during and following 3-minute leg-ischemia with the participant in an upright position. Total peripheral resistance (TPR) and cardiac output (CO) were calculated from finger BP waveforms. Maxima and minima responses in the variables were extracted and compared to resting conditions by repeated measures analysis of covariance., Results: During the hyperemic period, systolic BP decreased by -22±3 mmHg (finger) and -6±1 mmHg (brachial). Diastolic BP decreased by -14±5 mmHg (finger) and -4 ±1 mmHg (brachial). Calculated TPR and CO varied, with both decreasing by half and almost doubling during the hyperemic response period., Conclusions: Leg-cuff ischemia provides a controlled, non-pharmacological intervention for decreasing systemic arterial BP. This removes some of the limitations in testing, development and validation of cuffless BP techniques and devices.

Objective: Aortic pressure estimation requires reliable peripheral pulse waveform acquisition. The peripheral waveform can change with local vascular effects that can be independent of aortic pressure. This study quantifies the effects of peripheral vasculature changes on radial and brachial waveforms., Design and Method: In 20 subjects (37± 15 years, 7 female), brachial volumetric displacement (cuff-based) and radial tonometry waveforms were simultaneously measured whilst a cuff around the hand on the same arm was inflated to induce transmural pressures of -60, -30, -15, 0, 15 and 30 mmHg, altering local peripheral resistance and compliance by graded arterial wall unloading. Aortic blood pressure (BP), augmentation index (AIx) and ejection duration were calculated from the measurements using a generalized transfer function. The parameters under unloaded conditions were compared to baseline measurements., Results: Brachial systolic and diastolic BP did not change throughout the experiment. Altering peripheral resistance and compliance did not significantly change calculated aortic BP values, although changes were nominally greater for radial (maximum +8±1 mmHg) compared to brachial (maximum +2±1 mmHg) waveforms. AIx at 0 mmHg transmural pressure (maximum arterial wall unloading) was higher when derived from radial waveforms (+24±3%, p<0.001) but not when derived from brachial waveforms., Conclusions: Localized changes in peripheral resistance and compliance affect tonometer acquired radial waveforms but not volumetric displacement acquired brachial pressure waveforms, as judged by computed central aortic augmentation pressure parameters. This suggests aortic pressure estimation from the brachial cuff waveform is less sensitive to peripheral vasculature disturbances that alter the peripheral arterial pulse morphology.

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

Conventional blood pressure (BP) measurement devices based on an inflatable cuff only provide a narrow view of the continuous BP profile. Cuffless BP measuring technologies could permit numerous BP readings throughout daily life and thereby considerably improve the assessment and management of hypertension. Several wearable cuffless BP devices based on pulse wave analysis (applied to a photoplethysmography or tonometry waveform) with or without use of pulse arrival time are now available on the market. The key question is: Can these devices provide accurate measurement of BP? Microsoft Research recently published a complex article describing perhaps the most important and highest resource project to date (Aurora Project) on assessing the accuracy of several pulse wave analysis and pulse wave analysis-pulse arrival time devices. The overall results from 1125 participants were clear-cut negative. The present article motivates and describes emerging cuffless BP devices and then summarizes the Aurora Project. The study methodology and findings are next discussed in the context of regulatory-cleared devices, physiology, and related studies, and the study strengths and limitations are pinpointed thereafter. Finally, the implications of the Aurora Project are briefly stated and recommendations for future work are offered to finally realize the considerable potential of cuffless BP measurement in health care.

Automated 'oscillometric' blood pressure (BP) measuring devices (BPMDs) were developed in the 1970s to replace manual auscultatory BP measurement by mercury sphygmomanometer. Automated BPMDs that have passed accuracy testing versus a reference auscultatory sphygmomanometer using a scientifically accepted validation protocol are recommended for clinical use globally. Currently, there are many thousands of unique automated BPMDs manufactured by hundreds of companies, with each device using proprietary algorithms to estimate BP and using a method of operation that is largely unchanged since inception. Validated automated BPMDs provide similar BP values to those recorded using manual auscultation albeit with potential sources of error mostly associated with using empirical algorithms to derive BP from waveform pulsations. Much of the work to derive contemporary BP thresholds and treatment targets used to manage cardiovascular disease risk was obtained using automated BPMDs. While there is room for future refinement to improve accuracy for better individual risk stratification, validated BPMDs remain the recommended standard for office and out-of-office BP measurement to be used in hypertension diagnosis and management worldwide., (© 2022. The Author(s).)

