摘要:

Advances in molecular biology and in hematopoietic progenitor cell culture techniques have produced new tools with which to explore previously enigmatic aspects of developmental hematopoiesis. Studies using these tools are contributing mechanistic understanding to what was previously an entirely descriptive discipline and are generating new insight into the pathophysiology of various cytopenias in fetal and neonatal patients. This review of developmental hematopoiesis will address four related topics: 1) ontogeny of blood cells, 2) ontogeny of hematopoietic progenitors, 3) developmental regulation of hematopoietic growth factors, and 4) developmental aspects of interactions between hematopoietic progenitors and hematopoietic growth factors.

ISSN:0031-3998    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Whether severe hypoglycemia alone or in combination with hyperketonemia might cause deterioration of cardiac function has been controversial. Therefore, the influence of acute hypoglycemia (mean 33 mg/dL) with and without hyperketonemia (mean 1.3 and 3.3 mM) on cardiac function, substrate utilization, and myocardial high energy phosphate levels was studied in 10 mongrel dogs. After 45 min of hypoglycemia, mean aortic pressure, total peripheral resistance, and myocardial oxygen consumption had increased significantly, but other hemodynamic parameters and regional myocardial function had not changed. Additional infusion of 3-hydroxybutyrate did not affect hemodynamic variables significantly. During both metabolic interventionsin vivophosphorus-31 nuclear magnetic resonance spectroscopy showed stable levels of myocardial phosphocreatinine, ATP, as well as the phosphocreatinine/ ATP (3.0-3.2) ratio. Biochemical measurements revealed that hyperketonemia led to significant alterations in arterial concentrations and arteriocoronary venous differences of selected citric acid cycle intermediates, thus confirming previous reports which suggested a blockade of the 2- oxoglutarate-dehydrogenase reaction induced by ketone body oxidation. However, despite this blockade, the energy supply to the heart was not impaired as shown by normal nuclear magnetic resonance spectroscopy and cardiac performance. It is speculated, that the blockade might be due to an enhanced NADH/NAD ratio.

ISSN:0031-3998    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We studied the electrophysiological properties of adult (AD) and newborn (NB) rabbit papillary muscles in vitro with superfusion of normal Tyrode's solution, solutions with elevated [K+]o, and in solutions with various concentrations of tetrodotoxin. In control solutions, the NB papillary muscles had a more negative resting membrane potential (−83.6 ± 1.2versus−80.0 ± 1.5 mV), a higher rate of rise of phase 0 (134± 5versus120± 5 V/S) and a higher, longer-lasting action potential plateau than the AD papillary muscles. Exposure to elevated [K+]o led to a significant post-repolarization refractoriness in AD papillary muscles that was more than that for NB papillary muscles even when NB papillary muscles were depolarized to the same resting membrane potential as the AD papillary muscles. The NB papillary muscles were comparatively resistant to tetrodotoxin in terms of percent reduction of conduction velocity and percent rise in the current threshold for excitation. The conduction velocity for AD papillary muscles in control solution (66± 6 cm/s) was more than for NB papillary muscles (44 ±4 cm/s), which would not be expected from the data on the rate of rise of the action potential, suggesting that the cable properties of NB papillary muscles (specifically a greater surface to volume ratio of the ventricular cells) are also significantly different from the AD papillary muscles.

