Nuclear cardiology, Part III: Scintigraphic evaluation of cardiac perfusion

OBJECTIVE: After reading Part III of this series of nuclear cardiology articles, the technologist should be able to: (a) compare and contrast radiopharmaceuticals used for myocardial perfusion imaging; (b) describe imaging protocols used for detecting coronary artery disease; and (c) describe imaging patterns seen following reconstruction of myocardial images.     

Flash photolysis of the carbon monoxide compounds of wild-type and mutant variants of cytochrome bo from Escherichia coli

The carbon monoxide compounds of the fully reduced and mixed valence forms of cytochrome bo from Escherichia coli were laser photolysed under anaerobic conditions at room temperature. The carbon monoxide recombined with characteristic rate constants of 50 s-1 or 35 s-1 in the fully reduced and mixed valence forms, respectively. Rates of CO recombination with the fully reduced enzyme were examined in a variety of mutant forms of cytochrome bo, produced by site-directed mutagenesis. A method was developed to deconvolute cytochromes bo and bd, leading to some reassessment of histidine ligands to the metals. Significant changes in the rate constant of recombination of carbon monoxide occurred in many of these mutants and these results could be rationalised generally in terms of our current working model of the folding structure of subunit I. In the mixed valence form of the enzyme the transient photolysis spectra in the visible region are consistent with a rapid electron redistribution from the binuclear centre to the low-spin haem. This electron transfer is biphasic, with rate constants of around 10(5) and 8000 s-1. The process was also examined in the His-333-Leu mutant, in which a putative histidine ligand to CuB is replaced by leucine, and which results in the loss of the CuB. It appeared that rapid haem-haem electron transfer could still occur. The observation that CuB is apparently not required for rapid haem-haem electron transfer is consistent with the recently proposed model in which the two haems are positioned on opposite sides of transmembrane helix X in subunit I of the oxidase.     

Invasive group A streptococcal disease in Taiwan is not associated with the presence of streptococcal pyrogenic exotoxin genes

We reviewed the clinical features of 44 patients with invasive group A streptococcal (GAS) disease who were treated at two teaching hospitals in southern Taiwan from 1991 to 1994. Genes encoding streptococcal pyrogenic exotoxin types A (speA), B (speB), C (speC), and F (speF) and serotypes of M1, M6, and M12 were determined by polymerase chain reaction to target specific sequences in the 44 isolates recovered from these patients and in 28 isolates recovered from upper respiratory sites in 28 additional patients during the study period. The protease activity of these isolates was tested by using the casein plate method. Of the 44 patients with invasive diseases, 25 (57%) had no obvious underlying diseases, and 14 (32%) had preexisting neoplastic diseases or had previously used steroids. Twenty-five patients (57%) presented with cellulitis or necrotizing fasciitis, 24 (55%) had bacteremia, and eight (18%) had streptococcal toxic shock syndrome (STSS). Eight patients (18%) died of invasive GAS disease; seven had STSS, and seven had underlying diseases. All eight patients died within 48 hours after hospitalization. The presence of speA, speC, or speF was not implicated in any particular clinical syndrome in patients with invasive GAS disease. High-level protease activity and the M1 serotype of the isolates were significantly associated with the clinical signs of STSS and with mortality. M1 serotype and protease activity, as well as host immune status, might play significant roles in the pathogenesis of invasive GAS disease in Taiwan.     

Arsenic deactivation enhanced diffusion and the reverseshort-channel effect

The effect of enhanced diffusion caused by the electrical deactivation of arsenic on the reverse short-channel effect (RSCE) in NMOS devices is investigated. A simple four-mask process was utilized to fabricate deep sub-micron NMOS devices. Source/drain (S/D) implant and anneal conditions were varied in order to determine their implications on the RSCE. Results indicate that when high concentrations of arsenic deactivate, enhanced diffusion occurs, leading to significantly more RSCE. This implies that the dose of the arsenic implant and the subsequent anneals should be carefully considered in source/drain engineering     

Thyroid peroxidase: kinetics, pH optima and substrate dependency

The oxidation of iodide, guaiacol and 2,2'-azino-di[3-ethyl-benzthiazoline-(6)-sulphonic acid] and the iodination of tyrosyl residues in bovine serum albumin, catalysed by partly purified thyroid peroxidase, were studied. The enzyme showed pH optima with all electron donors. With the exception of guaiacol, the position of the pH optima depended upon both the electron donor and hydrogen peroxide concentrations. With increased hydrogen peroxide concentrations the optima shifted to lower pH, and with increased iodide concentration to higher pH. For monoiodotyrosine (MIT) formation in bovine serum albumin the position of the pH optimum was also dependent on the hydrogen peroxide concentrations. The position of the pH optimum of the oxidation of guaiacol was pH 9 and independent of substrate and hydrogen peroxide concentrations. It is obvious from these findings that iodination reactions must be studied under well-defined conditions.     

