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Biomedical subjects

A D Edwards

Publications and source records attributed to A D Edwards.

At least 127 records · Page 7Linked to original sources
PubMed1993

Effects of N-omega-nitro-L-arginine methyl ester on the cerebral circulation of newborn piglets quantified in vivo by near-infrared spectroscopy.

The effects of N-omega-nitro-L-arginine methyl ester (L-NAME) on basal cerebral vascular tone, the vasodilatory effects of acetylcholine (ACh), and the cerebrovascular response to alterations in arterial carbon dioxide tension (CBVR) were investigated using near-infrared spectroscopy. Seven newborn piglets were anesthetized and mechanically ventilated; mean arterial blood pressure (MAP) was monitored and near-infrared spectroscopy used to measure changes in total cerebral Hb concentration. At the beginning of the experiment, CBVR was measured and then 10, 20, 30, and 100 mg.kg-1 L-NAME were administered sequentially; ACh (1, 2, 3, and 5 micrograms) was given before and after each injection of L-NAME. At the end of this sequence, CBVR was measured again and finally sodium nitroprusside (1.5 mg.kg-1) was administered. Ten and 20 mg.kg-1 L-NAME caused a significant decrease in total cerebral Hb concentration of -0.59 (-3.21 to -0.02) and -1.46 (-6.50 to -0.15) mumol.L-1 (median and range), respectively (Wilcoxon p < 0.05), but subsequent injections did not. Ten, 20, and 100 mg.kg-1 L-NAME caused an increase in MAP (Wilcoxon p < 0.05). ACh caused an increase in total cerebral Hb concentration and a decrease in MAP that was impaired but not abolished by L-NAME (ANOVA p < 0.05). CBVR was not affected by L-NAME. Sodium nitroprusside caused a reduction in mean (SD) MAP of 4.7 (1.6) kPa, and a slower rise in [tHb] of 13.44 (2.03) mumol.L-1. Postmortem examination of three animals revealed NADPH-diaphorase staining in neurons, cerebral blood vessels, carotid artery, and jugular vein.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1992

Experimentally measured optical pathlengths for the adult head, calf and forearm and the head of the newborn infant as a function of inter optode spacing.

The Differential Pathlength Factor (DPF) has been measured for several different tissues. The results showed that the DPF varied with the type of tissue studied, and in the case of the adult calf with sex. However, the DPF for all tissues studied was constant once the inter optode spacing exceeded 2.5 cm. Thus, measurements can be made by NIR spectroscopy at a range of inter optode spacings, and a single DPF used in the calculation of chromophore concentration. The results also showed that the major source of error in the DPF lay in the measurement of the inter optode spacing. To improve accuracy, two options are possible. Firstly, some means of continuous measurement of inter optode spacing could be incorporated in the NIR instrumentation. The better alternative would be an instrument incorporating a method of directly measuring the optical pathlength at each wavelength. This could be done either by time of flight measurement, or if it can be validated, by phase shift measurement.

Adult↗
PubMed1992

Changes in human fetal cerebral hemoglobin concentration and oxygenation during labor measured by near-infrared spectroscopy.

OBJECTIVE: The purpose of this study was to measure by near-infrared spectroscopy changes in human fetal cerebral oxyhemoglobin, deoxyhemoglobin, and cerebral blood volume during labor and to calculate mean cerebral hemoglobin oxygen saturation. STUDY DESIGN: The effects of uterine contractions with and without fetal heart rate decelerations were compared in eight singleton term fetuses. Results were analyzed by analysis of variance. RESULTS: In six of eight fetuses normal uterine contractions were associated with proportional decreases in both oxyhemoglobin and deoxyhemoglobin and a fall in cerebral blood volume without desaturation of cerebral hemoglobin. Contractions with fetal heart rate decelerations produced different results in that oxyhemoglobin fell but deoxyhemoglobin rose, indicating cerebral desaturation. In two of the eight fetuses normal contractions were associated with increases in oxyhemoglobin, deoxyhemoglobin, and cerebral blood volume; no decelerations were seen in either fetus. Mean cerebral hemoglobin oxygen saturation calculated during normal contractions was 43% +/- 10% (SD). CONCLUSION: Uterine contractions were associated with detectable changes from baseline in cerebral oxyhemoglobin, deoxyhemoglobin, and cerebral blood volume.

