Hypertension Research (2010) 33, 592–599 & 2010 The Japanese Society of Hypertension All rights reserved 0916-9636/10 $32.00 www.nature.com/hr ORIGINAL ARTICLE Estimation of central systolic blood pressure using an oscillometric blood pressure monitor Hao-Min Cheng1,2, Kang-Ling Wang2,3, Ying-Hwa Chen2,3, Shing-Jong Lin1,4, Lung-Ching Chen2,3, Shih-Hsien Sung2,3, Philip Yu-An Ding2,3, Wen-Chung Yu2,3, Jaw-Wen Chen1,4 and Chen-Huan Chen1,2,4 Current noninvasive techniques for assessing central aortic pressure require the recording of an arterial pressure wave using a high-fidelity applanation tonometer. We therefore developed and validated a novel method to estimate the central aortic systolic pressure using an oscillometric blood pressure monitor alone. Invasive high-fidelity right brachial and central aortic pressure waves, and left-brachial pulse volume plethysmography from an oscillometric blood pressure monitor, were obtained at baseline and 3 min after administration of sublingual nitroglycerin in 100 patients during cardiac catheterization. In the initial 50 patients (Generation Group), Central systolic blood pressure was predicted by a multi-variate prediction model generated from the comprehensive analysis of the invasive brachial pressure wave, including brachial late-systolic shoulder pressure value and parameters related to wave reflection and arterial compliance. Another prediction model was similarly constructed from the noninvasively calibrated pulse volume plethysmography. Both models were validated in the subsequent 50 patients (Validation Group) with results: r¼0.98 (Po0.001) and mean difference¼0.5±4.5 (95% confidence interval À8.3 to 9.3) mm Hg for the invasive model, and r¼0.93 (Po0.001) and mean difference¼À0.1±7.6 (95% confidence interval À15.0 to 14.8) mm Hg for the noninvasive model. Thus, our results indicate that central aortic systolic blood pressure could be estimated by analysis of the noninvasive brachial pressure wave alone from an oscillometric blood pressure monitor. Hypertension Research (2010) 33, 592–599; doi:10.1038/hr.2010.37; published online 26 March 2010 Keywords: central blood pressure; oscillometric signals; pressure wave reflection; pulse volume plethysmography INTRODUCTION calibrated radial pressure wave, firstly proposed by Takazawa et al,2 Aortic and carotid systolic and pulse pressures, commonly referred to can be used directly to approximate central SBP without the need for a as the central blood pressure, may be different from the peripheral generalized transfer function.11–14 In either approach, a high-fidelity pressure in the radial and brachial arteries.1,2 The discrepancy between arterial tonometer is required to obtain faithful recording, in addition the central and peripheral blood pressures is mainly caused by the to an oscillometric blood pressure monitor. Therefore, we developed central-to-peripheral amplification of the pressure pulse and may and validated a novel method to estimate the central aortic SBP using magnify with administration of vasoactive agents.2–4 Furthermore, the oscillometric signals from an oscillometric blood pressure monitor. recent evidence from epidemiological studies,5,6 clinical observation,7 and a large clinical trial8 suggest that central blood pressure is more relevant than peripheral blood pressure in predicting target organ METHODS damage and cardiovascular outcomes. However, the implementation Study population of central blood pressure in the daily practice of hypertension Subjects referred for diagnostic catheterization for coronary anatomy through management may require the availability of its reliable measurements radial approach were potential candidates of the study. Subjects were not to both medical care providers in the clinics and patients at home. included if they had acute coronary syndrome, peripheral arterial disease, Central blood pressure can be estimated noninvasively from the rhythms other than normal sinus rhythm, or more than 3 mm Hg pressure radial or carotid pressure waves recorded by applanation tonometry.6,9 difference between left and right arms. The enrollment of the study subjects was prospective but not consecutive, depending on the daily schedules of the To obtain central blood pressure, the radial pressure wave calibrated cardiac catheterization and the investigators. Mid-upper arm circumferences, with brachial cuff systolic blood pressure (SBP) and diastolic blood height, waistline, body weight, and personal medical history were obtained pressure (DBP) can be mathematically transformed into a central before the cardiac catheterization. The study protocol adhered to the principles 9,10 aortic pressure wave using a generalized transfer function. Alter- of the Declaration of