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G S Thomas

Publications and source records attributed to G S Thomas.

16 recordsLinked to original sources
PubMed1995

Metabolic and ventilatory adjustments and tolerance of the bat Pteropus poliocephalus to acute hypoxic stress.

We have investigated the maximum tolerance and the ventilatory responses of a bat, P. poliocephalus (PP), to normobaric hypoxic stress. PP can tolerate inspired PO2s (PiO2) down to 30 torr. This bat is one of the most hypoxia-tolerant non-hibernating species of mammals known, and has a tolerance which lies within the range of PiO2s reported for different birds. Unlike most mammals in its size range, PP maintains its normoxic oxygen consumption rate even in deep hypoxia. The maximum hypoxic ventilatory response (HVR), the air convection requirement (Vi/MO2), and the lung oxygen extraction (EL) ability of PP in deep hypoxia are all greater than those of other mammals. These and other data indicate that PP has a superior mammalian tolerance for hypocapnia. The magnitudes of both the V1/MO2 and the EL value of PP fall between those reported for Pekin ducks at corresponding PiO2s, and are inferior to the maximum capabilities of bar-headed geese. Thus, the tolerance and ventilatory adjustments of PP to deep hypoxia are intermediate between those of typical non-flying mammals and the most tolerant avian species, and suggest that at least some of this bat's respiratory adaptations for flight may serve as preadaptations for withstanding acute hypoxic stress.

Acute Disease↗
PubMed1991

High-dose applications of gadolinium chelates in magnetic resonance imaging.

Administration of gadolinium chelates at doses greater than 0.1 mmol/kg IV can potentially improve both lesion detection and the assessment of tissue perfusion. Preliminary results are presented in clinical patients and two animal models. In human intracranial metastatic disease, administration of 0.3 (cumulative dose) mmol/kg gadoteridol (Gd HP-DO3A) has permitted detection of additional lesions not visualized at 0.1 mmol/kg. In a rabbit model of focal liver disease, 0.5 mmol/kg IV provided superior enhancement of both normal parenchyma and lesion rim compared to doses of 0.25 and 0.1. Dynamic imaging (T1-weighted turbo-FLASH) immediately following bolus injection of 0.5 mmol/kg permitted direct visualization (on unsubtracted images) of an acute perfusion defect in the cat brain not visible on conventional T1- and T2-weighted scans.

Animals↗
PubMed1990

31P spectroscopy in experimental embolic stroke: correlation with infarct size.

Serial 31P nuclear magnetic resonance spectra were acquired from the brain in 19 rats following microsphere embolization of the right internal carotid artery. The brains were sectioned and stained with 2,3,5-triphenyltetrazoline chloride 6 h post-embolization to visualize infarcted areas. There was a narrow dosage range for the effect of embolism measured by maximum decline in pH at 20 min, mortality, and infarct size. This narrow range effect may be due to occlusion of collateral channels by the 16 micron microspheres. There was a strong correlation between decline in pH at 20 min post-embolization and infarct size (r2 = 0.76); this decline was the best early marker for eventual infarct in our study. This animal model for macroscopically heterogenous brain ischemia may be useful for the evaluation of therapeutic interventions in stroke, and as an aid in the interpretation of phosphorus spectra from mixed volumes of ischemic and non-ischemic brain.

Adenosine Triphosphate↗
PubMed1990

Exercise electrophysiology testing: the effect of exercise on the induction of ventricular arrhythmias by programmed ventricular stimulation.

In order to assess the effect of acute, reversible myocardial ischemia on the outcome of programmed ventricular stimulation (PVS), ventricular stimulation was performed at rest, during exercise, and during recovery in 10 patients with coronary artery disease. Of these ten patients, four were tested while off antiarrhythmic drugs and six were tested on antiarrhythmic drug therapy. Nine of the ten patients developed acute myocardial ischemia during exercise PVS. However, in only two of these ten patients ventricular arrhythmia could be induced by PVS, one during exercise and one during recovery.

Aged↗
PubMed1983

Exercise and coronary heart disease.

The epidemiologic evidence examining the effect of physical activity on the development and course of coronary heart disease is reviewed. This evidence indicates that physically active individuals have a lower incidence of myocardial infarction and mortality from coronary disease. While there is no documentation that an exercise program following myocardial infarction will significantly increase patient survival, exercise does increase functional capacity, lessen angina pectoris, and improve self-image in patients with coronary heart disease. Possible mechanisms for the beneficial effects of exercise are considered.

Animals↗
PubMed1978

Aggression increase and water competition decrease in squirrel monkeys given physostigmine injections.

Six adult squirrel monkeys (Samiri sciureus) were tested in pairs for social dominance in a water competition task. Dominance was defined by two methods: (1) number and direction of aggressive responses, and (2) successful water competition as assessed by latency to the water bottle, latency to accumulate 15 seconds of drinking, and total drinking duration. Monkeys were assigned to pairs on a "round robin" basis so that each monkey was paired with all other monkeys under control, saline, and three levels of physostigmine sulfate (6.25, 12.5, and 25.0 microgram/kg). Under drug conditions only one member of each pair was drugged. The 12.5 microgram/kg dose of physostigmine resulted in a significant increase in aggressive responses. Both drinking duration and general motor activity decreased with increasing dose level of drug. It was also noted that the non-drugged partners of drugged monkeys accumulated 15 seconds of drinking faster and drank more at the 25 and 12.5 microgram/kg dose levels than under control and saline conditions. Physostigmine resulted in an increase in one measure of social dominance and a decrease in the other.

