PubMed Health⌕ Search

Biomedical subjects

J J Joyce

Publications and source records attributed to J J Joyce.

16 recordsLinked to original sources
PubMed2004

Direct observation of itinerant magnetism in the 5f-electron system UTe.

Our electron photoemission experiments demonstrate that the magnetization of the ferromagnetic state of UTe is proportional to the binding energy of the hybridized band centered around 50 meV below EF. This proportionality is direct evidence that the ferromagnetism of UTe is itinerant; i.e., the 5f electrons are not fully localized close to the atomic core. This mechanism of itinerant ferromagnetism differs from the traditional picture for 5f-electron magnetism in an essential and a novel way. We propose a simple model for the observed proportionality between the temperature dependence of the magnetization and the binding energy of the hybridized band near EF. This model allows us to estimate the effective magnetic interaction and to identify signatures of itinerant ferromagnetism in other materials.

Journal Article↗
PubMed2003

Photoemission and the electronic structure of PuCoGa5.

The electronic structure of the first Pu-based superconductor PuCoGa5 is explored using photoelectron spectroscopy and a novel theoretical scheme. Exceptional agreement between calculation and experiment defines a path forward for understanding the electronic structure aspects of Pu-based materials. The photoemission results show two separate regions of 5f electron spectral intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi level. The results for PuCoGa5 clearly indicate 5f electron behavior on the threshold between localized and itinerant. Comparisons to delta phase Pu metal show a broader framework for understanding the fundamental electronic properties of the Pu 5f levels in general within two configurations, one localized and one itinerant.

Journal Article↗
PubMed2000

Reliability of intraoperative transesophageal echocardiography during Tetralogy of Fallot repair.

UNLABELLED: There is limited information available concerning the accuracy of intraoperative transesophageal echocardiography (TEE) in predicting the extent of residual abnormalities after recovery from surgical repair of tetralogy of Fallot. Therefore, we investigated differences between the results of final postbypass TEE and those of postrecovery (mean, 6 days after surgery) transthoracic echocardiography in a total of 28 consecutive pediatric patients who underwent repair of tetralogy of Fallot with biplane or multiplane TEE. Both postbypass and postrecovery echocardiographic examinations included measurements of the right ventricle (RV)-main pulmonary artery (PA) and the main PA-branch PA peak instantaneous gradients, the degree of pulmonary valvar insufficiency, and color Doppler interrogation of the ventricular septum for residual defects. The RV-main PA gradient did not change significantly: 15 +/- 13 vs 18 +/- 14 mmHg (postbypass versus postrecovery, mean +/- SD). None of the patients had a decrease of > or = 10 mmHg; and only one patient had an increase of > or = 15 mmHg. There also was no change in the degree of pulmonary insufficiency (3.0 +/- 1.2 versus 3.1 +/- 1.1, using a scale of 0 to 4). Only one of the seven very small (< or = 2 mm) residual ventricular septal defects was not discovered during postbypass TEE. However, postrecovery transthoracic echocardiography detected significant branch PA stenosis (peak gradient, > or = 15 mmHg) in five patients (18%) that was not detected during postbypass TEE (P < 0.03). Of the branch PA stenoses that were not detected during TEE, four were left and one was right. CONCLUSIONS: Postbypass TEE after tetralogy of Fallot repair reliably predicts residual postrecovery hemodynamic abnormalities, except for branch PA stenosis.

Adolescent↗
PubMed1999

Mechanical function and substrate oxidation in the neonatal pig heart subjected to pacing-induced tachycardia.

