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Biomedical subjects

D A Thompson

Publications and source records attributed to D A Thompson.

At least 127 records · Page 7Linked to original sources
PubMed1989

The effect of 0.5% thymoxamine on the pattern-onset electroretinogram.

Thymoxamine constricts the pupil without significant effect on accommodation and was used in this study because of the extreme sensitivity of the pattern electroretinogram (PERG) to defocus at high spatial frequencies. Pilocarpine, used in previous studies, can cause an unpredictable spasm of accommodation. A reduction in pupil size has two effects on the PERG due to illuminance and optical degradation. Illuminance differences can be compensated by neutral density filters. This allows the effects of optical degradation on the PERG to be examined under conditions of constant adaptation. Our studies on a group of 10 subjects have shown the PERG to be proportional to contrast. As contrast degradation is reduced with a smaller pupil, a larger PERG amplitude is predicted. However the tuning of neural elements under constant adaptation should not alter. Pattern onset ERGs were recorded from a further 10 subjects in response to checkerboards of various spatial frequencies under two conditions, a) with pupils moised by thymoxamine hydrochloride 0.5% and b) with natural pupils. Adaptation level was equated by a 0.4 neutral density filter before the natural pupils. The group-averaged PERGs were analyzed into retinal illuminance and pattern-specific responses. A paired t-test showed the pattern-onset ERG amplitudes to be significantly different in the two conditions, but the computed pattern-specific responses were virtually identical. These results therefore support the theory and method used for the extraction of the pattern-specific response.

Contrast Sensitivity↗
PubMed1989

Prostaglandin-induced gastric mucosal protection against stress injury. Absence of a relationship to tissue glutathione levels.

The effects of 16,16 dimethyl prostaglandin E2 (dmPGE2) on the gastric mucosa of rats subjected to 1, 2, and 24 hours of water immersion stress were examined histologically. Results indicated a time-related increase in the total percentage length of glandular mucosa injured in normal saline (NS) pretreated rats that was significantly attenuated by subcutaneous dmPGE2 pretreatment (5 micrograms/kg) after 1 hour (46.0 +/- 12.9 vs. 16.8 +/- 2.3; p less than 0.005), 2 hours (45.4 +/- 1.0 vs. 13.8 +/- 2.2; p less than 0.001), and 24 hours (93.1 +/- 2.6 vs. 65.1 +/- 7.0; p less than 0.005) of water immersion stress. Moreover, dmPGE2 essentially prevented the occurrence of deep, glandular injury that, in NS controls, involved approximately 13% and 26% of the mucosal surface after 2 and 24 hours of immersion stress, respectively. Additionally, tissue levels of glutathione (mumole/g weight of wet tissue) were measured to determine its role under such conditions. After 1 hour of stress, there were no differences in glutathione levels between NS or dmPGE2 pretreated animals and fasted controls. After 2 and 24 hours of stress, there were likewise no differences in glutathione levels between NS and dmPGE2 pretreated groups, although levels in both groups were significantly decreased from fasted controls by approximately 30% at 2 hours and 37-47% after 24 hours. These histologic and biochemical data indicate that dmPGE2 attenuates both the extent and depth of glandular mucosal injury and does so in a manner unrelated to alterations in glutathione levels in gastric epithelium.

16,16-Dimethylprostaglandin E2↗
PubMed1989

A review of the clinical applications of the pattern electroretinogram.

The pattern electroretinogram (PERG) has recently been introduced as a clinical procedure. It has been thought by many to represent activity of the retinal ganglion cells, although this is still a matter of contention. The exciting prospect of a selective test of ganglion cell function led to the application of the PERG in a variety of ophthalmological conditions. In the course of these investigations the PERG was found to be diminished in cases of maculopathy, optic atrophy, optic neuritis, toxic optic neuropathy, neurotransmitter disorders, glaucoma and ocular hypertension and in retinal vascular disorders such as diabetes. It was also affected in some cases of amblyopia. This paper briefly describes the techniques used to record the PERG and reviews current literature pertaining to its clinical application.

Amblyopia↗
PubMed1988

Expression of a bovine rhodopsin gene in Xenopus oocytes: demonstration of light-dependent ionic currents.