Background: Many cuffless blood pressure (BP) measuring devices are currently on the market claiming that they provide accurate BP measurements. These technologies have considerable potential to improve the awareness, treatment, and management of hypertension. However, recent guidelines by the European Society of Hypertension do not recommend cuffless devices for the diagnosis and management of hypertension., Objective: This statement by the European Society of Hypertension Working Group on BP Monitoring and Cardiovascular Variability presents the types of cuffless BP technologies, issues in their validation, and recommendations for clinical practice., Statements: Cuffless BP monitors constitute a wide and heterogeneous group of novel technologies and devices with different intended uses. Cuffless BP devices have specific accuracy issues, which render the established validation protocols for cuff BP devices inadequate for their validation. In 2014, the Institute of Electrical and Electronics Engineers published a standard for the validation of cuffless BP devices, and the International Organization for Standardization is currently developing another standard. The validation of cuffless devices should address issues related to the need of individual cuff calibration, the stability of measurements post calibration, the ability to track BP changes, and the implementation of machine learning technology. Clinical field investigations may also be considered and issues regarding the clinical implementation of cuffless BP readings should be investigated., Conclusion: Cuffless BP devices have considerable potential for changing the diagnosis and management of hypertension. However, fundamental questions regarding their accuracy, performance, and implementation need to be carefully addressed before they can be recommended for clinical use., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Cuffless blood pressure (BP) measurement has become a popular field due to clinical need and technological opportunity. However, no method has been broadly accepted hitherto. The objective of this review is to accelerate progress in the development and application of cuffless BP measurement methods. We begin by describing the principles of conventional BP measurement, outstanding hypertension/hypotension problems that could be addressed with cuffless methods, and recent technological advances, including smartphone proliferation and wearable sensing, that are driving the field. We then present all major cuffless methods under investigation, including their current evidence. Our presentation includes calibrated methods (i.e., pulse transit time, pulse wave analysis, and facial video processing) and uncalibrated methods (i.e., cuffless oscillometry, ultrasound, and volume control). The calibrated methods can offer convenience advantages, whereas the uncalibrated methods do not require periodic cuff device usage or demographic inputs. We conclude by summarizing the field and highlighting potentially useful future research directions.

It is well known that non-invasive blood pressure measurements significantly underestimate true systolic blood pressure (SBP), and overestimate diastolic blood pressure (DBP). The aetiology for these errors has not yet been fully established. This study aimed to investigate the accuracy of Korotkoff sounds for detection of SBP and DBP points as used in brachial cuff sphygmomanometry. Brachial cuff pressure and Korotkoff sounds were obtained in 11 patients (6 males: 69.0 ± 6.2 years, 5 females: 71.8 ± 5.5 years) undergoing diagnostic coronary angiography. K2 Korotkoff sounds were obtained by high-pass filtering (>20 Hz) the microphone-recorded signal to eliminate low frequency components. Analysis of the timing of K2 Korotkoff sounds relative to cuff pressure and intra-arterial pressure shows that the onset of K2 Korotkoff sounds reliably detect the start of blood flow under the brachial cuff and their termination, marks the cuff pressure closely coincident with DBP. We have made the critical observation that blood flow under the cuff does not begin when cuff pressure falls just below SBP as is conventionally assumed, and that the delay in the opening of the artery following occlusion, and the consequent delay in the generation of K2 Korotkoff sounds, may lead to significant errors in the determination of SBP of up to 24 mmHg. Our data suggest a potential role of arterial stiffness as a major component of the errors recorded, with underestimation of SBP much more significant for subjects with stiff arteries than for subjects with more compliant arteries.

