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May RW, Maso Talou GD, Clark AR, Mynard JP, Smolich JJ, Blanco PJ, Müller LO, Gentles TL, Bloomfield FH, Safaei S. From fetus to neonate: A review of cardiovascular modeling in early life. WIREs Mech Dis 2023:e1608. [DOI: 10.1002/wsbm.1608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2022] [Revised: 01/31/2023] [Accepted: 03/03/2023] [Indexed: 04/03/2023]
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Smolich JJ. Understanding the physiology of immediate and delayed umbilical cord clamping at birth: Need for evidence-based pathway to reduce confusion. J Physiol 2022; 600:3627-3631. [PMID: 35819860 DOI: 10.1113/jp283393] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 06/17/2022] [Indexed: 11/08/2022] Open
Affiliation(s)
- Joseph J Smolich
- Heart Research, Murdoch Children's Research Institute, University of Melbourne, Parkville, VIC, Australia.,Department of Paediatrics, University of Melbourne, Parkville, VIC, Australia
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Smolich JJ, Cheung MMH, Mynard JP. Reducing lung liquid volume in fetal lambs decreases ventricular constraint. Pediatr Res 2021; 90:795-800. [PMID: 33504958 DOI: 10.1038/s41390-020-01352-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Revised: 10/28/2020] [Accepted: 12/22/2020] [Indexed: 01/13/2023]
Abstract
BACKGROUND This study evaluated whether an increased left ventricular (LV) pump function accompanying reduction of lung liquid volume in fetal lambs was related to increased LV preload, augmented LV contractility, or both. METHODS Eleven anesthetized preterm fetal lambs (gestation 128 ± 2 days) were instrumented with (1) an LV micromanometer-conductance catheter to obtain LV end-diastolic volume (EDV) and end-diastolic pressure (EDP), the maximal rate of rise of LV pressure (dP/dtmax), LV output, LV stroke work, and LV end-systolic elastance (Ees), a relatively load-independent measure of contractility; (2) an endotracheal tube to measure mean tracheal pressure and to reduce lung liquid volume. LV transmural pressure was calculated as LV EDP minus tracheal pressure. RESULTS Reducing lung liquid volume by 16 ± 4 ml kg-1 (1) augmented LV output (by 16%, P = 0.001) and stroke work (29%, P < 0.001), (2) increased LV EDV (12%, P < 0.001), (3) increased LV transmural pressure (2.2 mmHg, P < 0.001), (4) did not change LV dP/dtmax normalized for EDV (P > 0.7), and (5) decreased LV Ees (20%, P < 0.01). CONCLUSION These findings suggest a rise in LV pump function evident after reduction of lung liquid volume in fetal lambs was related to increased LV preload secondary to lessening of external LV constraint, without any associated rise in LV contractility. IMPACT This study has shown that reducing the volume of liquid filling the fetal lungs lessens the degree of external constraint on the heart. This lesser constraint permits a rise in left ventricular dimensions and thus greater cardiac filling that leads to increased left ventricular pumping performance. This study has defined a mechanism whereby a reduction in lung liquid volume results in enhanced pumping performance of the fetal heart. These findings suggest that a reduction in lung liquid volume which occurs during the birth transition contributes to increases in left ventricular dimensions and pumping performance known to occur with birth.
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Affiliation(s)
- Joseph J Smolich
- Heart Research, Murdoch Children's Research Institute, Parkville, VIC, Australia. .,Department of Paediatrics, University of Melbourne, Parkville, VIC, Australia.
| | - Michael M H Cheung
- Heart Research, Murdoch Children's Research Institute, Parkville, VIC, Australia.,Department of Paediatrics, University of Melbourne, Parkville, VIC, Australia.,Department of Cardiology, Royal Children's Hospital, Parkville, VIC, Australia
| | - Jonathan P Mynard
- Heart Research, Murdoch Children's Research Institute, Parkville, VIC, Australia.,Department of Paediatrics, University of Melbourne, Parkville, VIC, Australia.,Department of Cardiology, Royal Children's Hospital, Parkville, VIC, Australia.,Department of Biomedical Engineering, University of Melbourne, Parkville, VIC, Australia
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Smolich JJ, Kenna KR, Phillips SE, Mynard JP, Cheung MMM, Lambert GW. Characteristics and physiological basis of falls in ventricular outputs after immediate cord clamping at delivery in preterm fetal lambs. J Physiol 2021; 599:3755-3770. [PMID: 34101823 DOI: 10.1113/jp281693] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Accepted: 06/07/2021] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Controversy exists about the physiological mechanism(s) underlying decreases in cardiac output after immediate clamping of the umbilical cord at birth. To define these mechanisms, the four major determinants of ventricular output (afterload, preload, heart rate and contractility) were measured concurrently in fetal lambs at 15 s intervals over a 2 min period after cord clamping and before ventilation following delivery. After cord clamping, right (but not left) ventricular output fell by 20% in the initial 30 s, due to increased afterload associated with higher arterial blood pressures, but both outputs then halved over 45 s, due to a falling heart rate and deteriorating ventricular contractility accompanying rapid declines in arterial oxygenation to asphyxial levels. Ventricular outputs subsequently plateaued from 75 to 120 s, associated with rebound rises in ventricular contractility accompanying asphyxia-induced surges in circulating catecholamines. These findings provide a physiological basis for the clinical recommendation that effective ventilation should occur within 60 s after immediate cord clamping. ABSTRACT Controversy exists about the physiological mechanism(s) underlying