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Biomedical subjects

P Rolfe

Publications and source records attributed to P Rolfe.

117 records · Page 7Linked to original sources
PubMedDate not supplied

Fetal and neonatal cerebral oxygen monitoring with NIRS: theory and practice.

Near infra-red spectroscopy (NIRS) is a comparatively new method for monitoring the oxygenation in blood and tissue in the brain of the fetus and the neonate. Absorption of light in the wavelength range 700-1000 nm through such tissue is measured, which is then used to calculate changes in the concentration of cerebral oxygenated and de-oxygenated haemoglobin (HbO2 and Hb) and hence cerebral blood volume (CBV). Studies carried out on several groups of newborn babies have shown clear changes in HbO, Hb and CBV with hypoxia and bradycardia. These changes may well have implications in the occurrence of hypoxic/ischaemic brain injury. Intra partum NIR measurements on the fetal brain have demonstrated clear changes in HbO2, Hb and CBVm, coinciding with the onset of contractions.

Brain↗
PubMedDate not supplied

Physical and biological properties of compound membranes incorporating a copolymer with a phosphorylcholine head group.

A copolymer (PMB) having a polar head group 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymerized with n-butyl methacrylate (BMA) may provide a haemocompatible surface for implantable devices. Pure PMB membranes and compound membranes composed of PMB coated onto polyurethane (PU + PMB) and poly(vinyl chloride) (PVC + PMB) have been prepared. Fundamental studies on these membranes included the analysis of molecular distribution and orientation, the characterization of surface physical properties and the examination of blood membrane interactions. The experimental techniques used were Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Significant differences between PU + PMB and PVC + PMB membranes were found. Compound PVC + PMB and pure PMB membranes exhibited favourable surface properties for haemocompatibility and also showed low adhesion of blood components, whereas PU + PMB displayed the contrary. This leads to the hypothesis that the underlying material has a major influence on the surface properties of compound membranes.

Biocompatible Materials↗
PubMedDate not supplied

[Blood volume changes and oxygenation during labor--a laser spectroscopic analysis].

BACKGROUND: Hemodynamic patterns and the distribution of blood volume are influenced by the onset of labour. This study evaluates patterns of oxygenation and changes of blood volume after the induction of contractions. METHODS: A prototype NIR-laser spectrometer was applied in 28 cases. RESULTS: We found a rise of blood volume and oxygen saturation (HbO2) during the peak of contractions. Cerebral tissue oxygenation was monitored by registration of relative changes of cytochrome-aa3. No significant change of tissue oxygenation was detected during variable volume load. DISCUSSION: This implicates compliance of the redox state during labour.

Blood Volume↗
PubMedDate not supplied

Delayed vascular reactivity to ischemia in diabetic microangiopathy.

To investigate vascular responses in insulin-dependent diabetic patients both with and without retinopathy, we have assessed vasodilation by forearm transcutaneous pO2 measurement after 10 min of ischemia produced by a sphygmomanometer cuff. Diabetic patients with proliferative retinopathy had a delayed vasodilatory response at 60 s (mean +/- SD pO2 = 9 +/- 3 mm Hg) compared with those having diabetes without retinopathy (15 +/- 4 mm Hg, P less than 0.01) and matched normal subjects (14 +/- 4 mm Hg, P less than 0.01). Recently diagnosed insulin-dependent diabetic patients had a very similar response (15 +/- 5 mm Hg) to matched normal subjects (15 +/- 3 mm Hg). The diminished vascular reactivity may be a consequence of microangiopathy and neuropathy, although patients with an impaired vascular response might be particularly at risk from the development of capillary closure.

Adult↗
PubMedDate not supplied

Non-invasive optical methods for the study of cerebral metabolism in the human newborn: a technique for the future?

Two of the major causes of death and disability in the preterm newborn of the developed nations are cerebral ischaemia and intraventricular haemorrhage. It is estimated that intraventricular haemorrhage develops in 40-50% of infants with a birthweight of 1500 g or less but precisely how many individuals are affected by haemorrhage, or how many cases of disability are antedated by cerebral ischaemia, is not known because of the lack of effective low-cost instruments for the continuous, or at least frequent, assessment of cerebral metabolic status in the high-risk individual. In the future, however, fibre-optic-based spectrophotometric techniques for the measurement of cerebral redox state may provide low-cost, portable instruments for the noninvasive assessment of cerebral metabolism during the intensive care of the neonate.

Brain↗
PubMedDate not supplied

Assessment of a commercial pH electrode used with blood.

With the recent development of ion selective electrodes, potentiometry has entered a new era of usefulness ranging from pollution control to the investigation of single cells. Routine use of these sensors in the clinical environment is severely restricted due to errors associated with the reference electrode. Due to the Nernstian response of the potentiometric sensors the entire reference and ion selective electrodes are housed within a thermostatically controlled heater assembly. A clinically based thermostatically controlled combined ion selective/reference electrode system is discussed and a simple algorithm is presented to correct for the additional liquid junction potential encountered when monitoring biological solutions.

Blood Gas Analysis↗
PubMedDate not supplied

[The influence of umbilical cord compression on the fetal brain--an animal experiment using laser spectroscopy].

In order to evaluate the influence on the fetal brain due to compression of the umbilical cord biochemical and biophysical changes were traced during defined occlusions of 60 sec by means of NIR laser spectroscopy. Synchronously blood samples were drawn intermittently from a catheter positioned in the A. carotis and analysed for blood gases. The saturation values measured in the fetal blood correlated significantly with the dates of the HbO2 tracing of the NIR-system (r = 0.81, p less than 0.001). After induced occlusion of the umbilical cord a reproducible pattern of the NIR tracing occurred. While an immediate fall in HbO2 occurred, a synchronous rise in desaturated Hb was observed. For the changes of the cytochrome aa3 we detected a minor decrease that occurred with a lag time. Additionally there was an indication of a major change of blood volume as the total Hb content augmented during each compression. We concluded: Changes of Hb-saturation in the fetal blood are immediately indicated by NIR-laser spectroscopy. During cord occlusion of 60 sec. the intracellular oxygenation decrease only after a significant lag time and are reversible and furthermore it leads to a reproducible change of intracerebral blood volume.

Animals↗
PubMedDate not supplied

Near infrared spectroscopy in fetal monitoring.

Fetal monitoring using near infrared spectroscopy offers the first realistic prospect of documenting real-time changes in fetal cerebral oxygenation during labour. This article explores the technical background, presents some of the results obtained and speculates on potential future developments.

Female↗