The effect of carotid sinus denervation on fetal heart rate variation in normoxia, hypoxia and post-hypoxia in fetal sheep.
OBJECTIVE
To investigate whether carotid sinus nerve reflexes are linked to the increase in heart rate variation in acute (one hour) hypoxia in late gestation fetal sheep


METHODS
Comparison of short term variation between intact and carotid sinus denervated fetuses in normoxia, hypoxia and post-hypoxia.


METHODS
Sixteen chronically catheterised pregnant sheep in late gestation.


RESULTS
There was no significant difference in short term variation between intact and denervated fetuses in normoxia. In intact fetuses short term variation increased significantly in hypoxia. In denervated fetuses it tended to increase in hypoxia, but this was not statistically significant. During the post-hypoxia period, short term variation increased significantly in denervated fetuses, although at this time it was decreasing in intact fetuses. When the decrease in pH was small intact fetuses showed a significantly greater increase in short term variation than denervated fetuses in hypoxia. In contrast, short term variation increased similarly in both groups when the pH decrease was greater (> 0.03 in early hypoxia and > 0.05 in late hypoxia).


CONCLUSIONS
Carotid sinus nerve reflexes have an important influence on heart rate variation in hypoxia and post-hypoxia. It appears that other mechanisms (e.g. a rise in circulating catecholamines) are linked to an increase in heart rate variation when mild acidemia occurs in hypoxia.
Kozuma
S
S
Department of Obstetrics and Gynaecology, University College Hospital, London, UK.
Watanabe
T
T
Bennet
L
L
Green
L R
LR
Hanson
M A
MA
D000818:Animals; D001794:Blood Pressure; D002346:Carotid Sinus / Q000294:innervation*; D003714:Denervation; D005260:Female; D006340:Heart Rate, Fetal / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000503:physiopathology*; D011247:Pregnancy; D012756:Sheep