Retrograde lower body arterial reservoir discharge underlies rapid reversal of ductus arteriosus shunting after early cord clamping at birth in preterm lambs

Abstract

Arterial reservoir ("windkessel") function, whereby a part of left ventricular (LV) output is stored in elastic arteries during systole and discharged in diastole, is a well-established physiological phenomenon. However, its role in rapid reversal (to left-to-right) and a systolic-to-diastolic shift of shunting across the ductus arteriosus after birth is unknown. To address this question, ductal and aortic isthmus flows were measured with high-fidelity transit-time probes in six anesthetized preterm fetal lambs before and after cord clamping and subsequent early mechanical ventilation and for 30 min postbirth. Descending aortic flow was calculated as the sum of isthmus and ductal flows. Left-to-right ductal flow profiles were related to those of the isthmus and descending aorta, with upper body arterial reservoir discharge indicated by forward diastolic isthmus flow, and retrograde lower body arterial reservoir discharge by negative diastolic descending aortic flow. Left-to-right ductal shunting appeared immediately after cord clamping (P < 0.001), due entirely to newly emergent retrograde lower body reservoir discharge, and rose with ventilation via increased lower body reservoir discharge (P < 0.005), supplemented by upper body reservoir discharge after 45 s (P < 0.025) and LV systolic flow after 3 min (P = 0.025). The contribution of lower body reservoir discharge to left-to-right ductal shunting fell to 55 ± 8% at ≥15 min (P < 0.001) but remained higher (P < 0.002) than LV systolic flow (33 ± 8%) or upper body reservoir discharge (12 ± 5%). These results suggest that retrograde lower body arterial reservoir discharge plays a key role in rapid reversal and a systolic-to-diastolic shift of ductal shunting after cord clamping and early ventilation at birth.

Increased right ventricular power and ductal characteristic impedance underpin higher pulmonary arterial blood flow after betamethasone therapy in fetal lambs

“…We also cannot exclude the possibility that non-closure of the thoracotomy after completion of instrumentation may have altered fetal hemodynamic variables. However, any effects of an open-chest state were likely to have been quite minor, given that, as mentioned previously, [10][11][12]17,18,22 variables such as heart rate, Data are expressed as mean ± SD; n = 8 for the control and n = 10 for the betamethasone groups PA pulmonary artery, PT pulmonary trunk Data are expressed as mean ± SD; n = 8 for the control and n = 10 for the betamethasone groups RV right ventricle arterial blood pressure, the morphology of ductal and PA flow profiles, as well as mean ductal and PA flows in our preparation are similar to those reported in closed-chest (and chronically instrumented) fetal preparations.…”

“…The PT blood flow profile (i.e., RV outflow) was obtained as the sum of instantaneous ductal and main PA flows, with the latter calculated as the product of measured left PA flow and the total-to-left lung weight ratio. 18 Hemodynamic analyses were performed on ensemble-averaged signals typically generated from 40 to 50 individual beats.…”

Versatile microfluidic flow generated by moulded magnetic artificial cilia

“…For example, the duration of the flow profile and the peak flow speed can be adjusted by modifying the time period of the actuation and the amplitude of the actuation frequency accordingly. In that way, the flow generated by our LAP MAC can mimic physiological flow profiles such as actual blood flow in our vessels [27], especially when a more versatile control over the magnetic field is realized (e.g. using an electromagnet).…”

Antenatal betamethasone augments early rise in pulmonary perfusion at birth in preterm lambs: role of ductal shunting and right ventricular outflow distribution

“…The PT blood flow profile (i.e., RV output) was derived as the instantaneous sum of ductal and the total left and right PA flow, with the latter calculated as the product of left PA flow and the total-to-left lung weight ratio (31,33). Note that 1) with an open chest, mechanical ventilation after birth had very minor effects on calculated RV output (data not shown), and 2) to permit direct comparison with PT and ductal flows, reported PA flows refer to calculated total values.…”

“…The first is an increase in the contribution of RV-derived blood to PA flow, related to an elevation in RV output and/or a greater distribution of this output to the lungs. Second, reversal of shunting across the ductus from right-to-left in the fetus to left-to-right in the newborn is accompanied by emergence of a positive diastolic offset in the PA flow profile (8,33,35). An initially higher diastolic PA blood flow after birth following antenatal betamethasone ( 9) is therefore suggestive of a more rapid reversal in ductal shunting.…”