The Influence of Blood Pressure on Fetal Aortic Distensibility: An Animal Validation Study

Abstract

Background/Aims: Aortic distension waveforms describe the change in diameter or cross-sectional area over the cardiac cycle. We aimed to validate the association of aortic fractional area change (AFAC) with blood pressure (BP) in a fetal lamb model. Methods: Four pregnant ewes underwent open fetal surgery under general anesthesia at 107-120 gestational days. A 4-Fr catheter was introduced into the fetal femoral artery and vein, or the carotid artery and jugular vein. The thoracic aorta was imaged using real-time ultrasound; AFAC was calculated using offline speckle tracking software. Measurements of invasive BP and AFAC were obtained simultaneously and averaged over 10 cardiac cycles. BP was increased by norepinephrine infusion and the association of aortic distensibility with BP was assessed. Results: Baseline measurements were obtained from 4 lambs, and changes in aortic distensibility with increasing BP were recorded from 3 of them. A positive correlation was found between AFAC and systolic BP (r = 0.692, p = 0.001), diastolic BP (r = 0.647, p = 0.004), mean BP (r = 0.692, p = 0.001), and BP amplitude (r = 0.558, p = 0.016) controlled for heart rate. No association was found between BP and maximum or minimum aortic area. Conclusion: AFAC provides a quantifiable measure of aortic distensibility and correlates with systolic BP, diastolic BP, mean BP, and BP amplitude in a fetal lamb model.

Twin–twin transfusion syndrome: don't rely on fluids and bladders to catch it early

“…An alternative approach is to use the aortic distension waveform as a surrogate for the pressure waveform. In an animal model using cannulated fetal lambs, our group has confirmed that acute changes in fetal blood pressure translate into changes in aortic distensibility, measured using tissue tracking of the short axis of the descending aorta in the transverse abdominal view 25 . In a separate study of human monochorionic pregnancies complicated by TTTS, intertwin differences in aortic distensibility were present even in the early stages of TTTS, supporting the hypothesis that recipient hypertension is present in early TTTS 23 .…”

Fetal ventricular strain in uncomplicated and selective growth‐restricted monochorionic diamniotic twin pregnancies and cardiovascular response in pre‐twin–twin transfusion syndrome

“…Uncomplicated MCDA pregnancies, with no apparent functional abnormality, have shown altered vascular responses in childhood -and these have been attributed to fetal vascular programming in response to hemodynamic stressors and placental vasoactive products. [2][3][4][5][7][8][9][10][15][16][17][18][19][20][21] In contrast, few cardiac sequelae have been reported in childhood survivors of TTTS despite severe echocardiographic findings, demonstrating rapid cardiac remodeling once TTTS has been abolished by laser (or delivery after serial amnioreduction). [22][23][24] Currently, we know little of the effects of inter-twin transfusion and placental influences We observed gestational age reduction in both RV and LV strain, as in singleton pregnancies, 25 with no significant inter-twin pair differences in MCDAs remaining uncomplicated, or developing sIUGR.…”

“…In this study, sIUGR was present in 6/14 "pre-TTTS" pregnancies. There was absent or in DVeT% >3.6% up to 2 weeks prior to laser was evident in 8/13 "pre-TTTS" cases (1,4,5,6,10,11,13,14) indicating unbalanced inter-twin transfusion (Table 4).…”

“…1 Hence, the pathophysiological triggers involved in the transition from balanced to unbalanced inter-twin transfusion resulting in TTTS remain largely unknown. [2][3][4][5] In addition, selective intrauterine growth restriction (sIUGR) is common in MCDA pregnancies and is thought to be due to unequal early cytoplasmic division of the egg further compounded by unequal placental sharing. 6 However, the influence of sIUGR on cardiovascular function in monochorionic pregnancies and on the development of TTTS has not been characterized.…”

Ultrasound measurement of fetal arterial pulse pressure using phased‐tracking methods: A phantom study and clinical experience with antenatal corticosteroid therapy

“…With recent advancements in ultrasound technology, noninvasive methods of fetal blood pressure estimation have been sought 2–6 . Several studies have reported a linear relationship between blood pressure and internal diameter or fractional area change in the descending aorta in animal models 2–4 . Although this method gives us meaningful parameters regarding blood pressure changes, it is not intended for the direct determination of the fetal blood pressure.…”