The effect of 10% O2 on the continuous breathing induced by O2 or O2 plus cord occlusion in the fetal sheep.
Journal - Journal of developmental physiology (ENGLAND )
Although the administration of 100% O2 alone or combined with umbilical cord occlusion induces continuous breathing and arousal in the fetal sheep (Baier, Hasan, Cates, Hooper, Nowaczyk & Rigatto, 1990a), the individual contribution of O2 and cord occlusion to the response have not been determined. We hypothesized that if O2 is an important factor in the induction of continuous breathing, administration of O2 low enough (10%) to bring fetal arterial PO2 to about 20 torr while the fetus is breathing continuously should reverse these changes. Thus we subjected 12 chronically instrumented fetal sheep to 10% O2 for 10 minutes after the establishment of continuous breathing by O2 (4 fetuses; 137 +/- 1 days) or by O2 plus umbilical cord occlusion (8 fetuses; 134 +/- 1 days). Arterial PO2 decreased from about 250 torr to 20 torr during 10% O2. This induced a significant decrease in breathing output (EMGdi x f) related primarily to a decrease in frequency (f). In 3/5 experiments in 4 fetuses, with O2 alone, apnoea developed within 4 +/- 0.6 min; in 12/13 experiments in 8 fetuses, with added cord occlusion it developed at 5 +/- 0.6 min. With the decrease in PaO2, electrocortical activity (ECoG) switched from low to high-voltage within 6 minutes in 5/5 experiments (O2 alone) and in 11/13 (O2 plus cord occlusion). The findings suggest that umbilical cord occlusion alone is not sufficient to maintain breathing continuously and an increased PaO2 is needed. We speculate that in the fetus there is a vital link between PaO2, breathing and ECoG with low PaO2 inhibiting and high PaO2 favouring breathing and arousal.
|ISSN : ||0141-9846|
|Mesh Heading : ||Animals Apnea Electroencephalography Female Fetus Oxygen Partial Pressure Pregnancy Respiration Sheep prevention & control blood|
|Mesh Heading Relevant : ||Umbilical Cord physiology administration & dosage drug effects|
Sighs and their relationship to apnea in the newborn infant.
Journal - Biology of the neonate (SWITZERLAND )
To test the hypothesis that sighs are mechanistically important in triggering apnea, we studied 10 preterm infants, group 1: body weight 1.8 +/- 0.1 kg, gestational age 33 +/- 1 weeks, postnatal age 21 +/- 4 days, and 10 term infants, group 2: body weight 3.9 +/- 0.15 kg, gestational age 40 +/- 0.4 weeks, postnatal age 1.4 +/- 0.2 days. Instantaneous ventilatory changes associated with a sigh were studied in another 10 preterm infants, group 3: body weight 1.6 +/- 0.11 kg, gestational age 32 +/- 0.4 weeks, postnatal age 25 +/- 4 days. Ventilation was measured using a nosepiece and a flow-through system. Sleep states were recorded. Sighs were more frequent in preterm than in term infants (0.4 +/- 0.04 vs. 0.18 +/- 0.03 sighs/min; p = 0.03) and in rapid eye movement than in quiet sleep (0.5 +/- 0.05 vs. 0.3 +/- 0.05 sighs/min; p = 0.05). Of 722 apneas, 235 (33%) were associated with a sigh; of these, 113 (48%) preceded and 122 (52%) followed a sigh. Sighs induced with airway occlusion (groups 1 and 2) were more frequent after occlusion on 21 than on 35% O2, particularly when O2 saturation was low and negative airway pressure high. Instantaneous ventilation measured over 10 breaths preceding a sigh did not show any trend indicating the possible appearance of a sigh. Tidal volume increased from 7.5 +/- 0.7 before the sigh to 18.9 +/- 0.7 ml/kg (p < 0.01) during a sigh, with a significant increase in inspiratory drive. Ventilation increased from 0.327 +/- 0.041 to 0.660 +/- 0.073 l/min/kg.(ABSTRACT TRUNCATED AT 250 WORDS)
|ISSN : ||0006-3126|
|Mesh Heading : ||Airway Obstruction Analysis of Variance Anoxia Apnea Electromyography Humans Infant, Newborn Infant, Premature Pressure Respiration Respiratory Mechanics Respiratory Sounds Sleep Stages Tidal Volume complications physiopathology complications physiology physiology|
|Mesh Heading Relevant : ||etiology physiology physiology physiology physiology|