A hydrostatic method assessing accuracy and reliability while revealing asymmetry in blood pressure measurements

This study describes a method for noninvasive hydrostatic validation of blood pressure devices. It is based on the hydrostatic pressure exerted by a column of blood. The mid-position of an upward-held wrist blood-pressure cuff marks the top of the column, and a cuff on the opposite wrist pointed downward similarly determines the bottom of the column. Twenty-one healthy subjects comprising 12 right-handed and nine left-handed men and women entered this study. Each repeatedly alternated the arm positions ten times. Linear regression analysis yielded correlation coefficients for comparison of the Dinamap devices against the hydrostatic differences of 0.57, 0.70, and 0.70 for systolic pressure (SP), diastolic pressure (DP), and mean pressure (MP), respectively. These coefficients combined with the results of the graphic method of Altman and Bland demonstrated the best results for DP and matched least for SP. Overall results presented mean errors (ME: Dinamap-hydrostatic) +/- standard deviations (SD) of 9.3 +/- 10.1, -1.0 +/- 5.6, and 6.3 +/- 6.7 mmHg for SP, DP, and MP, respectively. These results are numerically comparable to some of the prior reports of ME +/- SD analysis of Dinamap devices by conventional validation studies. Numerically, DP is within and MP is close to the AAMI standards. The results of ME +/- SD, however, revealed a remarkable asymmetry for SP. The results of all the left-arm-up/right-arm-down position had ME +/- SD 12.3 +/- 11.1, -0.6 +/- 5.8, and 7.2 +/- 7.1 mmHg for SP, DP, and MP, respectively. The results of the opposite positioning were 6.3 +/- 7.9, -1.3 +/- 5.5, and 5.4 +/- 6.2 mmHg, respectively. This asymmetry of the SP differences seems independent of handedness (left or right) and gender, and may be related to the reflectance caused by intrathoracic vasculature asymmetry, which suggests that for validation purposes, the left-arm-down/right-arm-up position should be used. The alternative position may be used to detect and/or study this asymmetry. Such detection should have important clinical consequences for patient blood pressure monitoring. During surgery, if both arms must be placed shoulder-high, for instance, the right arm should provide more accurate and reliable blood pressure measurement.