Effect of calibration method on estimation of central pressure at rest and during cold pressor testing

Abstract

Non-invasive estimates of central blood pressure (CP) using a radial transfer function would be valuable in physiologic studies since central systolic pressure (CSP) better reflects myocardial demand. However, this technique appears to be dependent on the calibration method. The purpose of this study was to determine the effect of different calibration procedures on CP estimates at rest and during cold pressor testing. Fifteen healthy subjects (age 23.5 ± 2 years) underwent blood pressure measurement in the left brachial artery (BP) and simultaneous recording of brachial and radial artery waveforms in the right arm. The right foot was placed in ice water and measurements were repeated 90 seconds later. The radial pressure wave was calibrated using BSP and BDP (Cuff), diastolic and brachial mean arterial pressure (MAP) determined from the brachial wave (BM), or diastolic and MAP calculated as 1/3PP + DP (CM). CP was estimated for each calibration method from the radial wave via a transfer function. Cold pressure testing increased (p<0.05) BSP (109 ± 2 vs. 127 ± 3 mmHg) and BDP (62 ± 2 vs. 77 ± 3 mmHg). Radial SP varied from BSP by + 9 and + 7 mmHg when calibrated using BM and CM respectively. As a result BM-CSP was 6.1 ± 1 and 4.5 ± 1 mmHg greater (p<0.05) than Cuff-CSP and EM-CSP respectively however all 3 methods tracked the cold pressor response similarly. Estimates of CP using a radial transfer function are dependent on the method of calibration. However, the ability to track changes in CP using a transfer function is not dependent on calibration and may provide valuable physiologic information.