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Biomedical subjects

J A Eyre

Publications and source records attributed to J A Eyre.

At least 19 recordsLinked to original sources
PubMed1995

Temperature response to severe head injury and the effect on body energy expenditure and cerebral oxygen consumption.

This study examines the relationship between core temperature and whole body energy expenditure, cerebral oxygen consumption (CMRO2), cerebral blood flow (CBF), and intracranial pressure (ICP) in severely head injured children. A total of 107 serial measurements of temperature, energy expenditure, CMRO2, CBF, and ICP were made in 18 head injured children receiving neurointensive care. Energy expenditure was measured using indirect calorimetry, and CMRO2 and CBF using the Kety-Schmidt technique. The mean rectal temperature was 37.8 degrees C (34-39.1 degrees C) despite modification with paracetamol. Within each child there was a positive relationship between rectal temperature and energy expenditure, energy expenditure increasing by a mean of 7.4% per degree C. There was no evidence of significant relationships between rectal temperature and CMRO2, CBF, or ICP. Mild induced hypothermia in two children did not result in decreased CMRO2 or CBF measurements. The efficacy of interventions aiming to modify cerebral energy metabolism by changing core temperature cannot be readily assessed by the response of the whole body.

Adolescent↗
PubMed1995

Cerebral blood flow and metabolism in children with severe head injury. Part 1: Relation to age, Glasgow coma score, outcome, intracranial pressure, and time after injury.

Understanding the pathophysiology of paediatric head trauma is essential for rational acute management. It has been proposed that the response to severe head injury in children differs from that in adults, with increased cerebral blood flow (cerebral hyperaemia) representing the most common cause of raised intracranial pressure, but this has recently been disputed. The relation between the pathophysiological response and time after injury has not been defined in children. This paper describes 151 serial measurements of cerebral blood flow, arteriojugular venous oxygen difference (AJVDO2), and cerebral metabolic rate for oxygen (CMRO2) that were performed in 21 children with severe head injury, mean age 8 (range 2-16) years, Glasgow coma score < or = 8. Absolute cerebral hyperaemia was uncommon, only 10 (7%) of the 151 cerebral blood flow values being at or above the upper limit of the range published in normal children. There was an inverse correlation between cerebral blood flow and intracranial pressure. (r = -0.24, p = 0.009). Contrary to the widespread assumption that cerebral metabolic rate in patients with head injury is always low, CMRO2 was initially within the normal range in 17/21 (81%) children. Both CMRO2 and AJVDO2 fell significantly between the first and third days after injury. There was a non-significant rise in cerebral blood flow over time. These data represent the first evidence that the temporal change in cerebral metabolic rate reported in experimental models of traumatic brain injury also occurs in patients with head injury. The changes in the pathophysiological response over time suggest that the management may need to be modified accordingly. If cerebral metabolic rate and cerebral oxygen extraction are maximal shortly after injury in children with severe head injury then the children are most likely to sustain secondary damage during this period.

Adolescent↗
PubMed1995

Cerebral blood flow and metabolism in children with severe head injuries. Part 2: Cerebrovascular resistance and its determinants.

It has been proposed that in children with severe head injuries the cerebral circulation does not respond appropriately to normal physiological control mechanisms, making children more susceptible than adults to low cerebrovascular resistance, increased cerebral blood flow (cerebral hyperaemia), and raised intracranial pressure. To investigate this issue, 122 serial measurements of cerebrovascular resistance in 17 children with severe head injuries have been performed and related to cerebral perfusion pressure, arterial CO2 (PaCO2), arterial oxygen content (AO2), and the cerebral metabolic rate of oxygen (CMRO2). Cerebrovascular resistance values (mean (SD) 1.54 (0.61) mm Hg.ml-1.100 g.min) were normal or raised in most cases; 71 values (58%) were within the normal range, 39 (32%) above the upper limit, and only 12 (10%) below the lower limit. There was a significant correlation between cerebral perfusion pressure and cerebrovascular resistance (r = 0.32, p = 0.0003), suggesting preservation of pressure autoregulation. This correlation was absent in four of the five children who died or survived with severe handicap. Analysis by multilevel modelling indicated that, as in normal subjects, CMRO2, CPP, AO2, PaCO2, and cerebrovenous pH were important independent determinants of cerebrovascular resistance. The results indicate that normal cerebrovascular reactivity is often preserved in children with severe head injuries but may be impaired in the most severely injured patients.

