摘要:

The purpose of this study was to define the pattern of postnatal plasma cortisol concentrations during the first week of life in premature infants, and to evaluate the effect of developmental and clinical factors on this pattern. We measured plasma cortisol concentrations in the morning and afternoon on d 2, 4, and 6 in 120 premature infants (gestational age 24–36 wk) and examined the effects of gestational age, postnatal age, and illness. We described an inverse relationship between gestational age and cortisol concentrations, with the youngest infants having the highest random cortisol values (F= 5.14,p= 0.0073). Illness had a significant negative effect such that the cofactors ventilatory support pattern (F= 6.62,p= 0.0016) or “use of surfactant” (F= 6.63,p= 0.001) defined a pattern where cortisol values were lower in infants that had the highest ventilatory requirements or that received surfactant compared with values from those infants who did not have these requirements. The postnatal pattern in cortisol values depended on gestational age. Ill infants more than 27 wk gestational age increased their cortisol values from d 2 to d 6 although cortisol values decreased in well infants. These patterns resulted in a nonsignificant change over time for these age groups. In contrast, cortisol values significantly decreased from d 2 to d 6 in both well and ill infants that were less than or equal to 27 wk. We conclude that plasma cortisol concentrations in the premature infant are significantly correlated with gestational age and to markers of illness. Interpretation of the physiologic significance of random cortisol values in this patient population must be made with consideration for the statistically significant effects described above.

ISSN:0031-3998    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

We investigated the basic characteristics of the rat embryonic circulation and also looked at the hemodynamic effects of α- and β-agonists, digitalis, and atrial natriuretic peptide, using a modified organ culture system in which the embryo was placed in oxygenated Hanks' balanced salt solution, blood pressure was measured by a servo-null micropressure system, and blood flow pattern was obtained by a 20-MHz pulsed Doppler velocity meter. The peak pressure was 0.5 ± 0.04 (SEM) mm Hg at the atrium (n= 6), 2.3 ± 0.10 mm Hg at the ventricle (n = 15), 1.6 ± 0.03 mm Hg at the truncus (n= 7), and 1.0 ± 0.05 mm Hg at the umbilical artery (n= 21). There was a pressure drop from the ventricle to the truncus and then a smaller pressure decrease to the umbilical artery. The atrial a-wave was 20% of ventricular pressure and ventricular inflow blood flow pattern showed very low early-to-late filling ratio, indicating that the ventricle was stiff. These findings were essentially the same as in the chick embryo. We recorded the ventricular image by using a highspeed video system with a frame rate of 200/s, and the ventricular pressure-area loop showed a triangular shape with short isovolumetric phases, which was different from that of the chick embryo at a similar stage. Isoproterenol increased ventricular pressure from 2.3 ± 0.1 to 2.6 ± 0.1 mm Hg (n= 7,p< 0.05) and decreased umbilical blood pressure from 0.68 ± 0.05 to 0.61 ± 0.04 mm Hgn= 7,p< 0.05), suggesting contraction of the outflow tract, although positive change in pressure per unit time of ventricular pressure did not change. Ventricular negative change in pressure per unit time was increased with isoproterenol from 40 ± 4 to 51 ± 6 mm Hg/s (n= 7,p< 0.05), implicating improvement of diastolic function. Atrial natriuretic peptide and norepinephrine did not exert any significant responses, which was in contrast to the marked effects of these drugs seen in chick embryos. Acetylstrophanthidin, a rapid-acting digitalis, slowed the heart rate from 184 ± 4 to 171 ± 3 bpm (n= 6,p< 0.05) but did not change other parameters. In conclusion, basic characteristics of the circulation of the mammalian embryo are similar to those of the avian embryo, but responses to various cardiovascular agents known in the chick embryo cannot be extrapolated to the mammalian embryo.

ISSN:0031-3998    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

To study the influence of artificial ventilation rate on neonatal heart rate variability (HRV), ECG and respiratory impedance curves were recorded four times a day in 20 preterm infants (<33 wk) during the first 3 d after birth while the infants were ventilated at a wide range of ventilator rates. The contents of selected frequency bands within the R-R interval power spectrum were calculated for 3-min periods. Respiratory distress syndrome severity was assessed at each measurement. Respiratory sinus arrhythmia (RSA) induced by the ventilator appeared to mimic spontaneous RSA. As in spontaneous respiration, the amount of RSA (power in a frequency band around the respiratory rate) increases as the ventilation rate decreases. This phenomenon is most probably due to entrainment with baroreflex-related fluctuations in the heart rate. Although the artificial ventilation rate influences RSA and thus high-frequency HRV, an increase in respiratory distress syndrome severity results in a decrease in low-frequency HRV. Thus, the attenuation of low-frequency HRV by respiratory distress syndrome is not likely to be due to artificial ventilation.

ISSN:0031-3998    

出版商:OVID    

年代:1995

数据来源: OVID