Author + information
- Hao-Min Cheng, MD, PhD,
- Shao-Yuan Chuang, PhD and
- Chen-Huan Chen, MD∗ ()
- ↵∗National Yang-Ming University, Department of Public Health, 155 Li-Long St. Sec. 2, Shih-Pai, Taiwan 11221, Taipei
We thank Dr. Weber and colleagues for their interest in and comments on our paper (1) and are delighted that they also agree that establishment of event-based cutoff values for central blood pressures (BP) is an important step forward.
In the derivation cohort of our study, central BP were estimated, with carotid BP derived from carotid pressure waveforms calibrated to cuff brachial mean blood pressure (MBP) and diastolic blood pressure (DBP). By contrast, central BP in the validation cohort was obtained from radial pressure waveforms calibrated to cuff brachial systolic blood pressure (SBP) and DBP, and a validated generalized transfer function using the SphygmoCor device (AtCor Medical, West Ryde, New South Wales, Australia). It has been argued that cuff brachial MBP/DBP should be used in the calibration procedures for radial pressure waveforms to account for the small brachial-to-radial pressure amplification (2). However, cuff SBP usually underestimates and cuff DBP overestimates the invasive brachial BP. It is very likely that the calculated cuff MBP also suffers from a substantial error, no matter whether the 0.33 or 0.4 formula is used. We have demonstrated that whenever the cuff MBP underestimates the invasive MBP and the cuff DBP overestimates the invasive DBP, the pressure waveform calibrated by cuff MBP/DBP becomes severely compressed and produces a huge underestimation of the invasive central SBP. Instead, calibration to cuff SBP/DBP produces an acceptable error. We agree that the potential error in central BP readings might be large and might compromise the classification of patients. However, noninvasive brachial BP measurements may suffer from the same error as well (3).
Our study aimed to derive and validate the diagnostic thresholds of central BP for the diagnosis of hypertension and the corresponding discriminatory power for predicting cardiovascular mortality (1). We didn't account for the brachial BP in the multivariate model because we purported to validate the derived central BP cutoffs for predicting cardiovascular risks. The incorporation of brachial BP, with its close correlations with central BP, could cause considerable confusion of the results. However, it is reassuring that, as shown in the reclassification analysis in the Online Table 1 of our study (1), central BP had an additional contribution to the prediction of future cardiovascular outcomes across traditional cardiovascular risk factors, as compared with brachial BP.
Please note: This work was supported in part by a grant from the National Science Council (NSC 96-2314-B-010-035-MY3), an intramural grant from the Taipei Veterans General Hospital (grant V98C1-028), Grants-in-Aid from the Research Foundation of Cardiovascular Medicine (Taipei, Taiwan, Republic of China), Research and Development contract NO1-AG-1-2118, the Intramural Research Program of the National Institute on Aging, National Institutes of Health, National Health Research Institutes in Taiwan (NHRI-EX93-9225PP, NHRI-EX94-9225PP, NSC 5-2314-B-001-012-MY3) and by the Department of Health in Taiwan (DOH80-27, DOH81-021, DOH8202-1027, DOH83-TD-015, and DOH84-TD-006). Microlife Co., Ltd., and National Yang-Ming University have signed a contract for transfer of the noninvasive central blood pressure estimating technique.
- American College of Cardiology Foundation
- Cheng H.M.,
- Chuang S.Y.,
- Sung S.H.,
- et al.
- Smulyan H.,
- Safar M.E.