摘要:

A modle of hypothermic circulatory arrest has been developed in the newborn dog. Ten puppies were anesthetized with halothane, paralyzed, and artificially ventilated with 70% nitrous oxide 30% oxygen to arterial oxygen pressure >8.0 kPa (60 mm Hg), arterial carbon dioxide pressure of 4.4–5.6 kPa (33–42 mm Hg), and arterial pH of 7.35–7.42. Animals were surface cooled to 20°C, after which cardiac arrest was produced with i.v. KCI. Dogs remained asystolic without ventilation for 1.0 (n = 4), 1.5 (n = 3), or 2.0 (n = 3) th Rescucitation was accomplished with closed-chest compression, mechanical ventilation, i.v. epinephrine and NaHCO3, and rewarming to 37°C. Postarrest recovery was maintained for 3–4 h; thereafter, the puppies underwent perfusion-fixation of their brains for pathologic analysis. Plasma glucose (control = 8.3 mmol/L) increased slightly during hypothermic cardiac arrest (+30%) but was markedly elevated at 15 min postarrest (20 mmol/L). Blood lactate (control = 1.1 mmol/L) increased almost 200% during hypothermic circulatory arrest, with a further rise to 9.0 mmol/L at 15 min postarrest. Thereafter, lactate decreased in the 1-h arrested dogs bat increased progressively in the other groups. Mean arterial blood pressure returned to baseline (73 mm Hg) by 15 min postarrest, remained stable in the 1-h dogs, but fell at 3 h to 62 and 34 mm Hg in the 1.5-and 2.0-h groups, respectively. No neuropathologic alterations were seen in puppies arrested for 1 h, whereas all pnppies arrested for 1.5 or 2 h had varying degrees of cerebral cortical and hippocampal damage. Thus, newborn dogs tolerate 1 h of hypothermic circulatory arrest without brain damage, with graded neuronal injury thereafter. The experimental model has direct clinical relevance and can be used to study mechanisms of cellular injory in brain, heart, and other organs during prolonged ischemia. (Pediatr Res28:354–360, 1990)

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Developmental changes in regional cerebral blood flow (CBF) responses to hemorrhagic hypotension during normoxia and normocapnia were determined using radioactively labeled microspheres to measure flow to the cortex, brainstern, cerebellum, white matter, caudate nucleus, and choroid plexus in three groups of chromically catheterized lambs: 90− to 100-d preterm fetal lambs (n= 9); 125− to 136-d near-term fetal lambs (n= 9); and new born lambs 5− to 35-d-old (n= 8). Heart rate, central venous pressure, and arterial blood pressure were monitored continously and arterial blood gas tensions, pH. Hb. and oxygen saturation together with regional CBF were measured periodically. Hemorrhagic hypotension produced a mean decrease in arterial blood pressure of 27 \pm 4, 23 \pm 2, and 41 \pm 4% in the three groups, respectively, whereas reinfusion of the lamb's blood resulted in a return to control blood pressure within 3% in all three groups. In the preterm fetal lamb, CBF decreased significantly in all regions during hypotension. In the nearterm fetal lamb, only blood flow to the cortex decreased significantly during hypotension. In the newborn lamb, only the choroid plexus demonstrated a significant decrease in blood flow during hypotension The lower limit of regional CBF autoregulation was identical to the resting mean arterial pressure in fetal life but significantly lower in newborn lambs. These experiments demonstrate for the first time that vulnerability to hypotension decreases with increasing maturity and that the brainstem, the phylogenetically oldest region of the brain, is the least vulnerable to the effects of hypotension at any age in the lamb model. (Pediatr Res28: 361–366, 1990) Abbreviations CBF, cerebral blood flow

