title: Effect of hyperoxia (PaO2 50-90 mmHg) on fetal breathing movements in the unanaesthetized fetal sheep.
abstract: Hypoxia inhibits fetal breathing movements but after birth it stimulates breathing. These differences have long been thought to involve central nervous inhibitory mechanisms. Such mechanisms might exert a tonic inhibition of fetal breathing movements at normal fetal PaO2 and the rise in PaO2 at birth might lift this inhibitory effect. To test this hypothesis 7 fetal sheep were chronically instrumented at 125-130 days for recording electrocortical activity (ECoG), and the electromyograph (EMG) activity of the diaphragm and neck muscles. Catheters were placed in a fetal carotid and a brachial artery and in the fetal trachea. For an extracorporeal membrane oxygenation system a 12 F gauge silastic catheter was placed in the right atrium for draining fetal blood and a 9.6 F gauge catheter was placed in a carotid artery to return oxygenated blood. Three days after operation the fetuses were connected to the extracorporeal membrane oxygenation system and fetal PaO2 was raised to 65.2 +/- 4.4 mmHg (SEM) for 6 to 19 h without changing pH or PaCO2. Neither the incidence of high voltage ECoG (48.5 +/- SEM 2.0% vs 52.8 +/- 3.3%) nor of fetal breathing movements (37.3 +/- 2.6% vs 23.8 +/- 5.9%) changed during the periods of hyperoxia. Since fetal breathing movements did not become continuous, we conclude that the lower PaO2 in the fetus compared to the neonate does not exert a tonic inhibitory influence on fetal breathing movements.
authors: Neonatal Division, Academic Hospital Maastricht, The Netherlands.
authors: C E
authors: CE
authors: Blanco
authors: V
authors: V
authors: Chen
authors: W
authors: W
authors: Maertzdorf
authors: O S
authors: OS
authors: Bamford
authors: M
authors: M
authors: Hanson
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D015199:Extracorporeal Membrane Oxygenation; D005333:Fetus / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D010100:Oxygen / Q000493:pharmacokinetics / Q000494:pharmacology*; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D015656:Respiratory Mechanics / Q000187:drug effects*; D012756:Sheep
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen