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Biomedical subjects

P Rolfe

Publications and source records attributed to P Rolfe.

At least 55 records · Page 3Linked to original sources
PubMed1994

A non-invasive optical technique for intrapartum fetal monitoring: preliminary clinical studies.

A relatively new optical method based on near infra-red spectroscopy was evaluated in preliminary clinical trials for noninvasive intrapartum fetal monitoring. The measurements were performed using mainly the light reflection mode of monitoring. Continuous monitoring of changes in the concentrations of oxygenated and deoxygenated haemoglobin and thus changes in total haemoglobin concentration in the fetal brain was achieved. It was found that uterine contractions can influence in a distinctive manner the near infra-red derived cerebral haemoglobin concentration changes in the fetus. The results indicate that near infra-red spectroscopy could offer a non-invasive real-time monitoring method for in vivo monitoring of blood oxygenation in the fetal brain. We conclude that this technique may be useful for intrapartum fetal monitoring and in predicting fetal cerebral hypoxia.

Brain Chemistry↗
PubMed1994

Near infrared spectroscopy used to observe changes in fetal cerebral haemodynamics during labour.

Near Infrared Spectroscopy (NIRS) has been used in the neonate to observe changes in the cerebral haemodynamics and concentration of oxygenated haemoglobin. Specific changes have been demonstrated in response to spontaneous bradycardias and alterations in the inspired oxygen concentration. We report here changes in fetal cerebral haemodynamics using NIRS in response to rapid spontaneous delivery and the "topping up" of a maternal epidural with bupivacaine. NIRS offers a new way of observing changes in cerebral haemodynamics in the fetus during labour.

Brain Chemistry↗
PubMed1993

Electrical impedance plethysmography: its use in studying the cerebral circulation of the rabbit.

Electrical impedance plethysmography (EIP) is a noninvasive method that may be useful for both the continuous and serial measurement of changes in pulsatile cerebral blood volume and perhaps cerebral blood flow (CBF). It has not been well validated by comparison with other methods. To attempt to validate the EIP technique, the relationship between the peak amplitude of the transcranial, cardiac-synchronous impedance waveform (dZp) and cerebral blood flow measured by the radiolabelled microsphere technique (CBFrlm) and laser Doppler spectroscopy (CBFlds) was studied in rabbits. CBF was altered by inducing hypertension using metaraminol, hypotension by controlled haemorrhage or hypocarbia by hyperventilation. Twenty-three comparisons between dZp and CBFlds and 19 comparisons with CBFrlm were made in eight rabbits. The percentage change between each measurement using the three techniques in each animal was calculated. Using pooled data from all the animals, the linear regression equations were dZp = 0.5 CBFrlm + 33 (r = 0.38, p = 0.22, SE = 79) and dZp = 0.84 CBFlds + 19.6 (r = 0.46, p = 0.09, SE = 72). It is concluded that, in the anaesthetised rabbit, when large changes in CBF are induced by the manoeuvres described above, changes in dZp correlate very weakly with changes in either cortical or global CBF, and are influenced by other factors such as pulsatile intracranial blood volume.

Animals↗
PubMed1993

A survey of technology and temperature control on a neonatal unit in Kathmandu, Nepal.

An assessment of the incubators in use at the Kathmandu Maternity Hospital neonatal unit was undertaken; this was followed by a prospective survey of neonatal temperatures on the unit. In the incubator assessment 11 studies were carried out in five incubators. Three of the thermostats in the five incubators did not work at all and those in the other two incubators were more than 3 degrees C inaccurate. All the incubator thermometers gave recordings less than the actual temperature (with a range of error: 1.3-4.4 degrees C). Six out of the 11 babies studied were hypothermic (defined as rectal temperature < 36 degrees C). In the prospective survey of temperatures a high incidence of hypothermia was found on the neonatal unit at the time of first temperature measurement (64 per cent had a rectal temperature of < 36 degrees C). A significant association between admission hypothermia and mortality was noted. Sixteen per cent (10/64) of babies admitted with temperatures < 36 degrees C died within the first week, compared to 0 (0/36) of those admitted with temperatures > or = 36 degrees C.

Body Temperature↗
PubMed1993

Effect of fetal hemoglobin on the determination of neonatal cerebral oxygenation by near-infrared spectroscopy.

Near-infrared spectroscopy has been applied to the study of cerebral oxygenation and hemodynamics in the newborn. Fetal Hb is present in high concentrations in these infants. Because spectral absorption curves in the near-infrared range for fetal Hb are not identical to those for adult Hb, there is a potential for the measurements to be affected. This possibility has not previously been investigated. A quantitative analysis of cerebral oxygenation was undertaken in six newborn infants. The analysis used near-infrared spectroscopy multiplier coefficients derived from the absorption coefficients of both fetal and adult deoxygenated and oxygenated Hb. The results of both analyses were compared. It was concluded that the error in near-infrared spectroscopy analysis of neonatal cerebral oxygenation arising from the use of absorption coefficients derived from adult Hb is inconsequential, even in the presence of high concentrations of fetal Hb.

Adult↗
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↗