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

To study the effect of different high-frequency oscillatory ventilation parameters on airway pressure we measured oscillatory pressure amplitude (| Paw|) and mean airway pressure (Paw)at three sites in open-chested normal rabbits: proximal, trachea, and alveolus. Five animals were studied to test a new pleural capsule design, which was then used in two groups of animals to measure right upper (n= 4)or middle (n= 5) lobe alveolar pressures. Animals were randomly sequenced through combinations of frequency (10, 15, and 20 Hz) and fractional inspiratory time (T) (0.3 and 0.5) while normoxic and encapnic. During capsule testing, we noted that alveolar pressures increased (p< 0.05) with increasing capsule mass. suggesting that compressive forces from the capsule may alter the capsule measurement. We thus used a lowmass (430 mg) transducer system in the rabbit high-frequency oscillatory ventilation experiments. Using multifactorial analysis of variance, we found significant main effects of TionPaw, and of measurement site on both | Paw| andPaw(p< 0.009). Frequency did not influence variations in either | Paw|Paw. For both Tisettings, alveolar upper lobePawwas lower compared with that of the middle lobe (pi(03 to 0.5) increased trachealPawin each capsule group (p< 0.0005). At Ti= 0.5, trachealPawexceededPawmeasured proximally (p< 0.05). Our data support in vivo alveolarPawinhomogeneity and demonstrate significant changes in pressures within the lung related to Ti during high-frequency oscillatory ventilation.(Pediatr Res 28: 367–373,1990)

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Experiments were done on five lambs to determine if carotid denervation influences the arousal and cardiopulmonary responses to upper airway obstruction during sleep. Each lamb was anesthetized and instrumented for recordings of electrocorticogram, electro-oculogram, nuchal and diaphragm electromyograms. and measurements of arterial blood pressure and arterial Hb oxygen saturation. A tracheotomy was done and a fenestrated tracheotomy tube placed in the trachea. During the study, a 5 F balloon-tipped catheter was inserted into the tracheotomy tube so that air flow could be obstructed by inflating the balloon. No sooner than 3 d after surgery, measurements were made in quiet sleep and active sleep during control periods when the animal was breathing room air and during experimental periods of upper airway obstruction. Carotid denervation significantly affected the arousal response to upper airway obstraction. Arousal occurred during 14 of 14 epochs in quiet sleep and during 12 of 13 epochs in active sleep before the arterial Hb oxygen saturation decreased to 30%. However, the time to arousal was increased and the arterial Hb oxygen saturation at arousal was decreased in carotid-denervated lambs compared with what we have previously observed in carotid-intact lambs. These data provide evidence that the caroid chemoreceptors and/or carotid baroreceptors play a major role in causing arousal from sleep during upper airway obstruction in lambs. Our results may have implications for sudden infant death syndrome, because it is possible that alterations in the arousal response to respiratory stimuli play a role in sudden infant death. (Pediatr Res 28: 374–378, 1990)

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Lung elastin is an important extracellular structural protein and it has been postulated that it plays a regulatory role in alveolar formation. To study the developmental regulation of elastin gene expression, we examined the tropolastin (TE) production in primary culture of rat pulmonary fibroblasts (RPF). We found that developmental changes in elastin production as assessed by TE synthesis and 3.6-kb TE mRNA levels were similar for RPF and whole tissue except those results from iate gestation animals, with peak elastin expression occurring 7 d postnatally with a decline out to 21 d. At late gestation (20 d), TE mRNA was barely detectable in RPF but clearly detectable TE mRNA in the whole tissue, indicating that there are elastogenic cells other than RPF in the tissue at this age. When TE-producing cells were treated with dexamethasone, there was a dose-dependent stimulation of TE synthesis with the maximum response at 10-9to 10-7M. Interestingly, dexamethasone had no stimulatory effect on cells from late gestation animals. The developmental window of elastin synthesis in this RPF model between late gestation and 21 d postnatal seems to correlate with the reported period of secondary alveolar formation, and thus we speculate that RPF elastogenic activity reflects that of the alveolar wall. (Pediatr Res 28: 379–382, 1990)

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

We assessed fetoplacental blood volume flow and placental resistance prospectively with Doppler sonog-raphy in 74 normal human fetuses of 19 to 42 wk gestation to determine the changes in placental perfusion with gestational age. Placental blood volume flow was assessed from the umbilical vein as the product of the mean flow velocity integral and the cross-sectional area of the umbil-ical vein. Placental resistance was assessed as the ratio of maximum systolic and minimum diastolic blood flow velocities from an umbilical artery. Umbilical vein blood volume flow increased exponentially (r = 0.86) with gestational age from 19 wk to term, and did not decrease in postdate fetuses. Umbilical vein blood volume flow increased linearly with fetal weight (r = 0.77), although volume flow per unit body weight changed little with gestational age. Umbilical artery velocity ratio decreased progressively, indicating diminishing placental resistance with gestational age, but did not correlate closely with umbilical vein blood volume flow, We submit that fetoplacental blood volume flow can be readily calculated directly from the umbilical vein with Doppler ultrasound and may provide a better index of placental perfusion than the umbilical artery velocity ratio. (Pediatr Res 28: 383–387,1990)

