摘要:

Increasing reliance is being placed on the use of quantitative epidemiological methods in the conduct and evaluation of pediatric research. The basic design features of two common types of observational studies, the case-control study and the cohort study, are reviewed. Advantages and disadvantages of these two study designs are discussed with emphasis on aspects such as the selection of comparison groups, avoiding selection and recall bias, gathering exposure information, controlling for potentially confounding factors, and methods of analysis. Appreciation of the salient features of these study design approaches should aid the clinician/researcher in the conduct of research endeavors as well as in critically reviewing the medical literature.

ISSN:0031-3998    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

The time course of the transient ventilatory response to a sudden change in Inspired gas from room air to 4% CO2in air was examined in 11 healthy preterm neonates. Changes in minute ventilation (&OV0312;1), tidal volume (VT), and respiratory frequency (f) were determined over 4 to 5 min of CO2inhalation during both quiet (QS) and active sleep (AS) in each infant. In both states there was a brisk increase of mean &OV0312;1in response to 4% CO2, while mean VTincreased more slowly and mean f only increased transiently at 1 to 2 min. Exponential curve fitting to the change in Vi and VT for each infant accounted for 64 ± 20% of the variance in Vi during QS as compared to 30 ± 18% during AS (p<0.003). In only six infants did exponential curves fitted to the changes in &OV0312;1and VT during QS reach 90% of their steady state values within 4 to 5 min of CO2exposure. Their time to reach 90% of steady state was always shorter for &OV0312;1than VT (p<0.01). Frequency showed a biphasic response with a transient rise at 1 to 2 min (p<0.05) and return to control levels at steady state. These data indicate that not all preterm infants reach a new level of steady state ventilation within 4 to 5 min of 4% CO2inhalation. Furthermore, many infants exhibit a biphasic response of f over time which causes &OV0312;1to reach steady state prior to VT.

ISSN:0031-3998    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We studied properties of saliva and of dental plaque which affect the caries process in an effort to understand the low prevalence of caries in patients with chronic renal failure. Plaque pH, before and following carbohydrate exposure, saliva pH, and saliva composition were evaluated in children and adolescents with chronic renal failure (n=10) and successful renal transplantation (n=11), and in two comparison groups of healthy children with few caries (n=15) and numerous caries (n=15). Salivary urea nitrogen concentration was elevated in all subjects with elevated serum urea nitrogen concentration. Chronic renal failure subjects had significantly higher salivary urea nitrogen concentration than transplanted subjects. Plaque pH correlated directly with salivary urea nitrogen concentration and was significantly more alkaline in chronic renal failure than transplant or comparison groups. Salivary urea nitrogen concentration accounted for the majority of variability in plaque pH; salivary pH and salivary phosphorous contributed negligibly. Absolute pH drop following carbohydrate exposure did not differ among groups, but because baseline plaque pH was elevated for chronic renal failure subjects, minimum pH did not attain cariogenic levels. Our data support the hypothesis that the relative paucity of caries in patients with chronic renal failure results from alteration of plaque by metabolic end products of urea metabolism. Our data further suggest that transplanted patients whose renal function is normal may be at increased risk of caries, especially if enamel hypoplasia is present and oral hygiene is poor.

ISSN:0031-3998    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Metabolic balance studies were performed with six normal infants fed in a balanced cross-over design three formulas differing only in calcium concentration: 389, 659, and 1024 mg/liter. Absorption of phosphorus was significantly affected by increasing calcium intake decreasing from 68 to 63 to 52% of intake. However, since urinary excretion of phosphorus also decreased, there was no significant effect on retention of phosphorus. Absorption of fat was slightly (but significantly) depressed by calcium, decreasing from 97.5 to 95.5 to 92.1% as calcium intake increased. The level of dietary calcium had no significant effect on absorption or retention of nitrogen, magnesium, copper, and zinc. One of the subjects had consistently lower absorption of calcium and fat than the other subjects, suggesting an absorptive defect. The decrease in fractional absorption of calcium (57 to 47 to 39% of intake) with increasing intake of calcium is compatible with adaptive regulation. On the other hand, the observation that absorbed calcium (mg/kg/day) was linearly related to intake of calcium with a slope of 0.373 suggests an alternative explanation: constant passive, concentration-dependent (slope), and constant active (y-intercept) transport of calcium over the range of calcium intakes. Thus, the findings are explainable in more than one way and do not necessarily demonstrate regulatory changes.

