Human Obesity Is Characterized by a Selective Potentiation of Central Chemoreflex Sensitivity

The chemoreflexes are an important mechanism for regulation of both breathing and autonomic cardiovascular function. Obesity is associated with an increased risk of alveolar hypoventilation and carbon dioxide retention, suggesting that abnormalities in chemoreflex control mechanisms may be implicated. We tested the hypothesis that chemoreflex function is altered in obesity. We compared ventilatory, sympathetic, heart rate, and blood pressure responses to hypercapnia, hypoxia, and the cold pressor test in 14 obese subjects and 14 normal-weight subjects matched for age and gender. During hypercapnia, the increase in minute ventilation was significantly greater in obese subjects (7.0+/-0.3 L/min) than in normal-weight subjects (3.3+/-1.1 L/min; P=0.03). Despite higher minute ventilation during hypercapnia in obese subjects, the increase in muscle sympathetic nerve activity was similar in obese and normal-weight subjects. When the inhibitory influence of breathing during hypercapnia was eliminated by apnea, the increase in sympathetic nerve activity in obese subjects (99+/-16%) was greater than in normal-weight subjects (44+/-16%; P=0.02). The magnitude of the ventilatory and autonomic responses to hypoxia and the cold pressor test was similar in obese and normal-weight subjects. We conclude that chemoreflex responses to hypercapnia are potentiated in eucapnic obese subjects. In contrast, responses to hypoxia and to the excitatory cold pressor stimulus in obese subjects are similar to those in normal-weight subjects. Thus, obesity is characterized by selective potentiation of central chemoreflex sensitivity.