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Biomedical subjects

G Campbell

Publications and source records attributed to G Campbell.

At least 235 records · Page 13Linked to original sources
PubMed1975

Coccidioidal synovitis of the knee.

Four patients are described with documented coccicioidal synovitis of the knee joint. In two of them, no previous diagnosis of coccidioidomycosis had been made prior to diagnosis of coccidioidal synovitis. The other two had active disease after courses of amphotericin B administered both parenterally and intra-articularly for disseminated coccidioidomycosis and coccidioidal synovitis. After synovectomy and limited parenteral amphotericin B therapy, none of the four patients whos evidence of active synovial infection two to seven years later. Synovectomy appears to be an important aspect of the optimal therapy of coccidioidal synovitis of the knee, and when performed, the parenteral dosage of amphotericin B can be limited. Intra-articularly administered amphotericin B is also advocated when possible.

Adult↗
PubMed1975

Pancreatic cysts.

Explore the source record for details and available documents.

Adolescent↗
PubMed1970

Evidence that adenosine triphosphate or a related nucleotide is the transmitter substance released by non-adrenergic inhibitory nerves in the gut.

1. Stimulation of the vagal non-adrenergic inhibitory innervation caused the release of adenosine and inosine into vascular perfusates from the stomachs of guinea-pigs and toads.2. Stimulation of portions of Auerbach's plexus isolated from turkey gizzard caused the release of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP).3. ATP, added to solutions perfused through the toad stomach vasculature, was broken down to adenosine, inosine and adenine.4. Of a series of purine and pyrimidine derivatives tested for inhibitory activity on the guinea-pig isolated taenia coli, ATP and ADP were the most potent.5. ATP caused inhibition of twelve other gut preparations previously shown to contain non-adrenergic inhibitory nerves. The inhibitory action of ATP was not prevented by tetrodotoxin.6. Quinidine antagonized relaxations of the guinea-pig taenia coli caused by catecholamines or adrenergic nerve stimulation. Higher concentrations of quinidine antagonized relaxations caused by ATP or non-adrenergic inhibitory nerve stimulation.7. When tachyphylaxis to ATP had been produced in the rabbit ileum, there was a consistent depression of the responses to non-adrenergic inhibitory nerve stimulation but not of responses to adrenergic nerve stimulation.8. It is suggested that ATP or a related nucleotide is the transmitter substance released by the non-adrenergic inhibitory innervation of the gut.

Adenine↗
PubMed1966

The inhibitory innervation of the taenia of the guinea-pig caecum.

1. The inhibitory innervation of the taenia of the guinea-pig caecum has been studied, after blocking the responses to stimulation of excitatory cholinergic nerves with atropine.2. Stimulation of the perivascular nerves supplying the taenia caused relaxations. These nerves had properties which were typical of sympathetic post-ganglionic adrenergic nerves. The relaxations caused by stimulation were maximal at frequencies of stimulation above 30 pulses/sec and they were abolished by bretylium, guanethidine and 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP).3. The taenia is also innervated by intramural inhibitory nerves with their cell bodies in Auerbach's plexus. These nerves can be excited by electrical stimulation of the taenia or by the application of ganglion-stimulating drugs.4. The intramural inhibitory nerves have different properties from sympathetic adrenergic nerves. Relaxations in response to stimulation were maximal with frequencies of stimulation of about 5 pulses/sec and they were not blocked by bretylium, guanethidine or DMPP.5. Preganglionic cholinergic fibres in the caecal wall make synaptic connexions with the intramural inhibitory neurones.6. The role of the intramural inhibitory neurones in intestinal activity and their possible connexions with the central nervous system have been discussed.

Anesthetics, Local↗
PubMed1966

Nerve-mediated excitation of the taenia of the guinea-pig caecum.

1. A study was made of the responses of the isolated taenia of the guinea-pig caecum to stimulation of the intramural nerves.2. Four types of response are described, made up of a contraction and/or a relaxation occurring during stimulation and an after-contraction occurring when stimulation is stopped.3. A delayed relaxation which sometimes occurred at the end of stimulation is also described.4. Atropine usually abolished the contractions occurring during stimulation. After-contractions either appeared or were increased in amplitude in the presence of atropine, and delayed relaxations were abolished.5. The anti-cholinesterase drug neostigmine could convert the response during stimulation from a relaxation to a contraction. After-contractions were often abolished by neostigmine and delayed relaxations appeared.6. It is concluded that the contractions which occurred during stimulation were mediated by cholinergic nerves. The after-contraction appears to be a rebound phenomenon, following the hyperpolarization of the muscle caused by stimulation of the inhibitory nerves. It is suggested that the delayed relaxation is caused by the effects of persisting inhibitory transmitter substance on cells which do not undergo rebound excitation.

