Prolonged apnea and impaired survival in piglets after sinus and aortic nerve section

We examined the effects of carotid body denervation (CX, n = 9), CX + aortic nerve section (CAX, n = 9), and sham surgery (SHAM, n = 7) on cardiorespiratory and metabolic function in young piglets (less than 9 days). For comparison, 1-mo-old pigs were also studied. Studies were performed 1 day after surgery, during which time ventilation (barometric plethysmography), heart rate, blood pressure, arterial blood gases, and electroencephalogram were recorded under normoxia. CX and CAX piglets hypoventilated (arterial PCO2 = 47.1 +/- 2.6 and 45.4 +/- 3.1 Torr, respectively) compared with SHAM piglets (arterial PCO2 = 36.4 +/- 1.5 Torr). CX piglets had an average of 8.0 +/- 3.0 apneas/h, lasting, on average, 26 +/- 3 s. CAX piglets averaged 17.2 +/- 7.9 apneas/h, lasting 30 +/- 5 s. Such long apneas were never observed in SHAM animals. Mean heart rate and blood pressure in denervated piglets were not significantly different from those in SHAM piglets. In animals followed up poststudy, significantly high mortality was observed in CX (5 of 9) and CAX (6 of 9) piglets by 7 days after surgery but not in SHAM animals (0 of 7) despite identical environmental and feed conditions (P less than 0.05; chi 2). One-month-old denervated animals showed periodic breathing and hypoventilation, but none died. These results suggest that in the newborn piglet 1) peripheral chemoreceptors have an active role in maintaining normal ventilation and avoidance of prolonged apnea and 2) survivability in early life is critically dependent on peripheral chemoreceptors.