J. Grönlund

Elevated arterial blood pressure is associated with peri-intraventricular haemorrhage

In a prospective study, brain ultrasound scans were performed in 42 newborns (median birth weight 1700g, range 1020–3720 g; gestational age 32 weeks, 26–36) to reveal peri-intraventricular haemorrhage (PIVH) (grades I–IV) as well as echodensities (ED) and/or periventricular leucomalacia (PVL). ECG and arterial blood pressure were recorded on magnetic tape at 8h intervals during the first 24 h of life for further computer analysis. Heart rate (HR) and its variability (HRV) indices RMSM (long-term variability) and RMSSD (short-term variability), together with their coefficients of variation, were computed. Systolic (SBP), diastolic (DBP), and mean blood pressures (MBP) were detected as average values for 2-min stationary segments together with the respective minima and maxima. The indices of variability and their coefficients of variation were computed for the arterial pressure. PIVH was found in 12 newborns and ED in 8 (of whom two developed PVL). The remaining 22 served as controls. Neither HR, HRV nor BP variability differed between the groups. DBP was higher in the group with PIVH (39 mmHg) when compared to both the controls (33 mmHg,P<0.05) and the ED group (32 mmHg,P<0.01). MBP behaved respectively (45 mmHg, 38 mmHg, 37 mmHg,P<0.01). SBP behaved also similarly when gestational age and birth weight were used as covariates (57 mmHg, 48 mmHg, 47 mmHg,P<0.01).Our results suggest that elevated diastolic, mean and systolic blood pressure are significantly associated with peri-intraventricular haemorrhage in preterm newborn infants.

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

ObjectiveTo examine the influence of antenatally administered magnesium sulfate (MgSO4) and ritodrine on cerebral blood flow and systemic hemodynamics in preterm infants. DesignProspective, observational study. SettingNeonatal intensive care unit of a university central hospital. PatientsFifty-five preterm infants age <33 wks of gestation. InterventionsSerial 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. ConclusionsOur 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.

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.

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 3^1 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.

Transcephalic electrical impedance provides a means for quantifying pulsatile cerebral blood volume changes following head-up tilt

Transcephalic electrical impedance (delta Z) was used to assess pulsatile cerebral blood volume changes while tilting nine premature (30-34 weeks) infants 20 degrees head up. High-frequency (1.50-4.00 Hz) delta Z variability decreased 27% while heart rate did not show any change. We would like to suggest that the variability of transcephalic electrical impedance analysed with spectral estimation seems to provide a means for quantifying alterations in cerebral circulation.

Do β-adrenergic blockade and sleep state affect cardiorespiratory control in neonatal lambs ? Multivariate autoregressive modeling approach

ABSTRACT: β-Blockers are used in pregnancy-associated hypertension and in postnatal cardiac arrhythmias, and the neonate may get them in breast milk. We therefore studied the effects of β-adrenergic medication on interrelations between heart rate (HR), respiration, and arterial blood pressure (aBP) in newborn lambs. The influence of sleep state on these cardiorespiratory interrelations was also examined. HR, aBP, and respiration (based on transthorack electrical impedance) were recorded and the sleep state was visually documented in five healthy chronically instrumented newborn lambs before the age of 30 d. Propranolol was given (1 mg/kg). Two-min stationary segments of the three signals were analyzed using a multivariate autoregressive model, which yields oscillations of the signals and intersignal relationships as source contributions. The variabilities of aBP and HR were greatest at the low frequencies (<0.25 Hz) and so were their intersignal relationships (including baroreflex). The respiratory variability was greatest at the frequencies corresponding to the respiratory rate. Daring quiet sleep, the variabilities in HR, aBP, and respiration were lowest. The impact of respiratory oscillations on other signals increased but the impact of aBP variability decreased during quiet sleep. β-Blockade and sleep state affected separately the cardiovascular and respiratory variables and their interrelations. β-Blockade reduced HR and increased pulse pressure. The overall heart rate variability and the respiratory low-frequency contribution to heart rate variability decreased due to the β-blockade. We postulate that the β-adrenergic system is an important regulator of HR and HR variability IB neonatal lambs and also of the low-frequency components of the respiratory sinus arrhythmia. However, inasmuch as the interrelations between HR and aBP were not altered by the β-blockade, even high doses of propranolol do not seem hazardous for the cardiovascular system in neonatal lambs.

