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Biomedical subjects

W Burke

Publications and source records attributed to W Burke.

At least 109 records · Page 6Linked to original sources
PubMed1989

Tuberculous arthritis presenting as tophaceous gout.

A 73-year-old black man with chronic gout presented with a 1 1/2 year history of a swollen painful left wrist. Two draining ulcers over the ventral aspect of his wrist and radiographic changes of the affected area suggested chronic gouty arthritis, but culture of the fluid from the wrist grew Mycobacterium tuberculosis. This case extends the list of infectious agents producing septic arthritis in patients with gout to include Mycobacterium tuberculosis. The need for culture evaluation of joint fluid in patients with chronic as well as acute gout is emphasized.

Aged↗
PubMed1987

Hypertension and the genetics of red cell membrane abnormalities.

Hypertension represents the upper 15-25% of the blood pressure distribution in industrialized countries. The trait is practically absent in primitive societies and is made manifest by diet and lifestyles in industrialized countries. High blood pressure is an important risk factor for strokes, heart disease and renal disease. The frequency of hypertension is higher among blacks than among whites in the USA. Various twin, family and adoption studies indicate a strong genetic effect on blood pressure. The genetic mechanisms are unknown. Membrane transport variability has been studied in red cells as a surrogate for analogous alterations in smooth muscle or renal cells. Among the various transport systems, erythrocyte sodium-lithium countertransport (CT) has been consistently elevated in variable proportions of Caucasian hypertensives. Genetic studies of countertransport levels have shown familial aggregation and higher concordance for monozygotic than dizygotic twins. Complex segregation analysis suggests the action of a major gene superimposed on a polygenic background. The postulated gene (B) raises CT activity and has a population frequency of 0.25. CT levels of the common AA homozygotes and AB heterozygotes cannot be distinguished from each other, whereas CT activity of BB homozygotes (6% of the population) is significantly elevated. Although the CT gene contributes only 2.7% to 3.5% of the variability of blood pressure over its entire range, 14% to 20% of persons with systolic hypertension (greater than 140 mmHg) are BB homozygotes rather than the expected 6% to 7%. A much lower frequency of elevated countertransport activity among black hypertensives suggests genetic heterogeneity in the pathogenesis of high blood pressure. Further investigations on the mechanism and genetic linkage relationships of the putative CT gene may aid in elucidating an important mechanism of blood pressure elevation and will allow molecular approaches in the future.

Antiporters↗
PubMed1987

Respiratory drive during sudden cold water immersion.

Sudden decreases in cutaneous temperature induce an immediate ventilatory response, which has been termed the inspiratory or 'gasp' reflex. This respiratory response has been implicated as a contributing factor to cold water immersion drowning. In the present study, five subjects wearing either shorts or a variety of thermal protective apparel were immersed on separate occasions in 10 degrees C water. The observed peak mean skin temperature cooling rates (dTs/dt) for the different conditions varied from 6.9 +/- 2.1 degrees C/min for the shorts condition to 1.8 +/- 0.3 degrees C/min for a helicopter pilot suit made of cotton ventile material. During the immersion, recordings were made of respiratory drive, as indicated by the mouth occlusion pressure at 100 msec following the onset of inspiration (P0.1). The respiratory drive, an indicator of central inspiratory activity, correlated well with peak dTs/dt. The slope P0.1/(dTs/dt) was subject dependent and did not appear to be related to body composition. The substantial intersubject variability in the respiratory response is suggested to result from differences in the central integration of thermoafferent information. It is concluded that the inspiratory reflex is the result of cutaneous thermoreceptor activity.

Adult↗
PubMed1987

Function of the Y optic nerve fibres in the cat: do they contribute to acuity and ability to discriminate fast motion?

