Study of peripheral circulation in non-pregnant, pregnant and pre-eclamptic women using applied potential tomography

Profound changes are known to occur in the cardiovascular system during pregnancy, involving an increase in cardiac output and a fall in peripheral resistance. In some women these adaptations may be inappropriate and this may result in pregnancy-induced hypertension and pre-eclampsia.

The aims of the study were to evaluate the relatively new, non-invasive technique of applied potential tomography (APT) in measurements of peripheral blood flow, to study peripheral blood flow in a sample of non-pregnant, pregnant and pre-eclamptic women, and to investigate whether the adaptive changes in the peripheral circulation are different in pre-eclampsia compared with normal pregnancy. Applied potential tomography was used to assess peripheral vascular reactivity, by monitoring fluid distribution in calf muscles during postural change.

The APT technique was able to detect peripheral vasoconstriction in response to an increase in intramural pressure brought about by passive lowering of the leg (peripheral mechanisms). The peripheral vasoconstriction response was found to be more prominent in woman with pre-eclampsia.

The presence of a local reflex in the lower limb had been postulated and the effect of this reflex on the peripheral circulation could be detected using APT, regardless of how it was initiated. In normal pregnant women this reflex was diminished when compared to non-pregnant women, which might contribute to the reduction in peripheral vascular resistance seen in normal pregnancy. This reflex was defective in pre-eclampsia and this lack of adaptation may be a local reflex contributing to the raised peripheral resistance, which in turn may be a factor in high blood pressure in pre-eclampsia.