Adolescent↗
PubMed1995

Changes in cerebral oxygen consumption are independent of changes in body oxygen consumption after severe head injury in childhood.

This study examines the relation between cerebral O2 consumption (CMRO2) and the O2 consumption of the rest of the body (BVO2) after severe head injury. Seventy nine serial measurements of whole body O2 consumption, CMRO2, plasma adrenaline, T3, and glucagon concentrations were made in 15 children with severe head injuries receiving neurointensive care. Body O2 consumption was measured with indirect calorimetry and CMRO2 with the Kety-Schmidt technique. There was no evidence of a significant relation between CMRO2 and BVO2. Within each child there were statistically significant positive relations between BVO2 and adrenaline, T3, and glucagon. By contrast, there was only a weak significant positive relation between CMRO2 and T3. In conclusion, CMRO2 and BVO2 seem to be determined independently after severe head injury. Thus therapeutic measures aiming to reduce CMRO2 need to be specific to the brain and it should not be assumed that measures which decrease whole body energy expenditure will necessarily have the same effect on CMRO2.

Adolescent↗
PubMed1995

The effect of severe head injury on whole body energy expenditure and its possible hormonal mediators in children.

This study examines the effects of severe head injury in children on whole body energy expenditure and the mediators that influence this. One hundred five serial measurements of whole body energy expenditure and plasma adrenaline, triiodothyronine, glucagon, cortisol, insulin, and growth hormone concentrations were made in 18 children aged 2-15 y receiving neurointensive care for severe head injury. Energy expenditure was measured using indirect calorimetry by a modified Douglas bag technique, and hormones were measured by RIA or radioenzymatic assay. Energy expenditure varied markedly between and within children (mean 97% of predicted, range 60-137%) and was significantly lower in the four children with a poor outcome (p = 0.03). Within each child there were statistically significant positive relationships between energy expenditure and adrenaline (p < 0.0001), triiodothyronine (p < 0.0001), and glucagon (p < 0.0001). However, there was evidence that the effect of adrenaline on energy expenditure was attenuated. This may be due to the effects of the cerebral trauma itself on central nervous influences on energy expenditure, to interactions between hormones, or to a global impairment of O2 utilization by the body's tissues.

Adolescent↗
PubMed1991

Constancy of central conduction delays during development in man: investigation of motor and somatosensory pathways.

1. A cross-sectional study has been performed on 457 normal subjects to determine changes in conduction delays with age in central and peripheral motor and somatosensory pathways to the upper limb. 2. Electromagnetic stimulation was used to investigate central and peripheral conduction in motor pathways from the cortex to biceps brachii and hypothenar muscles in 308 normal human subjects aged from 32 weeks gestation to 55 years. The responses were recorded in the surface electromyogram. 3. Somatosensory potentials evoked by electrical stimulation of the median nerve have been recorded at Erb's point and over the somatosensory cortex in 149 normal subjects aged from 34 weeks gestation to 52 years to determine central and peripheral somatosensory conduction delays. 4. The conduction delays in the central components of both motor and somatosensory pathways rapidly decrease over the first 2 years after birth and thereafter remain constant at adult values. 5. The conduction delays in the peripheral components of both motor and somatosensory pathways also decrease initially but then from the age of 5 years progressively increase in proportion to arm length. 6. The threshold stimulus intensity for evoking muscle responses following electromagnetic stimulation of the cortex is high initially and falls progressively until the age of 16 years. A linear relationship exists between the threshold intensity and height for the height range 70-180 cm. 7. The threshold stimulus intensities for exciting peripheral motor and somatosensory nerves decrease up to the age of 5 years and then reach a plateau. 8. The results support the conclusion, already reported in the literature that peripheral nerves attain maximum value for fibre diameter and conduction velocity at approximately 5 years of age. 9. In contrast, it is concluded that the maximum fibre diameters in both motor and somatosensory central pathways increase in proportion to height, leading to constant central conduction delays with growth.

