Oxygen transport capacity of the capillary blood within the carotid body

Local deltaPo2 deltat in the carotid body after perfusion stop depends on the oxygen consumption of the tissue and the apparent O2 solubility coefficient alpha of the blood. Oxygen consumption of the carotid body tissue can be determined by measuring the local deltaPo2 deltat with Po2 needle electrodes after Krebs-Henseleit perfusion. Assuming the same deltaPo2 deltat for the blood-perfused carotid body the actual Po2 decrease can be used to estimate the hemoglobin content of the tissue. The influence of hemoglobin is described by the factor alpha/alpha. Control values measured in the Krebs-Henseleit-perfused carotid body yielded values of alpha/alpha = 0.8-3. In a series of 11 blood-perfused carotid body preparations with 105 perfusion stops the quotient alpha/alpha changed with arterial Po2. At Po2 values higher than 100 Torr alpha/alpha 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 alpha/alpha of about 128, we conclude that the carotid body is mainly perfused by plasma, and that with decreasing arterial Po2 more red cells flowed through the carotid body.