C. Delacourt et al., PREDOMINANT ROLE OF PERIPHERAL CHEMORECEPTORS IN THE TERMINATION OF APNEA IN MATURING NEWBORN LAMBS, Journal of applied physiology, 80(3), 1996, pp. 892-898
Apneas are very common and normal in newborns but may become life thre
atening if they are not terminated appropriately. The aim of this stud
y in newborn lambs was to investigate the influence on apnea terminati
on of postnatal maturation, peripheral chemoreceptor function, and hyp
oxia. Apneas were induced by passive hyperventilation at varying inspi
red Oz fraction levels. The apnea termination threshold Pco(2) (PATT(c
o2)) was defined as the arterial P-co2 value at the first breath after
the apnea. Three groups of awake intubated lambs were studied: I)inta
ct lambs tested at both 1 and 15 days of life, 2) intact i-day-old lam
bs with central tissue hypoxia induced by CO inhalation, and 3) i-day-
old lambs with carotid body denervation (CBD). In individual lambs and
regardless of age and carotid body function, there was a Po-2-Pco(2)
response curve that was a determinant for the termination of an apnea.
PATT(co2) invariably increased when arterial P-o2 increased, regardle
ss of age. During hypoxia and normoxia, PATT(co2) was significantly lo
wer in 15-day-old lambs compared with i-day-old lambs. No difference w
as seen during hyperoxia. PATT(co2) values were shifted to higher leve
ls after carotid body removal. Finally, hypoxia induced by either a lo
w inspired Oz fraction or CO inhalation consistently failed to induce
a depressive effect on the PATT(co2) even in CBD lambs. Ln conclusion,
in awake newborn lambs, the Pco, level for apnea termination changed
with postnatal age, and carotid body function was essential in lowerin
g PATT(co2), thus protecting the lambs against prolonged apnea. Furthe
rmore, hypoxia consistently failed to depress the reinitiation of brea
thing after apnea, even in CBD lambs.