Ventricular function in the newborn lamb

Downing, S. E.; Talner, Norman S.; Gardner, Thomas H.

doi:10.1152/ajplegacy.1965.208.5.931

Cited by 60 publications

(30 citation statements)

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“…The combination of limited inotropic reserve coupled with a predominant systemic vasoconstrictive response to high infusion rates of dopamine as evidenced by increased aortic pressure and systemic vascular resistance, led to an inotropic:afterload mismatch resulting in the fall in cardiac output. It was interesting that Downing et al (21) using an in situ model of the newborn lamb heart, reported a decrease in stroke volume as systemic pressure (afterload) was increased within the range of aortic pressures that we observed in our study.…”

Section: Effects Of Dopumine Infusionsupporting

confidence: 55%

The Effects of Dopamine Infusion on Regional Blood Flow in Newborn Lambs

et al. 1987

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ABSTRACT. The purpose of this project was to investigate the effects of high rates of dopamine infusion on cardiac output and regional blood flow in the lamb. We studied eight unanesthetized newborn lambs (mean age 7 + 2 days) during a 15-min baseline period and while infusing dopamine at 5-, 20-, 80-, and 160 pg/kg/min. We measured cardiac output and mean aortic, pulmonary arterial and left atrial pressures, and organ blood flow using radionuclidelabeled microspheres at each rate of dopamine infusion. Cardiac output increased significantly with increasing rates of infusion up to 80 pg/kg/min but decreased at 160 pg/kg/ min. Aortic, pulmonary arterial, and left atrial pressures increased at rates of infusion above 5 pg/kg/min. Blood flow to all organs was unchanged at the 5 pg/kg/min rate of infusion of dopamine while blood flow to the brain and heart increased at the 80 pg/kg/min rate of infusion and blood flow to the gut and kidney decreased. We conclude that dopamine is an effective inotropic agent in the newborn lamb but that an inotropic:afterload mismatch exists at high infusion rates. Despite an increase in cardiac output at low rates of infusion, dopamine did not selectively vasodilate the vascular bed of any organs tested. Furthermore, at high rates of infusion dopamine actually impaired blood flow to the gut and kidney. (Pediatr Res 21: 131-136, 1987) Dopamine remains an extensively used catecholamine in the management of shock in critically ill infants and children (1). We recently studied the effects of dopamine on hemodynamics in 2-to 3-wk-old lambs and found it to be an effective inotropic agent (2). However, inherent properties of neonatal myocardium may render it relatively unresponsive to the inotropic actions of dopamine and the same effects may not occur in the younger lamb. In the clinical setting, myocardial immaturity may prompt the use of rates of infusion of dopamine in excess of those currently recommended (1). The effects of high rates of infusion on regional blood flow in the newborn are unknown.The purpose of our study was to investigate the effects of dopamine on regional blood flow in newborn lambs over a wide range of infusion rates. We hypothesized that in the newborn lamb dopamine would not increase cardiac output at conventionally used rates of infusion but might at higher rates. At these higher rates, however, we anticipated that the a-adrenergic effect of dopamine would compromise blood flow to vital organs. MATERIALS AND METHODSSurgical preparations. We operated on eight lambs using halothane and nitrous oxide anesthesia delivered by a piston type ventilator. From a left hindlimb cutdown we inserted polyvinyl catheters into a peripheral artery and vein and advanced them into the descending aorta and inferior vena cava, respectively. We also inserted a 3.5 Fr thermistor wire (Edwards Laboratories, Inc., Irvine, CA) into a peripheral artery by separate hindlimb cutdown and advanced it into the descending aorta. Finally, we placed a polyvinyl catheter in a forelimb artery and ad...

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Section: Effects Of Dopumine Infusionsupporting

confidence: 55%

The Effects of Dopamine Infusion on Regional Blood Flow in Newborn Lambs

et al. 1987

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“…Likewise, measurements taken from isolated sheep myocardium performing isotonic (changing muscle length) contraction shows that both the extent and velocity of shortening are greater in the adult than the fetal heart over a range of applied loads (Friedman, 1972). From a whole-organ perspective, the increasing volume-density of myofibrils is consistent with the observation that stroke volume is significantly depressed in neonate lambs at afterloads that are modest for adults (Downing et al, 1965). From a whole-animal perspective, the hyperallometry of myofibril volume-density and absolute volume, and the associated increase in relative cardiac contractile performance, would augment cardiac output during in-pouch development and in the lead up to pouch vacation, and thus almost certainly facilitate the kangaroo's transition from ectothermy to endothermy (Hulbert, 1988;Loudon et al, 1985;Rose et al, 1998) and independent locomotion (Dawson, 2012).…”

Section: Discussionsupporting

confidence: 61%

Scaling of left ventricle cardiomyocyte ultrastructure across development in the kangaroo Macropus fuliginosus