Background: The use of wearable cuffless blood pressure (BP) devices is becoming commercially prevalent with little published validation information. Most devices rely, at least in part, on the relationship between pulse arrival time (PAT) and BP, a theoretical fundamental relationship that was first commercially exploited in 1993 with the release of the Casio BP-100 digital watch., Objective: This study explored the PAT method of BP estimation in a commercial device where it first began, the Casio BP-100 (Model No. 900) digital watch, which employs an individualized, two-point calibration method. Device accuracy was determined by comparison to a conventional cuff-based BP device measurements., Methods: Twenty participants (11 female, 9 male) had BP measured using both devices at rest, during a 5-minute isometric hand-grip exercise and at 1-minute post-exercise., Results: Due to bidirectional scatter of BP estimation by the BP-100 device, there was no significant difference between the reference device and the BP-100. The devices showed poor correlation for both systolic BP (SBP) (R=0.36, p=0.13) and diastolic BP (DBP) (R=0.044, p=0.37). However, on average the watch was able to provide correct directional changes in SBP but not DBP with exercise., Conclusions: Despite being an industry first, the Casio BP-100 watch employed a method that gives a great chance of accuracy: a two point, individualized calibration method - more detailed than calibration methods in more modern devices. The watch, on average across a cohort, provided some information on BP directional change but was uncorrelated with cuff-based BP measurement. If the utility of beat-by-beat BP estimation is to be utilized, limitations of this method need to be addressed.

Several novel cuffless wearable devices and smartphone applications claiming that they can measure blood pressure (BP) are appearing on the market. These technologies are very attractive and promising, with increasing interest among health care professionals for their potential use. Moreover, they are becoming popular among patients with hypertension and healthy people. However, at the present time, there are serious issues about BP measurement accuracy of cuffless devices and the 2021 European Society of Hypertension Guidelines on BP measurement do not recommend them for clinical use. Cuffless devices have special validation issues, which have been recently recognized. It is important to note that the 2018 Universal Standard for the validation of automated BP measurement devices developed by the American Association for the Advancement of Medical Instrumentation, the European Society of Hypertension, and the International Organization for Standardization is inappropriate for the validation of cuffless devices. Unfortunately, there is an increasing number of publications presenting data on the accuracy of novel cuffless BP measurement devices, with inadequate methodology and potentially misleading conclusions. The objective of this review is to facilitate understanding of the capabilities and limitations of emerging cuffless BP measurement devices. First, the potential and the types of these devices are described. Then, the unique challenges in evaluating the BP measurement accuracy of cuffless devices are explained. Studies from the literature and computer simulations are employed to illustrate these challenges. Finally, proposals are given on how to evaluate cuffless devices including presenting and interpreting relevant study results.

Background: Pulse transit time (PTT) and pulse arrival time (PAT) are promising measures for cuffless arterial blood pressure (BP) estimation given the intrinsic arterial stiffness-BP relationship. However, arterial stiffness (and PTT) is altered by autonomically-driven smooth muscle tension changes, potentially independent of BP. This would limit PTT or PAT as accurate BP correlates, more so in resistance vessels than conductance arteries., Objective: To quantify if there is a measurable neurogenic effect on PAT measured using photoplethysmography (PPG) (path includes resistance vessels) and radial artery tonometry (path includes only conductance vessels) during physiologically induced BP changes., Methods: PATs were measured continuously in participants (n=15, 35±15 years, 9 male) using an electrocardiogram and, simultaneously, a Finometer ® PRO finger sensor, a finger PPG sensor and radial artery tonometer during seated rest, cold pressor test, cycling and isometric handgrip (IHG) exercise. ΔBP/ΔPAT was calculated for each sensor and each condition., Results: All interventions significantly increased BP. A significant difference was observed in ΔBP/ΔPAT between cycling and both the cold pressor test and IHG exercise (p<0.05). ΔBP/ΔPAT did not differ whether measured via PPG or tonometry., Conclusions: Under the conditions tested, autonomic function does not have a BP-independent effect on PAT where the path includes resistance vessels (PPG signal), likely due to the speed of the wave and the short path length of resistance vessels. Autonomic function therefore does not limit the ability for use of PPG as a signal for potentially estimating BP without a cuff.

