The role of blood perfusion and tissue oxygenation in the postischemic transcutaneous pO2 response

The transcutaneous pO2 (TCpO2) response following release of tourniquet cuff occlusion is expressed as oxygen reappearance time (ORT) and oxygen recovery index (ORI). In the present study the effects of blood perfusion and tissue oxygenation on ORT and ORI in healthy control subjects and two patient groups with peripheral arterial insufficiency were assessed. In control subjects, ORT reflects diffusion time for O2 molecules from capillaries to the TCpO2 sensor. In patients with claudication, ORT was prolonged probably because of delayed postischemic reperfusion and reduced tissue oxygenation. In patients with critical ischemia, prolonged ORT seems to be attributed more to reduced tissue oxygenation than to delayed postischemic reperfusion. ORI in control subjects and patients with claudication apparently depends more on capillary pO2 than on magnitude and duration of the postischemic reperfusion. In patients with critical ischemia, ORI is more related to decreased O2 delivery subsequent to reduced or absent reactive hyperemia response. In addition, increased O2 extraction ("O2 steal") and extensive countercurrent O2 exchange during low flow states may reduce ORT and ORI in severely ischemic skin.