摘要:

To determine whether the hemodynamic responses to adrenergic agonists are altered during chronic hypoxemia secondary to an intracardiac right to left shunt, we studied seven lambs with surgically created pulmonic stenosis and atrial septal defect and nine controls during infusions of isoproterenol at 0.1 and 0.5 µ/kg/min and dopamine at 5 and 20 µ/kg/min. Isoproterenol increased heart rate by 89 ± 17% in control but only 46 ± 6% in experimental lambs (p< 0.05). However, because resting heart rate was higher in experimental lambs (213 ± 7versus177 ± 12 beats/min,p< 0.05), maximal heart rates were similar (310 ± 7versus326 ± 6 beats/min; NS). Cardiac output increased during isoproterenol from 219 ± 20 to 425 ± 54 mL/min/kg in experimental lambs (p< 0.05) and, similarly, from 180 ± 20 to 425 ± 71 in controls (p< 0.05) (experimentalversuscontrol; NS). Dopamine also increased cardiac output similarly in both groups, at both doses, but without changing heart rate. Isoproterenol did not alter aortic oxygen saturation and increased systemic oxygen transport more than oxygean consumption. In contrast, dopamine at both doses decreased aortic oxygen saturation in experimental lambs (rest, 71 ± 2%versusdopamine, 59 ± 2%;p< 0.05). With dopamine, the increase in systemic oxygen transport was equalled by an increase in oxygen consumption. Thus, circulatory responses to isoproterenol are similar in lambs with experimental cyanotic heart disease and controls, although higher resting heart rate in the experimental lambs reduces chronotropic reserve. Circulatory responses to dopamine are different, mainly due to the decrease is oxygen saturation in the experimental lambs. Inasmuch as the oxygen cost/benefit ratio of adrenergk agonists may be altered by chronic hypoxemia and associated hemodynamic abnormalities, further evaluation of this ratio in hypoxemic human infants receiving these agents is indicated. (Pediatr Res29: 323–328, 1991)

ISSN:0031-3998    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Cardiac output is affected by the diastolic filling characteristics of the ventricle. We hypothesized that the relative contributions of passive and active filling change as the ventricle develops from a smooth-walled tube to a trabeculated four-chamber heart. In stage 12 to 27 white Leghorn chick embryos, we simultaneously measured ventricular pressure with a servo-null micropressure system and dorsal aortic and atrioventricular velocities with a 20-MHz pulsed-Doppler velocity meter. The analog waveforms were sampled at 500 Hz and converted to digital format via an analog/digital board. We partitioned diastole into passive and active components. The passive phase began with the return of the pressure curve to baseline and extended to the onset of the a-wave. The active phase began with the upstroke of the atrial velocity curve and extended to the upstroke of the ventricular pressure curve at end-diastole. Data are presented as mean ± SEM (n± 6 at each stage) and analyzed by analysis of variance and regression analysis. At similar cycle lengths ranging from 480 to 600 ms (p> 0.05), end-diastolic pressure increased from 0.24 ± 0.02 mm Hg at stage 12 to 0.55 ± 0.01 mm Hg at stage 27. Passive and active filling volumes were 92 (0.0038 ± 0.0005 mm3) and 8% (0.0004 ± 0.0002 mm3), respectively, at stage 12 and changed to 24 (0.23 ± 0.08 mm3) and 76% (0.62 ± 0.08 mm3), respectively, at stage 27. The ratio of passive to active filling volume decreased from 7.89 to 0.35. Thus, active ventricular filling became dominant as the trabeculae formed in the embryonic ventricle. These observations define the diastolic filling characteristics of the embryonic heart during primary cardiac morphogenesis. (Pediatr Res29: 334–337, 1991)

ISSN:0031-3998    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

We hypothesized that developmental increases in both ventricular end-diastolic pressure (EDP) and the maximum time derivative of pressure (dP/dt) observed in stage 12 to 29 chick embryos are the result of observed cardiac cycle length (CL) decrease (heart rate increase). To test this hypothesis, we evaluated EDP and dP/dt changes that occur during acute CL alterations in the Hamburger-Hamilton stage 24 chick embryo (n= 18). Ventricular pressure measurements were obtained with a servo-null pressure system and digitally recorded at 500 samples/s. A 1-mm steel probe, heated (decrease CL) or cooled (increase CL), was applied to the sinus venosus. The average baseline CL was 454 ms. The heart rate perturbation resulted in CL that varied over a range of 200–2966 ms, assimilating the range of CL change observed during development. Changes in EDP ranged from 0.014 to 0.130 kPa (baseline = 0.061 kPa) and maximum dP/dt ranged from 0.33 to 13.33 kPa/s (baseline = 5.99) kPa/s). In each study, EDP varied directly with CLR2= 0.70). Conversely, maximum dP/dt changes were inversely related to CL alterations (R2= 0.54). Thus, we found that there is a direct relationship between changes in CL and EDP in the stage 24 chick embryo, whereas CL and dP/dt vary inversely. During cardiac development, observed increases in maximum dP/dt may be attributed to CL decreases. In contrast, developmental increases in EDP cannot be explained by CL decrease and must be accounted for by maturational changes in cardiac function in the chick embryo. (Pediatr Res29: 338–341, 1991)

