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Oxygen partial pressure in lungs (mm Hg)

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Oxygen partial pressure in lungs (mm Hg)

Figure 44-2

Quantity of oxygen dissolved in the fluid of the blood and in combination with hemoglobin at very high PO2s.

Oxygen Toxicity at High Pressures

Effect of Very High Po2 on Blood Oxygen Transport. When the Po2 in the blood rises above 100 mm Hg, the amount of oxygen dissolved in the water of the blood increases markedly. This is shown in Figure 44-2, which depicts the same oxygen-hemoglobin dissociation curve as that shown in Chapter 40 but with the alveolar Po2 extended to more than 3000 mm Hg. Also depicted by the lowest curve in the figure is the volume of oxygen dissolved in the fluid of the blood at each Po2 level. Note that in the normal range of alveolar Po2 (below 120 mmHg), almost none of the total oxygen in the blood is accounted for by dissolved oxygen, but as the oxygen pressure rises into the thousands of millimeters of mercury, a large portion of the total oxygen is then dissolved in the water of the blood, in addition to that bound with hemoglobin.

Effect of High Alveolar Po2 on Tissue Po2. Let us assume that the Po2 in the lungs is about 3000 mm Hg (4 atmospheres pressure). Referring to Figure 44-2, one finds that this represents a total oxygen content in each 100 milliliters of blood of about 29 volumes per cent, as demonstrated by point A in the figure—this means 20 volumes per cent bound with hemoglobin and 9 volumes per cent dissolved in the blood water. As this blood passes through the tissue capillaries and the tissues use their normal amount of oxygen, about 5 milliliters from each 100 milliliters of blood, the

Total O2 in blood

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