Isolated, paced, isovolumically beating, neonatal pig ( approximately 2 days) hearts were perfused with a crystalloid solution during four periods: (1) baseline, HR 150 bpm; (2) HR-response curves, HR 150-360 bpm; (3) tachycardia, HR 300 bpm; and (4) posttachycardia, HR 150 bpm. Group I was studied with glucose (5. 5 mM) as the sole substrate. During baseline, left ventricular peak systolic pressure (PSP) averaged 123 +/- 7 mm Hg; end diastolic pressure (EDP), 4.9 +/- 0.4 mm Hg; relaxation time constant (Tau), 29.5 +/- 3.9 ms; glucose oxidation (14CO2 from [14C]glucose), 1535 +/- 96 nmol/min/gdry; and myocardial oxygen consumption (MVO2), 17.4 +/- 0.4 micromol/min/gdry. During tachycardia, PSP was 83 +/- 4* mm Hg; EDP, 9.8 +/- 1.7* mm Hg; Tau, 29.9 +/- 5.4 ms; glucose oxidation, 1921 +/- 136* nmol/min/gdry; and MVO2, 21.1 +/- 0.7* micromol/min/gdry (*different from baseline, P < 0.05). Posttachycardia, all parameters returned to near baseline values, except EDP, which remained elevated. Group II was studied with glucose (5.5 mM) and palmitate (0.55 mM). When compared to those of Group I, the mechanical responses were similar. During baseline, glucose oxidation was 149 +/- 24 nmol/min/gdry; palmitate oxidation, 343 +/- 28 nmol/min/gdry; and MVO2, 18.4 +/- 0.7 micromol/min/gdry. Both oxidation rates increased significantly during tachycardia, indicating aerobic metabolic reserve. Posttachycardia, glucose oxidation returned to baseline, but palmitate oxidation remained elevated, suggesting enhanced beta oxidation. Group III was perfused with glucose (5.5 mM) and pyruvate (5.5 mM), along with iodoacetate (50 microM) to inhibit glycolysis. PSP was maintained, but Tau (HRs >/= 270 bpm) and EDP (HRs >/= 180 bpm) markedly increased. In conclusion, for the isovolumically beating, neonatal pig heart stressed with tachycardia: (1) PSP decreases, EDP increases, and Tau remains relatively constant; (2) substrate oxidation is enhanced; and (3) glycolysis, rather than glucose oxidation, appears to be important for supporting ventricular diastolic function.

Animals↗
PubMed1986

Osteochondritis dissecans following Perthes' disease. Arthroscopic-operative treatment.

Osteochondritis dissecans is seen after skeletal maturity is reached in approximately 3% of adults who have had Legg-Calvé-Perthes disease as children. This diagnosis should be considered in the patient with hip pain, locking or catching, or early degenerative joint disease. In a series of 465 patients treated for Perthes' disease, 14 later developed osteochondritis dissecans. In asymptomatic hips, no treatment is indicated. In symptomatic patients, arthroscopic surgery of the hip has been employed to remove the loose osteocartilaginous fragment and to diagnose degenerative joint disease. Although removal of the osteocartilaginous fragment may not be indicated in patients with severe degenerative arthritis, an osteotomy to redirect the femoral head (valgus extension osteotomy) may be beneficial.

Adolescent↗
PubMed1975

The treatment of trochanteric hip fractures using a compression screw.

One hundred and four consecutive intertrochanteric hip fractures treated with a compression screw were reviewed. Despite death and lack of follow-up, the late results in sixty-two cases of fracture were analyzed. Three non-unions and one malunion gave the technique a failure rate of only 6.4 per cent. Twenty-two patients with both stable and unstable fractures were allowed to bear weight as early as tolerated, in an average of fourteen days. Early weight-bearing did not appear to compromise the end result.

Adult↗
PubMedDate not supplied

Performance of the chronically hypoxic young rabbit heart.

Hearts isolated from 30 rabbits, raised from birth to approximately 5 weeks of age under either hypoxic (FIO2, 0.10) or normoxic (FIO2, 0.21) conditions, underwent retrograde aortic perfusion using a non-recirculating, well-oxygenated crystalloid solution. The left ventricular end diastolic pressure was initially set at approximately 5 mmHg. Aerobic performance was studied by measuring peak systolic pressure (PSP), coronary flow, glucose oxidation, and oxygen consumption. Anaerobic function was assessed by determining time for the onset of contracture (TOC) in the presence of zero coronary flow. Hypoxic vs normoxic hearts (mean+/-SEM): heart rate, 197+/-6 vs 190+/-5 beats per minute; PSP, 136+/-4* vs 108+/-4 mmHg; dP/dt(max), 2294+/-125* vs 1549+/-144 mmHg/sec; relaxation time constant (Tau), 26.9+/-1.1* vs 41.6+/-4.8 msec; (-) dP/dt(max), 1422+/-43* vs 1001+/-63 mmHg/sec; coronary flow, 86.3+/-4.2* vs 59.9+/-2.9 ml/min/g(dry); glucose oxidation, 3511+/-118* vs 2979+/-233 nmol/min/g(dry); oxygen consumption, 28.2+/-1.4* vs 22.7+/-1.4 micromol/min/g(dry); and TOC, 11.8+/-1.2* vs 22.9+/-2.2 min (*p < 0.05). Hearts isolated from young rabbits, exposed to hypoxia from birth, exhibited enhanced ventricular systolic and diastolic mechanical function, elevated coronary flow, retained capacity for aerobic metabolism, and a shorter TOC compared to their normoxic counterparts.

