title: Fetal breathing, sleep state, and cardiovascular responses to graded hypoxia in sheep.
abstract: Graded isocapnic hypoxemia was produced in unanesthetized fetal sheep by varying the inspired O2 concentration (21, 12, 10.5, and 9%) of the ewe. This produced corresponding mean preductal arterial O2 tension (PaO2) values of 25.2 +/- 1.1 (control), 20.1 +/- 1.0 (mild hypoxia), 17.8 +/- 0.9 (moderate hypoxia), and 16.8 +/- 1.4 Torr (severe hypoxia). These were associated with mean arterial O2 contents (CaO2) of 7.18 +/- 0.44, 5.19 +/- 0.34, 4.24 +/- 0.33, and 3.27 +/- 0.20 ml/dl, respectively. The most severe hypoxia was associated with metabolic acidosis and fetal bradycardia. Hypoxia did not reduce significantly the incidence of low-voltage electrocortical activity. The incidence of breathing and rapid eye movements was not affected by mild hypoxia; however, the incidence of both was significantly reduced during moderate and severe hypoxia. It is concluded that 1) acute reductions in the mean PaO2 of 5.9 +/- 0.6 Torr and CaO2 of 2.00 +/- 0.23 ml/dl are critical in that greater reductions inhibit fetal eye and breathing activity and 2) hypoxia probably inhibits eye and breathing movements by altering sleep state.
mesh_terms: D000818:Animals; D002319:Cardiovascular System / Q000196:embryology* / Q000503:physiopathology; D005133:Eye Movements; D005312:Fetal Blood / Q000032:analysis; D005333:Fetus / Q000502:physiology*; D006454:Hemoglobins / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000503:physiopathology*; D010100:Oxygen / Q000097:blood; D012119:Respiration; D012756:Sheep; D012890:Sleep
chemical_list: D006454:Hemoglobins; D010100:Oxygen