Effect of baseline oxygenation on the ventilatory response to
inhaled 100% oxygen in preterm infants.
Haider, A. Zia, Virender Rehan, Saad Al-Saedi, Ruben Alvaro, Kim
Kwiatkowski, Don Cates, and Henrique Rigatto.
University of Manitoba, Department of Pediatrics, Winnipeg, MB, R3E
0L8 Canada
APStracts 2:0318A, 1995.
We tested the hypothesis that the immediate (<1 min) ventilatory
response to 100% O2 in preterm infants, a test of peripheral
chemoreceptor activity characterized by a decrease in ventilation due
to apnea, is more pronounced at lower baseline O2 concentrations. We
studied 12 healthy preterm infants [birthweight 1425+/-103 g (mean+/
-SEM); study weight 1670+/-93 g; gestational age 30+/-1 wks; postnatal
age 27+/-7 days] during quiet sleep. The infants inhaled 15%, 21%,
25%, 30%, 35%, 40%, and 45% O2 for 5 min in a randomized manner
(control period), followed by 100% O2 for 2 min, and then the same O2
concentration inhaled before 100% O2 for 2 min (recovery period). A
nosepiece and a flow-through system was used to measure ventilation.
The immediate decrease in ventilation with 100% O2 was 46% on 15% O2,
24% on 21% O2, 11% on 25% O2, 8% on 30% O2, 12% on 35% O2, and 8% on
40% O2; there was no decrease on 45% O2 (p<0.01). The
corresponding mean duration of apnea was: 29 s during 15% O2, 18 s
during 21% O2, 8 s during 25% O2, 9 s during 30% and 35% O2, and 3 s
during 40% O2; only one infant developed a 5 second apnea during 45%
O2 (p<0.001). The findings suggest 1) the ventilatory decrease
in response to 100% O2 is dependent on the baseline oxygenation,
being more pronounced the lower the baseline oxygen concentration;
and 2) this ventilatory decrease is entirely related to more
prolonged apneas observed with lower baseline O2 concentrations. We
speculate that the peripheral chemoreceptors, being so active in the
small preterm infant with relatively low O2 tension, are highly
susceptible to changes in O2 tension and this makes them prone to
irregular or periodic breathing, especially during sleep.
Received 30 November 1994; accepted in final form 10 July 1995.
APS Manuscript Number A1219-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.