ISSN:0031-3998    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

The ductus venosus allows highly oxygenated blood returning from the umbilical-placental circulation to bypass the liver, and is believed thereby to facilitate preferential distribution of this blood to the fetal brain and heart. To examine this hypothesis, we developed a model that allows acute obstruction of the ductus venosus in chronically catheterized fetal lambs. In seven fetal lambs, a Swann-Ganz catheter was inserted into the inferior vena cava and the balloon tip advanced into the ductus venosus. Control measurements were obtained 1–2 d after surgery, before and during inflation of the balloon in the ductus venosus. At each sample time, radioactive microspheres were injected to determine organ blood flow and the distribution of umbilical venous blood flow. During balloon inflation, the percentage of umbilical venous return passing through the ductus venosus was reduced from 38 ± 15% to 1 ± 0.5%. Umbilical-placental blood flow was unchanged from control values of 181 ± 33 mL/min/kg. Total liver blood flow increased from 346 ± 98 to 553 ± 105 mL/min/ 100 g. Pressure in the inferior vena cava did not change, but umbilical venous pressure increased from 7.2 ± 2.7 to 8.7 ± 3.5 mm Hg. Total vascular resistance across the liver and ductus venosus increased from 0.013 ± 0.006 to 0.020 ± 0.011 during ductus venosus obstruction. Fetal heart rate, arterial blood pressure, and descending aortic pH and blood gases were unchanged, as was oxygen content in the descending aorta and carotid artery. Organ blood flows, combined ventricular output, and oxygen delivery were also unchanged. In five animals, these studies were repeated during maternal hypoxemia. Similar changes in liver blood flow were observed. Organ blood flows and oxygen delivery were not altered by ductus venosus obstruction during hypoxemia. We conclude that obstruction of the ductus venosus has no effect on regional blood flow distribution or oxygen delivery in normoxemic or hypoxemic animals. Because the hepatic microcirculation has such a high compliance, the ductus venosus is not crucial in regulating umbilical venous return to the central fetal circulation. (Pediatr Res29: 347–352, 1991)

ISSN:0031-3998    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Modified natural porcine surfactant was mixed with edema fluid sampled from the airways of hyperoxia-exposed adult rabbits. By varying the concentration of surfactant lipids (10, 25, and 50 mg/mL) and edema fluid proteins (0–280 mg/mL), we obtained a series of preparations with protein to surfactant lipid weight ratios ranging from 0 to 11.2. The surfactant activity of these various mixtures was analyzed with a pulsating bubble (at a lipid concentration of 10 mg/mL) or in experiments on immature new born rabbits (at lipid concentrations of 25 or 50 mg/mL). For the latter purpose, animals were delivered at a gestational age of 27 d and ventilated with a standardized sequence of insufflation pressures after receiving 0.1 mL of the surfactant-edema sample into the airways at birth. Nearly completein vitroinhibition of surfactant (markedly delayed film adsorption and a minimum surface tension of 23 mN/m during pulsation) was observed at a protein to surfactant lipid ratio of 4.5. Underin vivoconditions, nearly complete surfactant inhibition (tidal volumes reduced to less than 20% of the values for littermates ventilated with the same pressure after receiving surfactant without admixture of edema fluid) was documented at a protein to surfactant lipid ratio of 11.2. Our data suggest that the functional properties of an immature neonatal lung, in which serum proteins tend to leak into the airspaces after the onset of ventilation, depend on the stoichiometric relation between surfactant lipids and inhibitory proteins in the lung liquid. (Pediatr Res29: 353–356, 1991)

ISSN:0031-3998    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

To see if phosphodiesterase inhibition might enhance the effect of β-adrenergic stimulation on fetal lung liquid secretion, we studied the independent and combined effects of intrapulmonary terbutaline and aminophylline on net production of lung luminal liquid over time (Jv) in fetal lambs with chronically placed tracheal loop catheters. We calculated Jv during baseline and experimental periods (90–120 min each) by measuring serial concentrations of125I-albumin, an impermeant tracer that was well mixed in the luminal liquid. In 21 experiments, tracheal instillation of terbutaline (10-5M) decreased Jv from 11 ± 1 (mean ± SEM) to −3 ± 2 mL/h. In six other studies, aminophylline (10-3M) alone had no significant effect on Jv. In 12 experiments, we gave the two drugs sequentially: terbutaline decreased Jv from 11 ± 2 to −3 ± 2 mL/h and aminophylline further decreased Jv to −8 ± 2 mL/h. Amiloride (10-4M), an inhibitor of epithelial Na+transport, reversed the combined effect of terbutaline and aminophylline, increasing Jv to 8 ± 1 mL/h. Thus, phospho-diesterase inhibition enhances the β-adrenergic effect of terbutaline on Na+-dependent absorption of liquid from the lung lumen of fetal lambs. (Pediatr Res29: 357–361, 1991)

