215 Introduction Hemodialysis is the most common method used to treat renal failure, and in comparison to other methods causes rapid changes in the plasma levels of soluble substances and the ABSTRACT During dialysis process, excess water in the dialysis patient's body shifts firstly from intracellular to extracellular, and then passes into blood stream. Finally, it is removed from the body by dialysis. During this process, if the amount of water taken from the blood by dialysis be more than the amount of water transferred in to the blood from extracellular, the dialysis patient would suffer from a decreased blood volume followed by hypotension. Due to the hypotension occurred during dialysis, the blood pressure of dialysis patients should be monitored continuously during the dialysis process. Since, the continuous and direct monitoring of blood pressure is difficult and the devices in this regard are very expensive, in order to achieve this goal, the parameters associated with the blood pressure should be used. One of the associated parameters is the relative volume of blood (relative changes in blood concentrations RBV), because it involves both an easier measurement and also a good ability to demonstrate the hemodynamic status. To investigate the RBV and to calculate the blood pressure, a device provided during are search project in the Army Medical University was applied. In this project, the efficiency of RBV device was examined in hemodialysis patients, then, a scientific correlation between the parameter and hypotension of dialysis patients were found and evaluate during the clinical testing of the device on a group of dialysis patients and recording the data, including RBV measured by the device and the blood pressure rate. Based on the RBV definition, the changes in this factor and the blood pressure of hemodialysis patients during the hemodialysis process are inversely to each other. The results obtained using the device were pursuant to the definition with an acceptable accuracy more than80%. According to the accuracy of data obtained from the device, it can be concluded that this device can be used as a non invasive method with a good accuracy to detect the hypotension in this group of patients in order to prevent the occurrence of subsequent complications. However, firstly the accuracy, and secondly the manner of correlation between these two parameters differs depending onthe selected model of the correlation between RBV and hypotension. KEYWORDS Blood concentration, dialysis, hemodialysis, hypotension, relative volume of blood A study to evaluate the efficacy of RBV device (relative volume of blood) in hemodialysis patients and to determine the correlation between RBVand hypotensionin these patients (as in vivo) Banafsheh Dormanesh 1 , Gholamreza Motamedi 2 and Ali Mohammadshahi 3* 1 Department of Pediatric Nephrology, AJA University of Medical Sciences, Tehran, IR Iran 2 Department of Parasitology, Razi Vaccine and Serum Research Institute, Karaj, Iran 3 Department of Emergency Medicine, AJA University of Medical, Sciences, Tehran, Iran *Corresponding author ISSN: 2347-3215 Volume 2 Number 7 (July-2014) pp. 215-221 www.ijcrar.com