Adolescent↗
PubMed1991

Radiation of phasic stretch reflex in biceps brachii to muscles of the arm in man and its restriction during development.

1. The phasic stretch reflex in biceps brachii has been recorded in 372 normal subjects aged from 31 weeks gestation to 55 years. The stimulus used was a brief mechanical pulse delivered by a hand-held electromagnetic vibrator and the response was measured in the surface electromyogram. 2. The threshold for eliciting the reflex was low in the newborn and increased over the first 6 years to values corresponding to those of adults. 3. On the basis of timing it is concluded that the phasic stretch reflex has a monosynaptic component at all ages. 4. The surface electromyogram was also recorded in triceps brachii, pectoralis major, deltoid and hypothenar muscles. In some subjects evoking the phasic stretch reflex in biceps brachii resulted in short latency responses in these muscles, a phenomenon termed radiated response. 5. The probability of occurrence of radiated responses and their magnitudes were greatest at birth and decreased over 2-4 years. 6. Experiments were performed to determine how far mechanical transmission of the stimulus to biceps through the tissues of the arm might account for the radiated responses in the other muscles studied. It was concluded that the responses observed in triceps brachii, pectoralis major, deltoid and hypothenar muscles, following vibration of the biceps tendon, are primarily due to the radiation of the activity carried in biceps muscle afferents to the alpha-motoneurones of the respective muscles. 7. On the basis of timing it is concluded that in subjects below 2 years the radiated responses in the muscles studied have a monosynaptic component.

Adolescent↗
PubMed1991

A practical method of serial bedside measurement of cerebral blood flow and metabolism during neurointensive care.

Acute encephalopathy is a major cause of death and neurological handicap in children. The principle aims of treatment are to provide adequate cerebral blood flow for the brain's metabolic needs and to prevent intracranial pressure rising above the level at which brain herniation occurs. Rational management requires an understanding of the pathophysiological changes in cerebral blood flow and metabolism which occur. The paucity of data on this subject reflects the perceived difficulty of measuring cerebral blood flow and cerebral metabolism in children. A modification of the Kety Schmidt technique of measuring cerebral blood flow and cerebral metabolism is described. This modification makes it possible to perform serial bedside measurements in children receiving intensive care. This method was used to perform 348 measurements in 58 children. The method was reproducible and no significant complications were encountered. The results indicated that appreciable changes in cerebral blood flow and metabolism could occur in individual patients over time, emphasising the importance of serial measurements. This technique may provide a practical means of monitoring cerebral blood flow and metabolism in very sick children receiving neurointensive care and evaluating the efficacy of treatment.

Acute Disease↗
PubMed1990

Causes of fatal childhood accidents involving head injury in northern region, 1979-86.