Animals↗
PubMed1966

The inhibitory nerve fibres in the vagal supply to the guinea-pig stomach.

1. A comparison was made between the inhibitory responses of the isolated atropinized guinea-pig stomach to stimulation of the vagus and to stimulation of the perivascular nerves.2. When low frequencies of stimulation were used, the vagi were more effective than the perivascular nerves in causing relaxation of the stomach.3. The responses to vagal stimulation were faster in onset than were the responses to perivascular nerve stimulation.4. Responses to perivascular nerve stimulation were abolished by low concentrations of bretylium, whereas responses to vagal stimulation were only slight reduced. Vagal responses were strongly reduced by higher concentrations of bretylium.5. Amphetamine relieved the blockade of perivascular nerve responses which was caused by bretylium, but never relieved the reduction of the vagal responses.6. It is argued that the vagal inhibitory fibres are not susceptible to ;adrenergic neurone blockade', the observed reduction of the responses being due to some other action of bretylium.7. These differences between the vagal and perivascular inhibitory innervations of the stomach suggest that the post-ganglionic fibres in the vagal pathway and the intramural inhibitory nerves described in the guinea-pig caecum are similar.

Amphetamine↗
PubMedDate not supplied

Local histogram correction of MRI spatially dependent image pixel intensity nonuniformity.

We describe a computationally straightforward post-hoc statistical method of correcting spatially dependent image pixel intensity nonuniformity based on differences in local tissue intensity distributions. Pixel intensity domains for the various tissues of the composite image are identified and compared to the distributions of local samples. The nonuniformity correction is calculated as the difference of the local sample median from the composite sample median for the tissue class most represented by the sample. The median was chosen to reduce the effecters on determining the sample statistic and to allow a sample size small enough to accurately estimate the spatial variance of the image intensity nonuniformity. The method was designed for application to two-dimensional images. Simulations were used to estimate optimal conditions of local histogram kernel size and to test the accuracy of the method under known spatially dependent nonuniformities. The method was also applied to correct a phantom image and cerebral MRIs from 15 healthy subjects. Results show that the method accurately models simulated spatially dependent image intensity differences. Further analysis of clinical MR data showed that the variance of pixel intensities within the cerebral MRI slices and the variance of slice volumes within individuals were significantly reduced after nonuniformity correction. Improved brain-cerebrospinal fluid segmentation was also obtained. The method significantly reduced the variance of slice volumes within individuals, whether it was applied to the native images or images edited to remove nonbrain tissues. This statistical method was well behaved under the assumptions and the images tested. The general utility of the method was not determined, but conditions for testing the method under a variety of imaging sequences is discussed. We believe that this algorithm can serve as a method for improving MR image segmentation for clinical and research applications.

Adult↗
PubMedDate not supplied

Advances in statistical methodology for the evaluation of diagnostic and laboratory tests.

The ROC plot is a useful tool in the evaluation of the performance of medical tests for separating two populations. For a two-state decision rule based on such a test, the ROC plot is the graph of all observed (1-specificity, sensitivity) pairs. Each point on this empirical plot can be represented by a 2 x 2 contingency table. The non-parametric statistics of Mann-Whitney and Kolmogorov-Smirnov can be immediately identified on this plot. Local non-parametric confidence interval procedures related to the theoretical ROC curve are briefly reviewed. For continuous data, two new simultaneous confidence regions associated with the ROC curve are presented, one based on Kolmogorov-Smirnov confidence bands for distribution functions and the other based on bootstrapping. Two different tests on the same patients can be compared on the ROC scale. For continuous data, one important problem concerns the comparison of two ROC plots (as would arise from two correlated diagnostic tests on each patient) using a sup norm (this metric can detect differences that the ROC area cannot). The distribution of a statistic based on this norm is studied, using the bootstrap. A biomedical example illustrates the methodologies.

Clinical Laboratory Techniques↗