Comparative Measurements of Tissue PO2 in the Carotid Body
Measurements of local oxygen partial pressure (PO2) performed with microneedle electrodes (5) in the cat carotid body showed results that were at first different from what was expected. Although the arteriovenous oxygen partial pressure difference is small in the carotid body, the low PO2 values predominated. They were only about a third to a quarter as high as the venous PO2 (1). In addition, it could be shown that the activity of the sinus nerve increases with decreasing tissue PO2and decreases with increasing tissue PO2 (2). We deduced from the findings that the chemoreceptor activity depends on the low tissue PO2.If the low PO2 recorded in the carotid body is a basic phenomenon that accompanies the O2-chemoreception, then.tissue PO2 values lower than the venous PO2 must be present in the carotid bodies or comparable organs of other mammalian species that represent, e.g., a phylogenetic side branch of the cat, or of species such as amphibians that are at the beginning of the phylogenesis toward mammalians.
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