ISSN:0031-3998    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

To evaluate the central hemodynamic and regional blood flow changes associated with right ventricular hypertension in the newborn, 13 anesthetized, mechanically ventilated piglets less than 3 d old were acutely instrumented to permit measurements of central vascular pressures, cardiac output, and regional blood flow (radiolabeled microsphere technique). After initial measurements, right ventricular afterload was progressively increased by means of a pulmonary arterial mechanical occluder until right-to-left foramen ovale shunt was observed. An increase in pulmonary arterial pressure from 32 ± 2 to 55 ± 3 mm Hg was associated with a decrease in Pao2from 364 ± 16 to 88 ± 9 mm Hg and an increase in the shunt fraction from 13 ± 1 to 28 ± 1% (P< 0.01) during ventilation with oxygen. Right ventricular hypertension induced a significant decrease in systemic arterial pressure from 79 ± 3 to 63 ± 4 mm Hg, and left ventricular cardiac output from 156 ± 10 to 112 ± 11 mL · min-1· kg-1(P< 0.01), likely secondary to a reduction in left ventricular compliance. Oxygen delivery to the brain and heart were unaffected, due to a substantial increase in regional blood flow, but a significant reduction in delivery to the bowel and kidneys were observed. Contrary to what has been reported in the adult, myocardial blood flow to the right ventricle increased during hypertension. Metabolic acidosis was seen in all animals and the changes in serum bicarbonate and whole body oxygen consumption were directly related to the magnitude of decline in systemic O2delivery. In conclusion, right ventricular hypertension with right-toleft foramen ovale shunt is associated with a significant reduction in systemic arterial pressure and left ventricular cardiac output in the newborn. These changes coupled with a further decrease in arterial oxygen content secondary to the increase in shunt fraction, place the newborn animal with right ventricular hypertension at great risk for hypoxic- ischemic organ injury.

ISSN:0031-3998    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

This study compares the effects of prenatal exposure to terbutaline (a β-adrenergic agonist) and dexamethasone (a glucocorticoid) on the development of heart rate control mechanisms in the rat. Both drugs produced a persistent reduction in resting heart rate appearing during the 2nd postnatal wk, but by different mechanisms. Terbutaline affected the development of autonomic input from the CNS, characterized by a premature shift from sympathetic to parasympathetic dominance; thus, heart rate differences between terbutaline-exposed animals and controls resolved with acute treatment with a ganglionic blocking agent (chlorisondamine). Dexamethasone did not alter neural input to the myocardium (its actions were not reversed by ganglionic blockade), but instead reduced the intrinsic heart rate; the prenatal glucocorticoid treatment also reduced the sensitivity of the myocardium to β-adrenergic stimulation, a factor that could contribute to the alterations in intrinsic rate. These results suggest the potential need for studies of the functional cardiovascular consequences of fetal or neonatal therapeutic interventions with glucocorticoids or adrenergic agents.

ISSN:0031-3998    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We determined whether the simultaneous chest compression and ventilation (SCV) technique of cardiopulmonary resuscitation (CPR) enhances cerebral (CBF) and myocardial (MBF) blood flows and cerebral O2uptake in an infant swine model of CPR as it does in most adult animal CPR models. We also tested whether SCVCPR sustains CBF and MBF for prolonged periods of CPR when these flows ordinarily deteriorate. CPR was performed in two groups (n=8) of pentobarbital anesthetized piglets (3.5-5.5 kg) with continuous epinephrine infusion (10µg/kg/min). Conventional CPR was performed at 100 compressions/min, 60% duty cycle, 1:5 breath to compression ratio and 25-30 mm Hg peak airway pressure. SCVCPR was performed at 60 compressions/min, 60% duty cycle and 60 mm Hg peak airway pressure applied during each chest compression. Peak right atrial and aortic pressures in excess of 80 mm Hg were generated during CPR in both groups. At 5 min of conventional and SCV-CPR, MBF was 38 ± 7 and 46 ± 7 mL· min-1· l00 g-1 (±SE), respectively, and CBF was 15 ± 3 and 13 ± 2 mL· min-1· 100 g-1respectively. However, as CPR was prolonged to 50 min, the sternum progressively lost its recoil and the chest became more deformed. Lung inflation at high airway pressure with SCV-CPR did not prevent this chest deformation. Aortic pressure gradually declined, whereas right atrial and intracranial pressure remained constant in both groups. Consequently, MBF and CBF fell less than 10 mL· min-1· 100 g-1and cerebral O2uptake was markedly impaired during prolonged conventional and SCV-CPR. Therefore, SCV-CPR in an infant swine model does not enhance MBF and CBF during early CPR because intrathoracic pressure generation is already high with conventional CPR as reflected by the high right atrial pressure. In addition, SCV-CPR does not prevent the progressive chest deformation and the subsequent decline in CBF and MBF when CPR is prolonged, as is often required in pediatric resuscitation.

