Hemodynamic vulnerability to acute hypoxia in day 10.5-16.5 murine embryos.
OBJECTIVE
We tested the hypothesis that murine embryonic cardiovascular (CV) function is vulnerable to transient changes in maternal transplacental oxygen support during the critical period of CV morphogenesis.


METHODS
We measured maternal heart rate (MHR), maternal blood pressure (MBP), and embryonic heart rate (EHR) during mechanical ventilatory support, then induced transient maternal hypoxia daily from gestation day (ED) 10.5 to ED16.5 in pregnant ICR mice. Hypoxia was induced by suspending mechanical ventilation for 30 s or by the replacement of inspired oxygen with nitrogen (75% or 100%) for 30 s while maintaining ventilation.


RESULTS
We noted a rapid onset of maternal hypotension in response to hypoxia that quickly recovered following reoxygenation. Following a brief lag time that was not gestation specific, EHR decreased in response to hypoxia. The magnitude of embryo bradycardia and the rate of EHR decline and recovery displayed gestation specific patterns. The magnitude of embryo bradycardia was similar from ED10.5 to ED13.5 and then increased with gestation. Before ED13.5, only 40% of embryos recovered to the baseline EHR following transient maternal hypoxia (vs 80% of embryos after ED 13.5). EHR following recovery exceeded baseline EHR after ED15.5. Nitrogen inhalation (75% or 100%) produced changes in maternal and embryonic hemodynamics similar to suspended ventilation induced hypoxia.


CONCLUSIONS
The mammalian embryo is vulnerable to transient decreases in maternal oxygenation during the critical period of organogenesis and the gestational specific EHR response to hypoxia may reflect both increased embryonic oxygen demand and the maturation of neurohumoral heart rate regulation.
Furukawa
Seishi
S
Department of Obstetrics and Gynecology, Miyazaki Medical College, Miyazaki, Japan, and Department of Pediatrics, Children's Hospital of Pittsburgh Heart Center, PA 15213, USA.
Tinney
Joseph P
JP
Tobita
Kimimasa
K
Keller
Bradley B
BB
D000818:Animals; D001784:Blood Gas Analysis; D002319:Cardiovascular System / Q000196:embryology*; D004622:Embryo, Mammalian / Q000502:physiology*; D005260:Female; D005865:Gestational Age; D006339:Heart Rate / Q000502:physiology; D000860:Hypoxia / Q000503:physiopathology*; D051379:Mice; D008813:Mice, Inbred ICR; D038081:Organogenesis / Q000502:physiology; D021041:Placental Circulation; D011247:Pregnancy