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Biomedical subjects

P Rolfe

Publications and source records attributed to P Rolfe.

At least 19 recordsLinked to original sources
PubMed1992

Cellular interactions with NIR EM energy.

The electrical and electrochemical nature of cellular components, structure and function makes it important for the possible influences by externally applied electromagnetic fields to be studied thoroughly. This is an important aspect of cellular engineering. Thermal and non-thermal influences of EM, electric and magnetic fields on biological tissues are under investigation by several groups, to improve both diagnostic and therapeutic techniques. Within the EM spectrum there is an interesting band in the infra-red, from about 700 nm to 1000 nm, where absorption by enzymes within the intracellular respiratory chain can take place. This absorption phenomenon is now used as the basis for quantitative analysis of enzyme dynamics, both in vitro and in vivo, but implications for both therapeutic and potentially damaging influences on cellular behaviour and viability also need to be considered.

Animals↗
PubMed1992

Non-invasive optical monitoring of cerebral blood oxygenation in the foetus and newborn: preliminary investigation.

Near infra-red spectroscopy was applied as a non-invasive and continuous technique for the in vivo monitoring of blood and tissue oxygenation in human neonates. Monitoring of cerebral blood oxygenation in the wavelength range 775-904 nm was carried out on preterm infants after inducing a transient mild hypoxic change; the measurements were performed either by the transmission or reflection (backscattering) mode of monitoring. The results of these investigations were used to assess the application of the technique to foetal monitoring. A series of foetal monitoring studies was performed to investigate the influence of maternal contractions on foetal cerebral blood oxygenation. Although only changes in haemoglobin concentration can be monitored at present, the results suggest that near infra-red monitoring could provide a non-invasive, real-time monitoring method in intensive neonatal and intrapartum care.

Brain↗
PubMed1992

Electrical impedance tomography. A sensitivity region reconstruction algorithm using adjacent drive current injection strategy.

The 'sensitivity region' method of back projection is converted from polar drive to adjacent drive current injection strategy and individual sensitivity coefficients incorporated. For each projection sensitivity coefficients for each pixel were established and pixels were grouped together into the 'sensitivity regions'. These contain all pixels that have their largest sensitivity coefficients associated with a particular measurement pair. Back projection of measurement data was performed using these coefficients as the basis of the reconstruction and less sensitive measurement pairs were ignored. Formulae for the back projection are discussed and images from computer simulated data and raw data supplied by Sheffield as part of this concerted action are presented. Comparison with polar current injection strategy is discussed.

Algorithms↗
PubMed1992

Effect of post-delivery care on neonatal body temperature.

A prospective observational study of post-delivery care and neonatal body temperature, carried out at Kathmandu Maternity Hospital, was followed by a randomized controlled intervention study using three simple methods for maintaining body temperature. There were 500 infants in the initial observation study and 300 in the intervention study. In the observation study, 85% (420/495) of infants had temperatures < 36 degrees C at 2 h and nearly 50% (198/405) had temperatures < 36 degrees C at 24 h (14% were < 35 degrees C). Most of the infants who were cold at 24 h had initially become cold at the time of delivery (only seven infants had been both well dried and wrapped). In the intervention study, all infants were dried and wrapped before random assignment to one of the three methods: the "kangaroo" method, the traditional "oil massage" or a "plastic swaddler". All three were found to be equally effective. Overall, 38% (114/298) of the infants had temperatures < 36 degrees C at 2 h and 18% (41/231) at 24 h (when none was < 35 degrees C).

Body Temperature↗
PubMed1992

Cyclical fluctuations in cerebral blood volume.

Cyclical fluctuations of cerebral blood flow velocity have been reported previously using Doppler ultrasound. The same phenomena was detected during investigations of changes in cerebral blood volume using near infrared spectroscopy. Rhythmic fluctuations of cerebral blood volume at a frequency of 3.5 cycles/minute is reported here.

Blood Volume↗
PubMed1992

Plethysmographic validation of near infrared spectroscopic monitoring of cerebral blood volume.

