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Biomedical subjects

G Greisen

Publications and source records attributed to G Greisen.

At least 109 records · Page 6Linked to original sources
PubMed1988

Comparison of electrical impedance and 133xenon clearance for the assessment of cerebral blood flow in the newborn infant.

The peak amplitude of pulsatile cerebral electrical impedance (delta Zp) was compared with simultaneous 133xenon clearance estimations of cerebral blood flow (CBF infinity) on 28 occasions in nine infants receiving assisted ventilation who had changes in PaCO2 and thereby presumably in cerebral blood flow. Percentage changes from one measurement to the next in each infant were compared. Using linear regression the relationship was delta Zp = 0.5 CBF infinity-1.5 with r = 0.67. The 95% confidence interval for the regression coefficient was 0.2-0.8 and the mean residual was 28%. Changes in cerebral blood flow in these clinical conditions were similarly detected by the two methods but delta Zp underestimated the magnitude of the change in comparison with CBF infinity and its accuracy was insufficient to allow conclusions about the magnitude of small changes in cerebral blood flow in individual infants.

Blood Flow Velocity↗
PubMed1988

Cerebral electrical impedance: do indices derived from it provide information on cerebral blood flow in the neonate?

Cerebral electrical impedance was compared with simultaneous estimations of cerebral blood flow (CBF infinity) using the 133Xe clearance technique on 28 occasions in 9 neonates who had changes in PaCO2 and hence presumably cerebral blood flow between measurements. Various indices derived from the impedance waveform which have been reported in the adult to correlate with blood flow were analysed for their relationship with CBF infinity. Percentage change of the two variables was calculated and three indices showed a significant correlation using linear regression. They were peak amplitude (delta Zp), delta Zp times heart rate (delta Zp x HR), and backslope projection. The regression equation for the index with the closest correlation was delta Zp x HR = 0.57CBF infinity + 3.4 with r = 0.68 (p = 0.003) and standard error of the estimate = 29%. Some cerebral electrical impedance indices did correlate with cerebral blood flow changes under the conditions of this study and provide accurate information on the direction of changes but because of the wide confidence limits cannot be used for quantification of cerebral blood flow changes.

Blood Gas Monitoring, Transcutaneous↗
PubMed1987

Cerebral blood flow, PaCO2 changes, and visual evoked potentials in mechanically ventilated, preterm infants.

Two estimations of global cerebral blood flow (CBF) using 133-Xenon clearance were done with an interval of about one hour in 16 mechanically ventilated, newborn infants, of less than 33 weeks gestational age. In eight infants CBF was estimated just before a change in ventilator settings, and again when the PaCO2 was stable. In the remaining eight infants small spontaneous changes in PaCO2 occurred. The CBF-CO2 reactivity was similar in the two groups (+67%/kPa (95% confidence interval 13-146) and 52%/kPa (24-86)) and considerably higher than the CBF-CO2 reactivity estimated from the interindividual variation of flow and PaCO2 (+19%/kPa (4-36)). There were no significant relations between CBF and arterial blood pressure. Flash evoked potentials (VEP) were recorded during the 133-Xenon clearances in 8 of the infants. VEP showed no relation to changes in CBF, even when the blood flow rose from the lowest levels. CBF and VEP were obtained once in 9 other infants. Among the 17 infants, the latency of the first negative wave of the VEP was not related to the CBF level. Mean CBF in the 25 infants was 12.3 ml/100 g/min (range 4.3 to 18.9), mean PaCO2 was 4.2 kPa (range 2.3 to 6.4). Thus, CBF-CO2 reactivity appeared to be normal in these clinically stable, mechanically ventilated, preterm infants, suggesting that their low cerebral blood flow was well regulated. The absence of a relation of CBF with VEP suggested that cerebral blood flow was not critically decreased.

Blood Gas Monitoring, Transcutaneous↗
PubMed1987

Severe hypocarbia in preterm infants and neurodevelopmental deficit.