Xenopus oocytes express a gene encoding bovine rhodopsin as well as its SP6 RNA polymerase-derived transcripts and total retinal mRNA. The opsin produced is in unglycosylated (30 kDa) and two glycosylated (35 kDa and 41 kDa) forms. Incubation of the cells expressing the above proteins with 11-cis-retinal generates rhodopsin, which was purified by immunoaffinity chromatography. The purified protein shows the expected UV/visible absorption spectrum and characteristic light-dependent activation of the rod outer segment GTP binding protein. Oocytes expressing rhodopsin exhibit light-dependent ionic currents that are detected by voltage-clamp techniques.

Animals↗
PubMed1988

Effect of a rotating bed on the incidence of pulmonary complications in critically ill patients.

The risk of nosocomial pneumonia and atelectasis is high among critically ill immobilized patients. We hypothesized that continuous turning on the kinetic treatment table would reduce their incidence. Sixty-five critically ill patients, immobilized because of head injury or traction, were prospectively randomized for treatment in a conventional bed (n = 38) or the kinetic treatment table (n = 27). Patients were well matched for baseline demographic and pulmonary risk factors. Patients in the conventional bed group had a higher incidence of cigarette smoking. The combined incidence of significant atelectasis or pneumonia was higher (66%) in the conventional vs. kinetic treatment table (33%) groups (p less than .01). Atelectasis, pneumonia, adult respiratory distress syndrome, requirements for ventilator treatment, for PEEP, and for an FIO2 greater than 0.50 were not significantly different, but tended to be higher in the control group. Survival and the incidence of decubitus ulcers were similar.

Adult↗
PubMed1988

Urgent thoracotomy for pulmonary or tracheobronchial injury.

Three hundred eighty-eight of 7,283 (5.3%) admitted trauma patients underwent urgent thoracotomy. In 61 patients (15.7%), pulmonary or tracheobronchial injury prompted thoracotomy (11, blunt; 50, penetrating). Pulmonary hemorrhage necessitated thoracotomy in 54 patients (88.5%); tracheobronchial injury in five patients (8.2%). The mortality was 27.9%. Nine patients (14.8%) underwent pneumonectomy: eight died of intractable hemorrhagic shock during thoracotomy despite rapid control of pulmonary hemorrhage: one died of sepsis. Eleven patients (18.0%) underwent lobectomy: six (54.5%) died of concomitant injuries. Thirty-six patients (59.0%) underwent pneumonorrhaphy: one died of concomitant injuries. Five (8.2%) patients underwent tracheobronchial repair: one died of concomitant injuries. Pneumonectomy was uniformly fatal and should be a procedure of last resort in the treatment of pulmonary injury, as lobectomy and pneumonorraphy are better tolerated by these critically ill patients.

Bronchi↗
PubMed1988

Acute effects of exercise intensity on appetite in young men.

This study investigated the acute effects of two exercise intensities on three measures of appetite. Fifteen, 12-h-fasted, college-age males completed three experimental sessions in counterbalanced orders: no-exercise control; cycle exercise performed at 35% VO2max; and cycle exercise performed at 68% VO2max. Both exercise conditions involved a total energy expenditure of 4.1 kcal.kg-1 body weight. Dependent measures were intermittent hunger and sucrose palatability ratings, and food intake at a test meal given approximately 1 h post-exercise. Hunger was briefly suppressed in the high-intensity exercise condition compared to low-intensity exercise and control, while intake of liquid-source kilocalories and carbohydrates was higher after the exercise sessions. Total caloric intake remained stable. Sucrose palatability did not vary across sessions. Intensity is inferred to be an important variable mediating exercise effects on appetite. Relations between appetite measures are discussed, and validity of sucrose palatability ratings and common methods of measuring food intake questioned. Exercise, while not decreasing food intake, does not appear to increase it, and the benefits of exercise for body fat reduction are not immediately offset by compensatory caloric intake.

Adult↗
PubMed1987

Computation of the luminance and pattern components of the bar pattern electroretinogram.

