Transport of Oxygen in the Dissolved State
At the normal arterial PO2 of 95 mm Hg, about 0.29 mil-liliter of oxygen is dissolved in every 100 milliliters of water in the blood, and when the PO2 of the blood falls to the normal 40 mm Hg in the tissue capillaries, only 0.12 milliliter of oxygen remains dissolved. In other words, 0.17 milliliter of oxygen is normally transported in the dissolved state to the tissues by each 100 milli-liters of arterial blood flow. This compares with almost 5 milliliters of oxygen transported by the red cell hemo-globin. Therefore, the amount of oxygen transported to the tissues in the dissolved state is normally slight, only about 3 per cent of the total, as compared with 97 per cent transported by the hemoglobin.
During strenuous exercise, when hemoglobin release of oxygen to the tissues increases another threefold, the relative quantity of oxygen transported in the dissolved state falls to as little as 1.5 per cent. But if a person breathes oxygen at very high alveolar PO2 levels, the amount transported in the dissolved state can become much greater, sometimes so much so that a serious excess of oxygen occurs in the tissues, and “oxygen poi-soning” ensues. This often leads to brain convulsions and even death, in relation to the high-pressure breathing of oxygen among deep-sea divers.
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