We report significant neurological abnormality at 18 months of age in 3 of 7 very low birth weight infants (less than or equal to 1,500 g), who during mechanical ventilation inadevertently became severely hypocarbic (arterial carbondioxide tension less than 2.0 kPa (15 mmHg)) at some time during the first 24 h of life. Although the number is small the outcome was significantly worse than the outcome in two fairly similar groups of infants selected as controls (p = 0.026). The infants in one of the control groups were also mechanically ventilated but remained normocapnic. Germinal layer haemorrhage (GLH) was more frequent among these infants compared with the severely hypocarbic infants (p = 0.022). The infants in the other control group was not mechanically ventilated. In all the severely hypocarbic infants the Bayley mental developmental index uncorrected for prematurity was at or below the median for the total sample (p = 0.01). The results suggest that neonatal cerebral ischaemia, for instance due to hypocarbia, is of greater prognostic significance than GLH.

Blood Gas Monitoring, Transcutaneous↗
PubMed1987

EEG depression and germinal layer haemorrhage in the newborn.

Amplitude integrated EEG (aEEG) recordings from 32 mechanically ventilated infants, gestational age 32 weeks or less, were analysed. All recordings were started within 24 h of birth and continued for at least 50 h. Germinal layer haemorrhage (GLH) was diagnosed by repeated ultrasonography. In six infants neither GLH nor hypocalcaemia were diagnosed; aEEG in these infants rapidly became more active after birth: at 30 h of age continuous background activity was present for more than 20% of the time, and a seizure-like pattern was exceptional. In seven infants without GLH but with hypocalcaemia and other signs of metabolic derangement, continuous background activity appeared later and seizure-like activity was frequent. In the infants with GLH, depression of the background activity was apparent. This finding was particularly distinct in the presence of severe haemorrhages. Four infants developed GLH after 30 h of age. All these infants had depressed aEEG before the development of GLH, with less than 20% continuous activity at 30 h of age. In ten infants an analysis of the aEEG during the occurrence of GLH was possible. In six of these, cortical electrical activity decreased. Due to the limitation of GLH timing, it was not possible to decide whether this decrease closely preceded or followed GLH. We suggest that GLH primarily occurs in brains with a preceding metabolic and neurophysiologic abnormality, and that further functional deterioration is caused by the most severe haemorrhages.

Cerebral Hemorrhage↗
PubMed1986

Status at two years in 121 very low birth weight survivors related to neonatal intraventricular haemorrhage and mode of delivery.

All 121 infants with birthweight less than or equal to 1500 g (VLBW) discharged from our department through an 18-month period were followed up at two years of age. All but 10 infants were examined by cranial ultrasound scanning in the neonatal period. Six had died after discharge; and of these two had severe brain damage following neonatal intraventricular haemorrhage. Twelve children had definite neuromotor abnormality; of these, the nine children with spastic types of cerebral palsy had all been delivered vaginally. Of the remaining children, one half had at least one neurodevelopmental symptom suggesting perinatal brain damage. Outcome was associated to neonatal intraventricular/subependymal haemorrhage when complicated by ventricular dilatation. Outcome in children with simple haemorrhage was similar to that in children without haemorrhage. The association between outcome and haemorrhage was considerably reduced by simultaneously considering the associations of gestational age at birth and the use of mechanical ventilation in the neonatal period. Head circumference at follow-up was greatest in those children with haemorrhage complicated by ventricular dilatation, when adjusted for actual body weight, birth weight, and gestational age at birth.

Cerebral Hemorrhage↗
PubMed1986

Cerebral blood flow in preterm infants during the first week of life.

Forty-two preterm infants of 28-33 weeks of gestation were studied once during the first week of life by 133-Xenon clearance after intravenous injection to estimate global cerebral blood flow. Count rates detected over the chest were corrected for chest wall contribution and used as arterial input function. A neonatal blood-brain partition coefficient of Xenon was used for the calculation of a mean flow estimator (CBF-infinity). The technique was internally validated by use of differently obtained arterial input functions. In 11 infants without respiratory distress, CBF-infinity was 19.8 ml/100 g/min +/- 5.3 SD. In 24 infants treated with mechanical ventilation CBF-infinity was 11.8 ml/100 g/min +/- 3.2 SD. In 7 infants treated with continuous positive airway pressure CBF-infinity was 21.3 ml/100 g/min +/- 12.0 SD. When the reduction of CBF-infinity associated with mechanical ventilation was taken into account, the 9 infants with subependymal/intraventricular haemorrhage had increased CBF-infinity. The effects of gestational age, birthweight, mode of delivery, postnatal age, mean arterial blood pressure, PaCO2, blood haemoglobin and phenobarbitone medication were also analysed and found inconsistent. In conclusion, CBF was lower than expected and in infants requiring mechanical ventilation the values were lower still.

