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Biomedical subjects

D T Delpy

Publications and source records attributed to D T Delpy.

At least 127 records · Page 7Linked to original sources
PubMed1988

Brain metabolism and intracellular pH during ischaemia: effects of systemic glucose and bicarbonate administration studied by 31P and 1H nuclear magnetic resonance spectroscopy in vivo in the lamb.

Brain metabolism and intracellular pH were studied during and after episodes of incomplete cerebral ischaemia in lambs under sodium pentobarbitone anaesthesia. 31P and 1H magnetic resonance spectroscopy was used to monitor brain pHi and brain concentrations of inorganic phosphate (Pi), phosphocreatine (PCr), beta-nucleoside triphosphate (beta NTP), and lactate. Simultaneous measurements were made of arterio-cerebral venous concentration differences (AVDs) for oxygen, glucose, and lactate. Cerebral ischaemia was induced by a combination of bilateral carotid clamping and hypotension, and the acute effects of systemic administration of glucose and sodium bicarbonate were examined. The molar ratio of glucose to oxygen uptake by the brain (6G/O2) increased above unity during cerebral ischaemia. Statistically significant AVDs for lactate were not observed. Cerebral ischaemia was associated with a reduction in brain pHi PCr/Pi ratio, and an increase in brain lactate. No effect of arterial plasma glucose on brain lactate concentration or brain pHi was evident during cerebral ischaemia or in the postischaemic period. Administration of sodium bicarbonate systemically in the postischaemic period was associated with a rise in arterial and brain tissue PCO2. A fall in brain pHi occurred which was attributable in part to coincidental brain lactate accumulation. The increase in brain lactate measured by 1H nuclear magnetic resonance in vivo during ischaemia was insufficient to account for the change in buffer base calculated to have occurred from previous estimates of brain buffering capacity.

Animals↗
PubMed1987

Simulation of the point spread function for light in tissue by a Monte Carlo method.

We have been able by a Monte Carlo technique to generate the point spread function (PSF) for light in tissue for a generalized range of tissue characteristics. We have demonstrated that these can be described by an equation containing a gaussian, diffusion and exponential term. The PSF equation will allow one to estimate the limits of spatial resolution achievable with near infrared (NIR) imaging systems, and may be used in image deconvolution algorithms. Additionally an equation has been derived describing the average photon pathlength through the tissue. Finally, the light transmission and reflection (backscattering) have been illustrated as functions of scattering and absorption coefficients. These results can be used in attempting to quantify data from non-invasive NIR spectroscopy systems.

Brain↗
PubMed1987

Brain metabolism and intracellular pH during ischaemia and hypoxia: an in vivo 31P and 1H nuclear magnetic resonance study in the lamb.

Brain metabolism and intracellular pH were studied during and after episodes of ischaemia and hypoxia-ischaemia in lambs anaesthetised with sodium pentobarbitone. 31P and 1H magnetic resonance spectroscopy methods were used to monitor brain pHi and brain concentrations of Pi, phosphocreatine (PCr), beta--nucleoside triphosphate (beta NTP), and lactate. Simultaneous measurements were made of cerebral blood flow and cerebral oxygen and glucose consumption. Cerebral ischaemia sufficient to reduce oxygen delivery to 75% of control values was associated with a fall in brain pHi and increase in brain Pi. Progressively severe hypoxia-ischaemia was associated with a progressive fall in brain pHi, PCr, and beta NTP and increase in brain Pi. In two animals the increase in brain lactate during hypoxia-ischaemia measured by 1H nuclear magnetic resonance (NMR) could be quantitatively accounted for by the increased net uptake of glucose by the brain in relation to oxygen, but was insufficient to account for the concomitant acidosis according to previous estimates of brain buffering capacity. In four animals brain pHi, PCr, Pi, and beta NTP had returned to normal 1 h after the hypoxic-ischaemic episode. In one animal brain pHi had reverted to normal at a time when 1H NMR indicated persistent elevation of brain lactate.

