Comparison of the effects of antenatal magnesium sulphate and ritodrine exposure on circulatory adaptation in preterm infants.

We examined the effects of maternal magnesium sulphate (MgSO4) and ritodrine treatments on the autonomic cardiovascular control in preterm neonates with respiratory distress syndrome during the first 2 days of life. Serial measurements of heart rate (HR), blood pressure (BP) and respirogram were performed during the first 2 days of life in 28 preterm infants below 33 weeks of gestation with antenatal exposure to MgSO4 (n = 13) or ritodrine (n = 15), and in 12 nonexposed preterm controls. Spectral analysis was used for the quantification of HR and BP variability. Although antenatal MgSO4 exposure had no effect on HR or the systolic, diastolic or mean BP, it was associated with significant decreased beat-to-beat changes in BP. In contrast, ritodrine exposure had no consistent effects on the autonomic cardiovascular control during the first 2 days of life. Our data suggest that maternal MgSO4 treatment decreases the neonatal high frequency changes in BP. This early vascular stabilizing effect of antenatal MgSO4 exposure may contribute to a lowered risk of cerebral vascular catastrophes, in the vulnerable areas of the brain, among the preterm infants with respiratory distress syndrome.

High resolution ECG changes among Finnish pilots.

BACKGROUND: Abundant appearance of late potentials registered by high resolution ECG (HR-ECG) has been shown to predict a risk for cardiac arrhythmia. The aim of this study was to evaluate the appearance of normal and abnormal late potentials in a group of Finnish private and commercial pilots. METHODS: Standard 12-lead ECG and 40-250 Hz band-pass filtered HR-ECG were recorded in 168 healthy male pilots. The following parameters were estimated: the root-mean-square voltage in the terminal 40 ms (RMS40), the total filtered QRS duration (FQRSD) and the duration of terminal high frequency low amplitude signal (HFLAD) of less than 40 microV in the filtered QRS. RESULTS: Age (38 +/- 12 yr) and height (179 +/- 6 cm) had a significant (p < 0.005) and independent association with the total filtered QRS duration. No such correlations were observed for RMS40 or HFLAD. Mean +/- SD for RMS40 was 35.3 +/- 15.4 microV, for FQRSD 114.6 +/- 6.8 ms and for HFLAD 31.0 +/- 7.9 ms. Smokers tended to have longer late potentials (HFLAD) than non-smokers. Fasting blood glucose had a significant (p < 0.05) positive correlation with HFLAD. Serum cholesterol level had no correlation with the HR-ECG parameters. Age and height of the subject were associated with the total QRS duration as follows: FQRSD (ms) = -9.7* log age (yr) + 0.2*height (cm) + 94.6.

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 (delta Z) in six preterm newborns, three of whom had severe cerebral bleeding, peri-intraventricular haemorrhage (PIVH). The transcephalic electrical impedance delta Z 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 delta Z, HR, aBP and respiratory signals. MAR modelling describes a system where all the signals simultaneously explain each other. The inherent variability of delta Z was lower and the influences of respiration and aBP on delta Z 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.

Cerebral circulation assessed by transcephalic electrical impedance during the first day of life--a potential predictor of outcome?

Pulsatile changes in intracranial blood volume (transcephalic electrical impedance, delta Z), arterial blood pressure (aBP) and respiration were studied during the first day after birth in 42 neonates with a birth weight of 1040-3850 g and gestational age of 26-36 weeks. The neurological outcome was assessed at 1 year of age to study the predictive ability of delta Z. delta Z, ECG, respirogram and direct aBP were recorded at 8-h intervals. Outcome was adverse in seven infants of whom two died from severe peri-intraventricular haemorrhage. PCO2 was higher (6.2 kPa) in the infants with adverse outcome than in those infants with favourable outcome (5.0 kPa) (P = 0.004). Blood glucose (4.5 vs. 3.3 mmol/l, P = 0.030) and first day administration of fluid (80 vs. 63 ml/kg/day, P = 0.003) behaved, respectively. Of the infants receiving dopamine therapy, 60% had adverse outcome while only 11% of those not receiving dopamine had adverse outcome (P = 0.016). Of the infants with high diastolic blood pressure levels, 32% had adverse outcome, while none with low diastolic blood pressure levels had adverse outcome (P = 0.031). Spectral analysis was used to examine signal variabilities in the frequency domain. During the first 24 h of life, the variabilities of aBP and respiration were equal in all the infants. The high-frequency delta Z signal variability (1.50-4.00 Hz, heart rate level) was found to be lower in the infants with adverse outcome (330 units) than in the infants with favourable outcome (1280 units, P = 0.017). The low delta Z variability allowed us to assume that there is a decrease of pulsatile cerebral blood flow (CBF) in the infants with adverse outcome. We speculate that this may result from the 'no reflow phenomenon', increased tissue pressure due to ischaemia and/or PIVH, the 'brain sparing effect' or constriction of main cerebral arteries due to increased pressure support or metabolic factors (PCO2, glucose). We believe that transcephalic impedance provides a potential cot-side method for monitoring cerebral circulation in the neonatal period with an ability to predict outcome.

Elevated arterial blood pressure is associated with peri-intraventricular haemorrhage.

UNLABELLED: In a prospective study, brain ultrasound scans were performed in 42 newborns (median birth weight 1700 g, 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 8-h 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). CONCLUSION: Our results suggest that elevated diastolic, mean and systolic blood pressure are significantly associated with peri-intraventricular haemorrhage in preterm newborn infants.

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

Beta-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 beta-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 transthoracic 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 (less than 0.25 Hz) and so were their intersignal relationships (including baroreflex). The respiratory variability was greatest at the frequencies corresponding to the respiratory rate. During 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. beta-Blockade and sleep state affected separately the cardiovascular and respiratory variables and their interrelations. beta-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 beta-blockade. We postulate that the beta-adrenergic system is an important regulator of HR and HR variability in neonatal lambs and also of the low-frequency components of the respiratory sinus arrhythmia.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic control and inter-relationships between heart rate and blood pressure in neonatal lambs.

Our aim was to develop a signal analysis method for revealing interrelationships between heart rate and blood pressure and for displaying the influence of autonomic nervous control on these signals in a chronic lamb model. A chronically instrumented neonatal lamb model was made to record ECG and direct arterial blood pressure (N = 15). Continuous two-minute recordings of blood pressure (BP) and ECG were digitised. The instantaneous heart rate signal (IHR) was derived from the ECG. The IHR and BP signals were bandpass filtered. Autospectra, cross-spectra, coherence spectra and phase spectra for the signals were computed to study the relative magnitudes and inter-relationships of the cardiovascular signals under normal conditions and during beta-adrenergic blockade. It was noted that both in the BP and IHR there were oscillations at the frequency of less than 0.1 Hz and also at the respiratory rate around 0.6 Hz. Beta-blockade reduced the oscillations of the IHR in less than 30-day-old lambs. It did not affect the coherence spectra or the phase lag between the signals. During quiet sleep the variability of blood pressure was decreased. In over-30-day-old-lambs the beta-blockade did not affect the variabilities of the cardiovascular parameters. These findings indicate that in neonatal lambs the sympathetic control system is a major regulator of cardiovascular interactions.