OBJECTIVE: To examine the causes and circumstances surrounding fatal accidents involving head injuries in children in the Northern region. DESIGN: Retrospective review of the hospital case notes, necropsy reports, and records of the coroners' inquests. SETTING: Northern Regional Health Authority. PATIENTS: All 255 children aged less than 16 years who died with a head injury during 1979-86. MAIN OUTCOME MEASURES: Cause of injury and circumstances of accident according to reports of inquests; injury severity score; number of fatal accidents and mortality per 100,000 children in 10 groups of local authority wards ranked according to their score on the overall deprivation index; and distance of site of accident from child's home. RESULTS: Of the 255 children who died after a head injury, 136 (53%) children were playing at the time of the accident. 195 (76%) children sustained the head injury in road traffic accidents, 135 as pedestrians, 35 as cyclists, and 25 as passengers in a vehicle. In 120 accidents in child pedestrians the primary cause of accident was the unsafe behaviour of the child. 172 (67%) accidents occurred within one to two km of the child's home and 153 (63%) between 3 pm and 9 pm. The mortality was significantly related to social deprivation; excluding eight children injured while on holiday in the region, 15-fold decrease in mortality was recorded between the local authority wards that ranked highest on the overall deprivation index and those that ranked lowest (14.0/100,000 children, group 10 v 0.9/100,000, group 1 respectively, p less than 0.00001). CONCLUSIONS: The finding that most accidents occurred in children living in deprived areas who were playing unsupervised near their home suggests that childhood mortality might be appreciably reduced if children at play were protected from traffic, particularly in socially deprived areas.

Accidental Falls↗
PubMed1990

Avoidable factors contributing to death of children with head injury.

OBJECTIVE: To assess the incidence of potentially avoidable complications contributing to death of children with head injuries. DESIGN: Retrospective review of children who died with head injuries from 1979 to 1986 from data of the Office of Population Censuses and Surveys, Hospital Activity Analyses, case notes, coroners' records, and necropsy reports. SETTING: District general hospitals and two regional neurosurgical centres in Northern region. RESULTS: 255 Children died from head injury in the region, the mortality being 5.3 per 100,000 children per year. Head injury was the single most important cause of death in children aged greater than 1 year, accounting for 15% of deaths in children aged 1-15 years and a quarter for those aged 5-15 years. 121 Potentially avoidable factors possibly or probably contributing to death occurred in 81 children (32%). Half the children (125) died before admission, 27 of whom (22%) had potentially avoidable factors possibly or probably contributing to death, and 130 died after admission, 54 of whom (42%) had 93 such factors, which included failure of diagnosis or delayed recognition of intracranial haemorrhage or associated injury, inadequate management of the airways, and poor management of the transfer between hospitals. IMPLICATIONS: Regions should revise urgently their guidelines for optimal management and indications for neurosurgical referral to include children with severe head injuries and audit their systems of care for all patients with head injuries.

Adolescent↗
PubMed1990

Excitation of the corticospinal tract by electromagnetic and electrical stimulation of the scalp in the macaque monkey.

1. The responses evoked by non-invasive electromagnetic and surface anodal electrical stimulation of the scalp (scalp stimulation) have been studied in the monkey. Conventional recording and stimulating electrodes, placed in the corticospinal pathway in the hand area of the left motor cortex, left medullary pyramid and the right spinal dorsolateral funiculus (DLF), allowed comparison of the actions of non-invasive stimuli and conventional electrical stimulation. 2. Responses to electromagnetic stimulation (with the coil tangential to the skull) were studied in four anaesthetized monkeys. In each case short-latency descending volleys were recorded in the contralateral DLF at threshold. In two animals later responses were also seen at higher stimulus intensities. Both early and late responses were of corticospinal origin since they could be completely collided by appropriately timed stimulation of the pyramidal tract. The latency of the early response in the DLF indicated that it resulted from direct activation of corticospinal neurones: its latency was the same as the latency of the antidromic action potentials evoked in the motor cortex from the recording site in the DLF. 3. Scalp stimulation, which was also investigated in three of the monkeys, evoked short-latency volleys at threshold and at higher stimulus intensities these were followed by later waves. The short-latency volleys could be collided from the pyramid and, at threshold, had latencies compatible with direct activation of corticospinal neurones. The longer latency volleys were also identified as corticospinal in origin. 4. The latency of the early volley evoked by electromagnetic stimulation remained constant with increasing stimulus intensities. In contrast, with scalp stimulation above threshold the latency of the early volleys decreased considerably, indicating remote activation of the corticospinal pathway below the level of the motor cortex. In two monkeys both collision and latency data suggest activation of the corticospinal pathway as far caudal as the medulla. 5. The majority of fast corticospinal fibres could be excited by scalp stimulation with intensities of 20% of maximum stimulator output. Electromagnetic stimulation at maximum stimulator output elicited a volley of between 70 and 90% of the size of the maximal volley evoked from the pyramidal electrodes. 6. Electromagnetic stimulation was also investigated in one awake monkey during the performance of a precision grip task. Short-latency EMG responses were evoked in hand and forearm muscles. The onsets of these responses were approximately 0.8 ms longer than the responses evoked by electrical stimulation of the pyramid.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1990