Animals↗
PubMed1987

Brain intracellular pH and metabolism during hypercapnia and hypocapnia in the new-born lamb.

1. The effects of hypercapnia and hypocapnia on brain intracellular pH (pHi) and metabolism were investigated in new-born lambs under barbiturate anaesthesia. 2. 31P nuclear magnetic resonance (n.m.r.) spectroscopy was used to determine brain pHi and the relative concentrations of compounds containing mobile phosphorus nuclei including phosphocreatine (PCr), nucleoside triphosphates (NTP) and inorganic phosphate (Pi). Simultaneous measurements were made of the molar ratio of glucose to oxygen uptake by the brain. 3. During normocapnia (arterial partial pressure of CO2 Pa, CO2, 39 +/- 1 mmHg mean +/- S.E. of mean, n = 9) brain pHi was 7.13 +/- 0.02. Hypercapnia (Pa, CO2, 98 +/- 3 mmHg) was associated with a fall in brain pHi to 6.94 +/- 0.03 (n = 19, P less than 0.001), whereas no significant change in brain pHi occurred during hypocapnia (Pa, CO2, 16 +/- 1 mmHg; brain pHi 7.15 +/- 0.01). 4. During hypercapnia there was an increase in the ratio of Pi to NTP from 1.09 +/- 0.08 to 1.47 +/- 0.06 (P less than 0.001) and a decrease in the ratio PCr/Pi from 1.60 +/- 0.08 to 0.93 +/- 0.04 (P less than 0.001). There was a linear correlation between Pi/NTP and brain pHi. 5. Alterations in arterial PCO2 had no significant effect on the molar ratio of glucose to oxygen uptake by the brain, which remained close to unity. 6. The change in brain pHi observed during hypercapnia can be accounted for by the known physico-chemical buffering capacity of brain tissue. Homoeostasis of brain pHi during hypocapnia provides further evidence that additional regulatory mechanisms operate in these circumstances. 7. The observed changes in PCr and Pi can be accounted for in part by the [H+] dependence of the creatine kinase reaction.

Animals↗
PubMed1987

Cerebral monitoring in newborn infants by magnetic resonance and near infrared spectroscopy.

Phosphorus magnetic resonance spectroscopy (MRS) and near infrared spectroscopy (NIRS) have been used to study the brains of normal newborn infants and infants with cerebral disorders admitted to a neonatal intensive care unit. MRS, which involves transporting the infant to the spectrometer, allows measurement of mobile phosphorus compounds such as adenosine triphosphate and phosphocreatine in brain tissue, and has been performed on over 160 babies. NIRS gives cotside information about cerebral oxygenation and haemodynamics and has recently been introduced. These techniques, especially when used together, show promise of providing important information about the mechanisms and prognostic significance of hypoxic-ischaemic damage to the brain--the most important cause of permanent neurodevelopmental disabilities in infants who require intensive care.

Brain↗
PubMed1986

Quantification of cerebral oxygenation and haemodynamics in sick newborn infants by near infrared spectrophotometry.

New apparatus was made whereby indices of cerebral oxygenation and haemodynamics in sick newborn infants could be quantified by near infrared (NIR) spectrophotometry and displayed instantaneously at the cotside. The indices included oxygenated haemoglobin, reduced haemoglobin, oxidised cytochrome aa3, and total haemoglobin concentration: cerebral blood volume, mixed cerebral venous saturation, and changes in cerebral blood flow were then derived. Striking changes were observed in response to alterations in arterial oxygen saturation and carbon dioxide tension and to tilting of the infant. Abnormal responses were detected in cerebral oedema following birth asphyxia, patent ductus arteriosus, and cystic encephalomalacia. NIR spectrophotometry provides valuable quantitative data at the cotside for the management of sick infants and for exploring the pathophysiology of damage to the brain.

Blood Volume↗
PubMed1986

Impaired energy metabolism in brains of newborn infants with increased cerebral echodensities.

