![]() However, when changes are exponential in magnitude the situation becomes life threatening at the capillary level because the compensation mechanisms are inadequate. ![]() The interplay of most of the variables described by the Krogh cylinder structure and oxygen pressure field are easily compensated by making fractional changes. The 17% increase in intracapillary velocity represents another fractional factor change. Potentially, to prevent this, the body can increase the cardiac output by approximately 17% to maintain the normal capillary pO2 values. Those tissues farthest from the capillary and nearest the venous end of the tissue cylinder, because they already have the lowest pO2 concentration, would be particularly vulnerable to this reduced transfer of oxygen. Less oxygen is transferred to the tissues. Desaturation of the capillary blood obviously reduces the capillary-to-tissue-gradient, which in turn reduces the magnitude of the radial vectors. The result would be desaturation of the intracapillary blood (what we see as a reduced mixed venous saturation). If cardiac output remains unchanged, then intracapillary velocity would not be fast enough to prevent the reduction of the capillary pO2 as increased amounts of oxygen are transferred into the tissue. Both these are fractional increases of a factor that maintains the oxygen transfer to the cells, the radial vectors. Similarly, at the venous end the median tissue pO2 dropping from 10 mmHg to 5 mmHg would increase the gradient from 30 mmHg to 35 mmHg (also a 17% increase). ![]() With an arterial pO2 of 80 mmHg, the capillary-to-tissue gradient would increase fractionally from 60 to 70 mmHg (a 17% increase). Suppose that an increased O2 consumption drops the median tissue pO2 from 20 mmHg to 10 mmHg at the arterial end of the cylinder. However, these changes, at most, result in fractional changes in tissue pO2 concentrations. ![]() The level of oxygen consumption, the intracapillary velocity and the length of the cylinder are variables which affect the oxygen concentration at any particular area within the pressure field. As the relationship between the capillary and its surrounding tissue changes, the oxygen pressure field also changes. The Krogh cylinder predicts a wide range of tissue pO2 values called an oxygen pressure field surrounding individual capillaries. To View all of Gary Grist”s Posts Regarding OPFT- click here The Lethal Corner Authored by: Gary Grist, BS, RN, CCP, LCP ![]()
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