First results of an implantable sensor for blood flow measurement

Information about the hemodynamic state of the human organism is very important in the electrotherapy of the heart. In the therapy of tachycardias with implantable defibrillators ventricular and supraventricular tachycardias have to be discriminated from each other to avoid unnecessary electrical shocks. In this study two new implantable sensors for blood flow measurements are evaluated. The first sensor determines the change of conductivity of blood depending on the flow rate. This effect is based on shear forces which lead to an orientation of cellular blood components causing anisotropic electrical properties of the blood. For measuring the relative conductivity of blood a bipolar pacemaker lead is used. The second sensor principle is based on the measurement of the resistance of a heated resistor. This depends on the blood flow due to thermal transport of the blood. Both hemodynamic sensors were implanted in dogs in the coronary sinus, the vena cava superior and the right outflow tract. The sensor signal-the impedance of the blood or the powered resistor respectively-was measured during electrical stimulation of the heart and during atrial and ventricular fibrillation. The course of the signal of the blood conductivity sensor reflects the course of the mean arterial blood pressure (MAPB) during the heart cycle. The absolute values of the sensed signals depend on the position of the sensor. In conclusion, both sensor principles offer information about blood flow and cardiac output, which can be used for a better control of ICD therapy or new pacing algorithms.