Background: In adults, central systolic blood pressure (cSBP) and augmentation index (cAIx) are independently associated with cardiovascular events and mortality. There is increasing interest in central hemodynamic indices in children. We aimed to assess the accuracy of current techniques against invasive intra-aortic measurements in children., Methods: Intra-aortic pressure waveforms were recorded with simultaneous brachial, radial, and carotid waveforms in 29 children (6.7 ± 3.9 years old) undergoing cardiac catheterization. Adult and age-appropriate transfer functions (TFs) (brachial adult: b-aTF; radial adult: r-aTF; radial for 8-year-old children: TF8; and radial for 14-year-old children: TF14) were used to synthesize central aortic waveforms from peripheral waveforms calibrated either to invasively or noninvasively recorded BP. Central hemodynamic indices were measured by pulse wave analysis., Results: cSBP measured from invasively calibrated r-aTF (β = 0.84; intraclass correlation coefficient = 0.91; mean error ± SDD = -1.0 ± 5.0 mm Hg), TF8 (β = 0.78; intraclass correlation coefficient = 0.84; mean error ± SDD = 4.4 ± 5.6 mm Hg), and TF14 (β = 0.82; intraclass correlation coefficient = 0.90; mean error ± SDD = 2.0 ± 4.7 mm Hg)-synthesized central waveforms correlated with and accurately estimated intra-aortic cSBP measurements, while noninvasively calibrated waveforms did not. cAIx derived from TF-synthesized central waveforms did not correlate with intra-aortic cAIx values, and degree of error was TF-dependent., Conclusions: The currently available r-aTF accurately estimates cSBP with invasive pulse pressure calibration, while. Age-appropriate TFs do not appear to provide additional benefit. Accuracy of cAIx estimation appears to be TF dependent., (© American Journal of Hypertension, Ltd 2020. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Background: Central aortic SBP (cSBP) may have superior prognostic value compared with peripheral SBP (pSBP), but noninvasive cSBP measurement techniques have not been formally validated in children and adolescents., Method: This study assessed the accuracy of two automated devices and the radial tonometry/transfer function method (RT-TF) for estimating central pressures and pulse pressure amplification (PPA) in this population, with adherence to validation guidelines for central pressure devices. In 69 children/adolescents aged 3-18 years undergoing clinically indicated aortic catheterization, high fidelity ascending aortic cSBP was measured with a micromanometer-tipped wire and compared with values from SphygmoCor XCEL, Mobil-O-Graph (systolic/diastolic calibration, MoG-C1, or mean/diastolic calibration, MoG-C2) and RT-TF. Reference intra-arterial pSBP was derived from the tonometry pulse calibrated to central mean/diastolic pressures., Results: XCEL, MoG-C1 and MoG-C2 overestimated cSBP by 7.9 ± 6.8 mmHg (mean ± SD), 5.7 ± 10.3 mmHg, and 19.1 ± 14.9 mmHg, exceeding the validation cut-off (5 ± 8 mmHg). Brachial pSBP was also overestimated by XCEL (10.9 ± 8.4 mmHg) and Mobil-O-Graph (11.5 ± 12.3 mmHg). By contrast, central and brachial diastolic pressures were underestimated by the automated devices, albeit mostly within acceptable limits; pulse pressures were, therefore, substantially overestimated. Central-brachial PPA (4.5 ± 4.4 mmHg) was overestimated by XCEL (8.7 ± 3.2 mmHg) and MoG-C1 (11.1 ± 6.4 mmHg), but underestimated by MoG-C2 (-3.0 ± 6.6 mmHg). Given accurate pulse calibration, RT-TF achieved acceptable accuracy for cSBP (-0.2 ± 4.6 mmHg) and central-radial PPA (1.9 ± 5.1 mmHg)., Conclusion: In conclusion, XCEL and Mobil-O-Graph overestimated pSBP and cSBP in children and adolescents. cSBP can be obtained via the same transfer function used in adults, but accurate pressure pulse calibration is critical.Video Abstracts: http://links.lww.com/HJH/B222.