large decreases in cardiac output after immediate clamping of the umbilical cord at birth. To define these mechanisms, anaesthetized preterm fetal lambs (127(1)d, n = 12) were instrumented with flow probes and catheters in major central arteries, and a left ventricular (LV) micromanometer-conductance catheter. Following immediate cord clamping at delivery, haemodynamics, LV and right ventricular (RV) outputs, and LV contractility were measured at 15 s intervals during a 2 min non-ventilatory period, with aortic blood gases and circulating catecholamine (noradrenaline and adrenaline) concentrations measured at 30 s intervals. After cord clamping, (1) RV (but not LV) output fell by 20% in the initial 30 s, due to a reduced stroke volume associated with increased arterial blood pressures, (2) both outputs then halved over the next 45 s, associated with falls in heart rate, arterial blood pressures and ventricular contractility accompanying a rapid decline in arterial oxygenation to asphyxial levels, (3) reduced outputs subsequently plateaued from 75 to 120 s, associated with rebound rises in blood pressures and ventricular contractility accompanying exponential surges in circulating catecholamines. These findings are consistent with a time-dependent decline of ventricular outputs after immediate cord clamping, which comprised (1) an initial, minor fall in RV output related to altered loading conditions, (2) ensuing large decreases in both LV and RV outputs related to the combination of bradycardia and ventricular dysfunction during emergence of an asphyxial state, and (3) subsequent stabilization of reduced LV and RV outputs during ongoing asphyxia, supported by cardiovascular stimulatory effects of marked sympathoadrenal activation.
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Affiliation(s)
- Joseph J Smolich
- Heart Research, Murdoch Children's Research Institute, Parkville, Victoria, Australia.,Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia
| | - Kelly R Kenna
- Heart Research, Murdoch Children's Research Institute, Parkville, Victoria, Australia
| | - Sarah E Phillips
- Iverson Health Innovations Research Institute, Swinburne University of Technology, Hawthorn, Victoria, Australia.,Human Neurotransmitters Laboratory, Baker Heart and Diabetes Institute, Prahran, Victoria, Australia
| | - Jonathan P Mynard
- Heart Research, Murdoch Children's Research Institute, Parkville, Victoria, Australia.,Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia.,Department of Cardiology, Royal Children's Hospital, Parkville, Victoria, Australia.,Department of Biomedical Engineering, University of Melbourne, Parkville, Victoria, Australia
| | - Michael M M Cheung
- Heart Research, Murdoch Children's Research Institute, Parkville, Victoria, Australia.,Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia.,Department of Cardiology, Royal Children's Hospital, Parkville, Victoria, Australia
| | - Gavin W Lambert
- Iverson Health Innovations Research Institute, Swinburne University of Technology, Hawthorn, Victoria, Australia.,Human Neurotransmitters Laboratory, Baker Heart and Diabetes Institute, Prahran, Victoria, Australia
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Smolich JJ, Mynard JP. Antenatal betamethasone redistributes central blood flows and preferentially augments right ventricular output and pump function in preterm fetal lambs. Am J Physiol Regul Integr Comp Physiol 2021; 320:R611-R618. [PMID: 33596742 DOI: 10.1152/ajpregu.00273.2020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The glucocorticosteroid betamethasone, which is routinely administered prior to anticipated preterm birth to enhance maturation of the lungs and the cardiovascular system, has diverse fetal regional blood flow effects ranging from increased pulmonary flow to decreased cerebral flow. The aim of this study was to test the hypothesis that these diverse effects reflect alterations in major central flow patterns that are associated with complementary shifts in left ventricular (LV) and right ventricular (RV) pumping performance. Studies were performed in anesthetized preterm fetal lambs (gestation = 127 ± 1 days, term = 147 days) with (n = 14) or without (n = 12) preceding betamethasone treatment via maternal intramuscular injection. High-fidelity central arterial blood pressure and flow signals were obtained to calculate LV and RV outputs and total hydraulic power. Betamethasone therapy was accompanied by 1) increased RV, but not LV, output; 2) a greater RV than LV increase in total power; 3) a redistribution of LV output away from the fetal upper body region and toward the lower body and placenta; 4) a greater proportion of RV output passing to the lungs, and a lesser proportion to the lower body and placenta; and 5) a change in the relative contribution of venous streams to ventricular filling, with the LV having increased pulmonary venous and decreased foramen ovale components, and the RV having lesser superior vena caval and greater inferior vena caval portions. Taken together, these findings suggest that antenatal betamethasone produces a widespread redistribution of central arterial and venous flows in the fetus, accompanied by a preferential rise in RV pumping performance.
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Affiliation(s)
- Joseph J Smolich
- Heart Research, Murdoch Children's Research Institute, Parkville, Victoria, Australia.,Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia
| | - Jonathan P Mynard
- Heart Research, Murdoch Children's Research Institute, Parkville, Victoria, Australia.,Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia.,Department of Cardiology, Royal Children's Hospital, Parkville, Victoria, Australia.,Department of Biomedical Engineering, University of Melbourne, Parkville, Victoria, Australia
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