Age-dependent vulnerability to carotid chemodenervation in piglets.

We sought to determine the age of greatest vulnerability in piglets to the loss of carotid chemoreceptor function. We studied four groups of carotid body-denervated (CBD) piglets whose carotid bodies were surgically removed at 4-5, 9-10, 12-15, and 21-22 days and who are herein referred to, respectively, as the CBD5, CBD10, CBD15, and CBD20 groups. Four intact groups, at corresponding ages, underwent a sham surgical procedure. After a postsurgery recovery of at least 7 days, we studied all animals to detect the presence of apnea and the consequences of it, if any. Two days before the experiments, we implanted in all animals a fiber-optic arterial catheter for continuous monitoring of arterial O2 saturation, and electroencephalographic electrodes for the recording of sleep states. During quiet sleep in the CBD15 group, we found numerous prolonged central apneic events accompanied by a profound desaturation, tachycardia, a rise in blood pressure, and, eventually, a flattening of the electroencephalogram. No prolonged apneic events occurred, however, in the other CBD groups nor in the intact animals. During active sleep, no prolonged apneic events occurred at all. We thus conclude that, in piglets, the absence of normally functioning carotid chemoreceptors at approximately 2 wk of age can lead to life-threatening apneic events with severe hypoxemia, events that are state specific.