PubMed Health⌕ Search

Biomedical subjects

M Guthrie

Publications and source records attributed to M Guthrie.

At least 19 recordsLinked to original sources
PubMed2004

Formation and structure of a dense octahedral glass.

We have performed in situ x-ray and neutron-diffraction measurements, and molecular dynamics simulations, of GeO2, an archetypal network-forming glass under pressure. Below 5 GPa, additional atoms encroaching on the first tetrahedral shell are seen to be a precursor of local coordination change. Between 6 and 10 GPa, we observe structures with a constant average coordination of approximately 5, indicating a new metastable, intermediate form of the glass. At 15 GPa, the structure of a fully octahedral glass has been measured. This structure is not retained upon decompression and, therefore, must be studied in situ.

Journal Article↗
PubMed2002

Structure of high-density amorphous ice under pressure.

We report in situ neutron diffraction studies of high-density amorphous ice (HDA) at 100 K at pressures up to 2.2 GPa. We find that the compression is achieved by a strong contraction ( approximately 20%) of the second neighbor coordination shell, so that at 2.2 GPa it closely approaches the first coordination shell, which itself remains intact in both structure and size. The hydrogen bond orientations suggest an absence of hydrogen bonding between first and second shells and that HDA has increasingly interpenetrating hydrogen bond networks under pressure.

Journal Article↗
PubMed2001

Transition from cage clathrate to filled ice: the structure of methane hydrate III.

The structure of a new methane hydrate has been solved at 3 GPa from neutron and x-ray powder diffraction data. It is a dihydrate in which a 3D H-bonded network of water molecules forms channels surrounding the methane molecules. The network is closely related to that of ice-Ih and the methane-water system appears to be the first in which a cage clathrate hydrate is transformed into an ice-related hydrate (a "filled ice").

Journal Article↗
PubMed2001

Stable methane hydrate above 2 GPa and the source of Titan's atmospheric methane.

Methane hydrate is thought to have been the dominant methane-containing phase in the nebula from which Saturn, Uranus, Neptune and their major moons formed. It accordingly plays an important role in formation models of Titan, Saturn's largest moon. Current understanding assumes that methane hydrate dissociates into ice and free methane in the pressure range 1-2 GPa (10-20 kbar), consistent with some theoretical and experimental studies. But such pressure-induced dissociation would have led to the early loss of methane from Titan's interior to its atmosphere, where it would rapidly have been destroyed by photochemical processes. This is difficult to reconcile with the observed presence of significant amounts of methane in Titan's present atmosphere. Here we report neutron and synchrotron X-ray diffraction studies that determine the thermodynamic behaviour of methane hydrate at pressures up to 10 GPa. We find structural transitions at about 1 and 2 GPa to new hydrate phases which remain stable to at least 10 GPa. This implies that the methane in the primordial core of Titan remained in stable hydrate phases throughout differentiation, eventually forming a layer of methane clathrate approximately 100 km thick within the ice mantle. This layer is a plausible source for the continuing replenishment of Titan's atmospheric methane.

Journal Article↗
PubMed1995

Validity of clinical measures of shoulder subluxation in adults with poststroke hemiplegia.

OBJECTIVES: Shoulder subluxation after cerebrovascular accident has been associated with chronic pain, orthopedic complications, peripheral nerve damage, and autonomic dysfunction. Clinical diagnosis and gradation of subluxation is problematic due to the lack of precision in frequently used measures. The objective of this study was to assess the validity of clinical techniques used to assess inferior subluxation of the hemiplegic shoulder by comparing these techniques with radiographic measurement. METHOD: In 20 male subjects with hemiplegia, the presence, type, and degree of subluxation was assessed with three clinical measures: palpation, arm length discrepancy, and thermoplastic jig measurement. Anterior-posterior X rays of the hemiplegic shoulder were taken after clinical examination. RESULTS: Spearman rank correlation coefficients between the X rays and the three clinical measures were relatively low. Palpation had the highest correlation (rs = .76), followed by arm length discrepancy (rs = .46), and thermoplastic jig measurement (rs = .42). CONCLUSION: These findings provide cautious optimism about using these clinical measures to identify subluxation. Although detection was best with palpation, the likely inability to determine clinical overcorrecting of subluxation makes use of palpation alone suspect. Improved techniques of arm length measurement may provide a solution to this problem. These findings further necessitate that improved procedures for clinical assessment of subluxation be developed.

Adult↗
PubMed1993

Effects of erythropoietin on strength and functional status of patients on hemodialysis.

The strength, endurance, and functional status of 15 anemic (HCT 21.2 +/- 4.6) hemodialysis patients was quantified prior to the administration of erythropoietin (epoetin) and after the anemia was partially corrected (HCT 35.4 +/- 2.3). Subjects showed significant increases in strength, measured isometrically (p < .01) and isokinetically (p < .01 at four of five speeds). They also demonstrated improved endurance and rated their functional ability higher. Anemia contributes to significant debilitation in hemodialysis patients and, when reversed with epoetin therapy, results in significantly improved muscle function and endurance.

