10.4 COMPARISON OF BLOOD PRESSURE VARIABILITY CALCULATED FROM PERIPHERAL AND DERIVED AORTIC BLOOD PRESSURE

Abstract

Background: Systolic blood pressure variability (SBPV), conventionally calculated from peripheral sites such as the arm or finger, may be of more utility when computed from central aortic values, as this has greater applicability to the heart and the baroreceptor function, due to central location of baroreceptors. As the relationship between aortic and peripheral blood pressure is frequency dependent, particularly in the range of physiological heart rate frequencies, peripheral and aortic SBPV may not be identical. Differences between peripheral and aortic SBPV have not been previously quantified. Methods: In this study, peripheral and derived aortic SBPV was calculated in 30 healthy subjects (25–62 years). Continuous finger blood pressure was measured for 10 minutes in each subject (Finapres) and aortic blood pressure derived using a general transfer function. SBPV was quantified using a Short Time Fourier Transform in a time-frequency method to calculate the ratio of average power across the low frequency power band (0.05–0.15 Hz) to the high frequency power band (0.15–0.4 Hz). Results: Aortic SBPV (power band ratio) was correlated with peripheral SBPV (r2=0.961, p<0.001) with a mean difference of −0.67±2.07. However, there was a bias toward peripheral SBPV overestimation compared to aortic SBPV for higher values of SBPV. Conclusions: This study demonstrates that peripheral SBPV cannot be taken as equivalent to aortic SBPV, particularly where the low frequency to high frequency power ratio of SBPV is of higher magnitude.