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

During prolonged administration of β-ago-nists such as ritodrine directly to chronically cannulated fetal lambs, the cardiovascular, metabolic, and endocrine changes observed during the 1st day of administration, lessen and return to normal within 3–4 d despite continuing drug administration. In our investigation, heart rate, plasma FFA, lactate, glucose, and insulin concentrations all increased significantly during the 1st day of ritodrine infusion (10 μg/min) whereas blood Po2and base excess were significantly decreased. After 3 d. despite continued drug infusion, all these changes had ameliorated. To examine the hypethesis that this tachyphylaxis to ritodrine also results in decreased sensitivity to endogenous catecholamines, episphrine (1 μg/min i.v. for 60 min, then 2 μ/min i.v. for a further 60 min) was infused into fetal lambs (124–130 d gestation) 1 d before, then 5 \pm 1 d after, and again 10 \pm 1 d after beginning ritodrine infusion. Before ritodrine administration. epinephrine significantly increased plasma FFA, lactate, glucose, and glucagon concentration and decreased insulin. However, after ritodrine treatment for either 5 \pm 1 or 10 \pm 1 d, epinephrine resulted in no significant increases in FFA or glucagon, and those in lactate and glucose were significantly reduced. Decreases in insulin during epinephrine administration were unchanged by vitodrine. Initial responses of mean arterial pressure and heart rate to epinephrine were significantly greater during prolonged ritodrine treatment. Fetal responses to epinephrine mediated through β-adrenergic receptor mechasms were clearly decreased when administration of β-agonists was prolonged beyond 24 h. (Pediatr Res 28:388–393, 1990)

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

We studied the effects of growth hormone on retention of15N-labeled amino acids in 34 short, prepubertal, growth hormone-sufficient children and three growth hormone-deficient subjects. All 34 non-growth hormone-deficient children had apparently normal circulating growth hormone molecules and no mutations were detected in the growth hormone or IGF-I genes of any subjects. Fibroblasts from 34 children responded normally when challenged with recombinant human IGF-I. During the last 72 h of a 4-d challenges with recombinant human growth hormone (16 μg/kg body wt), retention of a mixed15N-amino acid dose varied between 5.7 and 50.5%. Whole body protein synthesis, breakdown, and net anabolism calculated from the15N kinetics were all increased by the acute growth hormone challenge. However, no routine clinical feature or laboratory determination correlated with the nitrogen retention response. After subsequent treatment (75 μg/kg three times a week) with recombinant human growth hormone for 1 y, there was a significant increase in height velocity. but this increase was not related significantly to pretreatment variables other than inversely to pretreatment height velocity. There was a significant (p= 0.03) correlation between the change in height velocity Z score and the degree of nitrogen retention to acute challenge with growth hormone, but this correlation was too weak (r = 0.37) to be of practical value in predicting the treatment growth response in an individual child. (Pediatr Res 28: 394–400.1990)

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

A simple and improved method for the quantification of urinary LH and FSH was developed. Urinary gonadotropin concentrations were determined by polyclonal double antibody RIA after ammonium sulfate extraction. Urinary LH and FSH concentrated by ammonium sulfate were coeluted with an iodinated LH and FSH tracer. Gel chromatography of the urine revealed that the majority of immunoreactive LH and FSH were eluted coincident with125I-LH and125I-FSH. Good correlation was observed between urinary gonadotropin/creatinine ratios in first morning voided and full 24-h urine collections. Age-de-pendent changes in urinary LH excretion were significant in normal boys and girls 6–17 y of age. Urinary FSH excretion in these children did not change in an age-dependent fashion. (Pediatr Res 28: 401–404,1990)

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID