摘要:

The conduction system functions of atrioventricular sequential contractions, atrioventricular delay, and coordination of ventricular contraction were examined in rat embryos at the earliest functional stage of cardiac development (before cardiac looping, n = 6) and shortly after looping (n = 5). Atrioventricular sequential contractions were observed in all embryos, and contractions appeared to originate in the left sinus horn. Atrioventricular delay was present in both prelooped (132 ± 32 ms) and looped (141 ± 15 ms) hearts. Before looping, contractions traveled from proximal ventricle to bulbus cordis, a distance of 253 ± 27 µm in 72 ± 22 ms. After looping, contractions crossed an increased intraventricular distance (520 ± 28µm, p <0.005) in substantially less time (16 ± 7 ms, p < 0.005). Sinoatrial and atrioventricular nodal functions are emulated in both prelooped and looped hearts of early mammalian embryos, and His-Purkinje system function is emulated in looped hearts.

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

摘要:

We examined anatomically the hearts, lungs, and great vessels of 269 WKY/NCrj rats at three fetal and three neonatal stages. Severe pulmonary valve thickening was present in 16 and ventricular septal defects with overriding of the aorta in 15 of the 90 near-term fetuses and in 10 and nine, respectively, of the 79 neonates at 2-4 d of age. These abnormalities occurred together (tetralogy of Fallot) in seven of the near-term fetuses and in five of the neonates. A narrow pulmonary outflow tract was present in 55% of the fetuses and in 56% of the neonates. The wall of the pulmonary arterial branch was abnormally thick in 19% of the fetuses and in 26% of the neonates, most of which did not have septal defects. In about 80% of the fetuses, the middle latitudinal muscle bundle of the ventricular septum was not continuous with the left ventricular free wall, but rather with the right; after birth, it was discontinuous with both free walls. The heart was abnormally heavy in 49% of the 79 neonates. In about half of the heavy hearts, there were no septal defects or pulmonary valvular and arterial lesions. There were double aortic arches in four and right aortic arches in six of the total WKY fetuses and neonates; the ductus arteriosus was abnormally small in 47% and the aorta was large in 51% of the near-term fetuses. This constellation of congenital heart disease is genetic in origin, but altered by hemodynamics late in fetal life.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Decreased diaphragmatic blood flow (Qdi) is associated with decreased contractility in adult animals. To see whether the decrease in Qdiassociated with a patent ductus arteriosus was associated with a decrease in diaphragmatic contractility Pdi, we prepared 11 near–term fetal lambs by infiltrating the ductus with formalin and placing a snare around it to regulate its patency. The lambs (with open chest) were delivered and mechanically ventilated, and the phrenic nerves and diaphragm were paced (using transvenous wires) at rates of 20/min, 60/min, and 100/min (Inspiratory time/total respiratory cycle time = 0.5) for 7–min contraction periods after 30-min recovery periods. Qdiwas measured with radiolabeled microspheres at the end of each contraction period. Diaphragmatic performance was determined by comparing Pdiat the start (Pdi–start) and end (Pdi–end) of the contraction period. When the ductus was closed, Qdiincreased 6.9-fold at 20/min and 9.8-fold at 100/min (compared with Qdiat rest). Pdi-end was less than Pdi–start at all contraction rates, but the reduction was significantly greater at 100/min (Pdi–end/Pdistart: 0.80 ± 0.10 at 20/min; 0.67 ± 0.17 at 100/min). Pdi–start also decreased with increasing rates of contraction. When the ductus was open, the left-to-right shunt was 64 ± 11% of left ventricular output.diin the unpaced diaphragm was significantly reduced (open 4.0 ± 3.8versusclosed, 7.4 ± 2.4 mL/min/100 g). However, with pacing,Qdiincreased with open ductus and so did not differ from Qdiwith closed ductus. Similarly, at each contraction rate, ductus patency did not alter diaphragmatic performance (Pdi–end/Pdi–start, openversusclosed: 20/min = 0.80 ± 0.15versus0.80 ± 0.10; 60/min = 0.76 ± 0.11versus0.73 ± 0.17; 100/min = 0.62 ± 0.14versus0.67 ± 0.17). We conclude that diaphragm performance decreases at faster contraction rates despite an increase in Qdi. Although a patent ductus arteriosus reducesdiin the noncontracting diaphragm, during contractionsQdican increase to levels achieved when the ductus is closed so that there is no change in diaphragmatic performance.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Beside measurement of functional residual capacity (FRC) in ventilated children is impractical. Using a simple technique based on open circuit N2washout, we measured FRC in ventilated children. The system was evaluated in the laboratory and in patients. Using a mechanical lung, the reproducibility of 200 studies over a range of 100-500 mL at each of four different flow rates (10 determinations at each level) was very high with a mean coefficient of variation of 2.3% (range 0.5-5.1%). Linearity of the integrated N2signal for volumes of 100-500 mL washed out at different flow rates was excellent (range 7.4-17.9 L/min), r = 0.99. The mean difference between measured and preset mechanical lung volumes was 2.4% (range 0-4.6%). Invivo, reproducibility of six to 10 FRC determinations in each of 30 children gave a mean coefficient of variation of 2.7%. Comparison to the conventional Douglas bag collection method showed a high correlation (r = 0.97). We conclude that this is an easy, highly reproducible, and accurate method for FRC determination suitable to ventilated infants and children.