Catheter PO2 Electrode with Low Flow Dependency and Fast Response

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Abstract
A catheter PO2 electrode of 2 mm diameter is described which offers a good compromise between the two central requirements of flow independency and fast response, and makes possible the continuous recording even of arterial PO2 fluctuations with respiration and heart beat. The cathode is a platinum foil about 3 μ thick sealed between a tube and cylinder made of polyvinyl chloride or glass. The ring of the silver anode also carries the membrane held by a silver cap. The polarograms show a broad horizontal plateau over a wide range of voltage at all levels of oxygen up to 100% O2. The calibration curve is linear and passes through the origin with a bias of -0.9 V in most cases. The current output of 0.6 μA for 100% O2 at 37°C with a 6 μ Teflon membrane is equivalent to that of a single wire cathode of 100 μ diameter. The stability is 0.5% over a period of 10 h and 2% during several days. The electrode is insensitive to pressure and moderate acceleration. The flow dependency in blood at 37°C is such that the reading remains within 2% of the full value at high flow for linear velocities above 5 em/sec with a 6 μ Teflon membrane and above 1.25 cm/sec with a 12 μ Teflon membrane. The response time for 95 % deflection is 0.3 sec in gas and 0.4 sec in blood with a 6 μ Teflon membrane; it increases in blood to 1 sec by decreasing the velocity to 10 cm/sec. The response of the electrode was also tested in vitro in the presence of flow rates oscillating in both directions at various frequencies and amplitudes as well as in the dog in order to show the reaction at various levels of oxygenation and the fluctuations with respiration and heart beat.

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