Snelling

Taggart

Maloney

et al. 2015

Journal of Experimental Biology

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The heart and left ventricle of the marsupial western grey kangaroo Macropus fuliginosus exhibit biphasic allometric growth, whereby a negative shift in the trajectory of cardiac growth occurs at pouch exit. In this study, we used transmission electron microscopy to examine the scaling of left ventricle cardiomyocyte ultrastructure across development in the western grey kangaroo over a 190-fold body mass range (0.355−67.5 kg). The volume-density (%) of myofibrils, mitochondria, sarcoplasmic reticuli and T-tubules increase significantly during in-pouch growth, such that the absolute volume (ml) of these organelles scales with body mass (M b ; kg) with steep hyperallometry: , respectively. The steep hyperallometry of organelle volumes and volume-densities across in-pouch growth is consistent with the improved contractile performance of isolated cardiac muscle during fetal development in placental mammals, and is probably critical in augmenting cardiac output to levels necessary for endothermy and independent locomotion in the young kangaroo as it prepares for pouch exit. The shallow hypoallometry of organelle volumes during post-pouch growth suggests a decrease in relative cardiac requirements as body mass increases in free-roaming kangaroos, which is possibly because the energy required for hopping is independent of speed, and the capacity for energy storage during hopping could increase as the kangaroo grows.

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“…As birth is associated with significant alterations of these determinants (36) and a doubling of cardiac output (26), there is significant interest and information available regarding the effects of isolated alterations of the determinants of cardiac output on cardiac function and output during the perinatal period. Most of the available information is focused on alterations of preload: studies on unanesthetized fetal and neonatal lambs have shown that an increase of preload is associated with an increase of stroke volume and cardiac output (10,15,22,24). The increase of pulmonary blood flow that occurs after the onset of respiration should increase left ventricular preload and this may account for some of the increase of cardiac output which occurs at birth.…”

Section: Discussionmentioning

confidence: 99%

The Effect of Atrial Pacing-Induced Tachycardia on Left Ventricular Contractile Function in Conscious Newborn and Adult Sheep

Fisher¹,

Gross²

1983

Pediatr Res

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SummaryIn order to determine if an increase in heart rate is associated with an increase of left ventricular contractile function during the neonatal period we recorded phasic and mean aortic blood pressure. left atrial mean or left ventricular end diastolic Dressure. phasic left ventricular blood pressure, aortic blood flow velocity and the instantaneous first derivatives of left ventricular blood pressure (dP/dt) and aortic blood flow velocity (dV/dt) during pacing-induced tachycardia in conscious newborn and adult sheep. There was a significant positive linear correlation between heart rate and both indices of contractility (dP/dt and dV/dt) in both age groups. Left ventricular end diastolic pressure was unchanged except for a decrease at the most rapid heart rate in the newborns. There was no change in aortic mean blood pressure during the study. Our data demonstrate that an increase of heart rate is associated with an increase of left ventricular contractile function in conscious neonatal and adult sheep. Investigations of the effects of potential inotropic agents on left ventricular contractile performance in newborns and adults must evaluate the independent effect of any simultaneously occurring increase in heart rate.The positive inotropic effect of an increase of contraction frequency was originally demonstrated in vitro by Bowditch (5). Multiple recent investigations in vitro have demonstrated that atrial pacing-induced tachycardia is associated with a small but significant increase in left ventricular contractile function in conscious adult humans and dogs (9, 17-19, 28, 33). Although there is some information available concerning the effect of a heart rate increase on left ventricular contractility in the unanesthetized lamb fetus (1, 23) and in neonatal cat and lamb heart muscle in vitro (1,8), to our knowledge there is no such information available in conscious neonates of any species. Therefore, we studied the effect of a pacing-induced heart rate increase on left ventricular contractile function in conscious newborn lambs. As species variability has been reported in adults (25) we also performed a pacing study in conscious adult sheep. MATERIALS AND METHODSSurgical technique. We operated on 1 1 Western newborn lambs 1-25 (9 + 2, mean + S.E.) days after birth and on 8 nulliparous female adult sheep. The lambs weighed 6.5 f 0.6 g. We anesthetized the animals with 1-2% fluothane (Halothane), intubated the trachea, and ventilated the lungs with an animal ventilator (Methomatic, Pittman-Moore). We performed a thoracotomy in the left fourth intercostal space and inserted polyvinyl catheters (inside diameter, 0.10 cm; outside diameter, 0.15 cm) into the ascending aorta via the left internal thoracic artery and into the left atrium through a purse-string suture in the atrial appendage. The catheters were closed after they were filled with heparin. We sutured a pair of stainless steel pacing wires (#A5633 hookup wire, Cooner Wire Co., Chatsworth, CA) to the left atrial epicardium. Through a separate incis...

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Ventricular function in the newborn lamb

Cited by 60 publications

References 0 publications

The Effects of Dopamine Infusion on Regional Blood Flow in Newborn Lambs

The Effects of Dopamine Infusion on Regional Blood Flow in Newborn Lambs

Scaling of left ventricle cardiomyocyte ultrastructure across development in the kangaroo Macropus fuliginosus

The Effect of Atrial Pacing-Induced Tachycardia on Left Ventricular Contractile Function in Conscious Newborn and Adult Sheep

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