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Biomedical subjects

D T Delpy

Publications and source records attributed to D T Delpy.

At least 91 records · Page 5Linked to original sources
PubMed1993

Optical oxygen sensor based on phosphorescence lifetime quenching and employing a polymer immobilised metalloporphyrin probe. Part 2. Sensor membranes and results.

A gaseous oxygen sensor is described based on the measurement of phosphorescence lifetime of the dye palladium coproporphyrin, immobilised in a range of membrane materials including polyvinyl chloride, polymethylmethacrylate, polystyrene and silicone rubber. The lifetime of the dye in these materials is described, measured using a simple system consisting of a pulsed xenon flash lamp light source and a PC-based data acquisition system. The linearity of the sensing membranes over the 0-100 per cent oxygen range is presented together with data on temperature sensitivity, the effects of CO2, N2O, H2O and halothane, and the effects of ageing over a 90 day period. The sensors based upon polystyrene immobilised dye appear to provide the optimum characteristics for a gaseous oxygen sensor.

Humans↗
PubMed1993

A Monte Carlo investigation of optical pathlength in inhomogeneous tissue and its application to near-infrared spectroscopy.

In order to quantify near-infrared spectroscopic (NIRS) data on an inhomogeneous medium, knowledge of the contribution of the various parts of the medium to the total NIRS signal is required. This is particularly true in the monitoring of cerebral oxygenation by NIRS, where the contribution of the overlying tissues must be known. The concept of the time point spread function (TPSF), which is used extensively in NIRS to determine the effective optical pathlength, is expanded to the more general inhomogeneous case. This is achieved through the introduction of the partial differential pathlength, which is the effective optical pathlength in the inhomogeneous medium, and an analytical proof of the applicability of the modified Beer-Lambert law in an inhomogeneous medium is shown. To demonstrate the use of partial differential pathlength, a Monte Carlo simulation of a two-concentric-sphere medium representing a simplified structure of the head is presented, and the possible contribution of the overlying medium to the total NIRS signal is discussed.

Brain↗
PubMed1993

Measurement of the optical properties of the skull in the wavelength range 650-950 nm.

The optical properties of samples of bone from pig skull have been measured over the wavelength range 650-950 nm. The scattering phase function was measured on thin samples of the bone using a goniometer, and a value for the mean cosine g, of the scattering angle, was calculated. The scattering and absorption coefficients, mu s and mu a were then determined from measurements of diffuse reflectance and transmittance made with a pair of integrating spheres, by a step-wise search through a table of diffuse reflectance and transmittance versus mu a and mu s generated by a Monte Carlo model incorporating the measured scattering phase function. Values for g measured on six samples varied from 0.925 +/- 0.014 at 650 nm to 0.945 +/- 0.013 at 950 nm. Corresponding values for mu a and mu s measured on 18 samples were mu a = 0.04 +/- 0.002 mm-1, mu s = 35 +/- 0.7 mm-1 at 650 nm to mu a = 0.05 +/- 0.002 mm-1, mu s = 24 +/- 0.6 mm-1 at 950 nm.

Absorption↗
PubMed1993

Measurement of hemoglobin flow and blood flow by near-infrared spectroscopy.

A noninvasive method of measuring hemoglobin flow through an organ by near-infrared spectroscopy (NIRS) is described that allows blood flow to be calculated. The method is derived from the Fick principle and uses a small change in arterial oxyhemoglobin concentration (brought about by a change in the fractional inspired O2 concentration) as an intravascular tracer. Changes in deoxyhemoglobin and oxyhemoglobin concentrations are quantified by monitoring variations in the absorption of near-infrared light in the organ, thus providing a measure of tracer accumulation. The tracer input function is calculated from the change in arterial O2 saturation, measured by pulse oximetry. The method was used to determine hemoglobin flow in the forearms of six healthy young adults on 10 occasions. Forearm hemoglobin flow ranged from 22.5 to 82.6 mumol.l-1.min-1. Calculated forearm blood flow ranged from 1.01 to 4.01 ml.100 g-1.min-1. For comparison, forearm blood flow was measured by venous occlusion plethysmography, and the relation between flow calculated by NIRS (y) and plethysmography (x) was y = 0.93x + 0.30 (r2 = 0.95). The mean difference between the methods was 0.14 ml.100 g-1.min-1. The technique may be widely applicable.

Adult↗
PubMed1993

Effect of indomethacin on cerebral oxidized cytochrome oxidase in preterm infants.

To determine the effect of i.v. indomethacin on cerebral intracellular oxygenation, as judged by changes in the concentration of oxidized cytochrome oxidase, studies were performed using near-infrared spectroscopy on 15 infants of 23 to 29 wk gestation, aged 8 to 30 d, who required the drug for closure of a patent ductus arteriosus. Indomethacin caused significant (p < 0.01) falls in cerebral blood flow, oxygen delivery, and blood volume and its reactivity to changes in arterial carbon dioxide tension, as previously reported. In 11 of the 15 infants, significant (p < 0.01) falls of 0.18 to 0.92 mumol.L-1 in the concentration of oxidized cytochrome oxidase were observed. Parallel experiments on synaptosomes derived from rat brain showed that indomethacin was most unlikely to have had a direct effect on mitochondrial respiration. These results are consistent with the hypothesis that the observed falls in the concentration of oxidized cytochrome oxidase resulted from hemodynamic perturbations that reduced cerebral intracellular oxygenation.

Animals↗
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

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

The theoretical basis for the determination of optical pathlengths in tissue: temporal and frequency analysis.

A concise theoretical treatment is developed for the calculation of mean time, differential pathlength, phase shift, modulation depth and integrated intensity of measurements of light intensity as a function of time on the surface of tissue, resulting from either the input of picosecond light pulses, or radio frequency-modulated light. The treatment uses the Green's function of the diffusion approximation to the radiative transfer equation, and develops this and its Fourier transform in a variety of geometries. Detailed comparisons are made of several of these parameters in several geometries, and their relation to experimentally measured clinical data. The limitations of the use of phase measurements is discussed.

Diagnostic Imaging↗
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

Near-infrared spectroscopy in peripheral vascular disease.

Near-infrared spectroscopy has been performed on the calf muscles of 38 subjects, 21 normal controls without vascular disease and 17 patients with peripheral vascular disease. Oxygen consumption was measured in the calf by calculating the rate of conversion of oxyhaemoglobin to deoxyhaemoglobin during a period of tourniquet-induced ischaemia. Postischaemic reoxygenation was also measured. Median oxygen consumption in patients with peripheral vascular disease was 0.10 ml 100 g tissue-1 min-1, while in the control group it was 0.20 ml 100 g tissue-1 min-1 (P less than 0.03, Mann-Whitney U test). The median time taken to reach maximum oxyhaemoglobin levels after ischaemia was 40 s in patients with peripheral vascular disease and 20 s in controls (P less than 0.02). The results indicate that oxygen consumption is reduced in peripheral vascular disease. Near infrared spectroscopy is a non-invasive method for assessing metabolic improvement resulting from surgical or pharmacological treatment.

Adult↗
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↗
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↗