Aggression↗
PubMedDate not supplied

Clinical comparison of three-dimensional MP-RAGE and FLASH techniques for MR imaging of the head.

Three-dimensional (3D) MP-RAGE (magnetization-prepared rapid gradient-echo) imaging was evaluated as a high-resolution 3D T1-weighted brain imaging technique for patients with suspected neurologic disease. Fourteen patients were studied. In five, 3D MP-RAGE images were compared with 3D FLASH (fast low-angle shot) images. Signal difference--to-noise ratios and T1 contrast were not statistically different for 3D MP-RAGE images as opposed to 3D FLASH images. Advantages intrinsic to the application of 3D MP-RAGE sequences include decreased imaging time and decreased motion artifact. With this technique, it is possible to perform a relatively motion-insensitive, T1-weighted screening brain study with voxel resolution of 1.0 x 1.4 x 2.0 mm or smaller, in an imaging time of 5.9 minutes or less--permitting offline (poststudy) reconstruction of high-resolution images in any desired plane.

Brain↗
PubMedDate not supplied

High-dose gadoteridol in MR imaging of intracranial neoplasms.

Twelve patients with a high suspicion of brain metastases by previous clinical or radiologic examinations were studied in a phase III investigation with magnetic resonance (MR) imaging at 1.5 T after a bolus intravenous injection of 0.1 mmol/kg gadoteridol followed at 30 minutes by a second bolus injection of 0.2 mmol/kg gadoteridol. All lesions were best demonstrated (showed greatest enhancement) at the 0.3-mmol/kg (cumulative) dose, with image analysis confirming signal intensity enhancement in the majority of cases after the second gadoteridol injection. More lesions were detected with the 0.3-mmol/kg dose than with the 0.1-mmol/kg dose, and more lesions were detected with the 0.1-mmol/kg dose than on precontrast images. In this limited clinical trial, high-dose gadoteridol injection (0.3-mmol/kg cumulative dose) provided improved lesion detection on MR images specifically in intracranial metastatic disease.

Adult↗
PubMedDate not supplied

Nuclear cardiology in a managed care environment.

Health maintenance organizations (HMO) and nuclear cardiology represent mutual threats and mutual opportunities for each other. On the one hand, nuclear cardiology represents a cost center with HMOs exerting tremendous financial pressure on nuclear cardiology programs. On the other hand, nuclear cardiology can act as a sage gatekeeper to the cardiac catheterization laboratory and help HMOs effectively control the health care of an increasing percentage of the population. Through the process of negotiation, of determining each other's needs, an accommodation can take place between the two. The ability to correlate scan results with coronary angiography provides individual nuclear cardiology programs with the opportunity to demonstrate their accuracy. A Nuclear Cardiology Report Card based on these data can be developed for use, with HMOs creating the opportunity to compete not only on price but also on value. Carved out capitation rates for nuclear cardiology can be estimated on the basis of actual experience with an HMO population and by extrapolation from test frequency of the U.S. population. The financial disincentives of capitation and of managed care challenge the physician-patient relationship. Advocacy of the role of nuclear cardiology and an understanding of negotiation strategies can aid nuclear cardiologists in their attempts to provide quality care with commensurate compensation.

Capitation Fee↗
PubMedDate not supplied

Treadmill exercise during adenosine infusion is safe, results in fewer adverse reactions, and improves myocardial perfusion image quality.

BACKGROUND: Combining low-level treadmill exercise with adenosine infusion may result in fewer bradyarrhythmic complications by increasing sympathetic tone and may improve myocardial perfusion image quality by decreasing background activity. METHODS: Patients referred for outpatient pharmacologic stress myocardial perfusion imaging performed simultaneous treadmill exercise (mean 2.2 metabolic equivalents) throughout 6-minute adenosine infusion (adenosine-exercise n = 507). Patients unable to exercise and those with left bundle branch block received adenosine infusion alone (adenosine-nonexercise n = 286). Adverse reaction data were collected on all patients and compared by sex. Background-to-target activity was calculated in a blinded fashion on 200 randomly selected patients. RESULTS: During the period from April 1996 to December 1998, 507 patients (64%) underwent adenosine-exercise testing, whereas 286 (36%) underwent adenosine-nonexercise testing. Hypotensive and arrhythmic (atrioventricular block, sinus bradycardia, and new onset atrial fibrillation or flutter) adverse reactions occurred less often during adenosine-exercise than during adenosine-nonexercise. Neither death nor myocardial infarction occurred in either group. In the adenosine-exercise group, 2.8% of patients experienced an adverse reaction versus 5.6% of the adenosine-nonexercise group (P = .04). The reduction in adverse reactions occurred in both men and women, although women had significantly more adverse reactions than men (5.7% vs 1.8%, P = .004). Liver/heart and gut/heart ratios were lower in the adenosine-exercise group (1.05+/-0.42 vs. 1.21+/-0.55 , P = .01; 0.61+/-0.21 vs. 0.69+/-0.24, P = .03, respectively). CONCLUSIONS: Compared with adenosine infusion alone, combining low-level treadmill exercise with adenosine in outpatients is safe, better tolerated, and improves image quality. Women were more likely to experience adverse reactions than men.

Adenosine↗