1. A controlled pressure block has been applied to the optic nerve of the cat, sufficient to bring about degeneration of the axons of the large (Y) nerve fibres caudal to the block site. This degeneration has been monitored by means of implanted electrodes in optic nerve and tract which have shown a loss of the short-latency (t1) response 4-6 days after the block, and also by histological examination of the optic nerve. 2. Cats with one optic nerve blocked in this way have been used in behavioural experiments, one or other eye being covered during the tests. Tested via the blocked nerve, all cats with loss of only Y fibres could perform certain tests: the visual placing reaction, the blink reflex, the pupillary (light) reflex and simple manoeuvres such as walking a plank and jumping from table to floor. 3. When acuity was tested by means of the Mitchell jumping apparatus, cats with loss of only Y fibres showed the same acuity using either eye. This was true also of one cat in which many X fibres had also degenerated, as evidenced by a 55% loss of the medium-latency (t2) response, but in another cat with 90% loss of the t2 response acuity was reduced to about half-normal. 4. Ability to discriminate fast motion was tested by a modification of the Mitchell apparatus. All cats were able to discriminate the motion of an 11.5 deg spot up to a velocity of 6260 deg/s, whether using their normal eye or their affected eye. However, the loss of the Y fibres reduced the ability to discriminate fast motion, so that for any given level of contrast the velocity which could be discriminated was about two-thirds of the velocity discriminated using the normal eye. The ability of the cat to discriminate fast motion seems to be similar to that of the human. 5. These results suggest that there is no sharp restriction of function between the Y and X systems but instead considerable overlap. However, each system possesses specialized features giving it superiority in certain conditions.

Animals↗
PubMed1986

Selective degeneration of optic nerve fibres in the cat produced by a pressure block.

Using a technique described previously, we have applied pressure to the optic nerve of a cat sufficient to cause conduction block of the t1 response (the response of the Y optic nerve fibres). A greater pressure, usually sufficient to cause a transient block of the t2 response (the response of the X fibres), leads to degeneration of the Y axons caudal to the block. This is demonstrated by the disappearance of the t1 response in this region after 4-5 days and by the presence in electron micrographs of degenerating large (Y) fibres. Some small fibres also show degeneration, but the medium (X) fibres are largely spared. The time course of loss of response in the Y fibres is similar whether the loss is due to a pressure block or to enucleation, suggesting that the pressure block as used by us causes a disruption of the axon. If the pressure is great enough to block part of the t2 response (X fibres) there is also a similarity in time course of loss of response to that following enucleation. Both for the enucleated and the pressure-blocked cat the t2 response fails about 1 day before the t1 response. This is in apparent disagreement with the morphological findings in the literature, confirmed here, indicating an earlier degeneration of the larger fibres. The post-synaptic response in the lateral geniculate nucleus to the t1 input (the r1 response) also fails about 1 day before the t1 response. In the visual cortex the loss of the r1 response reveals more clearly than is normally possible an r2 response, the response of the X optic radiation fibres. The response in the optic nerve or tract to a bright flash of light is dominated by the response of the Y fibres. When these are blocked the response is greatly reduced.

Action Potentials↗
PubMed1985

Synaptic delay in the lateral geniculate nucleus of the cat.

Unitary, presynaptic spike potentials were observed in single cell recordings from the dorsal lateral geniculate nucleus of the cat. In 11 cells, spontaneous S potentials (extracellularly recorded excitatory postsynaptic potentials) were preceded at a fixed interval by a small wave (the 'T' potential). In another 14 cells, a T potential, although not detected in single traces, was revealed by averaging 20-100 samples synchronized to the peak of the S potential. Provided the field response was not too large a T potential could also be detected in the response to a stimulus to the optic nerve. The T potential would appear to be the spike potential of the afferent optic axon which is excitatory to the geniculate cell because it precedes the S potential at a very exact interval and also follows the corresponding retinal ganglion cell spike at a very exact interval and because the interval between T potential and S potential is reversibly decreased by cooling with a temperature coefficient characteristic of synapses. T potentials ranged in amplitude from 8 to 134 microV and were all predominantly positive-going suggesting a failure of the nerve impulse to invade fully the terminals of the optic nerve. The time from the positive peak of the T potential to the start of the S potentials was taken as a good measure of the synaptic delay. The T-S interval averaged 0.29 ms (+/- 0.045 ms S.D.).

Action Potentials↗
PubMed1985

The absorption of beta-adrenoceptor antagonists in rat in-situ small intestine; the effect of lipophilicity.

