Date of this Version

9-4-2019

Keywords

arrhythmia, bias, cuff, inaccuracy, model, sphygmomanometer, stochastic, supraventricular

Abstract

Accurate measurement of blood pressure in the presence of atrial fibrillation remains an open problem. The present study combines the techniques of stochastic mathematical modeling with physiological models of the systemic circulation, cuff, and arm (1) to explore mechanisms underlying both the lack of accuracy and the lack of precision in cuff-based arterial pressure measurements during atrial fibrillation and (2) to develop strategies to correct for errors. Both the cardiovascular system and the measurement technique are described using mathematics, including both numerical techniques and analytical probability theory. Preliminary results with numerical models suggested that, despite variability, average systolic pressures tend to remain stable during atrial fibrillation, since longer inter-beat intervals are accompanied by greater filling of the pump, and in turn greater stroke volume, compensating for greater fall in arterial pressure during the previous beat. The mean or median of several repeated measures of systolic pressure is relatively precise and accurate. Individual diastolic pressure measurements also vary greatly from beat to beat; however, the average measured diastolic pressure underestimates true diastolic pressure to a clinically meaningful degree. To describe this phenomenon concisely an analytical model was created. Given the known statistical distribution of inter-beat intervals, it is possible to predict the distribution of potential diastolic endpoints. In turn, by modeling the rate of cuff deflation, it is further possible to predict the distribution of measured arterial pressure levels at which the last Korotkoff sound is heard. Exploration of the underlying patterns and mechanisms using such mathematical models leads to clinically useful insights, including a relatively simple equation to correct for the systematic underestimation of diastolic blood pressure during atrial fibrillation, based upon patient-specific average heart rate and the range of electrocardiographically derived cardiac cycle lengths. Future clinical tests are in order.

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