Maternal magnesium sulfate treatment is associated with reduced brain-blood flow perfusion in preterm infants.

OBJECTIVE: To examine the influence of antenatally administered magnesium sulfate (MgSO4) and ritodrine on cerebral blood flow and systemic hemodynamics in preterm infants. DESIGN: Prospective, observational study. SETTING: Neonatal intensive care unit of a university central hospital. PATIENTS: Fifty-five preterm infants age <33 wks of gestation. INTERVENTIONS: Serial Doppler examinations of the brain circulation, heart rate, systemic blood pressure, and echocardiographic assessment of ductus arteriosus shunting were performed during the first week of life in infants exposed antenatally to maternal MgSO4 (n = 19) or ritodrine treatment (n = 17), and in 19 nonexposed preterm controls. MEASUREMENTS AND MAIN RESULTS: Cerebral blood flow velocity measurements were obtained from the anterior cerebral artery and internal carotid artery. Perfusion pressure and indices of resistance and blood flow in both vessels were subsequently derived. Maternal MgSO4 had no effect on neonatal cerebral blood flow velocity or resistance, but was associated with decreased (p <.05) perfusion pressure and blood flow in the anterior cerebral artery and internal carotid artery during the first day of life. Systolic blood pressure and pulse pressure were also lower (p <.05) during the whole study period in the MgSO4-exposed infants when compared with the controls. Maternal ritodrine treatment, on the other hand, had no consistent effects on either neonatal cerebral or systemic hemodynamics. CONCLUSIONS: Our data indicate that maternal MgSO4 treatment, in contrast to antenatal ritodrine, is associated with lowered cerebral perfusion in preterm infants on the first day of life.

Antenatal magnesium sulphate exposure is associated with prolonged parathyroid hormone suppression in preterm neonates.

UNLABELLED: The effects of maternal magnesium sulphate treatment on neonatal mineral status and parathyroid hormone secretory response were studied in 8 exposed and 27 control preterm infants during the first 2 wk of life. Antenatal magnesium sulphate resulted in hypermagnesaemia during the first 3-7 d of life without affecting other serum mineral concentrations. CONCLUSION: Early hypermagnesaemia was associated with hypercalciuria during the first 3 d and parathyroid hormone suppression up to the age of 2 wk in the exposed infants.

Periodic spectral components of fetal heart rate variability reflect the changes in cord arterial base deficit values: a preliminary report.

Fetal distress changes the function of the autonomic nervous system. These changes are reflected in the fetal heart rate and can be quantified with power spectrum analysis of heart rate variability. The purpose of this study was to find out whether spectral components of fetal heart rate variability (FHRV) during labor are associated with fetal cord arterial base deficit values at birth. The association between FHRV and umbilical cord arterial base deficit was studied in 14 singleton fetuses with normal pregnancy at 35-40 weeks of gestation. Fetal ECG was recorded by scalp-electrode using a STAN Fetal ECG monitor (Cinventa Ab, Mölndal, Sweden). FHRV was quantified by computing Fast-Fourier-transformed heart rate (HR) spectra at three frequency bands: low-frequency (LF) 0.03-0.07 Hz, mid-frequency (MF) 0.07-0.13 Hz and high-frequency (HF) 0.13-1.0 Hz. We found that total FHRV and MF FHRV were lower in fetuses with cord arterial base deficit 8 to 12 mmol/L in comparison to the fetuses with normal cord arterial base deficit value (P=0.02 and P=0.01, respectively). A linear correlation was found between the spectral densities and the cord arterial base deficit values (r=0.4 and r=0.6, respectively). We conclude that the results suggest changes in the autonomic nervous cardiac control in fetuses with cord arterial base deficit between 8 to 12 mmol/L. The clinical applicability of our observations on FHRV in predicting fetal distress remains to be further studied.

Efficiency of left ventricular diastolic function increases in healthy full-term infants during the first months of life. A prospective follow-up study.