Neurophysiological observations on corticospinal projections to the upper limb in subjects with Rett syndrome.

The aim of the present study was to investigate the excitability of corticospinal neurons and the integrity of their projections to the alpha motor neurons through the corticospinal tract in subjects of different ages with Rett syndrome. Electromagnetic stimulation of the motor cortex and cervical motor roots was used to evoke motor action potentials in the biceps brachii and hypothenar muscles. The phasic stretch reflex in the biceps brachii was also recorded to study the excitability of spinal alpha motor neurons. Motor cortex stimulation evoked motor action potentials at low threshold and with abnormally short latencies and prolonged durations. In contrast cervical motor root stimulation resulted in responses of normal latency and duration. The phasic stretch reflex had a low threshold, short latency and prolonged duration. It is concluded that in Rett syndrome the corticospinal pathway is intact. The results suggest disordered synaptic control of the Betz cell of the motor cortex and/or the spinal alpha motor neuron, although the involvement of the latter might be a consequence of dysfunction in supraspinal descending motor pathways.

Adolescent↗
PubMed1990

Acute effects of electromagnetic stimulation of the brain on cortical activity, cortical blood flow, blood pressure and heart rate in the cat: an evaluation of safety.

The influence of repeated high intensity electromagnetic stimulation of the brain on cortical activity, cortical blood flow, blood pressure and heart rate has been investigated in the cat, to evaluate the safety of the method. The observations have been made in preparations under propofol anaesthesia before, during and after periods of anoxia. Electromagnetic stimulation of the brain evoked activity in descending motor pathways and was recorded by activity in the median nerve and by muscle twitches. Following repeated series of high intensity stimulation there were no systematic changes in somatosensory evoked potentials or background EEG, nor were there signs of epileptogenic activity during electromagnetic stimulation, before, during or after periods of anoxia. No systematic changes in cortical blood flow, blood pressure or heart rate were observed during electromagnetic stimulation, before or after periods of anoxia. In conclusion, no acute adverse consequences following electromagnetic stimulation in the normal and anoxic cat brain were demonstrated.

Animals↗
PubMed1988

A comparison of measurements of cerebral blood flow in the rabbit using laser Doppler spectroscopy and radionuclide labelled microspheres.

Laser Doppler spectroscopy has been evaluated for the measurement of cerebral blood flow (CBF) by correlation with simultaneous measurements by radionuclide labelled microspheres. The experimental procedures were carried out on five anaesthetised rabbits. The cortical tissue was exposed by means of a small burr hole and illuminated by a helium neon laser (632.8 nm). Reflected light was detected using a silicon photodiode, and CBF was calculated continuously from the power of the frequency weighted Doppler spectrum in the reflected light. Three successive measurements of CBF were made using the microsphere technique. Following an initial baseline measurement, CBF was increased by an infusion of metaraminol and then reduced by controlled haemorrhage. Laser Doppler spectroscopy provided continuous monitoring of blood flow fluctuations and during the haemorrhage it was possible to demonstrate CBF autoregulation until the mean blood pressure fell below 6.7 kPa (50 mmHg). A regression analysis was performed between the simultaneous CBF measurements from the two techniques using a least squares best fit straight line analysis (r = 0.92, P less than 0.001). It was concluded that the flow computed from laser Doppler spectroscopy varied linearly with CBF and offers the unique advantage of continuous and instantaneous measurements even during nonsteady state flow.

Animals↗