Blood Volume↗
PubMed1992

Relation between cerebral oxidative metabolism following birth asphyxia, and neurodevelopmental outcome and brain growth at one year.

Studies of cerebral oxidative metabolism were carried out by phosphorous magnetic resonance spectroscopy during the first week of life in 52 infants with clinical and/or biochemical evidence of birth asphyxia. 15 infants died and the 37 survivors were assessed by a wide range of neurodevelopmental tests at one year of age. The minimum recorded values for cerebral phosphocreatine/inorganic phosphate concentration ratio (an index of oxidative metabolism) were related to outcome. The results showed a significant relation between the extent of derangement of oxidative metabolism and the severity of adverse outcomes, including death, neurodevelopmental impairment and reduced head growth.

Adenosine Triphosphate↗
PubMed1992

Cerebral hemodynamic effects of treatment with modified natural surfactant investigated by near infrared spectroscopy.

The purpose of this study was to investigate the effects on cerebral hemodynamics of administering modified natural surfactant (Curosurf, 200 mg.kg-1) to infants requiring mechanical ventilation for hyaline membrane disease. Observations were made using near infrared spectroscopy on 20 infants for between 26 and 109 (median 57) min before and 22 to 112 (median 46) min after surfactant instillation. Changes in cerebral oxyhemoglobin concentration and cerebral blood volume (CBV) were monitored continuously; cerebral blood flow, oxygen delivery, and the response of CBV to changes in arterial carbon dioxide tension were measured while the infants were stable shortly before and after surfactant was given. Cerebral oxyhemoglobin concentration fell transiently in all infants immediately after surfactant by a median of -0.21 (range -0.46 to 0.05) mL x 100 g-1, but quickly recovered so that the median change during the 10 min after surfactant was 0.01 (-0.46 to 0.46) mL x 100 g-1. Alterations in CBV also occurred ranging from -0.44 to 0.40 (median 0) mL x 100 g-1, which represented -12 to 16% of total CBV; these changes rapidly resolved. When the infants were stable before and after surfactant, the values for mean (SD) cerebral blood flow were 20.5 (7.5) and 23.1 (5.2) mL.100 g-1 x min-1, respectively (n = 9); for mean cerebral oxygen delivery, values were 2.71 (0.89) and 3.15 (0.73) mL x 100 g-1 x min-1 (n = 9); and for response of CBV to changes in arterial carbon dioxide tension, they were 0.14 (0.09) and 0.11 (0.11) mL x 100 g-1 x kPa-1 (n = 16); these changes were not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Volume↗
PubMed1991

Effect of intervention on development of hip posture in very preterm babies.

Preterm babies are physiologically hypotonic, which causes their posture to be flattened when lying in the prone position. This flattened posture may persist beyond term. In a prospective, randomised, controlled, double blind trial of postural support carried out on 45 babies born at less than 33 weeks of gestation, we showed that infants positioned with specific hip support during the period of intensive care had significantly fewer features of flattened posture at the age equivalent to term.

Double-Blind Method↗
PubMed1991

Quantification of concentration changes in neonatal human cerebral oxidized cytochrome oxidase.

The oxygenation of cerebral cytochrome oxidase in vivo was investigated in eight newborn preterm infants. Near-infrared spectroscopy was used to quantify changes in the concentration of oxidized cytochrome oxidase ([CytO2]) observed during alterations in arterial oxygen saturation (SaO2) in the range of 85-99% and of carbon dioxide tension (PaCO2) in the range of 4.3-9.6 kPa. No relation was found between changes in SaO2 and [CytO2]. Alterations in PaCO2 were positively related both to changes in [CytO2] and total cerebral hemoglobin concentration [( Hb]t). The changes in [CytO2] ranged from 0.09 to 0.33 (median 0.21) mumol.l-1.kPa-1. The ratio [CytO2]/[Hb]t ranged from 0.06 to 0.12 (median 0.08). The relation of delta [CytO2] to the change in cerebral blood volume (delta CBV) was calculated: delta [CytO2]/delta CBV ranged from 0.09 to 0.18 (median 0.11) mumol/ml. These results define a fraction of cerebral cytochrome oxidase in the newborn infant that is oxidized after an increase in PaCO2 but demonstrate that a change in SaO2 in the range studied was not sufficient by itself to change [CytO2]. They differ from results of studies in adults; this may reflect significant differences between adult and neonatal brain.