Postnatal changes in left ventricular diastolic filling and systolic cardiac performance were studied monthly by serial echocardiographic measurements from days 3-5 up to six months in 20 healthy full-term infants. The fractional shortening area (FSA = (left ventricular end-diastolic area - end-systolic area)/end-diastolic area) was assessed for systolic performance, and transmitral pulsed-wave Doppler flow velocity patterns were analysed for diastolic function. FSA remained stationary during the observation. After birth, left ventricular peak early (E) and atrial (A) velocities and the respective integrals were lower than at one month of age (47+/-5 vs. 63+/-6 cm/s and 44+/-6 vs. 57+/-5 cm/s and 3.33+/-0.40 vs. 4.05+/-0.53 cm and 2.74+/-0.40 vs. 3.18+/-0.53 cm; P < 0.05). During the next five months, the early parameters (E velocity and E integral) increased but the atrial indices (A velocity and A integral) did not change. During the whole observation the E/A velocity ratio, the E/A integral ratio and the early filling fraction (EFF) increased. The early filling deceleration time was longer during the first month than later (87+/-10 vs. 72+/-13 ms; P < 0.05). In conclusion, age-related changes were observed in the diastolic but not in the systolic performance in healthy full-term infants during the first six months. The most intensive changes took place in the early and atrial transmitral parameters during the first month of life, suggesting an improvement in both left ventricular relaxation and compliance. During the following five months, the early mitral parameters increased but the atrial diastolic values remained stable. These changes may mainly be determined by the improvement in left ventricular relaxation.

Influence of maternal magnesium sulphate and ritodrine treatment on the neonate: a study with six-month follow-up.

Magnesium sulphate and ritodrine are commonly used drugs in the prevention of preterm delivery. However, the effects of these treatments on the newborn are controversial. It has previously been suggested that antenatal tocolytic magnesium sulphate decreases the incidence of cerebral palsy, but increases paediatric mortality. On the other hand, antenatal ritodrine treatment has been reported to increase the incidence of neonatal peri-intra-ventricular haemorrhage (PIVH). We investigated the cerebral ultrasonographic findings, neurological outcome and apparent life-threatening events (ALTE) among 63 infants, born before 33 wk of gestation, whose mothers were antenatally treated for premature birth with ritodrine or magnesium sulphate, and for pre-eclampsia with magnesium sulphate. Cerebral ultrasonography was performed during the first week of life and repeated before hospital discharge. The pathological findings were confirmed by a paediatric radiologist. A paediatrician and a physiotherapist performed the neurological follow-up examination of the survivors at 6 mo of age. We found Grade 3-4 PIVH in 15% of the infants exposed to maternal ritodrine treatment, in 9% of the infants whose mothers received tocolytic magnesium treatment, and in none of those exposed to maternal magnesium treatment for pre-eclampsia (p = 0.19). However, no differences were observed in 6-mo development or in the rate of paediatric mortality and ALTE among these three study groups. Because of the retrospective design and the limited number of subjects, the results of this study must be interpreted with caution.

Spectral analysis of heart rate and blood pressure variability.

The cardiovascular system contains negative feedback and time-delay mechanisms resulting in oscillations in heart rate and blood pressure, which are apparent when these signals are measured over time. Specifically, spectral analysis and nonlinear analysis techniques allow quantification of heart rate and blood pressure variability. Alterations in heart rate and blood pressure variability as evidenced from the spectral characteristics of these physiological signals allow the clinicians to have indicators of aberrations of neural control in various conditions or when drugs such as beta blockers, adrenergic agents, methylxanthines, etc., are being administered.

Increased amplitude modulation of continuous respiration precedes sudden infant death syndrome -detection by spectral estimation of respirogram.

The immaturity of the control of the autonomic nervous system has been suggested as one of the key factors in the pathophysiology of sudden infant death syndrome (SIDS). Therefore, the attenuated control of respiration may also cause more slow oscillatory breathing among infants at risk of SIDS. In this study, patterns of respiratory activity (RAV) and heart rate variability (HRV) were examined in Medilog-records prospectively obtained from 22 tape recordings made on 16 babies subsequently suffering from SIDS and from 22 matched control babies. A total of 248 signal segments, 120 s in duration, representing the state of regular breathing were visually selected for further analysis. The digitised signal sets were detrended, Fast-Fourier-transformed and autospectra as well as cross-spectra for the HRV and HRV were computed. The RAV and HRV were examined at two spectral bands: (1) a low frequency (LF) band 0.03-0.17 Hz (1.8-10 cycles/min) and (2) a high frequency (HF) band 0.3-1.3 Hz (18-90 cycles/min). Different parameters of each band were tested in the spectral analysis of cardiorespiratory control. The LF/HF-ratio of the spectral peak area of the respiratory activity and the LF/HF-ratio of the spectral band area of the respiratory activity were greater in the SIDS group when compared to the controls. No significant intergroup differences were found in the parameters of HRV, or the cross-spectral parameters. Interestingly, the technique appeared helpful in displaying that the victims of SIDS had a significantly greater amount of slow oscillation in the continuous respiratory signal (1.05+/-1.89 vs. 0.41+/-0.57, P=0.02). In the victims of SIDS the respiratory control system seems to be less stable and cause more slow oscillatory breathing and this can be detected using spectral analysis of respiratory activity even during breathing that visually seems to be regular.