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Biomedical subjects

D T Delpy

Publications and source records attributed to D T Delpy.

At least 73 records · Page 4Linked to original sources
PubMed1995

Late fetal heart decelerations and changes in cerebral oxygenation during the first stage of labour.

OBJECTIVE: To test the hypothesis that late fetal heart rate decelerations are associated with a decrease in cerebral oxygenation. DESIGN: Changes in fetal cerebral concentrations of oxyhaemoglobin and deoxyhaemoglobin were measured by near infrared spectroscopy, before, during and after contractions with late fetal heart rate decelerations and compared with changes during contractions with no alteration of heart rate. SETTING: Teaching hospital obstetric unit. SUBJECTS: Ten women in labour at term. RESULTS: The changes in fetal cerebral oxyhaemoglobin and deoxyhaemoglobin concentrations that occurred during contractions were quantitatively similar, irrespective of the fetal heart rate changes. However, late fetal heart rate decelerations were associated with a significantly greater fall, after the uterine contraction, in the mean concentration of fetal cerebral oxyhaemoglobin of 0.52 mumol/100 g (SD 0.25) (P < 0.001) and a significantly greater rise in the mean concentration of deoxyhaemoglobin of 0.36 mumol/100 g (SD 0.35) (P < 0.01). CONCLUSION: Late fetal heart rate decelerations are associated with a significant decrease in cerebral oxygenation.

Adult↗
PubMed1995

The effect of maternal posture on fetal cerebral oxygenation during labour.

OBJECTIVE: To measure the effect of changes in maternal posture on fetal cerebral oxygenation during normal labour. DESIGN: A prospective study comparing changes in the fetal cerebral concentrations of oxyhaemoglobin, deoxyhaemoglobin and cerebral blood volume, measured by near infrared spectroscopy, in women with effective epidural analgesia when moved from the left lateral to the supine position during labour. SETTING: A London teaching hospital obstetric unit. SUBJECTS: Fourteen women during uncomplicated labour at term. RESULTS: When compared with the left lateral position, the supine position was associated with a significant decrease in the mean concentration of fetal cerebral oxyhaemoglobin of 1.12 (SD 1.0, 95% CI 0.49 to 1.75) mumol. 100 g-1 (P < 0.01) without any significant change in the mean concentration of deoxyhaemoglobin and cerebral blood volume. These changes were associated with a significant decrease in the mean cerebral oxygen saturation of 8.3 (SD 8.8, 95% CI 1.5 to 15.1)% (P < 0.05, n = 9). CONCLUSION: Changes in maternal posture during labour, in women with effective epidural analgesia, are associated with a significant decrease in fetal cerebral oxygenation.

Adult↗
PubMed1995

The effect of maternal pushing on fetal cerebral oxygenation and blood volume during the second stage of labour.

OBJECTIVE: To measure the effect of maternal pushing during the second stage of labour on fetal cerebral oxygenation and blood volume. DESIGN: A prospective study comparing changes in the fetal cerebral concentrations of oxyhaemoglobin, deoxyhaemoglobin and cerebral blood volume, before and during maternal pushing in the second stage of labour. SETTING: Teaching hospital obstetric unit. SUBJECTS: Ten term fetuses during labour. RESULTS: Following the onset of maternal pushing, mean cerebral deoxyhaemoglobin concentration increased by a mean of 0.79 (SD 0.59) mumol.100 g-1, (P < 0.01) without any consistent change in the oxyhaemoglobin concentration. These changes were associated with a significant decrease in the calculated mean cerebral oxygen saturation from a mean of 46.8% (SD 8.6) to 38.1% (SD 5.2) (P < 0.01). Pushing was also associated with a significant increase in the mean cerebral blood volume, which rose by a mean of 0.33 ml.100 g-1 (SD 0.37) (P < 0.05). CONCLUSION: Maternal pushing during the second stage of labour leads to a significant decrease in fetal cerebral oxygenation, together with an increase in cerebral blood volume.

Adult↗
PubMed1995

The spatial resolution performance of a time-resolved optical imaging system using temporal extrapolation.