Anemia↗
PubMed1990

Recombinant erythropoietin improves exercise capacity in anemic hemodialysis patients.

The objective of this study was to quantitate the improvement in exercise capacity produced in anemic chronic hemodialysis (HD) patients after correction of their anemia with recombinant human erythropoietin (rHuEPO). The maximal exercise capacity and quadriceps strength of 19 anemic HD patients was tested before and after correction of the anemia with rHuEPO. A progressive work exercise protocol (PWET) on a cycle ergometer was used to compare measurements of maximal oxygen uptake (VO2max), maximal heart rate, and subjective assessment of fatigue during the test. Measurements of quadriceps strength were performed before the cycle ergometer studies. At baseline, all patients had reduced VO2max (15.3 +/- 5.4 mL/kg/min) and maximal exercise heart rates (138.5 +/- 23.9 beats/min). rHuEPO increased the mean hematocrit from 21.2% to 35%, and this was associated with a 17% increase (P less than 0.0005) in the VO2max. At any specified work load, rHuEPO treatment decreased heart rate, minute ventilation, and the subjective perception of fatigue. Both isometric and isokinetic measurements of quadriceps strength were improved following administration of rHuEPO. The maximal exercise heart rate was decreased in comparison to the baseline measurements (P less than 0.04), suggesting that in contrast to normal subjects, HD patients stop exercise before oxygen transport limitations are reached. In this unselected group of chronic HD patients, rHuEPO produced clinically significant improvements in both aerobic exercise capacity and isometric and isokinetic quadriceps strength. The improvement in aerobic capacity was substantially less than would have been expected from the correction of a comparable degree of anemia in non-HD patients. None of the 19 treated patients attained the exercise performance level predicted for a sedentary normal subject.

Adult↗
PubMed1984

Cardiac injury in myocarditis induced by Coxsackievirus group B, type 3 in Balb/c mice is mediated by Lyt 2 + cytolytic lymphocytes.

Male Balb/c mice inoculated with a heart-adapted variant of Coxsackievirus, group B, type 3 (CVB3) develop severe myocarditis 7 days later. The lesions are characterized by mononuclear cell inflammation and myocyte necrosis. Infected T-lymphocyte-deficient mice show either minimal or no cardiac injury, although virus concentrations in the hearts of T-cell-deficient and -sufficient animals are similar. Adoptive transfer of 2 X 10(6) CVB3 immune Thy 1+ cells into CVB3-infected T-cell-deficient mice effectively restored myocarditis to levels observed in intact animals. Similar reconstitution with immune Ig+ cells or serum resulted in only a minimal increase in cardiac injury. To determine whether T-lymphocyte-dependent humoral or cellular immunity was responsible for myocarditis. T lymphocytes were obtained from Balb/c mice 6 days after infection with CVB3, separated into Lyt 1+2- (helper) and Lyt 1-2+ (cytolytic/suppressor) cell populations, and 2 X 10(6) of the enriched helper and cytolytic cells were adoptively transfused into infected T-cell-deficient recipients. Animals receiving the immune Lyt2+ cells developed severe myocarditis, had cytolytic T lymphocytes to both CVB3-infected and uninfected myocytes, but lacked a detectable IgG antibody response. Recipients of the Lyt 1+ cells failed to develop either myocarditis or cytolytic T cells but had normal serum IgG antibody titers to the virus. These results demonstrate that cardiac myocarditis is the product of cellular immune mechanisms.

Animals↗
PubMedDate not supplied

When does metoclopramide facilitate transpyloric intubation?

Postpyloric feeding probably reduces the incidence of tracheobronchial aspiration and improves feeding tolerance. However, duodenal intubation is often unsuccessful in critically ill patients due to gastric atony. Metoclopramide improves gastric emptying. In a pilot study, 12 adult patients were administered 10 to 20 mg of intravenous metoclopramide after weighted nasal feeding tubes had failed to spontaneously pass distal to the pylorus. In no patient did metoclopramide induce transpyloric passage of the tube. A randomized prospective study involving 10 adult patients was conducted to examine the effect of preinsertion intravenous metoclopramide on transpyloric intubation. All patients had failed to achieve spontaneous duodenal intubation. Five patients received 20 mg of metoclopramide 10 min prior to nasal insertion of a weighed feeding tube. Five control patients received no premedication. Four metoclopramide patients achieved duodenal intubation immediately. In none of the control patients did transpyloric intubation occur (p = 0.048). Metoclopramide, administered after nasogastric intubation, is ineffective in promoting transpyloric advancement of feeding tubes. There is a significant increase in transpyloric intubation when metoclopramide is administered prior to tube insertion.

Adult↗