Intracellular energy metabolism was studied by phosphorus magnetic resonance spectroscopy in the brains of 27 preterm and term infants with increased echodensities consistent with hypoxic-ischaemic injury and 18 comparable normal infants. In the normal infants the phosphocreatine (PCr)/inorganic orthophosphate (Pi) ratio increased significantly from 0.77 +/- 0.24 (95% confidence limits) at a gestational plus postnatal age of 28 weeks to 1.09 +/- 0.24 at 42 weeks. 9 of the 15 infants with increased echodensities whose PCr/Pi ratios fell below the normal range died; in all 6 survivors cerebral atrophy developed (cysts in brain tissue or microcephaly). In contrast, all 12 infants with increased echodensities whose PCr/Pi ratios remained within the normal range survived, although cerebral atrophy developed in 3 with ratios towards the lower limit of normal.

Age Factors↗
PubMed1984

Cerebral energy metabolism studied with phosphorus NMR spectroscopy in normal and birth-asphyxiated infants.

Phosphorus (31P) nuclear magnetic resonance spectroscopy was used to study intracellular metabolism in the brains of 6 normal newborn infants and 10 infants who had been asphyxiated during delivery. In the normal infants spectral peaks mainly attributable to adenosine triphosphate, phosphocreatine (PCr), phosphodiesters plus phospholipids, and inorganic orthophosphate (Pi) were always detected, together with an additional large peak in the phosphomonoester region indicating the presence of a metabolite or metabolites (probably largely phosphoethanolamine) which may be involved in rapid growth of the brain. In the asphyxiated infants, data obtained on the first day of life showed no differences from those in normal infants, but by the second to ninth days inverse changes in the concentrations of PCr and Pi had caused a significant reduction in PCr/Pi. This latency suggest the possibility of effective early treatment before irreversible metabolic damage sets in. Mean intracellular pH when PCr/Pi was minimal was 7.17 +/- 0.10. Values for PCr/Pi below 0.80 were associated with a very bad prognosis for survival and early neuro-developmental outcome.

Adenosine Diphosphate↗
PubMed1983

Non-invasive investigation of cerebral metabolism in newborn infants by phosphorus nuclear magnetic resonance spectroscopy.

Intracellular metabolism in the brains of seven infants, born at 33-40 weeks' gestation and aged 44 h to 17 days, was studied on fourteen occasions by phosphorus nuclear magnetic resonance spectroscopy (31P NMRS). The characteristic spectral peaks of ATP, phosphocreatine (PCr), phosphodiesters, and inorganic orthophosphate (Pi) were always detected, together with a large peak attributed mainly to ribose-5-phosphate. The ratio of PCr to Pi NMRS signals (which are related to concentration) in one infant thought to have a normal brain was 1.7. In three infants who had severe birth asphyxia the PCr/Pi ratio ranged from 0.2 to 1.0 but increased as their clinical condition improved: infusions of mannitol solution caused a rapid increase in the ratio on four occasions in two of these infants. The PCr/Pi ratio was 1.4 in an infant with congenital cerebral atrophy and 0.7 in an infant with meningitis. Grossly abnormal 31P spectra antedated the detection by ultrasound of large porencephalic cysts in two infants. No systematic changes in intracellular pH (calculated from the chemical shift of the Pi resonance) were observed: the mean value for all observations was 7.2 +/- SD 0.1 (n = 14).

Adenosine Triphosphate↗
PubMed1980

Transcutaneous estimation of arterial PO2 and PCO2 in newborn infants with a single electrochemical sensor.

A transcutaneous electrochemical sensor designed to estimate arterial oxygen (PaO2) and carbon dioxide (PaCO2) tensions simultaneously and continuously was evaluated in newborn infants with respiratory illnesses. After calibration of the sensor against a sample of arterial blood from the infant, the accuracy of estimation of PaO2 and PaCO2 seemed sufficient for clinical purposes.

Arteries↗