Objective: Measuring arterial pulse transit time (PTT) to estimate blood pressure (BP) without conventional brachial cuff-based measurement is not new, but is a focus of current wearable technologies research. Much research pertains to efficient, accurate sensing of artery-related waveforms, yet the relationship between PTT and BP receives less attention despite being key for accurate BP estimation. This study investigated BP/PTT calibration by quantifying anatomical site variability (n = 10, 3 female, age 30 9 years) and individual variability ( n = 103, 50 female, age 53 22 years)., Methods: BP and pulse wave velocity (PWV) were measured in both seated and supine. Carotid-femoral PWV (cfPWV), carotid-radial PWV (crPWV), and carotid-finger-volume PWV (cvPWV) were measured with the wrist and hand positioned at the level of the upper thigh to achieve the same hydrostatic pressure effect across all measurements., Results: The postural change invoked a small (4 7 mmHg) change in brachial diastolic BP with an additional 27 2 mmHg change in hydrostatic pressure. cfPWV decreased in the supine position (1.75 0.17 m s -1 , p < 0.001), but crPWV and cvPWV were more variable. The calibration term (BP/PWV) across the sample population varied from 6.6 to 98.3 mmHg sm -1 (mean 22 14 mmHg sm -1 ) and was correlated with age, heart rate, diastolic and pulse pressure, and weight. These variables did not explain the majority of the variability (R 2 = 0.248)., Conclusion: There is anatomical site and between-individual variability in the calibration term for BP estimation from PTT., Significance: Using and accurately calculating hydrostatic changes in BP within the individual may be one method to increase the accuracy of this calibration term.

Estimating blood pressure (BP) from pulse arrival time (PAT) by image-based (skin video) photoplethysmography (iPPG) is of increasing interest due to the non-contact method advantage (over cuff-based methods) and potential for BP measurement to be built into portable devices such as mobile phones. The relationship between pulse transit time extracted from iPPG has been investigated during stable BP. The sensitivity of beat-to-beat iPPG-PAT to dynamic changes in BP has not been explored. This study investigated the correlation between iPPG-PAT and diastolic BP (DBP) during 1-minute seated rest and 3-minute isometric handgrip exercise. 15 healthy participants (9 female, 34±13 years) were recruited. Video was recorded from subjects' faces at 30 frames per second using a standard web-camera with simultaneous measurement of the electrocardiogram and noninvasive finger BP. The iPPG waveform was from the averaged green channel intensity of regions of the forehead or cheek. PAT was calculated from the R-wave ofthe electrocardiogram to the foot of the iPPG or finger BP waveform respectively for direct comparison. Handgrip exercise caused a steady increase in DBP (75±9 to 87±13 mmHg, p<0.001). Beat-to-beat iPPG-PAT and DBP was negatively correlated (mena ±SE -1.33±1.70 ms/mmHg, P=0.0024) as was finger-PAT (mean ±SE -0.5S ±0.39 ms/mmHg, P<0.001). The proportion of individual significant negative regression slopes between DBP and finger-PAT and between DBP and iPPG-PAT was not significantly different. Despite high variability of the correlation between iPPG-PAT and DBP among subjects, iPPG-PAT can track dynamic changes in BP.

Objective: N-point moving average (NPMA) is a simplified method of central aortic systolic pressure (CASP) estimation in comparison with the generalized transfer function (GTF). The fundamental difference or similarity between the methods is not established. This study investigates theoretical properties of NPMA relative to GTF and explores the integer and fractional denominator for the averaging process in the NPMA., Methods: Convolution of a specified square wave and the radial (or brachial) blood pressure waveform constituted the NPMA . A single uniform tube model-based TF (MTF) was employed to investigate potential physiological meaning of NPMA. In experimental analysis, invasive, simultaneously recorded aortic and radial pressure waveforms were obtained in 62 subjects under control conditions and following nitroglycerin administration. CASP was estimated by NPMA (), GTF ( ), and MTF (CASP MTF ) from radial waveforms by tenfold cross validation., Results: Theoretical analysis showed that NPMA was an inversed constant TF. Its spectrum matched that of MTF in low frequency (<4 Hz for radial and <5 Hz for brachial) by optimizing reflection coefficient and propagation time. Experiment results showed the NPMA optimized fractional denominator of K = 4.4 significantly decreased the mean difference between CASP NPMA and measured CASP to 0.0 ± 4.7 mmHg from -1.8 ± 4.6 mmHg for integer denominator of K = 4. CASP NPMA correlated with CASP MTF and CASP GTF (r 2 = 0.99 and 0.97, mean difference: -0.3 ± 1.8 and 0.5 ± 2.7 mmHg)., Conclusion: This study demonstrated that NPMA is similar in nature to the GTF.

