Oxygen extraction ratio

The Vo2 Do2 ratio (oxygen extraction ratio) can be used to assess adequacy of perfusion and metabolic response. Patients who are able to increase Vo2 when Do2 is increased are more likely to survive. However, low Vo2 and 02 extraction ratio values are indicative of poor 02 utilization and lead to greater mortality. 

It follows from the above that the ratio of cerebral blood flow to cerebral blood volume is a measure of cerebral perfusion reserve (Schumann et al. 1998). Below a ratio of approximately 6.0, even if cerebral blood flow is still normal, vasodilatation and cerebral blood volume are maximal and the reserve is exhausted, as shown by a rising oxygen extraction fraction on PET. 

Figure 7 The Vostok ice-core record (Petit et aL, 1999). (a)-(c) Carbon dioxide, methane, and oxygen isotope ratios (expressed as 5 0) of oxygen in air extracted from the ice. (d) Hydrogen isotope ratios (expressed as or 5D) in the ice. This record is a proxy for local temperature, (e) Sodium in the ice, a measure of sea salt aerosol deposition, (f) Dust in the ice, a measure of continental aerosol deposition, (a)-(c) are plotted against the estimated age of the iee air (d)-(f) are plotted against the estimated age of the ice.

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