ISSN:0031-3998    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

The use of13CO2excretion to measure the oxidation of13CO2labeled substrates is increasing as it is both noninvasive and lacks the radiation exposure associated with the use of14C. No standards are available for13CO2recovery in breath from the bicarbonate pool in the neonate. A primed constant infusion of NaH13CO3over 4 h was used with open circuit indirect calorimetry in 15 appropriate for gestational age newborn infants (gestational age 28-39 wk; postnatal age 2-52 days), on varying amounts of intravenous feeding (37-114 kcal · kg-1· day-1). Following a bolus of 6.9 μmol · kg-1of NaH13CO3, a maintenance infusion of 4.6 μmol · kg-1· h-1was started. TheI3C enrichment in breath rose rapidly to reach a plateau by 90 min with <5% variation of the plateau. Recovery of the tracer in breath ranged from 69.6-83.5% and was significantly correlated with 1) energy intake (37-114 kcal · kg-1·day-1); 2) metabolic rate (34.6-56.1 kcal · kg-1· day-1); 3) &OV0312;CO2(4.86-7.43 ml · kg-1· min-1). There was no correlation with the level of protein or fat intake. We provide an equation that can be used to calculate the correction factor when doing constant infusion substrate oxidation studies with a13C label in neonates.

ISSN:0031-3998    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

To evaluate the adaptation of electrodermal techniques for cystic fibrosis screening, skin surface bioelectric measurements were recorded from 37 established cystic fibrosis patients, 45 asthmatic patients, and 10 normal controls, ranging in age from 6 to 22 yr. Six skin potential and six skin conductance measures of sweat gland activity without the collection of sweat distinguished between the cystic fibrosis, normal, and asthmatic groups (F ratios>10.0; p<0.0001). Discriminant analysis using the two best electrodermal measures (the mean of five preresponse potential levels and the mean of five preresponse conductance levels for each subject) to assign experimental group membership matched actual group membership with 92.7% accuracy. We believe these results warrant further investigation of electrodermal procedures as a direct, simple, yet noninvasive means of screening for cystic fibrosis.

ISSN:0031-3998    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Metabolic acidosis in the neonate is often secondary to hypoxemia and cardiopulmonary disturbances. Sodium bicarbonate, an agent used to treat metabolic acidemia in newborns, is often administered during hypoxemia. In the absence of acid-base alterations, during hypoxemia a reciprocal relationship exists between arterial O2content (CaO2) and brain blood flow (BBF). However, when hypoxemia is compounded by acidemia it is unclear whether the increase in arterial pH achieved by infusions of sodium bicarbonate alters BBF. To investigate this, BBF (microsphere technique), arterial blood gases, and CaO2were measured in 14 ventilated piglets. Variables were assesed during a control period, a period of hypoxemia (50 min) associated with metabolic acidemia (hypoxemia + acidemia), and after infusions of either saline (n=6) or NaHCO3(n=8, 2 mEq/kg) during continued hypoxemia. Arterial pH was similar in both groups at control, and hypoxemia + acidemia resulted in comparable reductions of pH in both saline- and NaHCO3-treated piglets (7.21 ± 0.02versus7.21 ± 0.03, respectively). NaHCO3infusions produced a significant rise in pH, 7.30 ± 0.03versus7.15 ± 0.03,p<0.05. In each group CaO2paralleled changes in pH but did not differ between groups. In all animals BBF increased more than 2-fold during hypoxemia + acidemia and was unaltered by infusions of either saline or NaHCO3. Brain O2delivery decreased in both groups during hypoxemia + acidemia and was unchanged by infusions of saline or NaHCO3. During hypoxemia + acidemia the change in arterial pH induced by NaHCO3(2 mEq/kg) does not alter BBF or brain O2delivery.