ISSN:0031-3998    

出版商:OVID    

年代:1989

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The effect of early treatment of patent ductus arteriosus (PDA) on the acute course of hyaline membrane disease was tested in a primate model, after intratracheal administration of 100 mg/kg exogenous bovine surfactant phospholipids at mean ages between 2.3-2.4 h. Twentytwo premature baboons were divided into four groups: seven animals were controls (group A); five were treated with surfactant but PDA was not intervened (group B); in five surfactant treatment was followed by three doses of 0.2 mg/kg intravenous indomethacin beginning at a mean age of 5.5 h (group C); and in five surfactant treatment was followed by a surgical ligation of PDA between 5-5.5 h of age. After surfactant instillation in groups B, C, and D, a prompt and sustained improvement was noted in a/APO2, mean airway pressure, ventilator efficiency index and pulmonary compliance. However, no consistent differences were found in the respiratory variables within the surfactant treated groups during the 72-h experiment: the respiratory course in the animals treated for PDA (groups C and D) was generally similar to the animals in which PDA was not treated (group B). In animals treated with surfactant and indomethacin (group C) the mean aortic blood pressure was maintained more optimally as compared to the other three groups. These findings suggest that although a significant early ductal shunting does occur after exogenous surfactant therapy in this animal model, the expected pulmonary deterioration does not occur, and an early abrupt interruption of PDA does not seem to provide additional advantage to the immediate course of hyaline membrane disease.

ISSN:0031-3998    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

To examine the effect of a patent ductus arteriosus on water accumulation and protein permeability in the premature, ventilated lung, we studied 16 Iambs at 121-127 d gestation (term=145 d). Water accumulation was assessed by the wet:dry wt ratio of the blood-free left lung. Protein permeability was assessed by the albumin content and by the recovery of125I-albumin in the right lung lavage fluid 1 h after intravenous injection. Using a model that allows mechanical control of ductus patency, we compared nine lambs with patent ductus (left-to-right shunts 42 ± 18% of left ventricular output) with seven lambs with closed ductus. The animals were studied over 3 h. In the open ductus lambs, 0.85 ± 0.36 and 1.76 ± 1.87%/h of the injected125I-albumin was recovered in the lavage fluid and lung tissue, respectively. In the closed ductus lambs, the corresponding amounts were 0.71 ± 0.21 and 0.71 ± 0.22%/h; these differences were not statistically significant. Similarly, blood-free wet:dry ratios did not differ significantly between the two groups (7.01 ± 1.28 open ductus versus 6.55 ± 0.82 closed ductus). We concluded that patency of the ductus arteriosus does not significantly affect water accumulation and net protein transudation into the airways of preterm lambs in the first hours of life. Therefore, some other feature of immaturity must be responsible for the large protein leaks previously observed by others.

ISSN:0031-3998    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Reflex modification procedures were used to test sensory processing in premature infants to examine the relationship between respiratory abnormalities and brainstem neuronal function. A total of 73 premature infants at risk for apnea and/or infants receiving methylxanthine therapy was given a 12-h pneumocardiogram and reflex modification test at a comparable postconceptional age, before discharge. Reflex modification was tested using a controlled eyeblink-eliciting tap to the glabella presented either alone or with a 1 kHz 90-dB SPL tone. The amplitude of the glabellar tap eyeblink and acoustically modified blink were lower in infants discharged on cardiac/apnea monitors (n=36) than in the unmonitored group (1.44 and 1.59 voltsversus2.15 and 2.39 V,p<0.005, respectively). At follow-up, 12 monitored infants had clinically significant apnea after discharge. The records of this subgroup of infants revealed a significantly lower augmentation of the glabellar eyeblink response when compared to all infants screened for respiratory abnormalities and to the other monitored babies (p<0.01). The data suggest that abnormalities of the ventilatory pattern and occurrence of clinical apnea in preterm infants may in some measure be related to acoustic sensory processing, implying an alteration of brainstem neuronal function and organization.

ISSN:0031-3998    

出版商:OVID    

年代:1989

数据来源: OVID