Monitoring Water Content of Blood During Hemodialysis Based on Complex Permittivity Measurement

In hemodialysis treatment, it is necessary to accurately grasp the amount of waste products and the amounts of water in the blood. Real time monitoring of the water content of blood is effective for setting an appropriate dialysis time and thus reduce the burden on hemodialysis patients. In this study, we proposed a monitoring method of water content of blood based on Lichtenecker's exponential law for complex permittivity expression and measurement using a network analyzer and an open-ended coaxial probe. The Lichtenecker's exponential law expression in relation to the water content is a new attempt. To verify its validity, we first applied this method to apple juice with varying water content and aqueous solutions of glucose. The estimated water contents showed a relative error within 9% of actual ones, which ensured the validity of the proposed method. Then we applied this method to monitor the water content of blood during dialysis for 18 hemodialysis patients. The results showed a clear decrease of water content by dialysis for all hemodialysis patients. After dialysis, the estimated water contents of the blood were all between 35% and 45%, essentially falling in the normal range of water content of blood, nearly half. In addition, we also investigated the relationship between the water content and hematocrit in the blood, and found a strong correlation coefficient of -0.8 between them. The results demonstrated the feasibility to monitor the water content of blood during dialysis as well as hematocrit or anemia state based on the complex permittivity measurement.