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 < 5 percentage points of Svo 2 over the range of 50% to 80% Svo 2 and 15% to 45% hematocrit; (3) carboxyhemoglobin (HbCO)‐induced error of < 4 percentage points of Svo 2 with HbCO up to 20%; (4) a fibrotic sheath‐induced error of < 3 percentage points of Svo 2 in the range of 50% to 80% Svo 2 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° to 42°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% Svo 2 .