The validation of measurement of cerebral blood volume (CBV) and cerebral blood flow (CBF) using near infrared spectroscopy (NIRS) against jugular venous occlusion plethysmography is described. Repeated measurements in six infants were made using both techniques simultaneously. A close relationship between the two measurements of change in CBV was obtained in five infants. There was also a close relationship for measurement of CBF in four infants. This study confirms the possibility of using NIRS to monitor CBV continuously in the premature infant. This parameter may prove to be of greater clinical value than the intermittent measurement of CBF.

Blood Flow Velocity↗
PubMed1991

Critical appraisal and further development of the methodology for open circuit calorimetry in neonates.

A non-invasive technique for open circuit calorimetry based on a Vickers 79 incubator as the gas collection chamber was developed and evaluated. The technique, which involved drawing air from the incubator hood at 11 1/min for gas analysis, did not have a significant cooling effect on the infant and the noise levels within the incubator did not exceed current safety standards. A new technique for checking the calibration of the whole system was developed as the traditional alcohol burn method proved unsatisfactory. Either pure oxygen or carbon dioxide were fed into the incubator hood at controlled physiological rates using a calibrated throttling valve. Over a number of calibration checks the mean error of the system proved to be +/- 4.3% for oxygen and +/- 4.45% for carbon dioxide. Less than a fifth of this error was attributable to the pump and flow meter. When oxygen is introduced to the system at a constant physiological rate it takes 30 min for a plateau to be reached. Therefore it is recommended that this system is used when readings are to be taken in a steady state situation or data is to be cumulated over a long period of time such as in an energy balance study. A run in period of 30 min before collecting data is essential. It is recommended that a calibration check is performed before each study.

Acoustics↗
PubMed1991

Non-invasive in vivo near-infrared optical measurement of the penetration depth in the neonatal head.

The non-invasive optical technique of near-infrared spectroscopy (NIRS) was used to measure the depths of light penetration at four wavelengths in the NIR region. Near-infrared absorbance measurements were carried out on 10 preterm infants. The apparent absorbance data (in optical density units) collected at 775, 805, 845, and 904 nm were measured at different positions on the head. Linear relationships that satisfy the Lambert law were obtained when the apparent absorbance at a given wavelength was plotted against the inter-optrode distance. From the slopes of the resulting straight lines, the depth of penetration of the NIR light was calculated and found to be independent of the position of the probes on the head. Calculated average values of the depth of penetration of near-infrared light in the whole neonatal head ranged between 6.3 and 8.5 mm.

Head↗
PubMed1991

Effects of hypoxaemia and bradycardia on neonatal cerebral haemodynamics.

Near infrared spectroscopy has been used to assess the effects of bradycardia and hypoxia on the cerebral circulation in the premature neonate. The technique is well tolerated and can be applied in almost any infant. Continuous monitoring of changes in cerebral oxygenated, deoxygenated, and total haemoglobin is possible. Total haemoglobin is analogous to cerebral blood volume; thus information on circulatory changes as well as oxygenation state can be obtained. Twenty five babies had cerebral monitoring carried out using this technique. During episodes of hypoxia, both spontaneous and induced, impairment of haemoglobin oxygenation within the brain was detected together with an overall increase in the total mean haemoglobin concentration, which was 0.8 x 10(-2) mmol/l. Bradycardia with apnoea also led to impairment of cerebral oxygenation, and to a rapid fall in the concentration of total mean haemoglobin to 1.4 x 10(-2) mmol/l, which was followed in some cases by an increase to above the resting value on recovery of the heart rate to a mean of 0.7 x 10(-2) mmol/l. These disturbances to total haemoglobin concentration represent abnormalities of cerebral blood volume that may be implicated in the pathogenesis of neonatal cerebral injury.

Bradycardia↗
PubMed1990

The non-invasive monitoring of cerebral tissue oxygenation.

