Assessment of Cerebral Blood Flow Based on Bioimpedance

Cerebral blood flow (CBF) is responsible for oxygen and nutrient delivery to the brain and clearance of the byproducts of brain metabolism. CBF is an important biomarker of brain health and function. Transcranial Doppler ultrasound (tCD), which is ease-of-use, non-invasiveness, and excellent temporal resolution, is utilized to monitor CBF. However, tCD is relatively expensive and bulky, which is not convenient for outdoor setting. In this study, bioimpedance technology was adopted to assess CBF taking tCD as a reference. A low-cost, portable, battery powered, high-precision bioimpedance measurement system (BMS), using quadrature amplitude demodulation and 4-wire measurement technique, was designed for assessing CBF. An Qos index to evaluate the quality of bioimpedance signal based on power spectrum was proposed. Thirteen healthy volunteers were recruited for measuring CBF using both tCD and BMS simultaneously. Pearson correlation coefficient was used to evaluate the correlation between tCD and BMS. The result showed significant correlation between CBF data measured by BMS and tCD (r=0.71-0.89, P<0.05) when average quality of signal Qos ≥ 5.1. Pearson correlation coefficient between Qos and r was 0.56 and between Qos and P was -0.61. The research suggests that bioimpedance technique may be valuable for assessing changes in CBF in the future and the Qos index proposed in this paper may be used to evaluate the reliability of CBF assessment.