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

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          Abstract

          Objectives:

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

          Methods:

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

          Results:

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

          Conclusion:

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

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          Most cited references20

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          Measuring agreement in method comparison studies.

          Agreement between two methods of clinical measurement can be quantified using the differences between observations made using the two methods on the same subjects. The 95% limits of agreement, estimated by mean difference +/- 1.96 standard deviation of the differences, provide an interval within which 95% of differences between measurements by the two methods are expected to lie. We describe how graphical methods can be used to investigate the assumptions of the method and we also give confidence intervals. We extend the basic approach to data where there is a relationship between difference and magnitude, both with a simple logarithmic transformation approach and a new, more general, regression approach. We discuss the importance of the repeatability of each method separately and compare an estimate of this to the limits of agreement. We extend the limits of agreement approach to data with repeated measurements, proposing new estimates for equal numbers of replicates by each method on each subject, for unequal numbers of replicates, and for replicated data collected in pairs, where the underlying value of the quantity being measured is changing. Finally, we describe a nonparametric approach to comparing methods.
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            Prospective evaluation of a method for estimating ascending aortic pressure from the radial artery pressure waveform.

            Pressure wave reflection in the upper limb causes amplification of the arterial pulse so that radial systolic and pulse pressures are greater than in the ascending aorta. Wave transmission properties in the upper limbs (in contrast to the descending aorta and lower limbs) change little with age, disease, and drug therapy in adult humans. Such consistency has led to use of a generalized transfer function to synthesize the ascending aortic pressure pulse from the radial pulse. Validity of this approach was tested for estimation of aortic systolic, diastolic, pulse, and mean pressures from the radial pressure waveform. Ascending aortic and radial pressure waveforms were recorded simultaneously at cardiac surgery, before initiation of cardiopulmonary bypass, with matched, fluid-filled manometer systems in 62 patients under control conditions and during nitroglycerin infusion. Aortic pressure pulse waves, generated from the radial pulse, showed agreement with the measured aortic pulse waves with respect to systolic, diastolic, pulse, and mean pressures, with mean differences <1 mm Hg. Control differences in Bland-Altman plots for mean+/-SD in mm Hg were systolic, 0.0+/-4.4; diastolic, 0.6+/-1.7; pulse, -0.7+/-4.2; and mean pressure, -0.5+/-2.0. For nitroglycerin infusion, differences respectively were systolic, -0.2+/-4.3; diastolic, 0.6+/-1.7; pulse, -0.8+/-4.1; and mean pressure, -0.4+/-1.8. Differences were within specified limits of the Association for the Advancement of Medical Instrumentation SP10 criteria. In contrast, differences between recorded radial and aortic systolic and pulse pressures were well outside the criteria (respectively, 15.7+/-8.4 and 16.3+/-8.5 for control and 14.5+/-7.3 and 15.1+/-7.3 mm Hg for nitroglycerin). Use of a generalized transfer function to synthesize radial artery pressure waveforms can provide substantially equivalent values of aortic systolic, pulse, mean, and diastolic pressures.
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              Estimation of central aortic pressure waveform by mathematical transformation of radial tonometry pressure. Validation of generalized transfer function.

              Central aortic pressures and waveform convey important information about cardiovascular status, but direct measurements are invasive. Peripheral pressures can be measured noninvasively, and although they often differ substantially from central pressures, they may be mathematically transformed to approximate the latter. We tested this approach, examining intersubject and intrasubject variability and the validity of using a single averaged transformation, which would enhance its applicability. Invasive central aortic pressure by micromanometer and radial pressure by automated tonometry were measured in 20 patients at steady state and during hemodynamic transients (Valsalva maneuver, abdominal compression, nitroglycerin, or vena caval obstruction). For each patient, transfer functions (TFs) between aortic and radial pressures were calculated by parametric model and results averaged to yield individual TFs. A generalized TF was the average of individual functions. TFs varied among patients, with coefficients of variation for peak amplitude and frequency at peak amplitude of 24.9% and 16.9%, respectively. Intrapatient TF variance with altered loading (> 20% variation in peak amplitude) was observed in 28.5% of patients. Despite this, the generalized TF estimated central arterial pressures to < or = 0.2 +/- 3.8 mm Hg error, arterial compliance to 6 +/- 7% accuracy, and augmentation index to within -7% points (30 +/- 45% accuracy). Individual TFs were only marginally superior to the generalized TF for reconstructing central pressures. Central aortic pressures can be accurately estimated from radial tonometry with the use of a generalized TF. The reconstructed waveform can provide arterial compliance estimates but may underestimate the augmentation index because the latter requires greater fidelity reproduction of the wave contour.
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                Author and article information

                Journal
                J Hypertens
                J. Hypertens
                JHYPE
                Journal of Hypertension
                Lippincott Williams & Wilkins
                0263-6352
                1473-5598
                April 2014
                10 March 2014
                : 32
                : 4
                : 865-872
                Affiliations
                [a ]International Centre for Circulatory Health, Imperial College London & Imperial College Healthcare NHS Trust
                [b ]Department of Bioengineering, Imperial College London, London, UK
                Author notes
                Correspondence to Alun Hughes, UCL Institute of Cardiovascular Science, University College London, 170 Tottenham Court Road, London W1T 7HA, UK. Tel: +44 0 20 3108 2350; e-mail: a.Hughes@ 123456imperial.ac.uk
                Article
                10.1097/HJH.0000000000000082
                3966921
                24379000
                1888341f-16f7-4142-8122-125cde679121
                © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivitives 3.0 License, where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially.

                History
                : 11 September 2013
                : 20 November 2013
                Categories
                ORIGINAL PAPERS: Blood vessels
                Custom metadata
                TRUE

                brachial cuff,central blood pressure,invasive,noninvasive,tonometry

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