Hypoxia and the carotid body.

Since the publication of the classical studies of Heymans et al (1930) it has been accepted that the carotid body is a chemoreceptor which monitors the oxygen tension of systemic arterial blood, and it has been extensively investigated by physiologists (Biscoe, 1971). Because chronic hypoxia is a major hazard of life at high altitude and ofcardiorespiratory disease at sea level, it might be thought that much is known about the pathology of the carotid body in such situations. This, however, is not the case. It was not until 1969 that Arias-Stella reported enlargement of the cartoid bodies in high-altitude dwellers in the Peruvian Andes and 1970 that Heath et al described such enlargement in sea-level patients with emphysema. Thus until the last decade, the only condition of the carotid body which the general pathologist was aware of was the rare tumour known as the chemodectoma. Since the pioneering observations of Arias-Stella, pathological studies by Heath and Edwards (1971) of the carotid body have been made on human subjects and animals born and living at high altitude, and also on animals living at subatmospheric pressure in hypobaric chambers. These chambers are very convenient for working with small animals in the laboratory without the inconvenience and expense of long journeys to countries with mountain ranges over 3600 metres high. However, a distinction must be made between the examination of animal tissues derived from experiments using hypobaric chambers and the examination of tissues from human subjects and animals born and living for many years at high terrestrial altitude. Hypobaric chambers can accurately reproduce the low atmospheric pressure ofhigh altitude but not the climatic and other environmental features of life in a high mountainous region. This paper briefly reviews the structure and function of the normal carotid body, and then deals with the morphological changes associated with acute and chronic alveolar hypoxia in human subjects and animals.