Background: Current aortic SBP estimation methods require recording of a peripheral pressure waveform, a step with no consensus on method. This study investigates the possibility of aortic SBP estimation from radial SBP and DBP using artificial neural networks (ANN) with [ANNSBP.DBP.heart rate (HR)] and without HR (ANNSBP.DBP)., Methods: Ten-fold cross validation was applied to invasive, simultaneously recorded aortic and radial pressure during rest and nitroglycerin infusion (n = 62 patients). The results of the ANN models were compared with an ANN model using additional waveform features (ANNwaveform), to an N-point moving average method (NPMA) and to existing, validated generalized transfer function (GTF)., Results: Estimated aortic SBP for all methods was on average less than 1 mmHg away from measured aortic SBP with the exception of NPMA (difference 2.0 ± 3.5 mmHg, P = 0.62). Variability of the difference was significantly greater in ANNSBP.DBP.HR and ANNSBP.DBP (both SD of ± 5.9 mmHg, P < 0.001 compared with GTF, ± 4.0 mmHg, P < 0.001). Inclusion of waveform features decreased the variability (ANNwaveform ± 3.9 mmHg, P = 0.264). Estimated aortic SBP in all models was correlated with measured SBP, with ANN models providing statistically similar results to the GTF method, only the NPMA being statistically different (P = 0.031)., Conclusion: These findings indicate that use of radial SBP, DBP, and HR alone can provide aortic SBP estimation comparable with the GTF, albeit with slightly greater variance. Pending noninvasive validation, the technique provides plausible aortic SBP estimation without waveform analysis.

Office blood pressure measurement has been the basis for hypertension evaluation for almost a century. However, the evaluation of blood pressure out of the office using ambulatory or self-home monitoring is now strongly recommended for the accurate diagnosis in many, if not all, cases with suspected hypertension. Moreover, there is evidence that the variability of blood pressure might offer prognostic information that is independent of the average blood pressure level. Recently, advancement in technology has provided noninvasive evaluation of central (aortic) blood pressure, which might have attributes that are additive to the conventional brachial blood pressure measurement. This position statement, developed by international experts, deals with key research and practical issues in regard to peripheral blood pressure measurement (office, home, and ambulatory), blood pressure variability, and central blood pressure measurement. The objective is to present current achievements, identify gaps in knowledge and issues concerning clinical application, and present relevant research questions and directions to investigators and manufacturers for future research and development (primary goal).

Background: Local blood pressure (BP) changes induced by arm tilting may influence pressure wave transmission and reflection. We investigated the effects of upper-limb tilting on radial augmentation index (rAIx) and related central measures [aortic augmentation index (aAIx)]., Methods: In 45 volunteers (age 49 ± 19 years), supine brachial BP and radial artery waveforms were obtained by applanation tonometry with the dominant arm stretched and gently supported in three different positions: at the heart level, with the BP cuff 15 cm above heart level (approximately +30°), and 15 cm below heart level (-30°)., Results: Brachial SBP/DBP was 120/68 ± 17/8 mmHg. Mean arterial pressure changed predictably with arm tilting (99 ± 12 mmHg at -30°, 88 ± 10 mmHg at 0°, 77 ± 11 mmHg at +30°, all P < 0.001). rAIx decreased at -30° (69 ± 22%), and increased at +30° (93 ± 20%) compared with 0° (82 ± 20%, all P less than 0.001). Changes in rAIx (value at +30° minus value at -30°) showed an inverse relationship with age (r = -0.32, P = 0.03). Heart rate, BP and rAIx did not change in the contralateral arm, which was held at the heart level during the examination. aAIx followed the same pattern as rAIx (123 ± 27% at -30°, 144 ± 33% at +30°, 136 ± 31% at 0°, all P less than 0.001); changes in rAIx and aAIx were strongly related each other (r = 0.82, P < 0.001)., Conclusion: Acute gravitational upper-limb BP changes generate opposite, profound changes in rAIx, and major artifactual changes in aAIx. These findings provide a rationale for recommending to keep the upper limb at the heart level during radial waveform assessment.