Animals↗
PubMedDate not supplied

A direct comparison of right and left ventricular performance in the isolated neonatal pig heart.

A comparison is presented between the performance of the right ventricle (RV) and the left ventricle (LV) in neonatal hearts studied under conditions of volume loading and tachycardia. Isolated, atrially paced (150 or 300 bpm), isovolumically beating pig hearts (1-3 days of age) underwent retrograde aortic perfusion with a nonrecirculating, crystalloid solution. Ventricular pressure was assessed with saline-filled balloon catheters, which allowed separate loading of the RV or LV. Both ventricles showed an initial increase followed by a leveling off, but no decline, in peak systolic pressure (PSP) and +dP/dt(max) with volume loading up to an end-diastolic pressure (EDP) of 18 mmHg. The LV generated a higher PSP and +dP/dt(max) compared to the RV at equivalent pressure or volume preloads. However, the maximal systolic elastance (E(max)) was comparable for both ventricles. Although the RV demonstrated a greater compliance than the LV, the myocardial relaxation time constant (tau) was similar for both chambers at equivalent volume preloads (sarcomere stretch). Positive dP/dt(max) correlated closely and in the same linear fashion with -dP/dt(max) for both ventricles, indicating that the RV and LV exhibited similar contraction-relaxation coupling. Increasing the heart rate to 300 bpm decreased PSP, +dP/dt(max), and -dP/dt(max) and increased EDP for both ventricles, whereas E(max) and tau were not significantly altered. Thus, although there are differences between the functional properties of the neonatal RV and LV, there are also important similarities, especially with regard to myocardial relaxation.

Animals↗
PubMedDate not supplied

Estimation of right ventricular free-wall mass using two-dimensional echocardiography.

Echocardiographic methods based on geometric models have long been in use for estimating left ventricular mass, but there is currently no similar method for estimating right ventricular (RV) free-wall mass. We hypothesized that a one-quarter prolate ellipsoid model could be used with two-dimensional echocardiography to approximate RV mass. Over a 2-year period 39 patients who had both a complete cardiac magnetic resonance imaging (MRI) scan and an echocardiogram within 2 weeks of each other were retrospectively analyzed. MRI-derived RV mass was used as the standard for comparison. Echocardiographic RV mass was estimated using three equations based on the geometric model. Linear regression analysis was performed to determine the correction factors used in the final formulae. The formula with the lowest standard error of the estimate was then prospectively analyzed for accuracy using a separate group of 88 subjects. The most accurate echocardiographic equation derived was RV mass = 5.84 (apical four-chamber RV cavity planar area) (RV free-wall thickness) + 1. Compared to MRI-RV mass the correlation coefficient was 0.97 and the standard error of the estimate was 16.8%. The positive and negative predictive values for diagnosing RV hypertrophy were 95% and 88%, respectively. We conclude that RV free-wall mass can be estimated by two-dimensional echocardiography using a one-quarter prolate ellipsoid shell model.

Adolescent↗
PubMedDate not supplied

Innominate artery steal syndrome after stage I palliation for hypoplastic left heart syndrome.

Four neonates with hypoplastic left heart syndrome (HLHS) were found to have innominate artery steal syndrome (IASS) following stage I palliation with a modified Blalock-Taussig (B-T) shunt. All patients presented in the early postoperative period with a persistent supplemental oxygen requirement. Two-dimensional echocardiography with Doppler flow analysis and cardiac catheterization with angiography demonstrated obstruction at the origin of the innominate artery. This obstruction was associated with intermittent retrograde flow through the right vertebral and common carotid arteries into the distal innominate artery and modified B-T shunt. An ascending neoaorta to right pulmonary artery shunt, with takedown of the B-T shunt, was performed in two of the patients. The other two patients were treated with percutaneous balloon dilatation of the obstructed area. Both procedures improved arterial blood oxygen saturations and eliminated the need for supplemental oxygen. In three of four patients, the left common carotid artery was found to be larger than the right. All four patients developed microcephaly, and one patient had encephalomalacia in the distribution of the right anterior and middle cerebral arteries. The development of IASS following stage I palliation for HLHS and the association of neurologic sequelae from this complication are discussed.

Brachiocephalic Trunk↗