Design and construct an optical device to determine relative blood volume in patients undergoing hemodialysis

Occurrence of hypotension during hemodialysis in nearly 20-30% of patients, shows is the necessity of continuous monitoring the patients' blood pressure during hemodialysis. Since directly and non-invasively continuous blood pressure monitoring, is not easy, finding a parameter related to blood pressure, for indirect monitoring is of great value. Related blood volume (RBV) is one of the parameters, related to blood pressure and have a good potential to reflect the patient's hemodynamic condition.

The main objective of this study was to design and construct an optical device to determine the RBV in patients undergoing hemodialysis, during the process.

After initial studies in order to select a proper sensor, using the ORCAD software, an analog circuit was designed. The implementation and modification of the circuit was done by the clinical tests, using expired blood. Afterwards, for calculation the RBV, controlling the display, data storage and sending it to the computer, an ATmega16 microcontroller was used. For programing the microcontroller, CodeVision software and then Altium Designer software were used for the circuit compression, in order to design the printed circuit board. Finally, all parts of the analog and digital circuit, AC to DC converter and the LCD were embedded in a box.

After finalization of the device and before testing it in a real situation, expired blood was used for final evaluation. The evaluation was done by changing the blood concentration, at the start point by adding water to it. In fact, the device can track the changes in blood concentration and display the RBV. After this evaluation, the device was tested in a clinical situation. The results showed there are no interactions between this device and the other devices used in the dialysis section and it can work properly in order to measure the RBV.

Considering the hypotension and its consequences in a patient on hemodialysis, solving this problem seems necessary. One method for preventing this, is to use the blood pressure related parameters and one of these parameters is the RBV. In this study, in order to measure the RBV, a device was designed and evaluated by expired blood and also tested in a clinical situation. Results showed that the device could work properly in order to measure the RBV.