Pattern onset electroretinograms (PERGs) were recorded from four normal subjects. Square-wave gratings of 75% contrast were presented in three approximately contiguous, concentric zones of outer angular radius, 5.1 degrees, 12.6 degrees, and 23.6 degrees. The zones were calculated to give equal numbers of ganglion cell receptive fields. The recorded PERGs were considered to include luminance and pattern components which have low and bandpass spatial tuning functions respectively. These components combine in the PERG to produce a broad spatial tuning characteristic. The amplitude of PERGs in response to low spatial frequency stimuli is widely reported to be linearly related to contrast. The retinal illuminance response at every spatial frequency was computed from the eye's modulation transfer function. This function characterizes the reduction in contrast that occurs because of optical degradation. The computed retinal illuminance response was subtracted from the PERG waveform and a pattern-specific response was revealed. The latter had a highly tuned bandpass function which peaked at higher spatial frequencies than the PERG at corresponding peripheral angles.

Electroretinography↗
PubMed1987

The effects of image degradation on retinal illuminance and pattern responses to checkerboard stimuli.

The contrast of a retinal image is less than that of the external stimulus owing to a process of optical degradation. Theoretical studies have shows that this affects the pattern and illuminance detectors of the retina differently and provides a new insight into the nature of contrast stimulation and the mechanisms responsible for the pattern electroretinogram. Consensus data on the optical transfer function of the eye are applied to the Fourier transform of the pattern stimulus and the retinal illuminance distribution is determined. The checkerboard image is shown to undergo substantial degradation for those check sizes used in experimental and clinical observations. Current concepts of contrast and modes of stimulation are examined and methods are described for quantifying the effects on stimulation of illuminance and pattern detectors. The findings are applied to experimental data on spatial tuning functions of electroretinograms elicited by checkerboard pattern stimulation. It is concluded that the signal predominantly originates from local illuminance, but that this can account for only part of the response with small check sizes. The remainder must be a highly selective response to spatial frequency. If the predicted degradation is accepted, a similar conclusion must be reached for many previously reported tuning functions of the pattern electroretinogram as well as to the present experiment on eight normal eyes.

Electroretinography↗
PubMed1987

An improved method for using the DTL fibre in electroretinography.

An improved method using DTL fibre for electroretinography is described. The DTL fibre is comfortable and easy to apply. Corneal anaesthesia is unnecessary. The DTL fiber does not interfere with the retinal image and has been used successfully to record both pattern and flash electroretinograms from subjects of all ages.

Electrodes↗
PubMed1987

Complementary components and local variations of the pattern electroretinogram.

Pattern electroretinograms have been presumed to arise from a combination of luminance and pattern detection activities. Since the responses at low spatial frequencies are linearly related to contrast and contain negligible pattern specific components, it is proposed that a retinal illuminance response for higher spatial frequencies can be computed from the optical transfer function of the eye. These computed responses are subtracted from pattern electroretinograms to reveal a pattern-specific response with a marked bandpass characteristic. The peak spatial frequency of the bandpass curve declines with increasing peripheral angle. For central vision, the peak amplitude of the pattern-specific response is larger than the retinal illuminance response, but, in the peripheral retina, the two responses are found to be almost equal. The possible origins of these signals are discussed, and it is concluded that the technique provides a method of obtaining separated illuminance and pattern responses from retinal regions having different properties of spatial selectivity.

Electroretinography↗
PubMed1986

Effects of 2-deoxy-D-glucose on food and water intake and body temperature in rats.

Comparisons between early daytime and early nighttime effects of 2-deoxy-D-glucose (2DG) injections on food and water intake and rectal temperature were made. Food intake was significantly enhanced by 2DG injections regardless of the phase of the light cycle. In the daytime, water intake was increased by a lower dose of 2DG (200 mg/kg, IP) but there was no further increase at a higher dose (400 mg/kg). At night, the lower dose of 2DG had no effect on water intake but the higher dose suppressed the water intake normally associated with feeding. Administration of 2DG reduced preprandial rectal temperature in a dose dependent fashion in both phases of the light cycle. However, preprandial rectal temperatures were decreased more at night than during the daytime after injection of the higher dose of 2DG. Therefore, 2DG-induced hypothermia is dependent on both the dose of 2DG injected and the phase of the light cycle in which glucoprivation is produced. Furthermore, below a certain level of body temperature, rats markedly reduced drinking behavior while maintaining but not increasing their feeding response to 2DG-induced glucoprivation. These results suggest that behaviors may be directed toward preservations of body temperature in preference to relief of hunger by eating and of thirst by drinking.

