Pediatric research
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The influence of left-right ductal shunting on early hemodynamic responses, namely left ventricular performance, contractility, and systemic perfusion was evaluated in nine preterm lambs (120 days gestational age) treated with surfactant. Blood gases were maintained in the physiological range using mechanical ventilation; hemodynamic and blood flow measurements (radionuclide labeled microspheres) were obtained before and after occlusion of the patent ductus arteriosus with a catheter balloon. The mean left-right ductal shunt before occlusion (1.2 h postnatal age) was 59 +/- 11% SD. ⋯ Thus, during the 1st h of life the hemodynamic profile of preterm lambs with patent ductus arteriosus was characterized by large magnitude left-right shunt and a "high" cardiac output state sufficient to maintain unchanged systemic perfusion. The increased left ventricle output was accomplished by increasing end-diastolic volume (Frank-Starling mechanism), but left ventricle contractility remained unchanged. We speculate that the preterm left ventricle may be unable to sustain the high level of pump performance and contractility required to compensate for the ductal "steal" of systemic blood flow.
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Estradiol-producing ovarian cysts were found in four very preterm females at a postconceptional age that slightly preceded the expected time of delivery. The serum concentration of estradiol was very high. In the first infant one cystic ovary was removed surgically. ⋯ In infants 3 and 4 the cysts disappeared and the serum estradiol normalized spontaneously. Measurements of serum concentrations of luteinizing hormone and follicle-stimulating hormone before and after an iv injection of luteinizing hormone releasing hormone showed that preterm girls with early estradiol-producing ovarian cysts have a postpubertal type of response to luteinizing hormone-releasing hormone. When the test is repeated some months later they have a prepubertal type of response, which is normal for their age.
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Lobar atelectasis is common among infants and children with obstructive lung diseases. However, the effect of lobar collapse in the presence of diffuse lung disease on gas exchange in the pediatric age group has not been described. We developed an infant model of lobar atelectasis using piglets and tested the hypothesis that diffuse alveolar hypoxia increases shunt fraction (Qs/QT) associated with lobar atelectasis by redirecting pulmonary blood from the well-ventilated portion of the lung into the collapsed region. ⋯ The percentage of cardiac output perfusing the left lower lobe fell by an average of 70 +/- 17% in response to lobar collapse. When animals were ventilated with 12% oxygen, shunt fraction increased to 18.7 +/- 7.1% and blood flow to the collapsed left lower lobe increased from 9 +/- 3 to 22 +/- 3% of cardiac output. Lobar atelectasis in conditions where diffuse alveolar hypoxia is present may be associated with a significantly greater intrapulmonary shunt than lobar atelectasis in children with otherwise normal lungs.
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In order to determine the relative roles of O2 tension and content, CO2 tension, hydrogen ion concentration, arterial blood pressure, and cardiac output in the regulation of fetal cerebral blood flow (CBF), we used radioactively labeled microspheres to measure flow to 20 major brain regions in 24 chronically catheterized fetal lambs. We continually monitored fetal heart rate and blood pressure, and periodically measured arterial PO2, PCO2, pH, and hematocrit. In addition to CBF measurements during control periods, we measured CBF during: 1) hypoxia (O2 content less than 6 ml X dl-1; O2 tension less than 15 torr) induced by having the ewe breathe a gas mixture with low O2 concentration, 2) hypercapnia (PCO2 greater than 50 torr) induced by increasing the maternal inspired CO2, 3) acidosis and alkalosis (7.60 greater than pH greater than 6.60) induced by infusing lactic acid or bicarbonate into the fetus, and 4) hypotension (blood pressure less than 35 mm Hg) and hypertension (blood pressure greater than 55 mm Hg) induced by rapidly phlebotomizing or transfusing the fetus. We used multiple regression analysis and analysis of covariance to examine the dependence of total cerebral blood flow on arterial O2 tension and content, CO2 tension, pH, blood pressure, and cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)
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The use of a multiple gas rebreathing method for the measurement of cardiopulmonary function in mechanically ventilated neonates was evaluated. The following indices of cardiopulmonary function were assessed in 20 piglets (mean weight, 2.3 kg): 1) pulmonary capillary blood flow (Qc), 2) diffusing capacity for carbon monoxide (DLCO), 3) lung gas volume (FRC), 4) oxygen consumption (VO2), and 5) volume of the pulmonary tissues and capillaries (VTPC), the latter an estimate of total lung water. During mechanical ventilation at zero end expiratory pressure, all rebreathing parameters correlated well with body weight. ⋯ Unlike the situation with the normal piglets, when PEEP was increased from zero to 10 cm H2O in the oleic acid-infused piglets, the values for FRC and VTPC significantly increased. Mean VTPC at 10 cm H2O was 20 +/- 2 ml/kg which correlated well (r = 0.93) with the postmortem total lung water value of 19 +/- 1 g/kg. Thus, multiple gas rebreathing methodology is applicable to studies using small animals.(ABSTRACT TRUNCATED AT 250 WORDS)