ISSN:0031-3998    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Total glutathione levels and the activity of enzymes associated with antioxidant protection in neonatal lung are increased in response to hyperoxia. Glutathione levels in developing rat lung decreased from 24 nmol/mg protein on day 19 of gestation to approximately 12 nmol/ mg protein at birth. The initial decrease in glutathione may be due to emergence of other antioxidant systems. Newborn rats placed in 100% oxygen showed a rapid and sustained increase in total glutathione levels which was primarily due to an increase in reduced glutathione. Explants obtained from 16-wk gestation human fetal lung or from 17- to 18-day fetal rat lung also showed increased total and reduced glutathione when cultured in 95% oxygen, 5% CO2as compared with explants cultured in room air. Type II cells isolated from neonatal rats maintained in oxygen for 6 days also showed glutathione levels twice those found in cells isolated from animals in room air. The activity of antioxidant enzymes (glucose-6-phosphate dehydrogenase, glutathione peroxidase, glutathione reductase) was increased in lungs of newborn rats exposed to 100% oxygen either at birth or 2 days of age. Antioxidant enzyme activity of lung explants cultured in 95% oxygen, 5% CO2was also higher than in explants maintained in room air. These results suggest that the increases in glutathione and of antioxidant enzymesin vivoandin vitroare a direct effect of oxygen exposure in lung and that the increase of both glutathione and antioxidant enzyme activity is intrinsic to the lung cell itself. It is likely that increases in glutathione in lung represent an important protective mechanism against oxidant injury.

ISSN:0031-3998    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We measured the cortisol and corticosterone responses to insulin-induced hypoglycemia in 13 growth hormone (GH)-deficient children and 30 short children without GH deficiency. Although there was no difference between the two groups in 1) degree of hypoglycemia attained, 2) baseline cortisol, 3) baseline coricosterone, or 4) cortisol 40 min after insulin injection, GH-deficient children had a significantly greater corticosterone response to this stress (3.6 ± 0.4versus1.9 ± 0.2μg/dl). (All data are presented as mean ± SEM.) In order to explore the effect of GH on corticosterone secretion, we measured cortisol and corticosterone responses to synthetic (1-24) ACTH before and after 3 days of exogenous GH (0.2 unit/ kg/day). In 13 GH-deficient children, GH treatment caused a significant decrease in the corticosterone response to ACTH (2.2 ± 0.2μg/dl before GH to 1.6 ± 0.2μg/dl;t=5.22,p<0.001; pairedttest) despite the fact that there was no significant change in the cortisol response to ACTH (18 ± 2μg/dl before and 16 ± 2μg/dl after). When seven short children who were not GH deficient underwent a similar 3-day course of GH, the decrease in their corticosterone response was much less although still statistically significant (2.0 ± 0.5 to 1.8 ± 0.5μg/dl; pairedttest,p<0.05). Again, the stimulated levels of cortisol were not affected by GH treatment (19 ± 4versus18 ± 3μg/dl) These results indicate that GH modulates the adrenal response to ACTH by suppressing corticosterone secretion without affecting cortisol secretion. In summary, this study presents two new findings. First, corticosterone levels are elevated during insulin tolerance testing in children with GH deficiency and, second, a 3-day course of GH replacement therapy causes a reduction in corticosterone serum levels after ACTH administration to more normal levels without altering the corresponding cortisol concentrations. As corticosterone is a less potent glucocorticoid, it might function as a cortisol antagonist when present in increased amounts and play a role in the poor recovery from hypoglycemia frequently observed in individuals with GH deficiency.

ISSN:0031-3998    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We investigated the effect of captopril, an orally active angiotensin converting enzyme inhibitor, on urinary protein excretion in puromycin aminonucleoside nephrotic rats. The administration of captopril (10 mg/100 g body weight) decreased proteinuria on days 10-14 following the administration of puromycin aminonucleoside (73.0versus125.0 mg,p<0.01), without affecting glomerular filtration rate. The beneficial effect of captopril was not abolished by the continuous intravenous infusion of angiotensin II (10μg/kg/h for 9 days) or subcutaneous injections of aprotinin (50,000 KIU/day for 3 days). Indomethacin, in moderate (5 mg/kg/day for 3 days) or high (10 mg/ kg/day) doses, abolished the captopril attenuation in urinary protein excretion. The salutory effect of captopril was characteized by a reduction in the fractional excretion of protein without compromising the glomerular filtration rate. No difference in renal ultrastructure was noted in captopril-treatedversuscontrol animals. Captopril was ineffective in reducing urinary protein excretion in rats with adriamycin-induced glomerulopathy. We conclude that captopril acts to reduce proteinuria in renal disease states arising from depletion of the glomerular basement membrane polyanion. The mechanism of action is postulated to be an alteration in renal hemodynamics, namely increased blood flow and a decrease in the ultrafiltration coefficient, that are the consequence of increased intrarenal prostaglandin production.

ISSN:0031-3998    

出版商:OVID    

年代:1985

数据来源: OVID