Cerebrovascular Circulation↗
PubMed1986

Mild anaemia in African school children: effect on running performance and an intervention trial.

Blood haemoglobin concentrations and reticulocyte counts were determined in 430 school children in grades 1, 3 and 5 in a small township in rural Zambia at the end of the rainy season. Running capacity was estimated by the 12-min running test. Age, sex, height, weight, social and nutritional indicators were recorded. Mean haemoglobin was 125.3 g/1 +/- 12.3 SD. Low haemoglobin was associated with indicators of a traditional way of life. After a controlled trial of iron, folic acid, tetrachlorethylene and chloroquine lasting for 6 weeks, mean haemoglobin in all the children was 128.8 g/1 +/- 10.0 SD. The mean haemoglobin was significantly higher in the 218 children who received iron than in the 212 children who did not receive iron. There were no other significant differences among the treatment groups. In a subgroup of 377 children who completed two running tests, those with lower haemoglobin ran significantly shorter distances, even when possible confounding factors were partialled out. The effect was reduced by excluding 12 children with haemoglobin less than 100 g/1 or 48 children with reticulocyte counts of 15% or more, but remained statistically significant.

Adolescent↗
PubMed1986

Analysis of cerebroarterial Doppler flow velocity waveforms in newborn infants: towards an index of cerebrovascular resistance.

Doppler ultrasound has been used extensively to study cerebral hemodynamics in the human newborn. This report presents a continuous recording in an infant with epileptic seizures. Heart rate, mean aortic blood pressure and mean flow velocity, obtained from the anterior cerebral artery by Doppler ultrasound, all increased markedly during the seizures. The Poucelot index was calculated from the cerebral blood flow velocity waveform and is supposed to reflect cerebrovascular resistance. This index decreased. Three mutually contradictive interpretations were possible in terms of cerebral metabolic rate, cerebral blood flow, metabolism-flow coupling and pressure-flow autoregulation. Sympathetic activation and its effects on cerebral hemodynamics is discussed. It is pointed out that the competence of the pressure-flow autoregulation may not be studied reliably during changes in blood pressure associated with altered sympathetic activity. An electrical model of the systemic arterial system is presented and used to demonstrate that the resistance index is likely to be severely affected by changes in cerebroarterial compliance, peripheral resistance, duration of systole as a fraction of heart cycle and patency of the arterial ductus. A pulsatility index ratio, which is corrected for arterial pulse pressure, is suggested to avoid some of these errors.

Aorta↗
PubMed1985

Three-year follow-up of eight patients delivered by symphyseotomy.

Eight symphyseotomies were carried out in a small hospital in rural Africa by a medical generalist during a 2-year period. There were no maternal or infants deaths. Follow-up after 3 years demonstrated the absence of long-term complications. Five patients had later delivered, all normally, four of them at home unattended by medically-trained personnel.

Adolescent↗
PubMed1985

Blood pressure responses to care procedures in ventilated preterm infants.

Responses of mean aortic blood pressure to sequences of routine care procedures in 22 ventilated, preterm infants were studied daily for the first 3 days of life. In the first 11 infants standard care procedures were used, whereas the next 11 infants were preoxygenated by a preceding 10% increase in inspired oxygen concentration; in these infants, chest physiotherapy was entirely omitted while the frequency of endotracheal suctioning was reduced. A total of 259 blood pressure responses were recorded. In general, responses were biphasic, consisting of an initial blood pressure drop followed by a greater blood pressure rise of longer duration. Baseline blood pressure, as well as the minimum and maximum blood pressure during the care procedures, increased with gestational age and with postnatal age. The blood pressure drop was most pronounced in the infants requiring the most intensive ventilatory support and was reduced by modifying the care procedures. The blood pressure rise was the least in the infants receiving pancuronium and phenobarbitone. Eight infants, 4 in each group, had intraventricular haemorrhage; in these infants, the care procedures induced more pronounced blood pressure drops in the first day of life when compared to the infants without haemorrhage.

