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Muscle sympathetic nerve activity peaks in the first trimester in healthy pregnancy: a longitudinal case study
Sarah L Hissen1, Khadigeh El Sayed2, Vaughan G Macefield2,3,4
1School of Science and Health, Western Sydney University, Campbelltown Campus, Locked Bag 1797, Penrith, Sydney, NSW, 2751, Australia.
Objective And Methods:
Muscle sympathetic nerve activity and baroreflex sensitivity were examined at rest before, during (weeks 6, 11, 17, 22, 25, 33 and 36) and after a normotensive pregnancy.
Results:
Muscle sympathetic nerve activity is elevated during pregnancy with a large peak in the first trimester (Δ17 bursts/min) and a secondary peak in the third trimester (Δ11 bursts/min). Cardiac baroreflex sensitivity peaked in the first trimester (10 vs. 6 ms/mmHg pre-pregnancy), whereas sympathetic baroreflex sensitivity was greater throughout.
Interpretation:
The increase in sympathetic outflow early in pregnancy cannot be explained by a reduction in baroreflex sensitivity, while the secondary increase in burst frequency in the third trimester may, in part, be explained by the elevated heart rate.
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