Brain↗
PubMed1991

Response of cerebral blood volume to changes in arterial carbon dioxide tension in preterm and term infants.

The response of cerebral blood volume (CBVR) to a small induced change in arterial carbon dioxide tension was studied by near-infrared spectroscopy in 17 newborn infants born from 26 wk of gestation to term. All 17 infants were undergoing mechanical ventilation but had apparently normal brains. The CBVR per kPa change in arterial carbon dioxide tension within the range 3.9 to 9.6 kPa was calculated from the change in total cerebral Hb concentration ([TCHb]) using the equation: delta CBV = delta [TCHb] x 0.89/[H] where [H] is the large vessel Hb concentration. A least-squares regression line with 95% confidence limits was derived for CBVR against gestational age. A highly significant linear increase in CBVR was found: mean CBVR from the regression increased from 0.07 mL.100 g-1.kPa-1 at 26 wk to 0.51 mL.100 g-1.kPa-1 at 40 wk.

Arteries↗
PubMed1991

New non-invasive methods for the investigation of cerebral oxidative metabolism and haemodynamics in newborn infants.

Magnetic resonance spectroscopy and near infrared spectroscopy provide complimentary information about cerebral oxidative metabolism and haemodynamics and are valuable methods for investigating normal brain development and the pathogenesis of perinatal brain injury. Magnetic resonance spectroscopy can be used to measure in brain tissue the concentrations of important phosphorus compounds that are involved in oxidative metabolism, notably adenosine triphosphate, phosphocreatine and inorganic orthophosphate: intracellular pH can also be estimated. Abnormalities indicating impaired oxidative phosphorylation have been detected in a range of situations where hypoxic-ischaemic brain injury was known or suspected to have occurred, such as birth asphyxia and periventricular leucomalacia. Following acute cerebral injury a latent period of many hours has frequently been found before evidence of impaired oxidative phosphorylation developed, suggesting the possibility of effective early treatment. The extent of the metabolic impairment was related to long term outcome. Near infrared spectroscopy provides cotside information about cerebral oxygenation and haemodynamics. Quantitative information can be obtained about oxyhaemoglobin, deoxyhaemoglobin and the redox state of cytochrome aa3. Methods have been described for calculating cerebral blood flow, oxygen delivery, blood volume and carbon dioxide reactivity; and maturational changes are being defined. In birth-asphyxiated babies, abnormalities are detectable well before oxidative phosphorylation becomes impaired.

Asphyxia Neonatorum↗
PubMed1990

Effects of indomethacin on cerebral haemodynamics in very preterm infants.

Near infrared spectroscopy was used to investigate the effects of intravenously administered indomethacin (0.1-0.2 mg/kg) on cerebral haemodynamics and oxygen delivery in 13 very preterm infants treated for patent ductus arteriosus. 7 infants received indomethacin by rapid injection (30 s) and 6 by slow infusion (20-30 min). In all the infants cerebral blood flow, oxygen delivery, blood volume, and the reactivity of blood volume to changes in arterial carbon dioxide tension fell sharply after indomethacin. There were no differences in the effects of rapid and slow infusion. These falls in cerebral oxygen delivery and the disruption of cerebrovascular control might compromise cellular oxygen availability, particularly in regions of the brain where the arterial supply is precarious. Care should be taken to ensure that oxygen delivery is optimum before the administration of indomethacin to preterm infants.

Blood Gas Monitoring, Transcutaneous↗
PubMed1990

Quantitation of cerebral blood volume in human infants by near-infrared spectroscopy.

Current methods for measuring cerebral blood volume (CBV) in newborn infants are unsatisfactory. A new method is described in which the effect of a small change (5-10%) in arterial oxygen saturation (SaO2) on cerebral oxyhemoglobin [HbO2] and deoxyhemoglobin [Hb] concentration is observed by near-infrared (NIR) spectroscopy. Previous experiments in which the NIR absorption characteristics of HbO2 and Hb and the pathlength of NIR light through the brain were defined allowed changes in [HbO2] and [Hb] to be quantified from the Beer-Lambert law. It is shown here that CBV can then be derived from the expression CBV = (delta[HbO2] - delta[Hb])/(2. delta SaO2.H.R.), where H is the large vessel total hemoglobin concentration and R to the cerebral-to-large vessel hematocrit ratio. Observations on 12 newborn infants with normal brains, born at 25-40 wk of gestation and aged 10-240 h, gave a mean value for CBV of 2.22 +/- 0.40 (SD) ml/100 g, whereas mean CBV was significantly higher 3.00 +/- 1.04 ml/100 g in 10 infants with brain injury born at 24 to 42 wk of gestation and aged 4-168 h (P less than 0.05).

