Poster Presentation & Flash Talk 46th Annual Meeting of the Fetal and Neonatal Physiological Society 2019

Combining fetal blood flow as determined by phase contrast magnetic resonance imaging with blood pressure waveforms to understand vascular biomechanics (#113)

Jack R.T. Darby 1 , Rakhi Tilak 2 , Brahmdeep S Saini 2 , Greg Stortz 2 , Eric M Schrauben 2 , Stacey L Holman 1 , Mitchell C Lock 1 , Mike Seed 2 , Christopher K Macgowan 2 , Janna L Morrison 1
  1. University of South Australia, Adelaide, Australia
  2. University of Toronto and The Hospital for Sick Children, Toronto, Canada

Prenatal insults such as preeclampsia, placental insufficiency or maternal undernutrition have the capacity to influence progeny vascular remodelling and is associated with arterial hypertension and  poorer cardiovascular outcomes in later life. Although vascular biomechanics and responsiveness can be extensively studied ex vivo using techniques such as pressure or wire myography, these techniques do not necessarily reflect the physiological complexity of vascular function in an in vivo environment. Herein, we present an in vivo technique of determining parameters describing fetal vascular biomechanics. At 108-110 days (d) gestation, pregnant Merino ewes (n=7) underwent surgery to implant vascular catheters into the fetal femoral artery, vein and amniotic cavity. At 126-127d gestation, pregnant ewes underwent a magnetic resonance imaging (MRI) scan. During the scan, fetal blood pressure was obtained from the catheter in the fetal femoral artery, where the tip of the catheter was in the fetal descending aorta (fDAo) at the level of the renal artery. The fetal blood pressure trace was used to trigger the MRI to acquire blood flow within the fDAo using phase-contrast (PC) MRI and the area of the fDAo lumen was determined using the contouring feature in the post processing software Segment (Medviso, Lund, Sweden). Blood pressure and flow waveforms averaged over multiple cardiac cycles (Figure 1) were analyzed with custom built software written in Python to calculate vascular biomechanical properties including vascular resistance, characteristic impedance, pulse wave velocity and input impedance. Calculation of such values may inform on vessel stiffness, impedance within the given blood vessel and vascular remodelling and architecture of the downstream tissue bed. Overall, we have developed an in vivo technique to characterise fetal vascular biomechanics. Such a technique would be well placed to inform on fetal vascular biomechanics in the setting of preclinical studies of in utero substrate restriction.

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