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Biomedical subjects

D T Delpy

Publications and source records attributed to D T Delpy.

At least 109 records · Page 6Linked to original sources
PubMed1990

The investigation of osteoradionecrosis of the mandible by near infrared spectroscopy.

The results of near infrared spectroscopy in eight patients with osteoradionecrosis of the mandible are presented. These suggest that sites of osteoradionecrosis may be marked by decreased amounts of deoxygenated haemoglobin. The advantages and potential of near infrared spectroscopy are discussed but the technique requires further refinement.

Adult↗
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

Thermal clearance blood flow sensor--sensitivity, linearity and flow depth discrimination.

A thermal clearance blood flow sensor has been designed which incorporates four separate sensing elements, permitting flow changes at four differing depths to be measured. Static and dynamic laboratory tests have confirmed the differing flow depth response of the sensor and demonstrated a linear response to flow over the physiological skin blood flow range. Flow depth response has been shown to be dependent upon sensor geometry. Response should also in theory be dependent on the thermal conductivity of the sensor body material. However, using conventional encapsulation materials, it does not seem possible to obtain a depth sensitivity of less than 0.2 mm.

Biomedical Engineering↗
PubMed1989

A topical metabolic inhibitor to improve transcutaneous estimation of arterial oxygen tension in adults.

The use of Eugenol as a contact medium in the measurement of transcutaneous oxygen (tcPO2) partially inhibits the metabolism in the underlying tissue, thereby reducing oxygen consumption and increasing tcPO2. Oxygen consumption in the tissue can be estimated from the rate at which tcPO2 falls when blood flow is occluded, and blood flow in the tissue can be estimated from the rate at which tcPO2 increases when the subject changes from breathing air to pure oxygen. Both these measurements have been made with Eugenol and distilled water as contact media. From these measurements it has proved possible to estimate the arterial oxygen tension (aPO2) of healthy adults at a relatively low sensor temperature (43 degrees C).

Administration, Cutaneous↗
PubMed1989

Phosphorus metabolites and intracellular pH in the brains of normal and small for gestational age infants investigated by magnetic resonance spectroscopy.

The brains of 30 normal preterm and term infants whose birth wt were appropriate for gestational age and 13 who were small for gestational age but healthy were studied by phosphorus magnetic resonance spectroscopy to determine values for metabolite concentration ratios and intracellular pH. In the AGA infants, phosphocreatine/inorganic orthophosphate increased between 28 and 42 wk of gestational plus postnatal age, suggesting a rise in the phosphorylation potential of brain tissue. At the same time, the concentration of phosphomonoester (mainly phosphoethanolamine) fell and that of phosphodiester (including phosphatidylethanolamine and phosphatidylcholine) increased. These changes reflected myelination and proliferation of membranes. Intracellular pH was approximately 7.1 and did not change with brain maturation. No differences were detected in these variables between the infants who were small for gestational age and those who were appropriate for gestational age.

Body Fluids↗
PubMed1989

Prognosis of newborn infants with hypoxic-ischemic brain injury assessed by phosphorus magnetic resonance spectroscopy.

To investigate the prognostic significance of abnormalities of oxidative phosphorylation, the brains of 61 newborn infants born at 27-42 wk of gestation and suspected of hypoxic-ischemic brain injury were examined by surface-coil phosphorus magnetic resonance spectroscopy. Of these infants, 23 died, and the neurodevelopmental status of the 38 survivors was assessed at 1 y of age. Of the 28 infants whose phosphocreatine/inorganic orthophosphate (PCr/Pi) ratios fell below 95% confidence limits for normal infants, 19 died, and of the nine survivors, seven had serious multiple impairments (sensitivity 74%, specificity 92%, positive predictive value for unfavorable outcome 93%). Of the 12 infants with ATP/total phosphorus ratios below 95% confidence limits 11 died (sensitivity 47%, specificity 97%, positive predictive value 91%). Among the 46 infants with increased cerebral echodensities, PCr/Pi was more likely to be low, and prognosis poor, in infants whose echodensities were diffuse or indicated intraparenchymal hemorrhage than in infants whose echodensities were consistent with periventricular leukomalacia. We conclude that when reduced values for PCr/Pi indicating severely impaired oxidative phosphorylation are found in the brains of infants suspected of hypoxic-ischemic injury, the prognosis for survival without serious multiple impairments is very poor, and that when ATP/total phosphorus is reduced, death is almost inevitable.

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↗
PubMed1988

Characterization of the near infrared absorption spectra of cytochrome aa3 and haemoglobin for the non-invasive monitoring of cerebral oxygenation.

Near infrared (IR) spectroscopy can give continuous, direct information about cerebral oxygenation in vivo by providing signals from oxygenated and deoxygenated haemoglobin and cytochrome aa3. Due to a lack of precise spectral information and uncertainties about optical path length it has previously been impossible to quantify the data. We have therefore obtained the cytochrome aa3 spectrum in vivo from the brains of rats after replacing the blood with a fluorocarbon substitute. Near infrared haemoglobin spectra were also obtained, at various oxygenation levels, from cuvette studies of lysed human red blood cells. Estimates of optical path length have been obtained. The data were used to construct an algorithm for calculating the changes in oxygenated and deoxygenated haemoglobin and oxygenated cytochrome aa3 in tissue from changes in near IR absorption.

Animals↗
PubMed1988

Developments in oxygen monitoring.

The review article describes some of the recent developments in clinical blood and tissue oxygen monitoring. Some of the monitoring problems which remain to be solved are identified and possible solutions discussed.

Forecasting↗
PubMed1988

Estimation of optical pathlength through tissue from direct time of flight measurement.

Quantitation of near infrared spectroscopic data in a scattering medium such as tissue requires knowledge of the optical pathlength in the medium. This can now be estimated directly from the time of flight of picosecond length light pulses. Monte Carlo modelling of light pulses in tissue has shown that the mean value of the time dispersed light pulse correlates with the pathlength used in quantitative spectroscopic calculations. This result has been verified in a phantom material. Time of flight measurements of pathlength across the rat head give a pathlength of 5.3 +/- 0.3 times the head diameter.

Animals↗