Concepts of “Tissue PO₂” In Relation to O₂Delivery

Abstract

Resistance to O2 diffusion is reflected in the difference in pO2 between O2 reservoirs of hemoglobin (Hb) and myoglobin. The very low normal myocyte pO2 (less than one torr but adequate for optimal oxidative ATP synthesis) compared to venous pO2 indicates that blood does not achieve equilibrium with tissue during its passage through capillaries. In the lung, diffusion rate of O2 from alveolus to capillary is normally sufficient to achieve essential equilibrium. However, system-wide capillary pathology and reduced Hb saturation has been observed with distal local ischemia. In peripheral vascular disease (PVD) patients, we found a mean arterial pO2 of 77 torr (normal over 90 torr). Classical concepts based on "tissue pO2" values derived from venous blood or oxygen electrodes inserted into tissue need re-evaluation. Readings of O2 electrodes moved through tissue range widely from intracapillary levels down toward intracellular levels and do not reflect the pO2 of any particular site. Intravenous pO2 is the result of residual O2 after incomplete diffusion out of capillaries during transit through a tissue, and is not an equilibrium value with some tissue pool. The effect of HbO2 p50 on oxygen release during the passage of blood through a capillary bed, generally judged on the basis of percentage percent saturation at "tissue pO2", should be judged on the basis of the change in pO2 (the diffusion driving force) associated with a particular degree of HbO2 saturation at a particular p50. The thesis that O2 diffusion rate is a major determinant of oxygen delivery is supported by pO2 responses to treatment of PVD that does not alter blood flow or p50.

Perfluorocarbon NVX-108 increased cerebral oxygen tension after traumatic brain injury in rats

“…An electrode-based technique provides a combined histogram of intravascular and interstitial oxygen values, and thus the readings have a wide range from intracapillary to intracellular. For this reason these techniques have been criticized as being unable to precisely reflect the oxygen tension within any particular compartment (Weiner, 1994). Nonetheless, the two methods have provided comparable results as our PbtO2 values measured by PQM are similar to a previous rat study using a Licox Clark oxygen electrode (GMS, Kiel, Germany) (Mendez et al, 2004).…”

“…In most instances, the difference between oxygen measurements in a small arteriole/capillary compared to nearby tissue is expected to be small (Torres Filho et al, 1996;Wilson et al, 2006), and arteriolar/capillary oxygen levels are used as proxies for tissue levels. However, for evaluating the efficacy of an oxygen therapeutic fluid, whether or not it is able to appropriately off-load oxygen to hypoxic tissue makes it critical to measure oxygen tension in the tissue interstitium (Weiner, 1994). Thus the decision to measure interstitial tissue oxygen via local probe application was considered essential.…”

Blood Gas Tension and Acidity Level of Caries Exposed Vital Pulps in Primary Molars

“…The values of gases partial pressures in our study are higher than values found in blood capillaries, where pCO 2 is 35.00 45.00mmHg and pO 2 is 75.00 100.00mmHg [26,33,34]. The literature lacks agreement between results on tissues pO 2 distribution [35]. Differences are introduced by the method for exposing the tissue, the variability between tissue, differences in measurement methods and the intrinsic potential variability due to the location of the measurement site along the microvasculature [35].…”

“…The literature lacks agreement between results on tissues pO 2 distribution [35]. Differences are introduced by the method for exposing the tissue, the variability between tissue, differences in measurement methods and the intrinsic potential variability due to the location of the measurement site along the microvasculature [35]. Therefore, we compared the values measured between the two groups of teeth and more studies are needed to provide further data on pulp gases partial pressures.…”

Sanguinate's effect on pial arterioles in healthy rats and cerebral oxygen tension after controlled cortical impact

“…For this reason, these techniques have been described as being unable to precisely reflect the partial pressure of oxygen (PO 2 ) within any particular compartment (Weiner, 1994). However, for the evaluation whether oxygen therapeutics can successfully deliver O 2 to tissue parenchyma, it is critical to detect changes in O 2 pressure in the parenchyma alone (Weiner, 1994).…”