Helsinki and was approved by the Institutional Review natively, identification of the late systolic shoulder (SBP2) of the Board at Taipei Veterans General Hospital. Informed consent was obtained 1Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan; 2Department of Medicine, National Yang-Ming University, Taipei, Taiwan; 3Department of Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan and 4Cardiovascular Research Center, National Yang-Ming University, Taipei, Taiwan Correspondence: Dr C-H Chen, Department of Medical Research and Education, Taipei Veterans General Hospital, No. 201, Sec. 2, Shih-Pai Road, Taipei,Taiwan. E-mail: [email protected] Part of the work was presented at 2009 American College of Cardiology Annual Scientific Meeting. Received 17 December 2009; revised 29 January 2010; accepted 3 February 2010; published online 26 March 2010 Oscillometric central BP monitor H-M Cheng et al 593 from all patients. A total of 100 subjects fulfilled the inclusion and exclusion the level of mid-humerus. The micromanometer has a flat frequency response criteria and completed the study. Their characteristics are given in Table 1. The from 0 to 1000 Hz. The frequency range of our catheterization laboratory first 50 subjects were designated as the Generation Group (age range 36–82 amplifier is 0–400 Hz for pressure measurement (À50 to 400 mm Hg) with the years) to produce the invasive and non-invasive prediction models. The accuracy of ±1mmHg or ±3% exclusive of transducer. Baseline invasive subsequent 50 subjects were prospectively enrolled to serve as the Validation brachial pressure waves were recorded for consecutive 20–30 beats to cover at Group (age range 29–90 years) for assessing the performance of the prediction least two respiratory cycles. Afterwards, the catheter was advanced further to the models. The two Groups differed slightly in the arm circumference, diagnosis of ascending aorta in less than 10 s. The central aortic pressure waves were then hypertension and coronary artery disease and the cuff DBP values (Table 1). recorded simultaneously with left-arm PVP performed at mean cuff pressure of 60 mm Hg for 30 s, followed by automatic measuring of the left brachial cuff blood pressures. Subsequently, a sublingual nitroglycerin (NTG) was Study protocol administered. Three minutes later, the left brachial cuff blood pressures were With the study subject resting on the catheterization table, cuff blood pressure measured again, followed by simultaneous recording of the central aortic values over both arms were simultaneously obtained to ensure minimal pressure waves and left-arm PVP. Immediately after the completion of the pressure difference between both arms and the absence of peripheral arterial post-NTG PVP, the micromanometer catheter was pulled back until its tip was disease, using a commercially available oscillometric blood pressure monitor at the level of mid-humerus for recording of 20–30 beats of invasive brachial (VP-2000, Colin Corporation, Komaki, Japan) with cuff size of 11Â20 cm, pressure waves, and then was removed to continue the routine diagnostic 13Â24.5 cm or 15.5Â34 cm, corresponding to arm circumference of 17 to coronary angiography. The study procedure, from cannulation of right radial 23 cm, 20 to 32 cm and 30 to 38 cm, respectively. After taking two consecutive artery to removal of the micromanometer catheter, could be completed in less measurements of cuff blood pressure, the blood pressure monitor performed than 10 min. All signals were digitized instantaneously at a sampling frequency the pulse volume recording, also known as pulse volume plethysmography of 250 Hz for off-line analysis. Left ventricular ejection fraction (LV EF) was (PVP), at user-defined levels of cuff pressure. The validity and reproducibility routinely measured from single-plane left ventriculogram after diagnostic ofthedevicehavebeendocumented.15 The recorded cuff pressure signals coronary angiography. during PVP have been found to correspond to the intra-arterial pressure contours.16 The cuff blood pressure readings were the averages of two Data analysis consecutive measurements. The digitized signals were analyzed using custom-designed software on a No sedatives or premedications were used before or during the catheteriza- commercial software package (Matlab, version 4.2, The MathWorks, Natick, tion procedure. After local injection of 2–3 cc 1% lidocaine and successful MA, USA). All processed individual signals were subject to fully automatic placement of a 6F arterial sheath in the right radial artery, 2.5 mg verapamil was batch analysis to avoid inter- and intra-observer variations. Consecutive 20–30 administered intra-arterially to prevent vasospasm during the catheterization.