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Positive end expiratory pressure (PEEP) is an accepted treatment for children with acute respiratory failure secondary to restrictive lung diseases. Using a simple technique based on open circuit nitrogen washout, we determined the functional residual capacity (FRC) in 25 ventilated children (age 3 wk-10 y) with acute respiratory failure secondary to restrictive lung disease (pulmonary edema, bilateral pneumonia). FRC measured at a physiologic level of PEEP (2-4 cm H2O) was 45.0 ± 3.6% (mean ± SEM; range 12-80%) lower than normal predicted values. At the PEEP level chosen clinically (4-10 cm H2O, mean = 6.0), the FRC was below normal predicted values for nonintubated children by a mean of 31.8% (range 0-73%) (p = 0.0001) and only seven patients (28%) had FRC within 20% below predicted normal values. FRC normalized at PEEP levels of 6-18 cm H2O (mean = 11.6), which was up to 200% above the clinically chosen PEEP level. In six children without lung disease who were ventilated at a PEEP level of 2-4 cm H2O, the FRC was within normal range in two, but significantly higher (by 45%) in the other four. We conclude that FRC in ventilated children with acute restrictive lung disease is significantly lower than normal and the clinically chosen PEEP fails to normalize the FRC in most of the cases.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Sodium deficiency is associated with decreased muscle growth and protein synthesis. We investigated the influence of diet-induced sodium deficiency on the rate and extent of compensatory growth of the right lung after left pneumonectomy in young rats of 83 ± 1 g body weight. Starting 1 wk before surgery, all rats were fed a diet deficient only in sodium (2-9 µmol Na+/g of food)ad libitum. Sodium-deficient rats were supplied with distilled water, whereas sodium-replete controls were supplied water containing 37 mM NaCl. After 7 d on the experimental diets, both groups were divided and subjected either to sham thoracotomy (Sham) or to left pneumonectomy (PNX). Somatic growth and both normal and compensatory growth of the lungs were assessed 3, 4, and 7 d later. Sodium-deficient animals grew more slowly than control animals. In control PNX rats, right lung weight to body weight ratio (LW/BW) increased to equal that of the combined LW/BW in control Shams by postoperative d 4, and remained at the Sham combined LW/BW value on postoperative d 7. Compensatory lung growth was less rapid in sodium-deficient PNX animals. At postoperative d 4, right LW/BW was low relative to combined LW/BW of sodium-deficient Shams. This ratio approached but did not reach the sodium-deficient Sham combined LW/BW value by d 7. Sodium deficiency thus reduced the rate of compensatory growth of the right lung. RNA/g dry tissue and RNA/DNA were low in sodium-deficient lungs relative to control at d 0 and 7 but during the rapid phase of compensatory growth (d 3 and 4), both groups responded with a 20% increase in tissue RNA concentration. Similar protein/DNA ratios between PNX and Sham-operated animals in both sodium-deficient and control groups, along with elevated total DNA content in the right lung of both PNX groups, suggest that the compensatory growth was hyperplastic rather than hypertrophic. Our study demonstrates that diet-induced sodium deficiency decreases somatic growth and slows the compensatory growth of the right lung after PNX.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Acute saline volume expansion (VE) in the developing animal is associated with a blunted natriuretic response when compared with that in adults. Recent studies have suggested that renal interstitial hydrostatic pressure (RIHP) plays an important role in mediating VE-induced natriuresis in the adult. The purpose of our study was to determine whether abnormalities in the RIHP response to VE could be involved in the blunted natriuretic response in the developing animal. The effect of an acute saline load (5% body wt) on RIHP and sodium excretion was examined in adult pigs (>70 d) and piglets (26-43 d). In response to an acute saline load, the piglets excreted significantly less sodium than the adults (1.7 ± 0.5versus3.8 ± 0.7 µmol/ min/g kidney wt). The increase in fractional excretion of sodium in response to VE was also significantly less in the piglets. There was no significant change in GFR in either group. Associated with the blunted natriuretic response in the piglet was an absence of an increase in RIHP (6.1 ± 1.1versus6.1 ± 1.6 mm Hg) in response to VE. In contrast, the adult pig, which exhibited a normal natriuretic response, showed a significant increase in RIHP (8.8 ± 1.3 to 12.3 ± 1.5 mm Hg) during VE. When RIHP was prevented from increasing during VE in the adult pigs, the natriuretic response was significantly attenuated, as it was in the piglets. The results of our study indicate that the piglet does not exhibit a normal adult RIHP response to VE. The absence of any discernible increase in RIHP during VE may explain, in part, why piglets have a limited ability to excrete a saline load.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