Intestinal absorption characteristics of eleven beta-adrenoceptor antagonists were measured by monitoring their disappearance from in-situ intestinal loops in the anaesthetized rat. All have basic pKa values of around 9.5 (with the exception of sotalol) but show a wide range of lipophilic character (octanol-water log P values from -0.79 to 3.65). The results show two types of absorption behaviour, indicating different mechanisms for 'hydrophilic' and 'lipophilic' beta-adrenoceptor antagonists. The four most hydrophilic molecules (sotalol, atenolol, nadolol and practolol) show virtually identical absorption rate constants. Absorption is slow and relative rates in jejunum (mean pH 6.5) and ileum (mean pH 7.3) are not consistent with pH-partition (jejunum greater than or equal to ileum). The more lipophilic members of the series (pindolol, timolol, metoprolol, oxprenolol, alprenolol and propranolol) are all absorbed much more rapidly. Absorption rate constant rises rapidly with log P and the expected pH effects are seen (ileum greater than jejunum). Acebutolol shows anomalously slow absorption for its log P value.

Adrenergic beta-Antagonists↗
PubMed1985

Selective block of Y optic nerve fibres in the cat and the occurrence of inhibition in the lateral geniculate nucleus.

A method of selectively blocking the larger nerve fibres in the optic nerve of the cat is described. The optic nerve is compressed between a small balloon and the inside of a small metal cylinder. The block is monitored by stimulating and recording on opposite sides of the blocked region. The t1 (Y) response can be eliminated usually with some loss of the t2 (X) response. Stimulation of the blocked optic nerve initially excites certain cells (r2 or X) in the dorsal lateral geniculate nucleus (d.l.g.n.) but this is followed by an inhibition of both r1 (Y) and r2 (X) cells. This inhibition is similar in time course to that produced by stimulation of t1 fibres, suggesting that the effect may be mediated via a similar mechanism. The effect is present in a preparation in which all t1 fibres have degenerated, removing the possibility that it might have been due to inadvertent stimulation of t1 fibres. Experiments on a small number of r2 (X) d.l.g.n. cells have confirmed the inhibitory effect of stimulation of the smaller optic nerve fibres on X cells.

Action Potentials↗
PubMed1983

Uptake of horseradish peroxidase by axons of passage and its modification by poly-L-ornithine and dimethylsulphoxide.

It has been shown that transected axons of passage in the optic tract can take up horseradish peroxidase (HRP) and transport it back to the cell bodies. This effect is considerably reduced if the HRP is injected from a small-tipped micropipette 6-12 h after insertion into the injection site. HRP is not taken up by uninjured axons of passage. The use of poly-L-ornithine and dimethylsulphoxide dramatically increases the numbers of labeled cells. These numbers are undiminished after 6-12 h waiting periods. From this and from calculation it is clear that much of this effect must occur via uninjured axons. These substances should not be used in any situation where it is important not to label axons of passage. If other HRP conjugates and additives have the same effect as those described here, the results of experiments with these substances should be interpreted with caution.

Animals↗
PubMed1981

An unusual case of Bjork-Shiley mitral valve dysfunction corrected nonsurgically.

A case of Bjork-Shiley mitral valve dysfunction is presented. The patient has not responded to anticoagulant therapy and had hypotension, dyspnea, chest pain, and a pulse deficit but normal sinus rhythm. Simultaneous echocardiogram, ECG, and arterial pulse tracing were used as noninvasive means of monitoring. Nonsurgical correction of a clinical emergency restored the patient to prior normal baseline cardiovascular function. This case illustrates the possibility of restoring normal prosthetic function by supporting the patient medically while undertaking diagnostic testing and arranging surgical intervention. To our knowledge, this is the first reported case of a malfunctioning Bjork-Shiley mitral valve corrected without surgery.

Aspirin↗
PubMed1978

The effect of Mycoplasma contamination on the in vitro assay of pyruvate dehydrogenase activity in cultured fibroblasts.

Cultured fibroblasts contaminated with mycoplasma were shown to have increased in levels of apparent pyruvate dehydrogenase and pyruvate dehydrogenase complex enzyme activity. The apparent pyruvate dehydrogenase specific activity was about 1000-fold greater in cultured Mycoplasma pneumoniae than in cultured fibroblasts. Several acid hydrolytic enzyme activities were also shown to be present in M. pneumoniae though a lower apparent specific activity than in cultured fibroblasts.

Cell Line↗
PubMed1978

Effects of induced hyperopia.

Hyperopia of 1.00, 1.50, and 2.00 D was induced in 42 subjects by means of concave lenses. A significant decrease in performance on a standard intelligence test occurred with the highest-power lenses. Symptoms induced indicate that the results are applicable to hyperopia. Prescriptions and vision screening criteria for hyperopia are indicated.

Adolescent↗