In vivo and in vitro studies of a chronic oxygen saturation sensor

An oxygen saturation sensor, for the purpose of chronically controlling the heart rhythm produced by a pacemaker, should be specific to oxygen saturation and should be minimally affected by the harsh blood environment. For the sensor type we tested we found: (1) one sensor failure in 205.5 canine-months of chronic implantation (n = 11, range 4 to 50 months); (2) hematocrit-induced error of less than 5 percentage points of SvO2 over the range of 50% to 80% SvO2 and 15% to 45% hematocrit; (3) carboxyhemoglobin (HbCO)-induced error of less than 4 percentage points of SvO2 with HbCO up to 20%; (4) a fibrotic sheath-induced error of less than 3 percentage points of SvO2 in the range of 50% to 80% SvO2 due to fibrotic sheath thicknesses up to 0.22 mm; (5) no significant error induced by velocity variations local to the sensor; (6) no significant error due to temperature in the range of 30 degrees to 42 degrees C; and (7) that the sensor could be as close as 0.3mm to the ventricular wall and still only produce an error of 5% SvO2.