The instrument drift was found to be less than 0.004 OD/hour and from measurements on glass filters of 8 optical density units, a coefficient of variation of 0.01 over the 30 second averaging time was observed. The instrument is sufficiently sensitive to enable monitoring of changes in the cerebral oxygen saturation level of haemoglobin and to enable changes in the concentration of cyt aa3 (oxidised form), to be measured with reasonable confidence. It is of the utmost importance in NIRS investigations to be certain of the specificity of the technique, and it is vital that reliable determinations of the amount of cytochrome aa3 in brain are made in addition to measurements of the extinction coefficients. This is still a matter of considerable debate, not only in the isolation and properties of the multisubunit structured membrane bound protein, which many enzymologists have been investigating for the last 50 years, (Keilin and Hartree, 1939; Brunori et al, 1981) but also in relating to in-vivo versus in vitro comparisons. An additional point for consideration is the validity of employing multiplier coefficients derived from the rat brain, as several groups have done (Wyatt et al 1986, Ferrari et al 1985,) and applying them to the human brain and to the infant brain. There may be significant differences in the activity of the enzyme, and the profound physiological effects which will arise during the end point fluorocarbon studies: the presence of fetal haemoglobin must also be considered (Carta et al., 1987). The clinical determination of the optical path length is a considerable problem (Cope etal., 1988,) and once again estimates of the pathlength correction factor made in animals and dead fetuses may not be valid for living human tissue. Results from our animal studies indicate that NIRS can be used to monitor changes in the oxygenation level of Hb and, in extreme hypoxia, changes in the level of the redox state of cyt aa3 can be reliably measured and are well within the sensitivity of the instrument. The results indicate that under small change in saturation the redox state of cyt aa3 appears to be unaltered. It may be that under normal physiological conditions the redox state of aa3 appears to be apparently unchanged under episodes of mild hypoxia of short duration.

Algorithms↗
PubMed1990

Continuous cerebral electrical impedance monitoring in sick preterm infants.

Cerebral electrical impedance (dZ) and intra-arterial blood pressure were measured continuously during the first 48 h after birth in 26 sick ventilated preterm infants with a birth weight less than 1500 g. The aim was to establish whether any patterns of dZp or the variability of either blood pressure or dZp would allow identification of those infants who developed intraventricular haemorrhage (IVH), periventricular leucomalacia (PVL) or a poor neurological outcome. IVH and PVL were diagnosed by ultrasound image obtained every 6 h. Cerebral electrical impedance recordings were unsuitable for analysis in three patients and a further three died within 14 h of birth. In the remaining 20 patients, no step changes that may have been related to the onset of IVH or PVL were evident and whilst three patterns of dZp were identified, they were not useful in distinguishing between normal infants or those who developed IVH, PVL or had a poor neurological outcome. Using multiple linear regression, the coefficient of variation of dZp was significantly associated with both IVH and outcome, as was the coefficient of variation of blood pressure. Continuous measurement of cerebral electrical impedance, whilst technically feasible in sick preterm infants, was not found useful as a method of identifying those who developed IVH, PVL or had a poor neurological outcome.

Blood Pressure Determination↗
PubMed1990

In vivo chemical sensors for intensive-care monitoring.

There is a need for rapid assessment of a patient's biochemical status during intensive care so that therapies may be optimised. Chemical sensors for key species have the potential to allow continuous in vivo monitoring, and some progress is being made with certain sensors. Gases, ions and certain catabolites such as glucose and urea may be measured with devices based on mass spectrometric, electrochemical or optical principles. The physical form, and size of sensors must be matched to the measurement site, which can include the airway, the intravascular space, tissue and the skin surface. Electrochemical sensors for measurement of O2, pH and glucose have been the most widely used to date, although fibre-optic devices are currently attracting considerable interest. Invasive sensors still suffer from the problem of poor biocompatibility, particularly devices used in arteries and veins. Noninvasive methods may be successful in certain circumstances and in some patient groups, but peripheral measurements are often significantly influenced by circulatory phenomena such as shock. Further research is required if these limitations of both invasive and noninvasive sensors are to be overcome and continuous chemical monitoring is to be established as a routine clinical technique.

Biocompatible Materials↗