Oxygen transport capacity of the capillary blood within the carotid body

Local\(\frac{{\Delta P_{O_2 } }}{{\Delta t}}\) in the carotid body after perfusion stop depends on the oxygen consumption of the tissue and the apparent O₂ solubility coefficient α^* of the blood. Oxygen consumption of the carotid body tissue can be determined by measuring the local\(\frac{{\Delta P_{O_2 } }}{{\Delta t}}\) with\(P_{O_2 } \) needle electrodes after Krebs-Henseleit perfusion. Assuming the same\(\frac{{\Delta P_{O_2 } }}{{\Delta t}}\) for the blood-perfused carotid body the actual\(P_{O_2 } \) decrease can be used to estimate the hemoglobin content of the tissue. The influence of hemoglobin is described by the factor α^*/α. Control values measured in the Krebs-Henseleit-perfused carotid body yielded values of α^*/α = 0.8 −3. In a series of 11 blood-perfused carotid body preparations with 105 perfusion stops the quotient α^*/α changed with arterial\(P_{O_2 } \) values higher than 100 Torr α^*/α was between 0.8 and 2. This value thus was in the same range as the control values. Below 100 Torr higher values up to 11 were observed. Since a blood-perfused tissue (15 g % Hb) would have an α^*/α of about 128, we conclude that the carotid body is mainly perfused by plasma, and that with decreasing arterial\(P_{O_2 } \) more red cells flowed through the carotid body.