Pulsatility effects of flow on vascular tone in the fetoplacental circulation

The regulation of vascular tone in the fetoplacental circulation is governed by endocrine and mechanical forces yielding a relaxed basal state in normal pregnancy. Flow mediated vasodilation, induced by shear stress and endothelial nitric oxide signalling, is key to driving vasorelaxation in this circulation. The pulsatile property of blood flow, as opposed to the flow rate, could provide an additional factor in this regulation, but its effects and signalling have never been explored in the fetoplacental microvasculature.

Here, we studied the effects of non-pulsatile and pulsatile flow modalities on vascular resistance in the fetoplacental microcirculation of the human placenta using an ex vivo perfusion model; and examined a potential role for nitric oxide. We also explored whether the placental Doppler velocimetry waveform is sustained within subchorial arteries in vivo.

Pulsatile flow reduced basal impedance to flow during steady state perfusion compared to non-pulsatile flow, signalled through enhanced nitric oxide production. Doppler velocimetry waveforms were visible within the subchorial arteries in vivo.

This work suggests that the pulsatile property of flow through the fetoplacental circulation is sensed by the fetoplacental vasculature to mediate a signalling response and provide additional vasodilation of this microcirculation. We speculate that in pregnancy disease, altered amplitude and frequency of the subchorial pulse might impact on vascular function in a compromised high-resistance placental microcirculation.