Optical imaging methods are being explored as a potential means of screening for breast cancer. Previous investigations of time-resolved imaging techniques have suggested that due to the lack of photons with sufficiently small pathlengths, the spatial resolution achievable through a human breast would be unlikely to be better than a centimeter. Experimental results presented here indicate, however, that higher resolution may be achieved by extrapolating the measured temporal distribution of transmitted photons. This is performed using a least-squares fit between data and an analytic model of photon transport. The spatial resolution of a time-resolved imaging system was evaluated by measuring the edge response produced by an opaque mask embedded in the center of a 51-mm-thick, very highly scattering medium. The limiting spatial resolution was improved from about 13 mm to about 5 mm.

Breast Neoplasms↗
PubMed1995

The finite element method for the propagation of light in scattering media: boundary and source conditions.

This paper extends our work on applying the Finite Element Method (FEM) to the propagation of light in tissue. We address herein the topics of boundary conditions and source specification for this method. We demonstrate that a variety of boundary conditions stipulated on the Radiative Transfer Equation can be implemented in a FEM approach, as well as the specification of a light source by a Neumann condition rather than an isotropic point source. We compare results for a number of different combinations of boundary and source conditions under FEM, as well as the corresponding cases in a Monte Carlo model.

Biophysical Phenomena↗
PubMed1994

Use of the water absorption spectrum to quantify tissue chromophore concentration changes in near-infrared spectroscopy.

We describe a simple method for measuring the 'differential pathlength' of photons in a scattering medium utilizing the spectral absorption features of water. Determination of this differential pathlength is a prerequisite for quantifying chromophore concentration changes measured by near-infrared spectroscopy (NIRS), and the method proposed here achieves this without the need for time- or frequency-resolved measurements. The quantification of tissue chromophore concentration measurements is a major goal in NIRS research, allowing, for example, the non-invasive measurement of blood flow and volume in the brain and other organs. We present the results of validation experiments performed on tissue phantoms comparing the differential path estimates yielded by water absorption and time-resolved measurements, finding that the weak water absorption feature at 820 nm can yield a differential path estimate in addition to the main feature at 975 nm. We also present results from in vivo studies in which we find that whilst the 820 nm feature is measured with lower accuracy for a given light flux than the 975 nm feature, it is intrinsically a more accurate differential path estimator. Studies on the adult forearm showing differences between time-resolved and water absorption differential path estimates suggest that the measurement of both could aid in quantifying NIRS signals in heterogeneous tissues.

Adipose Tissue↗
PubMed1994

A phantom for the testing and calibration of near infra-red spectrometers.

This note describes a simple phantom which can be used to check the long term stability and accuracy of relative attenuation measurements made by near infra-red (NIR) spectrometers. The phantom has been calibrated, and the results of the calibration are shown to agree with theoretical predictions of the relative attenuation.

Calibration↗
PubMed1994

Relation between frequency of uterine contractions and human fetal cerebral oxygen saturation studied during labour by near infrared spectroscopy.

OBJECTIVE: To investigate the effect of the frequency of uterine contractions on fetal cerebral oxygenation, using near infrared spectroscopy. DESIGN: An observational study relating changes in the fetal cerebral concentrations of oxyhaemoglobin and deoxyhaemoglobin, measured from the start of one contraction to that of the next, to the time interval between contraction peaks observed by external tocography. SETTING: A teaching hospital obstetric and neonatal unit. SUBJECTS: Ten term fetuses during labour. RESULTS: Changes in cerebral oxyhaemoglobin concentration were positively, and in deoxyhaemoglobin negatively, correlated with the time interval between contractions (P < 0.001). A mean contraction interval of 2.3 min was found below which the concentration of oxyhaemoglobin usually fell and that of deoxyhaemoglobin rose, indicating a fall in cerebral haemoglobin saturation. Conversely, longer contraction intervals were associated with findings indicative of a rise in cerebral haemoglobin saturation. CONCLUSION: Short contraction intervals (< 2.3 min) were associated with a decrease, and longer contraction intervals with an increase in fetal cerebral oxygen saturation. Contractions occurring repeatedly at intervals less than 2.3 min are likely to result in progressive cerebral desaturation.

