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Biomedical subjects

A R Evans

Publications and source records attributed to A R Evans.

16 recordsLinked to original sources
PubMed1991

Responses of medullary raphespinal neurons to electrical stimulation of thoracic sympathetic afferents, vagal afferents, and to other sensory inputs in cats.

1. Medullary raphespinal neurons antidromically activated from the T2-T5 segments were tested for responses to electrical stimulation of cervical vagal and thoracic sympathetic afferents (by stimulating the left stellate ganglion), somatic probing, auditory stimuli, and visual stimuli in cats anesthetized with alpha-chloralose. A total of 99 neurons in the raphe nuclei were studied; the locations of 76 cells were histologically confirmed. Neurons were located in raphe magnus (RM, 65%), raphe obscurus (RO, 32%), and raphe pallidus (RPa, 4%). The mean conduction velocity of these neurons was 62 +/- 2.9 (SE) m/s with a range of 1.1-121 m/s. 2. A total of 60/99 tested neurons responded to electrical stimulation of sympathetic afferents. Quantitation of responses was obtained for 55 neurons. With one exception, all responsive neurons were excited and exhibited an early burst of spikes with a mean latency of 16 +/- 1.2 ms. From a spontaneous discharge rate of 5.2 +/- 1.2 spikes/s, neuronal activity increased by 2.9 +/- 0.3 spikes/stimulus. In addition to an early peak, 15 neurons (25%) exhibited a late burst of spikes with a latency of 182 +/- 12.9 ms; neuronal activity increased by 5.0 +/- 1.3 spikes/stimulus. Duration of the late peak (130 +/- 18.5 ms) was longer than for the early peak (18 +/- 0.7 ms), but threshold voltages for eliciting each peak were comparable. Sixteen of 29 spontaneously active neurons exhibited a postexcitatory depression of activity that lasted for 163 +/- 19.1 ms. All but one tested neuron in RO responded to stimulation of sympathetic afferents, but 65% of neurons in RM responded to this stimulus. 3. In response to vagal afferent stimulation, 19% of 57 neurons exhibited inhibition only, 11% were only excited, and 9% were either excited or inhibited, depending on the stimulus paradigm used; the remaining 61% of neurons were unresponsive. From a spontaneous rate of 7.9 +/- 3.8 spikes/s, excited cells increased their discharge rate by 1.6 +/- 0.3 spikes/stimulus. Activity of inhibited cells was reduced from 21.3 +/- 5.8 to 7.8 +/- 3.1 spikes/s. The conditioning-test (CT) technique was used to assess 11 neurons' responses. Stellate ganglion stimulation was the test stimulus, and vagal stimulation the conditioning stimulus. Vagal stimulation reduced the neuronal responses to stellate ganglion stimulation by an average of 50% with a CT interval of 60-100 ms, and cell responses returned to control after 300 ms. With spontaneous cell activity, low frequencies of vagal stimulation were generally excitatory, and high frequencies (10-20 Hz) inhibitory.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1991

Responses of medullary raphespinal neurons to coronary artery occlusion, epicardial bradykinin, and cardiac mechanical stimuli in cats.

1. A total of 59 medullary raphespinal neurons antidromically activated from the T2-T5 segments were tested for responses to coronary artery occlusion, epicardial application of bradykinin, and mechanical probing of the epicardium in cats anesthetized with alpha-chloralose. With the exception of five neurons, only those neurons that were responsive to electrical stimulation of the left stellate ganglion were tested for responses to these stimuli. Neurons in this study are a subset of those in the companion report. 2. Six neurons (12%) responded to epicardial bradykinin. Five cells were excited, and one was inhibited. Nine neurons (18%) had cardiac receptive fields, and one neuron (2%) had a field confined to the pericardium. 3. Neurons were tested for responses to separate occlusions of the left anterior descending (LAD) and circumflex (CX) coronary arteries. Overall, 13/34 (38%) of tested raphespinal neurons were responsive to coronary artery occlusion. Responses to coronary artery occlusion consisted of two major patterns. One pattern consisted of either an increase or decrease in neuronal firing rate after the heart became ischemic; this pattern was termed an ischemic (IS) response. Ten neurons (29%) exhibited an IS response to occlusion of the LAD and/or CX coronary arteries. Because four neurons exhibited IS responses to occlusion of each artery, there were a total of 14 IS responses. Of these, 10 were inhibitory, and 4 were excitatory. The second pattern of response consisted of a rapidly adapting excitation or inhibition at the onset or release of occlusion, but cell activity was unchanged during cardiac ischemia; this pattern was termed an onset (ON) response. Three neurons (9%) exhibited ON responses; two were excited, and one was inhibited. No neurons demonstrated both ON and IS responses during occlusion. 4. Twenty-one neurons were tested for responses to occlusion of each artery. Seventeen neurons (81%) exhibited similar patterns of responses to occlusion of each artery; that is, they either showed the same pattern of response to occlusion of each artery or they were unresponsive to either occlusion. For the 5 of these 17 neurons that were responsive, direction of change in neuronal activity (excitation or inhibition) was the same for occlusion of each artery. 5. All raphespinal neurons tested for responses to epicardial bradykinin and coronary artery occlusion were responsive to electrical stimulation of the left stellate ganglion. In addition, 16/28 (57%) of neurons tested for responses to occlusion were responsive to electrical stimulation of the right cervical vagus nerve.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Heart rate variability before and after myocardial infarction in conscious dogs at high and low risk of sudden death.