Blood Volume↗
PubMed1990

Measurement of optical path length for cerebral near-infrared spectroscopy in newborn infants.

The time taken for an extremely short pulse of near-infrared laser light to traverse the heads of 6 preterm infants was measured after death. The values obtained were used to calculate a differential path length factor (DPF), defined as the mean distance travelled by the photons divided by the distance between the points where light entered and left the head. The DPF was found to be 4.39 +/- 0.28. Knowledge of this factor will permit accurate quantitative measurements to be made by near-infrared spectroscopy of a range of indices of cerebral oxygenation and haemodynamics in live infants.

Brain Chemistry↗
PubMed1989

Magnetic resonance and near infrared spectroscopy for investigation of perinatal hypoxic-ischaemic brain injury.

Hypoxic-ischaemic injury to the brain is an important cause of perinatal death and seems to be the commonest cause of permanent neurodevelopmental disability in newborn infants who survive after intensive care. If this type of brain injury is to be prevented and treatment put on a rational basis, non-invasive methods are required for defining its mechanisms. This review has considered two such methods: magnetic resonance spectroscopy and near infrared spectroscopy. Magnetic resonance spectroscopy is used to measure, in brain tissue, the concentrations of the 'high energy' phosphorus metabolites that are dependent for their synthesis on the processes of oxidative phosphorylation. Intracellular pH can also be measured. Normal maturational changes in the brain have been defined and abnormalities detected in a range of conditions where hypoxic-ischaemic injury was suspected to have occurred. In laboratory animals the acute effects of curtailment of oxygen supply to the brain ('primary' energy failure) have been observed, and the effects of two commonly used treatments, infusions of sodium bicarbonate and glucose, have been tested. After resuscitation of newborn infants from severe intrapartum asphyxia, a latent period has often been noted before energy failure became detectable. This 'secondary' energy failure is due to a variety of damaging reactions initiated by the acute hypoxicischaemic episode and reperfusion of the brain. It is possible that in the future irreversible injury to brain cells following the episode may be prevented or ameliorated by the prompt use of cerebroprotective agents. The extent of abnormalities detected by magnetic resonance spectroscopy has prognostic implications: evidence of severe energy failure in the first days of life was regularly associated with subsequent death or with severe neurodevelopmental impairments. Many technical developments in magnetic resonance spectroscopy are under way, particularly employing proton (1H) spectroscopy, which will allow the intracerebral concentrations of a wide range of metabolites, including neurotransmitters, to be measured. The combination of spectroscopy with magnetic resonance imaging will permit quantitative data to be obtained from selected volumes within the brain. Near infrared spectroscopy is used to make observations at the cotside of the intracerebral concentrations of the chromophores oxyhaemoglobin, deoxyhaemoglobin, and oxidised cytochrome aa3, and it therefore provides information complementary to that obtained by magnetic resonance spectroscopy. Measurements can also be made of cerebral blood flow, cerebral blood volume, and other haemodynamic indices; in addition, the rea

Asphyxia Neonatorum↗
PubMed1988

Cotside measurement of cerebral blood flow in ill newborn infants by near infrared spectroscopy.

A new method of quantifying cerebral blood flow which allows repeated cotside measurements is described. 31 observations were made on nine ill, mostly very preterm, infants. Cerebral blood flow was usually about 18 ml.100 g-1.min-1, but ranged from 7 ml.100g-1.min-1 (after the administration of indomethacin to a very preterm infant) to 33 ml.100 g-1.min-1 in a birth-asphyxiated post-term infant.

Cerebrovascular Circulation↗
PubMed1986

Infective endocarditis affecting the eustachian valve.

A previously fit 44 year old man presented with acute staphylococcal pneumonia. Despite appropriate antibiotics he showed signs of continuing sepsis and eventually died. At necropsy endocarditis of the eustachian valve was found.

Adult↗