Pulmonary and ductus arteriosus circulation in the fetal lamb before and after birth

Assali, N.S.; Sehgal, Nalini; Marable, Samuel A.

doi:10.1152/ajplegacy.1962.202.3.536

Cited by 32 publications

(19 citation statements)

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“…A further decrease in afterload may be explained by the exposure of the LV to the lower-resistance pulmonary circulation through the ductus arteriosus. A left-to-right shunt through the ductus, accounting for up to 30% of LV output, has been found to exist in the early transitional circulation (11, 41,42).…”

Section: Volumementioning

confidence: 99%

Determinants of Increased Left Ventricular Output during In Utero Ventilation in Fetal Sheep

et al. 1994

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A model of in utero ventilation was used to elucidate the mechanisms by which left ventricular (LV) output increases with the transition from a fetal to a neonatal circulation. Using a conductance catheter, LV volumes were measured in seven anesthetized, near-term fetal sheep. Pressure-volume data was recorded before and with oxygen ventilation and again after occlusion of the umbilical cord. Ventilation caused increases in LV end-diastolic volume (2.3 2 0.9 to 2.9 2 0.6 mL/kg; p < 0.05), stroke volume (1.2 2 0.3 to 1.9 2 0.2 mL/kg; p < 0.001), and ejection fraction (52.8 + 11.1 to 66.4 + 8.8%; p < 0.001).Contractile state, as assessed by end-systolic elastance, did not change during the transition. Heart rate also remained ' constant. Afterload, as assessed by effective arterial elastance, decreased from 1.80 2 0.37 to 1.04 2 0.33 kPa/mL @ < 0.01). Occlusion of the umbilical cord did not result in any further change in hemodynamic parameters.Pressure-volume analysis revealed that a decrease in effective LV afterload and an increased LV end-diastolic volume are the major determinants of, and contribute comparably to, the profound increase in LV output with in lttero ventilation. Enhanced contractility is not required for the increase in LV output to occur. (Pediatr Res 36: 373-379, 1994) Abbreviations LV, left ventricle RV, right ventricle dP/dt,,,, the maximum of the first time derivative of the LV pressure wave form E,,, end-systolic elastance E,,,, effective arterial elastance (afterload opposing LV ejection) PV, pressure-volume Adaptation of the fetus to extrauterine life involves a number of rapidly occurring processes. Among these, the initiation of breathing and the transition from a fetal to a neonatal circulation are the paramount events. In the fetal heart, which is characterized by RV dominance (1-3), the ventricles operate in parallel. After birth, the ventricles function serially and LV output increases 2-to 3-fold (4-10). The mechanism by which the L V increases its output to such an extent remains a mystery.In utero ventilation is associated with a marked increase in LV output identical with the increase observed in the immediate postpartum state. Either an increase in end-diastolic volume, ejection fraction, or both may underlie the augmented LV stroke volume. Ejection fraction could increase due to an increase in contractility or a reduction in afterload. Augmented LV end-diastolic volume as a result of increased pulmonary venous return (1 1-15) and an increase in contractility (16, 17) have both been suggested to play a role in augmenting LV output at birth. Because systemic pressure is increased or unchanged at birth, it has been suggested that a decrease in afterload is unlikely to occur (18). On the other hand, afterload may decrease due to the exposure of the LV to the pulmonary circulation through the patent ductus arteriosus (19). The individual contribution of each component to the augmentation of LV performance at birth is unknown. We applied the conductance catheter technique to the in...

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Section: Volumementioning

confidence: 99%

Determinants of Increased Left Ventricular Output during In Utero Ventilation in Fetal Sheep

et al. 1994

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“…Labor, delivery, rhythmic gaseous expansion of the lung (ventilation), increased oxygenation, umbilical cord clamping, and decreased environmental temperature are all components of the birth process and each may individually or in concert affect the circulation. Previous studies either have compared fetal measurements with those obtained postnatally after the entire birth process has been completed (6), or have been performed on acutely exteriorized, open-chest sheep fetuses (2,(7)(8)(9), in which cardiovascular responses may be greatly altered (10). A recent study has investigated the in zttero effects of oxygen ventilation on left ventricular output in fetal sheep ( I I), but the effects of ventilation prior to oxygenation and of umbilical cord occlusion were not studied, nor were the changes in right ventricular output and blood flow through the central shunts.…”

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Effects of Birth-Related Events on Central Blood Flow Patterns

