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A method for measuring brain partial pressure of oxygen in unanesthetized unrestrained subjects: The effect of acute and chronic hypoxia on brain tissue PO2

Abstract:

The level of tissue oxygenation provides information related to the balance between oxygen delivery, oxygen utilization, tissue reactivity and morphology during physiological conditions. Tissue partial pressure of oxygen (PtO<inf>2</inf>) is influenced by the use of anesthesia or restraint. These factors may impact the absolute level of PtO<inf>2</inf>. In this study we present a novel fiber optic method to measure brain PtO<inf>2</inf>. This method can be used in unanesthetized, unrestrained animals, provides absolute values for PO<inf>2</inf>, has a stable calibration, does not consume oxygen and is MRI compatible. Brain PtO<inf>2</inf> was studied during acute hypoxia, as well as before and after 28 days of high altitude acclimatization. A sensor was chronically implanted in the frontal cortex of eight Wistar rats. It is comprised of a fiber optic probe with a tip containing material that fluoresces with an oxygen dependent lifetime. Brain PtO<inf>2</inf> declines by 80% and 76% pre- and post-acclimatization, respectively, when the fraction of inspired oxygen declines from 0.21 to 0.08. In addition, a linear relationship between brain PtO<inf>2</inf> and inspired O<inf>2</inf> levels was demonstrated r<sup>2</sup>=0.98 and r<sup>2</sup>=0.99 (pre- and post-acclimatization). Hypoxia acclimatization resulted in an increase in the overall brain PtO<inf>2</inf> by approximately 35%. This paper demonstrates the use of a novel chronically implanted fiber optic based sensor for measuring absolute PtO<inf>2</inf>. It shows a very strong linear relationship in awake animals between inspired O<inf>2</inf> and tissue O<inf>2</inf>, and shows that there is a proportional increase in PtO<inf>2</inf> over a range of inspired values after exposure to chronic hypoxia. © 2010 Elsevier B.V.