ISSN:0031-3998    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

To test the hypothesis that ventilatory responses to exercise mature during growth in healthy children, we examined CO2production (Vcco2) and minute ventilation (VE) before, during, and for 10 min after 1-min bursts of cycle ergometry exercise. Ten children (range: 7–11 y old) and 13 adults (26–42 y old) exercised at work rates corresponding to 50 and 80% of the anaerobic or lactate threshold, 50% of the difference between anaerobic threshold and maximum O2consumption, 100% of maximum O2consumption, and 125% of maximum O2consumption (125% max). Gas exchange was measured breath by breath. Children recovered faster from high-intensity (above anaerobic threshold) exercise as judged by the time constant of single exponential curve-fits to postexercise Vco2[55 ± 10 s (1 SD) at 125% max in children compared with 92 ± 17 s at 125% max in adults:p< 0.001] and VE(58 ± 10 s at 125% max in children compared with 125 ± 37 s in adults,p< 0.001). Although we found no significant difference between Vco2and VErecovery times in children, VEwas significantly slower than Vco2in adults for high-intensity exercise. Moreover, recovery times in adults increased with work intensity but were independent of them in children. Whereas the CO2costs (calculated as total CO2produced above baseline per unit work done (mL - J-1)*** increased with work intensity in adults, no similar significant relationship was observed in children. Finally, at 125% max, the ratio of CO2cost to O2cost was 1.48 ± 0.07, less than the ratio in adults (1.83 ± 0.07,p< 0.01). These results demonstrate marked differences in dynamic ventilatory response to short bursts of exercise reflecting maturation of both respiratory control and cellular metabolic factors. (Pediatr Res29: 362–368, 1991)

ISSN:0031-3998    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

The perinatal ontogeny of preprotachykinin-A gene expression was assessed in central respiration-related structures. On the day of birth, there was an enhanced expression of preprotachykinin-A mRNA in the region of the nucleus tractus solitarii, the primary relay station for respiratory and cardiovascular reflexes. This increased expression was also seen in the pups delivered by cesarean section and allowed to breathe for a couple of hours as compared with their littermates, which were not allowed to breathe at all. On the basis of this finding, we suggest that the commencement of continuous breathing at birth, unlike the episodic breathing of fetal life, is associated with the enhanced expression of preprotachykinin-A mRNA in the nucleus tractus solitarii. (Pediatr Res29: 369–371, 1991)

ISSN:0031-3998    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Neonatal rats usually lose their marked tolerance to hyperoxia at about 1 mo of age. We examined the hypothesis that the marked dietary change that occurs at weaning might be important to this loss of O2tolerance. We, therefore, prematurely weaned rat pups at 15–17 d of age, expecting to find an earlier loss of O2tolerance. Surprisingly, the prematurely weaned rats showed consistently prolonged relative O2tolerance compared with normally weaned rats at all ages tested from 35–85 d of life. For example, when challenged with > 95% O2exposure for 7 d, the composite survival rate of the prematurely weaned rats (at 35–85 d of age) was nearly twice that of the normally weaned group (83 of 107 = 78%versus44 of 107 = 41%,p< 0.01). In the two experimental groups, nearly all comparative parameters examined were similar, including:1) growth rate; 2) lung DNA, RNA, and protein;3) lung antioxidant enzymes and enzyme responses to hyperoxia; 4) lung morphometry; and 5) lung elastin and collagen content. Only serum corticosterone and triiodothyronine levels differed considerably in the two groups. We conclude that premature weaning has a very marked and sustained positive effect on the relative retention of O2tolerance in the growing rat. (Pediatr Res29: 376–380, 1991)

ISSN:0031-3998    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

We have compared the roles of neurologic maturity and environmental time cues in the development of the entrained circadian sleep-wake rhythm in the preterm and term human infant. The preterm infants (n= 19) spent some time after birth in a hospital nursery with no environmental time cues, whereas the term infants (n= 22) were exposed from birth to a cyclical light and dark environment with one major caregiver. The circadian sleep-wake rhythm in the preterm infants entrained after a similar time of exposure to an environment with daily time cues but at an earlier postconceptional age when compared with the term group. We conclude, therefore, that it is the length of exposure to environmental time cues, rather than neurologic maturity, that determines the entrainment of the circadian rhythm of sleep and wakefulness in the human infant. (Pediatr Res29: 381–384, 1991)

ISSN:0031-3998    

出版商:OVID    

年代:1991

数据来源: OVID