Pulse wave for analysis: comparation of data obtained with different methods

Background Central aortic blood pressure has received in recent years more interest as a more accurate predictor of outcome than brachial artery blood pressure. Number of techniques exists to assess the aortic pressure. Objetive To compare the values of central systolic pressure and peripheral augmentation index in hypertensive patients calculated by the Omron and the SphygmoCor systems. Methods Eighty-four (84) hypertensive subjects (40 males and 44 females), mean aged 58 ± 12 years were examined at the Hypertension Unit at San Luca Hospital (Istituto Auxologico Italiano) Milan Italia. All 84 subjects were treated with antihypertensive therapy. Results Statistics Data were analyzed using Statistica software version 9.0 (StatSoft Tulsa, Oklahoma. Inc). Pearson product–moment correlation coefficient (r) was used to determine associations between variables. Bland–Altman plots were used to assess agreement between methods. Dependent t tests were used to compare means. 1) Comparison between central pressure values provided by Sphygmocor and by Omron. There was a good correlation between cSBPsphy and cSBPomr (r=0.76; r²=58, P=< 0.001), but with a mean difference of -16 ± 13 mmHg, indicating a systematic underestimation by Omron device. 2) Comparison between cSBPsphy and pSBP2omr values showed also a good correlation, r= 0.74; r²=55, P <0.001, with a mean difference of only -0.8 ± 13 mmHg, indicating a good mean agreement. 3) Peripheral augmentation index measured by both devices showed close correlation (r=0.66; r²= 43 P < 0.001) but a mean difference Sphy-Omr of 62 ± 19, indicating important overestimation by the Sphygmocor. Discussion When comparing the original pSBP2omr values with the cSBP calculated by SphygmoCor, the mean difference was only -0.8 ± 13 mmHg. Direct invasive measurements of aortic pressure must be developed for a better algorithm to convert pSBP2omr to cSBPomr. Peripheral augmentation index is calculated by the same formula in both devices, there was a good correlation between the values of pAIx calculated by each device (r=0.66; r²= 0.43, P=< 0.001), but a very poor agreement. In summary estimated cSBP provided by the Omron system good correlation and limited agreement with values obtained from the SphygmoCor system. Conversely cSBP with Sphygmocor showed good agreement with pSBP2 measured by OMRON. Further investigations should compare estimates of pSBP2 by the Omron system to direct measurements of aortic pressure by cardiac catheterisation. The results suggest that the Omron system has an accurate of pSBP2 which show strong correlations with those of the SphygmoCor device.