Carotid bodies and ventilatory response to hypoxia in aminophylline‐treated piglets

Peripheral chemoreceptors may be immature in neonatal animals, exhibiting maturational changes in the perinatal period. Even though methylxanthines are respiratory stimulants, many premature neonates do not respond to them. Thus, we hypothesized that carotid body activity is necessary for aminophylline to reverse hypoxia‐induced respiratory depression. We exposed 16 anesthetized newborn piglets (age 2‐7 days) to hypoxia (inhalation of 12% oxygen) for 5 min. Aminophylline (15 mg/kg iv) was administered either prior to (11 piglets) or following (5 piglets) carotid body denervation (CBD). Before CBD, hypoxia elicited transient initial increases in tidal volume (from 79 ± 4 to 99 ± 1% of maximum, mean ± SE), minute ventilation (from 64 ± 5 to 93 ± 4%), and peak phrenic electroneurogram (from 63 ± 8 to 91 ± 6%, all P < 0.05). This was followed by a decrease in tidal volume, minute ventilation and phrenic electroneurogram (all P < 0.05). Prior to CBD, aminophylline pretreatment prevented the decrease in all the measures of respiratory output during late hypoxia. After CBD, hypoxia induced an initial and sustained depression of ventilation (tidal volume from 100 to 33 ± 14%; frequency from 94 ± 4 to 42 ± 17%; minute ventilation from 100 to 32 ± 14%, all P < 0.05)and phrenic electroneurogram (peak phrenic from 100 to 47 ± 18%; minute phrenic from 85 ± 6 to 55 ± 21%, both P < 0.05). Administration of aminophylline after CBD did not prevent the profound respiratory depression elicited by hypoxia in the chemodenervated piglets. We conclude that aminophylline prevents respiratory depression during late hypoxia, however, in the absence of afferent input generated by the carotid bodies, aminophylline does not reverse respiratory depression induced by hypoxia in anesthetized newborn piglets. Pediatr Pulmonol. 1995; 20:94–100. © 1995 Wiley‐Liss, Inc.