We present a novel approach to improve the estimation of systolic (SBP) and diastolic blood pressure (DBP) from oscillometric waveform data using variable characteristic ratios between SBP and DBP with mean arterial pressure (MAP). This was verified in 25 healthy subjects, aged 28 ± 5 years. The multiple linear regression (MLR) and support vector regression (SVR) models were used to examine the relationship between the SBP and the DBP ratio with ten features extracted from the oscillometric waveform envelope (OWE). An automatic algorithm based on relative changes in the cuff pressure and neighbouring oscillometric pulses was proposed to remove outlier points caused by movement artifacts. Substantial reduction in the mean and standard deviation of the blood pressure estimation errors were obtained upon artifact removal. Using the sequential forward floating selection (SFFS) approach, we were able to achieve a significant reduction in the mean and standard deviation of differences between the estimated SBP values and the reference scoring (MLR: mean ± SD = -0.3 ± 5.8 mmHg; SVR and -0.6 ± 5.4 mmHg) with only two features, i.e., Ratio2 and Area3, as compared to the conventional maximum amplitude algorithm (MAA) method (mean ± SD = -1.6 ± 8.6 mmHg). Comparing the performance of both MLR and SVR models, our results showed that the MLR model was able to achieve comparable performance to that of the SVR model despite its simplicity.

Objective: We validated against invasive measurements a measure of central SBP based on the QKD interval. The present objective is a comparison to the SphygmoCor device., Materials and Methods: A first cohort was used to redefine an algorithm for estimating ascending aorta SBP (cSBP) with respect to SphygmoCor. This algorithm was then tested in a second cohort under static conditions and in a third cohort during a head-up tilt to study blood pressure variations., Results: The first cohort (36 patients, mean age: 46 ± 20 years, SBP: 114 ± 19 mm Hg) defined the estimation algorithm as cSBP =62.687+1.35 × meanBP-0.207 × heart rate-0.251 × height-0.1 × QKD (mean difference with SphygmoCor=0 ± 7 mmHg).In the second cohort (105 patients, mean age: 51 ± 19 years, SBP: 132 ± 22 mmHg), the average difference between the two techniques was 2 ± 6 mm Hg (R=0.93). The dynamic cohort included 31 patients (mean age: 49 ± 23 years, SBP: 110 ± 19 mmHg) with 224 pairs of measurement. We studied the changes in central blood pressures compared with the basal state of each of the two techniques during head-up tilt. With QKD, the average cSBP was 104 ± 19 mmHg, the average variation was -13.00 mmHg ± 15 (range 7-74 mmHg). With SphygmoCor, average cSBP was 10  mmHg ± 18, the average variation was -14 mmHg   ± 16 (range 2-81 mmHg). The variations in blood pressure with the two techniques were well correlated (R=0.93)., Conclusion: cSBP estimation based on the QKD interval is comparable in precision to the SphygmoCor. Its ability to measure cSBP variations suggests that it could be employed for ambulatory measurements over 24 h.

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

The most common method of clinical measurement of arterial blood pressure is by means of the cuff sphygmomanometer. This instrument has provided fundamental quantitative information on arterial pressure in individual subjects and in populations and facilitated estimation of cardiovascular risk related to levels of blood pressure obtained from the brachial cuff. Although the measurement is taken in a peripheral limb, the values are generally assumed to reflect the pressure throughout the arterial tree in large conduit arteries. Since the arterial pressure pulse becomes modified as it travels away from the heart towards the periphery, this is generally true for mean and diastolic pressure, but not for systolic pressure, and so pulse pressure. The relationship between central and peripheral pulse pressure depends on propagation characteristics of arteries. Hence, while the sphygmomanometer gives values of two single points on the pressure wave (systolic and diastolic pressure), there is additional information that can be obtained from the time-varying pulse waveform that enables an improved quantification of the systolic load on the heart and other central organs. This topical review will assess techniques of pressure measurement that relate to the use of the cuff sphygmomanometer and to the non-invasive registration and analysis of the peripheral and central arterial pressure waveform. Improved assessment of cardiovascular function in relation to treatment and management of high blood pressure will result from future developments in the indirect measurement of arterial blood pressure that involve the conventional cuff sphygmomanometer with the addition of information derived from the peripheral arterial pulse.