Brain Chemistry↗
PubMed1994

The effect of maternal oxygen administration on human fetal cerebral oxygenation measured during labour by near infrared spectroscopy.

OBJECTIVE: To test the hypothesis that intrapartum maternal oxygen administration increases fetal cerebral oxygenation during normal labour. DESIGN: A prospective study comparing changes in fetal cerebral concentrations of oxyhaemoglobin, deoxyhaemoglobin and cerebral blood volume measured by near infrared spectroscopy, before, during and after maternal oxygen administration using a 60% Ventimask. SETTING: Teaching hospital obstetric unit. SUBJECTS: Ten term fetuses during uncomplicated labour. RESULTS: Maternal oxygen administration for 15 min resulted in a significant increase in the mean concentration of fetal cerebral oxyhaemoglobin (0.78 mumol (SD 0.42) 100 g-1 brain tissue, P < 0.001) and a significant decrease in the mean concentration of deoxyhaemoglobin (0.80 mumol (SD 0.51) 100 g-1, P < 0.001). These changes were associated with a significant increase in the calculated mean cerebral oxygen saturation from 43.9% (SD 6.3) to 57.3% (SD 5.6) (P < 0.001). The maximum rise in cerebral oxyhaemoglobin concentration occurred at a mean of 10.7 min (SD 3.9) following commencement of oxygen administration. On returning to air breathing these changes reversed. There were no changes in cerebral blood volume. CONCLUSION: Maternal oxygen administration during normal labour leads to a significant rise in fetal cerebral oxygenation.

Adult↗
PubMed1994

Quantification of adult cerebral hemodynamics by near-infrared spectroscopy.

Near-infrared spectroscopy was used to measure global cerebral blood flow and volume in 10 healthy adult volunteers. High- and low-cerebral blood flow compartments were detected with mean flows for all 10 subjects of 59 +/- 21 (SD) and 11 +/- 4 ml.100 g-1.min-1, respectively. The mean cerebral blood volume of the group was 2.85 +/- 0.97 ml/100 g. Analysis of spontaneous changes in the cerebral concentrations of oxyhemoglobin and deoxyhemoglobin demonstrated strong correlations between respiratory rate and the oscillation frequency of cerebral oxyhemoglobin concentration (r = 0.99) and arterial oxygen saturation (SaO2) (r = 0.99). An estimate of the mean cerebral oxygen saturation for all subjects averaged 59.4 +/- 12.4% when their mean SaO2 was 91.8 +/- 2.4% (equivalent to 67.6 +/- 13.8% at a normoxic SaO2 of 98%). These results demonstrate that near-infrared spectroscopy can be used as a noninvasive bedside technique for both qualitative and quantitative evaluation of cerebral hemodynamics and oxygenation in adults.

Adult↗
PubMed1993

Measurement of adult cerebral haemodynamics using near infrared spectroscopy.

Near infrared spectroscopy (NIRS) is a non invasive, portable, safe technique for monitoring cerebral oxygenation and haemodynamics. Since it does not involve the use of ionising radiation it may be used repeatedly to produce serial measurements of CBF and CBV in patients, and continuously to provide trend data about cerebral circulation changes. NIRS allows measurements to be made at the bedside with minimal disturbance to other monitoring and treatment procedures. Although regional information is not yet available, good time resolution allows rapid changes in cerebral haemodynamics to be observed.

Adult↗
PubMed1993

Optical oxygen sensor based on phosphorescence lifetime quenching and employing a polymer immobilised metalloporphyrin probe. Part 1. Theory and instrumentation.

A review of the theory of phosphorescence quenching is given, and its particular application to the sensing of oxygen is outlined. The advantages of measuring phosphorescence lifetime as opposed to phosphorescence intensity are reviewed. The advantages of using the metalloporphyrins as such sensors are identified and in particular the characteristics of palladium coproporphyrin are discussed. The exceptionally long room temperature lifetime of this material makes it possible to use relatively simple PC-based instrumentation to measure lifetimes, with a xenon flashlamp light source. The design of such a system is given and its performance in measuring phosphorescence lifetime in aqueous solutions is demonstrated.

Fiber Optic Technology↗