A Pulse Arrival Time Based Method to Establish Blood Pressure Limits of Autoregulation and Optimal Blood Pressure in Individual Patients During Surgery

The regulation of blood flow into peripheral organ systems is imperative to maintain adequate perfusion and prevent tissue damage. The human body accomplishes this task through autoregulation, a mechanism which maintains relatively constant cerebral blood flow despite changes in blood pressure. Autoregulation, however, works only within a limited range of blood pressures and fails to ensure constant cerebral blood flow outside of this range. Under current standards, cerebral oximetry has been used as a surrogate for cerebral blood flow in non-invasive multimodal monitoring of the cerebral autoregulation. However, this method is expensive and thus not widely used in the operating room and intensive care unit (ICU).

In this project, we propose a novel method using real-time continuous electrocardiography and arterial blood pressure data to establish the limits of autoregulation and establish the optimal blood pressure for individual patients in the operating room and ICU. Our method uses a combination of pulse arrival time (PAT), the time it takes the pulse to reach the end organ, and the mean arterial pressure (MAP) to derive the individualized autoregulation limits. Based on the observation that the variance of PAT differs within and outside of the autoregulation limits, the Brown–Forsythe test for constancy of variance is applied between sliding windows across MAP and an adaptive control window, in order to draw the boundaries for the lower and upper limits of autoregulation. Using this method, we were able to determine the autoregulation limits of 100 patients. Future work should include evaluating the performance of our technique against the results of the cerebral oximetry based method.