Animals↗
PubMed1986

Healing following meniscoplasty, eminectomy, and high condylectomy in the monkey temporomandibular joint.

The healing of meniscoplasty, eminectomy, and high condylectomy was studied in five Macaca fascicularis monkeys. After five months of healing, no discontinuity defects were found in any of the plicated menisci, and all recontoured bone surfaces had new soft tissue linings. Fibrous adhesions to the adjacent plicated meniscus developed in 62.5% of the recontoured bony surfaces.

Animals↗
PubMed1985

Plasma dihydroxyphenylglycol (DHPG) in the in vivo assessment of human neuronal norepinephrine metabolism.

We investigated the utility of deaminated norepinephrine (NE) metabolites in the study of human sympathetic nervous pathophysiology. Plasma levels of the NE metabolite dihydroxyphenylglycol (DHPG) appear to be related to intraneuronal NE stores. Plasma DHPG increases when sympathetic nervous activity or circulating NE increase and decreases when neuronal NE is depleted or neuronal NE reuptake is blocked. Changes in plasma dihydroxymandelic acid (DOMA) related less closely to changes in plasma NE. The coupling of measurements of plasma NE with its deaminated metabolites and DHPG may improve understanding of human NE metabolism and neuronal NE reuptake.

Glycols↗
PubMed1985

Gastrointestinal myoelectric activity in fasting and nonfasting canine models of ileus.

We studied postoperative gastrointestinal (GI) tract myoelectric activity (MEA) in three fasting and nonfasting models of ileus. After implantation of a gastric cannula and bipolar electrodes in the antrum, duodenum, proximal jejunum, midjejunum, terminal ileum, and ascending and descending colon, five dogs underwent ileus-producing laparotomies, including handling, in which the entire GI tract was manually crushed, obstruction, in which a distal ileal obstruction was created and released 24 hours later, and peritonitis, in which an ileal perforation was created and closed 24 hours later. The fasting 24-hour postoperative colonic MEA in the handling and obstruction models was significantly less than control levels but returned to normal by 48 hours. The nonfasting 24-hour postoperative duodenal and jejunal MEA in the obstruction model was significantly less than control levels. These significantly decreased MEA levels persisted for 72 hours. Nonfasting 24-hour postoperative ileal and colonic MEA in the peritonitis model was significantly greater than control levels and remained significantly elevated for 48 to 72 hours before returning to normal.

Action Potentials↗
PubMed1985

Pharmacological evidence for opioid and adrenergic mechanisms controlling growth hormone, prolactin, pancreatic polypeptide, and catecholamine levels in humans.

A group of 14 healthy subjects received 50 mg/kg body weight of 2 deoxy-D-glucose (2DG) IV in a 20-minute infusion to induce glucoprivation and stimulate the release of growth hormone (GH), prolactin (PRL), pancreatic polypeptide (hPP), and catecholamines. Six subjects having spontaneously high GH baseline levels (greater than 8 ng/mL) failed to mount a GH response to 2DG-induced glucoprivation while eight subjects having low GH baseline levels (less than 8 ng/mL) all had increases (greater than 10 ng/mL) of GH levels after 2DG (P less than 0.05). Baseline level of GH was a reliable predictor of subsequent GH response to 2DG. Administration of the alpha 2-adrenoreceptor agonist clonidine (0.5 mg po) reliably increased GH levels (P less than 0.05). Elevated GH levels following clonidine administration abolished GH responses to subsequently infused 2DG (P less than 0.05). While these data do not exclude the possibility of a short loop feedback control of GH secretion, they strongly suggest that the direction of the GH response to a provocative stimulus is determined by the antecedent GH level and that an alpha-adrenoreceptor mechanism is involved in such a biphasic modulation of GH levels. Clonidine administration significantly reduced total catecholamine, pancreatic polypeptide, and prolactin response to 2DG while opiate receptor blockade with naloxone (10 mg IV bolus followed by 2 mg/hr) did not affect catecholamine and pancreatic polypeptide response but did slightly attenuate the GH and PRL response to glucoprivation. We conclude that alpha adrenoreceptor mechanisms are of major importance while opiate receptor mechanisms are of relatively minor importance in modulating the effects of glucoprivation on sympathetic outflow and hPP, GH, and PRL levels.

Adolescent↗