Aortic stiffness, an independent predictor of cardiovascular risk and all-cause mortality, can be estimated non-invasively by measuring carotid to femoral (aortic) pulse wave velocity (aPWV). The Vicorder device has been developed to measure aPWV with little operator training in a non-intrusive manner. The aim of this study was to assess the repeatability of aPWV measured with the Vicorder device and to compare aPWV values with those obtained using the SphygmoCor system. Vicorder and SphygmoCor aPWV was assessed in 122 subjects (53+/-18 years, 46 male) using both the manufacturers' and a standardized approach. Vicorder aPWV measurement proved to be highly repeatable (within-subject coefficient of variation 2.8%). Transit time differed significantly between the two devices (mean difference 22+/-9 ms, P<0.001), independent of the different algorithms used to calculate transit time. However, aPWV was similar between the two devices (mean difference 0.31+/-1.54 m s(-1), P<0.001) though with an inherent bias toward lower Vicorder aPWV values at high values of SphygmoCor aPWV. Bias was reduced by subtracting the additional femoral artery segment measured by the Vicorder device, also bringing the measure of transit time in closer agreement to SphygmoCor values (mean difference 5+/-9 ms, P<0.001). Transit time values significantly differed between the two devices and the Vicorder device reported lower aPWV values at higher SphygmoCor values of aPWV. This difference in transit time and inherent bias was reduced when adjustment for the additional femoral artery segment measured by the Vicorder device was made.

Wave reflections affect the proximal aortic pressure and flow waves and play a role in systolic hypertension. A measure of wave reflection, receiving much attention, is the augmentation index (AI), the ratio of the secondary rise in pressure and pulse pressure. AI can be limiting, because it depends not only on the magnitude of wave reflection but also on wave shapes and timing of incident and reflected waves. More accurate measures are obtainable after separation of pressure in its forward (P(f)) and reflected (P(b)) components. However, this calculation requires measurement of aortic flow. We explore the possibility of replacing the unknown flow by a triangular wave, with duration equal to ejection time, and peak flow at the inflection point of pressure (F(tIP)) and, for a second analysis, at 30% of ejection time (F(t30)). Wave form analysis gave forward and backward pressure waves. Reflection magnitude (RM) and reflection index (RI) were defined as RM=P(b)/P(f) and RI=P(b)/(P(f)+P(b)), respectively. Healthy subjects, including interventions such as exercise and Valsalva maneuvers, and patients with ischemic heart disease and failure were analyzed. RMs and RIs using F(tIP) and F(t30) were compared with those using measured flow (F(m)). Pressure and flow were recorded with high fidelity pressure and velocity sensors. Relations are: RM(tIP)=0.82RM(mf)+0.06 (R(2)=0.79; n=24), RM(t30)=0.79RM(mf)+0.08 (R(2)=0.85; n=29) and RI(tIP)=0.89RI(mf)+0.02 (R(2)=0.81; n=24), RI(t30)=0.83RI(mf)+0.05 (R(2)=0.88; n=29). We suggest that wave reflection can be derived from uncalibrated aortic pressure alone, even when no clear inflection point is distinguishable and AI cannot be obtained. Epidemiological studies should establish its clinical value.

This review analyses methods and devices used worldwide to evaluate the arterial stiffness. Three main methodologies are based upon analysis of pulse transit time, of wave contour of the arterial pulse, and of direct measurement of arterial geometry and pressure, corresponding to regional, systemic and local determination of stiffness. They are used in clinical laboratory and/or in clinical departments. Particular attention is given to the reproducibility data in literature for each device. This article summarizes the discussion of the dedicated Task Force during the first Conference of Consensus on Arterial Stiffness held in June 2000 (Paris, France).