Blood Pressure↗
PubMed1985

Catecholamine response to chest physiotherapy and endotracheal suctioning in preterm infants.

Adrenaline and noradrenaline was measured just before and just after chest physiotherapy and endotracheal suctioning in 13 preterm, ventilated, newborn infants. Mean aortic blood pressure was also recorded. Eight of the infants received phenobarbitone. Catecholamine levels were five-fold higher in the 5 infants with blood pH less than 7.30 compared to the other 8 infants. After the procedure, both adrenaline and noradrenaline were significantly higher than baseline levels. The adrenaline response to the procedure was a two-fold increase and significantly greater than the noradrenaline response. Analysis of the effects of phenobarbitone treatment and acidosis on catecholamine responses by multiple linear regression demonstrated that the adrenaline response was reduced by phenobarbitone while the noradrenaline response was unaffected. There were no associations of blood pressure, responses with catecholamine responses, with acidosis or with phenobarbitone treatment.

Acidosis↗
PubMed1985

Sleep-waking shifts and cerebral blood flow in stable preterm infants.

Cerebral blood flow was estimated on 60 occasions in 15 well infants, 29-34 wk of gestational age, 5-17 days after birth, using 133-Xenon clearance after intravenous injection. The sleep state of the infants was determined by biparietal electroencephalography, clinical observation, and tracings of heart rate and respiration. Blood flow was 22% higher in the 11 estimations made during wakefulness, when compared to the 17 estimations made during quiet sleep. There was no difference between blood flow in active and quiet sleep. Also there was no difference between blood flow during periods of trace alternant and blood flow during periods of continuous electroencephalographic activity. It is suggested that flow-metabolism coupling is present in stable, preterm infants. The absence of an increase in cerebral blood flow during active sleep as compared with quiet sleep suggests that the neurophysiologic and neurometabolic mechanisms of rapid eye movement sleep are not yet fully developed in preterm infants.

Brain↗
PubMed1984

Cerebral blood flow in the newborn infant: comparison of Doppler ultrasound and 133xenon clearance.

Two techniques of Doppler ultrasound examination, continuous-wave and range-gated, applied to the anterior cerebral artery and to the internal carotid artery, were compared with 133xenon clearance after intravenous injection. Thirty-two sets of measurements were obtained in 16 newborn infants. The pulsatility index, the mean flow velocity, and the end-diastolic flow velocity were read from the Doppler recordings. Mean cerebral blood flow was estimated from the 133Xe clearance curves. The correlation coefficients between the Doppler and the 133Xe measurements ranged from 0.41 to 0.82. In the subset of 16 first measurements in each infant, there were no statistically significant differences between the correlation coefficients of the various Doppler ultrasound variables, but the correlation coefficients were consistently lower for the pulsatility index than for mean flow velocity or end-diastolic flow velocity, and they were consistently higher for the range-gated than for the continuous-wave Doppler technique.

Blood Flow Velocity↗
PubMed1984

Analysis of cranial 133-Xenon clearance in the newborn infant by the two-compartment model.

Cranial and chest clearance curves after intravenous administration of 133-Xenon was obtained on 112 occasions in 62 newborn infants admitted to our neonatal intensive care unit. The mean postnatal age was 5.1 days. The cranial clearance curves were submitted to two-compartment analysis. The compartmental clearance rate constants were 1.49 +/- 0.61/min and 0.099 +/- 0.033/min respectively while the fractional flow to the fast compartment was 0.51 +/- 0.14. Possible artefacts, particularly relevant to newborns, were analysed by computer simulation. It is concluded that the cranial 133-Xenon clearance curves varied considerably within the group of ill newborns and that the mean two-compartment parameter values differed considerably from those of healthy premature infants or adults, with or without cerebral illness. But the computer simulations demonstrated that the two-compartment parameters had high coefficients of variation and were significantly biased by right-to-left shunting of blood through the foramen ovale, by heterogeneity of the flow to the fastest compartment and by contamination of the cranial clearance curves by 133-Xenon in the airways. The radiation dose was 1.3 mGy to the lungs and 0.2 mGy to other tissues.

Adult↗