Multivariate autoregressive modeling of autonomic cardiovascular control in neonatal lambs

The neonatal cardiovascular control system is a complicated interactive system which is under vigorous development at birth. From the measurement point of view the cardiovascular control is a closed-loop system. However, it can be examined on a beat-by-beat basis by analyzing circulatory-controlled variables with advanced signal analysis techniques. This paper proposes to use a multivariate autoregressive modeling technique in the analysis of several simultaneous physiological signals in order to examine interactions and inherent properties in the system. With the proposed multivariate autoregressive modeling technique, a signal is modeled as a linear combination of its own past and the past values of the other simultaneous signals plus a predictive error term of the model. The interactions in the system after the model identification are analyzed in frequency domain utilizing power spectrum estimates of the signals and signal contributions. The applicability of the proposed method was examined by a three-variable model between heart rate, blood pressure and respiration in the study of autonomic cardiovascular control in a chronic neonatal lamb model, in which the cardiovascular status was changed by using a beta-adrenergic autonomic nervous blockade. The study showed that the multivariate autoregressive modeling technique is a feasible technique in studying complicated interactions within the cardiovascular control system.

Multivariate autoregressive modelling combined with transcephalic electrical impedance: method to relate neonatal systemic circulation and respiration to cerebral circulation.

We studied the pulsatile component of cerebral circulation with transcephalic electrical impedance (ΔZ) in six preterm newborns, three of whom had severe cerebral bleeding, peri-intraventricular haemorrhage (PIVH). The transcephalic electrical impedance ΔZ signal, ECG, arterial blood pressure, (aBP) and respirogram were recorded on analogue magnetic tape for 30 min. Artefact-free stationary segments (lasting for 2 min) of the four signals were digitised. A digital multivariate autoregressive (MAR) model was used to study frequency-specific variability in the signals and to quantify interrelations between the variabilities of ΔZ, HR, aBP and respiratory signals. MAR modelling describes a system where all the signals simultaneously explain each other. The inherent variability of ΔZ was lower and the influences of respiration and aBP on ΔZ significantly greater in infants with severe PIVH than in controls. These changes were observed at high frequencies corresponding to respiration and heart rate. This may be interpreted as a marker of pressure passivism in the cerebral circulation following PIVH. We conclude that in preterm babies the application of MAR modelling, together with transcephalic impedance, may be a new, helpful and quantitative method for the study of simultaneous interrelations between variables of cerebral and systemic circulations and respiration.

Transcephalic electrical impedance in the study of cerebral circulation in a juvenile pig model

Transcephalic electrical impedance offers a technique for non-invasive, cotside monitoring of neonatal cerebral circulation but the exact nature of the signal is somewhat ambiguous. The impedance signal is examined in an animal project where the ventilator settings are adjusted (20 min−1–10 min−1–40 min−1 for 10 min periods each) to produce circulatory changes. Six juvenile pigs are intubated, and ECG, arterial blood pressure, carotid flow (CF) by electromagnetic flowmeter and impedance are continuously monitored and stored on analogue tape. Cardiac output by thermodilution, blood oxygen (pO2) and carbon dioxide (pCO2) tensions are measured. ECG is converted to heart rate, mean blood pressure is integrated, and the high-frequency (1.50–4.00 Hz) component of the impedance signal ΔZ is computed using autoregressive spectral estimation. Stroke volume, peripheral vascular resistance (PVR) and cerebral vascular resistance (CVR) are calculated. pCO2 and CF increase and pO2 decreases during hypoventilation. CF correlates positively with cardiac output, stroke volume, ΔZ and pCO2, and negatively with pO2 and CVR. ΔZ correlates positively with heart rate and cardiac output, and negatively with PVR and CVR. It is concluded that the impedance signal is related to the amount of blood transmitted to the brain by every beat of the heart, depending on the changes in both the systemic circulation and the cerebral vascular compliance.