A Role for the Carotid Body in Cardiovascular Control in Man

Abstract

The carotid bodies play a role in the pressor response to hypoxemia in experimental animals. To determine the importance of the carotid bodies in cardiovascular control in man, we investigated eight subjects who had had (at other institutions) bilateral carotid body resection (CBR), without baroreceptor denervation, for bronchial asthma. Five normal subjects and three asthmatic patients served as controls. The subjects breathed air, 12 percent O₂ in N₂, and 5 percent CO₂, 21 percent O₂ in N₂ at rest and during cycle ergometer exercise. During hypoxia (PaO₂ = 40 mm Hg), the tachycardia was not affected by CBR; the heart rate increase averaged 15 beats per minute during rest and exercise. The systolic, diastolic and pulse pressures slowly decreased in the CBR subjects (avg systolic ↓ = 14 mm Hg), whereas it increased in the control subjects (avg systolic ↑ = 12 mm Hg). Following return to air breathing, blood pressure decreased in the control, whereas it increased in the CBR subjects. In contrast to the altered response of blood pressure in CBR subjects during hypoxia, the pressor response to hypercapnia was not different in the two groups. We conclude that in man, the carotid bodies are essential for normal pressor responses during hypoxia, but not for the tachycardia of hypoxia or the cardiovascular responses to hypercapnia.