Temporal Variation In Tissue Oxygen Tension And Perfusion Response To Hypoxia And Ischaemia: The Importance Of Local Control Of The Microcirculation

Introduction: The relationship between tissue oxygenation and perfusion is important since hypoxia remains a core component of many acute and chronic diseases, particularly those leading to admission to the intensive care unit. We hypothesised that skeletal muscle perfusion and oxygenation would behave similarly regardless of whether tissue hypoxia was caused by reducing blood flow or arterial oxygen content. Methods: We performed a prospective laboratory study in 18 Sprague-Dawley rats. We measured (simultaneously) tissue oxygen tension and perfusion in hind limb skeletal muscle. Rats were allocated to three groups: control (n=6), ischaemia-anoxia (n=6) and anoxia-ischaemia (n=6). Ischaemia was induced by aortic occlusion for 30 minutes and anoxia by reducing the inspired oxygen concentration to zero for 90 seconds. Results: Tissue perfusion and PtO2 changed according to an exponential mathematical model during ischaemia, anoxia, reperfusion and reoxygenation. Irrespective of whether ischaemia was the initial or subsequent insult, both LDF and PtO2 decreased. This was followed by a hyperaemic LDF response with partial recovery of PtO2. In contrast, LDF increased when anoxia was the first intervention but not when it was preceded by ischaemia; this combination resulted in reduced perfusion. Following reoxygenation, PtO2 and LDF generally recovered to baseline values. Conclusions: We conclude that changes in tissue oxygen tension and perfusion during ischaemia and anoxia depend on the order in which the insults occur, and that they may be described by an exponential model. These data also confirm the presence of exhaustible local hypoxic control mechanisms in the microcirculation.