Age-based differences between mercury sphygmomanometer and pulse dynamic blood pressure measurements

BACKGROUND: Both the mercury sphygmomanometer and oscillometric measurement methods are widely in use for pediatric, adult, and geriatric patients. However, inherent differences between the methods of measurement may create varying degrees of sensitivity to age and potentially result in differences between measurements for these two techniques. DESIGN: Measurements of systolic and diastolic blood pressures in 154 subjects were obtained using the mercury sphygmomanometer and pulse dynamic oscillometric methods in accordance with the 1987 Association for the Advancement of Medical Instrumentation guidelines. Subjects were separated into three age groups and their data analyzed for differences between measurements for these two techniques. METHODS: Two qualified nurses derived systolic and diastolic blood pressures using phase I and phase IV Korotkoff sounds, respectively, during simultaneous monitoring with the pulse dynamic oscillometric method. RESULTS: Inter-nurse variabilities for measurement derived by mercury sphygmomanometer were 1.8 +/- 4.1 for systolic and 0.9 +/- 3.9for diastolic blood pressure. Mean differences (reference-device) of -5 +/- 5 mmHg (pulse dynamic value higher) for systolic and 1 +/- 5 mmHg (pulse dynamic value lower) for diastolic blood pressure between pulse dynamic and mercury sphygmomanometer values were found for all subjects. However, pulse dynamic systolic blood pressure was significantly higher than mercury sphygmomanometer systolic blood pressure for group 1 (n = 51, aged 11-22 years, mean difference -5.6 mmHg, P = 0.03). A similar trend was observed with group 2 (n = 51, aged 23-54 years, mean difference -4.3 mmHg, P = 0.06). We observedf no significant difference for systolic blood pressure with group 3 (n = 52, aged 55-85 years, mean difference -3.8 mmHg, P > 0.1). For all three groups we found no significant difference for diastolic blood pressure. CONCLUSION: The variation in the agreement of systolic blood pressure measurements can be attributed to the differing effects of age-dependent arterial changes on the measurement methods. The findings indicate that, although the pulse dynamic oscillometric method and mercury sphygmomanometer correlate well when patients of all ages were evaluated as a group, agreement between measurements of systolic blood pressure is dependent on age and the method of measurement employed.