We studied the effects of maternal uterine artery ligation on fetal rat tissue glucose utilization (GU). Unilateral uterine artery ligations were performed on the 19th d of gestation (term 21.5 d) and 2-[3H]deoxy-D-glucose was used to measure GU of placenta, liver, brain, muscle, kidney, and heart from fetuses in the ligated (IUGR) and nonligated (control) uterine horns 24 and 48 h after the procedure. At both periods, IUGR fetuses weighed significantly less and had lower fetal/maternal plasma glucose ratios than controls. Twenty-four h after ligation, placenta, liver, brain, and muscle from IUGR fetuses had lower relative GU rates than corresponding tissues from control fetuses (p < 0.01-0.05). However, at 48 h, IUGR liver, muscle, kidney, and heart had higher relative GU rates than control tissues (p < 0.01-0.05). The lower GU of IUGR fetal tissues observed at 24 h postligation was likely related to the acute decrease in fetal glucose availability. Other factors, such as hypoxemia and acidosis, that affect cellular metabolism may also have led to lower GU rates. The increase in GU by IUGR tissues at 48 h occurred despite a persistence of low fetal glucose concentrations and can be explained by either: 1) an attempt by IUGR fetal tissues to compensate for the persistently low plasma glucose; 2) an increased demand for metabolic fuel for repair processes; or 3) a less efficient use of glucose due to alterations in cellular respiration. We speculate that this increase in fetal tissue GU may be partially responsible for the supranormal glucose requirements seen in small-for- gestational-age newborns.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

To evaluate in a developmental context the effect of congenital hypothyroidism on concentrations of the neurotransmitters norepinephrine, dopamine, and serotonin (5HT) in selected brain areas of the ovine fetus, we studied the effect of thyroidectomy at three ages on the concentrations of these neurotransmitters and their major metabolites, homovanillic acid and 5-hydroxyindoleacetic acid. Fetuses underwent thyroidectomy at 90-95 or 105- 115 d gestation (term = 147-150 d) or 1-5 d after birth. Approximately 25 d after thyroidectomy, at d 120-125 or 130-135 of gestation or 25-30 d after birth, respectively, the ewes were killed and fetal brains removed. Neurotransmitters and their metabolites were measured by HPLC with electrochemical detection. Thyroidectomy in the 2nd trimester increased 5HT in five brain areas: anterior hypothalamus, dorsal medial hypothalamus, pons, medulla, and cerebellum. Thyroidectomy in the 3rd trimester increased 5HT in the pons and medulla, increased norepinephrine in the dorsal medial hypothalamus and pons, and increased homovanillic acid in the posterior hypothalamus. Thyroidectomy in the newborn period decreased NE in the anterior hypothalamus, ventral medial hypothalamus, and midbrain, decreased 5-hydroxyindoleactic acid in the posterior hypothalamus, lateral hypothalamus, dorsal medial hypothalamus, and ventral medial hypothalamus, and decreased homovanillic acid in the dorsal medial hypothalamus and ventral medial hypothalamus. From these data we conclude the following: 1) Hypothyroidism causes changes in neurotransmitter concentrations only in selected brain areas of the ovine fetus, rather than causing generalized and similar changes in all brain ares; and 2) 5HT 5- hydroxyindoleacetic acid concentrations are affected more often than the other neurotransmitters evaluated, perhaps because the 5HT neurotransmitter system is developing at these times.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID