P6.13: Impact of Calibration on Estimates of Central Blood Pressure

We included 122 patients with type-II-diabetes and hypertension. They were characterized as having controlled (CH), uncontrolled (UH) or resistant (RH) hypertension based on ambulatory blood pressure measurement and number of antihypertensive agents. CBP was estimated using Sphygmocor. We calibrated the radial pressure wave as recommended by the manufacturer using brachial systolic (BSBP) and diastolic (BDBP) BP and used the generalized transfer function for estimation of the aortic pressure waveform. Afterwards we recalibrated the radial pressure wave using BDBP and mean arterial pressure (BMAP). Data were analyzed offline in customized software. Estimates of CSBP were significantly correlated (R2=0.83, P<0.0001 at baseline and R2=0.71, P<0.0001 after six months). As shown in figures 1 and 2 CSBP was 6.1 mmHg to 6.6 mmHg lower when calibrated with BSBP and BDBP and variation of difference ranged from 14.6 mmHg to 22 mmHg. Differences between BSBP and CSBP lost significance in patients with RH after six months when alternatively calibrated with BDBP and BMAP as did reduction in CSBP. Although we found good correlation between estimates of CBP using either calibration, variation of difference was high suggesting that the difference between the 2 calibration methods is more than a systematic error. And our results show that it could be important to take into account measures used for calibration when interpreting clinical effect on non-invasive estimates of CBP.