title: Fetal breathing adaptation to prolonged hypoxaemia in sheep.
abstract: Prolonged (6 days) fetal hypoxaemia was produced by placing pregnant ewes in an environmental chamber. A constant flow of N2 into the chamber reduced the fraction of inspired oxygen (Fi02) to 0.139 +/- 0.001, simulating an altitude of 4270 m. This reduced maternal PaO2 by about 39 mmHg and PaCO2 by nearly 5 mmHg, which produced a hypocapnic (delta PaCO2 = -5 mmHg) hypoxaemia (delta PaO2 = -8 mmHg) in the fetus. An analysis of the first 4 h of breathing recorded each day (1800-2200 h; start of hypoxaemia: 1200 h) showed that the incidence (12 +/- 2.0 min/day) during the first day of hypoxaemia was significantly less (P less than 0.05) than that (24 +/- 3.1 min/h) during the same time of the control day. By the second day, breathing had returned to normal. Further analysis indicated that a normal incidence of breathing may have occurred as early as 14 h after starting hypoxaemia. These results suggest that fetal breathing movements adapt rather quickly to this degree of hypocapnic hypoxaemia.
mesh_terms: D000064:Acclimatization; D000532:Altitude Sickness / Q000196:embryology / Q000503:physiopathology; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D005260:Female; D005312:Fetal Blood / Q000032:analysis; D005333:Fetus / Q000502:physiology*; D000860:Hypoxia / Q000196:embryology* / Q000503:physiopathology; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D011247:Pregnancy; D012119:Respiration; D012756:Sheep
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen