The effect of cooling on breathing and shivering in unanaesthetized fetal lambs in utero.
The effects of cooling have been studied in chronically instrumented unanaesthetized fetal lambs of 106-132 days gestation. Cold stimulation of cutaneous thermoreceptors by means of a coil placed around the fetus in the amniotic cavity induced continuous breathing which was associated with high-voltage electrocortical activity throughout the cooling period. Direct internal cooling by means of an intragastric cooling coil did not alter fetal breathing or sleep-state patterns. Shivering occurred in response to both external and internal cooling, and this response was present as early as 106 days gestation, well before the appearance of high-voltage sleep. In older fetuses there was evidence of a reduction in thermoregulatory responses during low-voltage electrocortical activity, but not of the complete suspension of thermoregulation characteristic of low-voltage (r.e.m.) sleep seen in mature animals. It is concluded that deep regular breathing associated with high-voltage electrocortical activity can be induced by cold stimulation of cutaneous thermoreceptors, but not by a reduction in core temperature alone. Furthermore, fetal responses to cooling are present as early as 106 days gestation.
D000818:Animals; D001794:Blood Pressure; D001831:Body Temperature; D003080:Cold Temperature; D004569:Electroencephalography; D005260:Female; D005333:Fetus / Q000502:physiology*; D006339:Heart Rate; D011247:Pregnancy; D012119:Respiration; D012756:Sheep / Q000502:physiology*; D012768:Shivering; D012890:Sleep / Q000502:physiology