American Journal of Hypertension Advance Access published June 17, 2016
Original Article
Comparison of Central Blood Pressure Estimated by a Cuff-Based Device With Radial Tonometry Xiaoqing Peng,1 Martin G. Schultz,1 Walter P. Abhayaratna,2 Michael Stowasser,3 and James E. Sharman1
METHODS Consecutive CuffCBP (SphygmoCor Xcel) and TonCBP (SphygmoCor 8.1) duplicate recordings were measured in 182 people with treated hypertension (aged 61 ± 7 years, 48% male). Agreement between methods was assessed using standard calibration with brachial SBP and DBP (measured with the Xcel device), as well as with brachial mean arterial pressure (MAP; 40% form factor method) and DBP. RESULTS The mean difference ± SD for central SBP (cSBP), central DBP (cDBP), and central PP (cPP) between methods were −0.89 ± 3.48 mm Hg (intra-class correlation (ICC) 0.977; 95% confidence interval (CI)
0.973–0.982), −0.50 ± 1.54 mm Hg (ICC 0.992, 95% CI 0.987–0.993), and −0.42 ± 3.57 mm Hg (ICC 0.966, 95% CI 0.958–0.972), indicating good agreement. Wider limits of agreement were observed for central AP (cAP) and central AIx (cAIx) (−0.91 ± 5.31 mm Hg; ICC 0.802; 95% CI 0.756–0.839, −0.99 ± 10.91%; ICC 0.749; 95% CI 0.691–0.796). Re-calibration with brachial MAP and DBP resulted in an overestimation of cSBP with CuffCBP compared with TonCBP (8.58 ± 19.06 mm Hg, ICC 0.164, 95% CI −0.029 to 0.321).
CONCLUSION cSBP, cDBP, and cPP derived from CuffCBP are substantially equivalent to TonCBP, although the level of agreement is dependent on calibration method. Further validity testing of CuffCBP by comparison with invasively measured central BP will be required. Keywords: arterial blood pressure; blood pressure; blood pressure determination; diagnostic equipment; hemodynamics; hypertension; oscillometry; pulse wave analysis. doi:10.1093/ajh/hpw063
Central blood pressure (BP) is associated with cardiovascular events and all-cause mortality independent of brachial BP,1–4 and is recognised as being of pathophysiological, pharmacological, and therapeutic interest.5 Central BP can be measured noninvasively using several available methods, the most widely published being radial tonometry. This technique enables derivation of a central (aortic) BP waveform from the radial BP waveform via application of a validated generalized transfer function (GTF).6 Nonetheless, this device has not been widely utilized in routine clinical practice, in part due to operator-dependency and complexity of measurement. The potential clinical applicability of central BP estimation has been improved recently with the development of a number of “cuff-based” devices.7 One such device, Sphygomocor Xcel (AtCor Medical, Sydney, Australia), records cuff brachial artery pressure waveforms at sub-diastolic pressure, and derives central BP via a brachial-to-aortic GTF.
Estimation of central BP using the Xcel cuff-based device has been shown to be comparable to radial tonometry in one study comprising 30 healthy subjects.8 However, performance of the Xcel device among people with hypertension has not been undertaken, nor has the effect of different calibration methods been assessed (an issue that could have ramifications on accuracy of central BP estimation).9 The aim of this current study was to compare central BP (systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP)) and central BP waveform indices (augmentation pressure (AP), and augmentation index (AIx)) estimated from the Xcel device (CuffCBP) with the radial tonometry method (TonCBP) in a large, well-characterised population of hypertensive patients, using (i) standard brachial systolic blood pressure (bSBP) and brachial diastolic blood pressure (bDBP) for calibration, and (ii) following re-calibration with brachial mean arterial pressure (bMAP) and bDBP. Additionally, we sought to compare differences in
Correspondence: James E. Sharman (
[email protected]).
1Menzies Institute for Medical Research, University of Tasmania, Hobart, Australia; 2College of Medicine, Biology and Environment, Australian National University, Canberra, Australian Capital Territory, Australia; 3Princess Alexandra Hospital, School of Medicine, The University of Queensland, Brisbane, Australia.
Initially submitted February 10, 2016; date of first revision February 24, 2016; accepted for publication May 25, 2016.
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American Journal of Hypertension 1
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BACKGROUND New techniques that measure central blood pressure (BP) using an upper arm cuff-based approach require performance assessment. The aim of this study was to compare a cuff-based device (CuffCBP) to estimate central BP indices (systolic BP (SBP), diastolic BP (DBP), pulse pressure (PP), augmentation pressure (AP), augmentation index (AIx)) with noninvasive radial tonometry (TonCBP).
Peng et al.
estimated central BP indices when stratified by participant clinical characteristics including age, sex, and antihypertensive medications. METHODS
Study protocol. All participants attended clinic facilities for baseline assessment. Each participant was asked to refrain from consuming caffeine-containing products, cigarettes, alcohol, and to avoid heavy meals and exercise before the visit. Anthropometric measures were recorded prior to BP measurements. Following guideline recommendations,5 seated BP measures were recorded using correct cuff size over the upper-arm supported at heart level. CuffCBP and TonCBP measurements were recorded sequentially at 8 and 10 minutes following quiet seated rest. CuffCBP. CuffCBP central BP waveform indices were estimated by an oscillometric cuff-based device (Sphygomocor Xcel, AtCor Medical, West Ryde, Australia). Measurement involved the placement of a BP cuff on the upper-arm and automatic recording of standard oscillometric brachial BP, immediately after which the cuff automatically re-inflated to sub-diastolic pressure where it was held for a ten second period during which time a brachial artery waveform was captured. This brachial BP waveform was default calibrated with the bSBP and bDBP values as measured during the first inflation. A device specific brachial-aortic GTF was then applied to derive a central BP waveform. Central PP (cPP) was defined as the difference between cSBP and central DBP (cDBP). Central AP (cAP) was calculated as the difference between the second and the first systolic peaks (P2-P1). Central AIx (cAIx) was defined as the ratio of cAP to cPP × 100. The CuffCBP estimated cSBP was also recalibrated using bMAP and bDBP applied to the exported digital waveform signal, with bMAP calculated using a form factor equation, 2 American Journal of Hypertension
TonCBP. TonCBP central BP waveform indices were estimated immediately after each CuffCBP measurement. A highfidelity radial pressure sensor (SPC-301; Millar Instruments, Houston, TX) was used to applanate the radial artery, and a 10-second recording of the radial BP waveform was captured to generate an ensemble average radial BP waveform. A GTF was then applied to derive a central BP waveform. Waveforms were calibrated firstly with bSBP and bDBP values measured by CuffCBP. Waveforms were also recalibrated using bMAP and bDBP as described for CuffCBP. Central BP waveform indices (cPP, cAP, and cAIx) were also calculated as described for CuffCBP. The quality of the radial BP waveform was evaluated by a built-in operator index, with only waveforms with an operator index >75 accepted in this study. Statistical analysis. All data were analyzed using SPSS for Windows software (version 22.0; SPSS Inc., Chicago, IL). CuffCBP and TonCBP measures were compared using intraclass correlation coefficient (ICC) with absolute agreement. Linear regression was used to evaluate the relationship of measures of CuffCBP and TonCBP. Bland–Altman analysis was performed to assess agreement and variability between CuffCBP and TonCBP. Systematic bias was assessed from within Bland–Altman plots by Pearson correlation. Comparisons of the mean difference between TonCBP and CuffCBP in subgroups were performed using independent-samples t-test or one-way analysis of variance with a Z-statistic calculated to compare differences in regression slopes. P