1987

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ABSTRACT. We determined the effects of three components of the birth process on central blood flow patterns in fetal sheep. We instrumented 16 fetal sheep at 133.0 f 1.2 days gestation, inserting various intravascular catheters, intubating the trachea, and placing an inflatable balloon around the umbilical cord. After 2-3 days, we determined central blood flow patterns using radionuclidelabeled microspheres under control conditions, during positive pressure ventilation without oxygenation, during ventilation with 100% Oz, and after umbilical cord occlusion. The foramen ovale right to left shunt was essentially abolished, decreasing from 102 f 48 to 66 f 40 ml/min/ kg with ventilation, and to only 13 f 10 ml/min/kg with oxygenation. The ductus arteriosus right to left shunt decreased progressively, from a control level of 224 2 64 to 6 f 10 ml/min/kg after umbilical cord occlusion. A ductus arteriosus left to right shunt appeared with oxygenation (41 f 26 ml/min/kg) and increased to 65 f 43 ml/ min/kg after cord occlusion. Left ventricular output increased progressively a s a percentage of combined ventricular output (from a control value of 34.8 to 59.5% after cord occlusion), and increased absolutely with ventilation (from 134 f 44 to 211 f 87 ml/min/kg). However, right ventricular output decreased (from a control value of 258 f 75 to 144 f 36 ml/min/kg after cord occlusion) so that combined ventricular output did not change. Although the transition from the fetal to neonatal circulatory pattern was accomplished by simulating these three components of the birth process, none is alone responsible for the large increase in combined ventricular output normally seen a t birth. The adaptation of the fetus to extrauterine life involves numerous processes that occur rapidly. Paramount among these is the change in the pattern of circulation of blood. The fetal circulation is characterized by the presence of central shunts that direct systemic venous return to the systemic arterial circulation ( Fig. 1): the foramen ovale directs the more highly oxygenated umbilical venous blood from the right atrium to the left heart to supply oxygen to the heart, brain, and other organs, and the ductus arteriosus directs the less oxygenated right ventricular output via the descending aorta to the placenta for oxygen uptake. The right ventricle ejects about 50% more blood than the left ventricle in the sheep fetus (1). As part of the transition from fetal to neonatal life, these central blood flow patterns change abruptly. The right to left shunts through the foramen ovale (2) and through the ductus arteriosus (3) cease rapidly, and a transient left to right shunt occurs until the ductus arteriosus closes fully within a few hours after birth (3,4). The two ventricles eject the same volumes once the ductus arteriosus does close. Associated with the increased oxygen requirements after birth, left ventricular output increases 2-to 21/2-fold (5, 6).The specific factors that cause this dramatic change in central blood flow patterns and thei...

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“…T he fetu s w as th e n m arsu p ialized to th e tite rin c w alls to p ro te c t th e um bilical cir c u latio n b y a te c h n iq u e p rev io u sly described [5,6,7,8], T he com m on um bilical vein w as exposed insid e th e fetal p erito n eu m th ro u g h a sm all ab d o m in al incision a n d w as fitted w ith an electro m ag n etic flow tra n sd u c e r. In d w ellin g c a th e te rs w ere placed in to in te rc o ty le d o n a rv trib u ta rie s of th e u m b ilical a rte ry an d vein, a n d served for anaero b ic collection o f fetal a rte ria l a n d ven o u s blood an d for recording a rte ria l a n d venous p ressures. T ech n ical d etails of these proced u res h av e been p u b lish ed elsew here [5,6,7,8,9].T h e e x p e rim e n ta l design w as as follow s: 1. A 3 0 -6 0 m in perio d d u rin g w hich th e ew e w as n o rm o te n siv e and w as b re a th in g a ir-5 % CO., m ix tu re serv ed as c o n tro l; 2. a 20-30 m in p erio d o f sp inal b lo ck ad e w as in d u ced b y su b a ra c h n o id a d m in istra tio n o f 2 -5 m l o f 1% lidocaine h y d ro ch lo rid e (X y lo cain e); 3. a 20-30 m in period of in tra v e n o u s m e ta ra m in o l a d m in istra tio n followed using a ra te o f 4 /tg m /m in /k g a n d b eg in n in g a t m a x im u m spinal blockade as ju d g ed b y blood p ressu re re d u c tio n ; 4. th e m atern al a rte ria l pressure was allow ed to stab ilize a t n o rm a l levels for 30-40 m in ; 5. a second ep i sode of sp in al b lo ck ad e sim ilar to th e first was in d u c e d ; a n d 6. th e ew e's lun g s w ere v e n tila te d w ith a 9 5 % ()2-5 % C 0 2 gas m ix tu re.…”

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confidence: 99%

mentioning

confidence: 99%

Effects of Autonomic Blockade with Spinal Anesthesia on Uterine and Fetal Hemodynamies and Oxygen Consumption in the Sheep

Lucas¹,

Kirschbaum²,

Assali³

et al. 1966

Neonatology

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Pulmonary and ductus arteriosus circulation in the fetal lamb before and after birth

Cited by 32 publications

References 0 publications

Determinants of Increased Left Ventricular Output during In Utero Ventilation in Fetal Sheep

Determinants of Increased Left Ventricular Output during In Utero Ventilation in Fetal Sheep

Effects of Birth-Related Events on Central Blood Flow Patterns

Effects of Autonomic Blockade with Spinal Anesthesia on Uterine and Fetal Hemodynamies and Oxygen Consumption in the Sheep

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