Nerve axons in carotid body hyperplasia. A quantitative study.

The nerve density, expressed as total length of nerve fibers per square millimeter of tissue section, was measured in both carotid bodies from five subjects free from cardiopulmonary disease and from eight subjects with carotid body hyperplasia. Six of the cases with enlargement of the carotid body had been exposed to chronic hypoxemia in life (due to panacinar pulmonary emphysema in five instances and the pickwickian syndrome in one case), and the other two cases had had systemic hypertension. The cases of carotid body hyperplasia showed an increased nerve density associated with the characteristic proliferation of elongated cells. These findings confirm that the proliferating cells in carotid body hyperplasia are both sustentacular and Schwann's cells, not fibroblasts, and suggest that these cells develop to support an increased number of nerve axons. The mechanisms by which two such different stimuli as chronic hypoxemia and raised intravascular pressure bring about an increased nerve density are obscure.