Heart rate variability has been demonstrated both experimentally and clinically to be of prognostic importance in determining mortality after myocardial infarction. However, no paired studies have been reported to examine heart rate variability before and after myocardial infarction. The hypothesis was tested that low values of heart rate variability provided risk assessment both before and after myocardial infarction with use of an established canine model of sudden cardiac death. Risk for sudden death was assessed 1 month after myocardial infarction by a protocol in which exercise and myocardial ischemia were combined; dogs that developed ventricular fibrillation were classified at high risk for sudden death (susceptible) and the survivors were considered low risk (resistant). In resistant dogs, myocardial infarction did not affect any measure of heart rate variability: 1) mean RR interval, 2) standard deviation of the mean RR interval, and 3) the coefficient of variance (standard deviation/RR interval). By contrast, after myocardial infarction, susceptible dogs showed significant decrease in all measures of heart rate variability. Before myocardial infarction, no differences were seen between susceptible and resistant dogs. However, 30 days after infarction, epidemiologic analysis of the coefficient of variance showed high sensitivity and specificity (88% and 80%, respectively), predicting susceptibility. Therefore, results of analysis of 30 min of beat to beat heart period at rest 30 days after myocardial infarction are highly predictive for increased risk of sudden death.

Analysis of Variance↗
PubMed1989

Retinal detachment and its relation to cataract surgery.

In Western Australia during the period 1 January 1976 to 31 December 1987 1089 eyes of 1044 patients in hospital were operated upon for primary rhegmatogenous retinal detachment due to causes other than penetrating trauma. Of these eyes 295 (27%) were aphakic or pseudophakic. During this period the annual number of cataract operations in the State increased by a factor of 245%, while aphakic and pseudophakic retinal detachment operations rose by only 55%. The declining risk of retinal detachment following cataract surgery is attributed to improvements in microsurgical techniques. In 1983 and 1984 the incidence of aphakic and pseudophakic retinal detachments dropped significantly (p less than 0.05). At about this time extracapsular cataract surgery became widespread in the State, and this may explain the observed fall in retinal detachment operations. Since 1984 the incidence has risen owing to the rapidly increasing prevalence of pseudophakia in the resident population.

Adult↗
PubMed1985

A study of the use of free-text fields within a computer medical records system.

At present, the general practitioner considers any imposed rigidity or standardisation in his record keeping as an encroachment on his clinical practice. Thus, computerised clinical records are regarded with some suspicion. This paper explores the likely requirements of a computerised records system which will leave the clinician all his freedom, but at the same time give him all the potential advantages of a structured information gathering system. This investigation formed part of a joint project between IBM and the University of Sheffield Medical School, in conjunction with two general practices in the Sheffield area. The overall objective of the project was to investigate the requirements for computers in general practice, and develop an experimental GP computer system.

Computers↗
PubMed1985

Computers and audit.

A computerized information system was installed in a large group practice. This paper describes how the computer system was used for the systematic auditing of clinical activities, and also demonstrates how it acted as a catalyst for the review and changes of administrative and management procedures. An analysis of the issues that arose in an audit group is used to identify how the objectives and activities of the group evolved with experience. It is demonstrated that a computer system and audit can complement and enhance each other to the benefit of clinical and managerial decision making.

Electronic Data Processing↗
PubMed1984

Results in children with local and regional neuroblastoma managed with and without vincristine, cyclophosphamide, and imidazolecarboxamide. A report from the Children's Cancer Study Group.

Members of children's cancer study group designed Study CCG 351 to determine whether three drug chemotherapy improved the survival experience of children with localized neuroblastoma. Patients in stages I-III were treated with surgical removal of the primary tumor and those in stages II and III received radiation therapy to the tumor bed and chemotherapy. Treatment included cyclophosphamide, imidazolecarboxamide, and vincristine given in 5-day pulses each month for 12 courses. The results were compared to those from a previous study, CCG 011, for localized neuroblastoma, in which children were randomized between a treatment regimen that included cyclophosphamide and one with no chemotherapy. There were 133 evaluable patients, subdivided as follows: stages I-26, stages II-74, and stages III-33. The 3-year life-table survival rates by stage of 96, 89 and 50% were not significantly different from the patients in CCG 011 similarly staged who received either no chemotherapy or oral CPM. These data suggest that multiagent chemotherapy, as prescribed, did not improve the outlook for children with locally advanced but nonmetastatic neuroblastoma. The staging criteria employed showed a modest difference in outcome between patients in stages I and II, but a significant poorer survival for stage III as compared to either stage I or II.

Aminoimidazole Carboxamide↗
PubMed1977

A small cluster of Hodgkin's disease.

Nine cases of Hodgkin's disease and one of acute lymphoblastic leukaemia occurred in 1972-5 in an area of less than 1 km. Clinical, social, and drug histories provided no relevant information, and definite patient-to-patient contacts before the onset of disease were not established. There was a higher incidence of malignant neoplasms in first-degree relatives of the patients than in those of a small control group living in the same area. There was no apparent reason for this cluster of cases, but geographical, climatic, and entomological studies are being carried out.

Adult↗
PubMed1976

The use of sodium valproate in a case of status epilepticus.

A child in status epilepticus, who did not respond to intravenous diazepam, was treated with sodium valproate by naso-gastric tube. Subsequent clinical and encephalographic improvement appeared to be related to the sodium valproate, and its value in cases of status epilepticus is discussed.

Child↗