Increased analytical precision in the hollow cathode discharge emission source by improved discharge current control.

A significant improvement in the precision of the hollow cathode as an emission source is reported. Precision of 1% or less has been observed several times over periods of several hours. An average long-term stability of 4.3% for Ll and 6.0% for Na in the emission signal from microsamples (less than 50 nL) deposited in the hollow cathode discharge source is reported. The improved precision is attributed primarily to the introduction of electronics that hold the discharge current more nearly constant and to the shielding of all wiring to the source from the power supply. A current-controlled switch that is capable of driving a hollow cathode discharge in either dc or pulsed mode is described. This switch is capable of generating current pulses as short as 2 microseconds through a resistive load and greatly improves the discharge stability and repeatability at turn-on in both the dc and pulsed modes. The characteristics of pulses produced by this switch are presented; however, analytical performance is reported only for the dc mode. Temporal current plots are presented for the new instrumentation and compared to plots taken with commonly used current-controlled power supplies. Instrumentation, operation, and sample preparation procedures are described. Typical temporal profiles of the emission signal from microsamples deposited in AI and stainless steel hollow cathodes are given.     

alpha B-crystallin and hsp25 in neonatal cardiac cells--differences in cellular localization under stress conditions

OBJECTIVES: The aim of this study was to determine (a) whether delay in femur fracture stabilization beyond twenty-four hours in patients with head injury increased the risk of pulmonary complications and (b) whether immediate (up to twenty-four hours) femur fracture stabilization increased the risk of central nervous system (CNS) complications. DESIGN: Retrospective analysis. MATERIALS AND METHODS: Thirty-two patients with femur fracture and head injury were identified. Fourteen underwent immediate stabilization of their fractures, and eighteen underwent delayed (four-teen patients) or no (four patients) stabilization of their fractures. RESULTS: In the immediate stabilization group, five patients had severe head injuries [Glasgow Coma Score (GCS) < or = 8] and nine had mild head injuries (GCS > 8). In the mild head injury group, no patient had a pulmonary complication and one had a CNS complication. In the severely head-injured group, one patient had a pulmonary complication and no patient had a CNS complication. In the delayed stabilization group, six patients had mild head injuries (GCS > 8) and twelve had severe head injuries (GCS < or = 8). In the mildly head injured group, one patient had a pulmonary complication, two patients had CNS complications, and one patient died. In the severely head injured group, nine patients had pulmonary complications, three patients had CNS complications, and one patient died. Logistic regression identified delay in femur stabilization as the strongest predictor of pulmonary complication (p = 0.0042), followed by severity of chest Abbreviated Injury Score (AIS; p = 0.0057) and head AIS (p = 0.0133). Delaying fracture stabilization made pulmonary complications forty-five times more likely. Each point increase in the chest AIS and head/neck AIS increased the risk of pulmonary complication by 300 percent and 500 percent, respectively. A statistically significant predictor of CNS complications could not be identified by using logistic regression. CONCLUSION: Delay in stabilization of femur fracture in head-injured patients appears to increase the risk of pulmonary complications. However, due to selection bias in this patient sample, this question cannot be definitively answered. Early fracture stabilization did not increase the prevalence of CNS complications.     

Performance and tissue zinc and metallothionein accumulation in chicks fed a high dietary level of zinc

Four experiments were conducted to identify several factors that might improve the accuracy and reproducibility of Zn bioavailability assays for chicks. Response of tissue Zn and metallothionein (MT) concentrations to various elevated levels and soluble sources of dietary Zn were measured, as well as the effect of delaying high Zn administration until 7 d posthatching to alleviate the detrimental effect of Zn sulfate on feed intake to 3 wk of age. Bone Zn increased (P < 0.01) in all experiments in response to increasing dietary Zn concentrations. Liver and pancreas MT were affected (P < 0.01) by a source by age interaction and variability that made this criterion unsuitable for bioavailability assays. Lastly, 1-d-old chicks were used to study the effect of delaying feeding of a high-Zn diet up to 7 d of age. The basal diet was fed continuously for 21 d as a control. A diet containing 1,000 ppm Zn was either fed continuously from Day 1, or started on Day 3, 5, or 7. Chicks given high Zn on Day 3, 5, or 7 decreased (P < 0.01) feed intake within 24 h of feeding. Delayed feeding of high dietary Zn might help to alleviate decreased feed intake observed in previous studies. Delaying the onset of high Zn feeding by several days may help alleviate feed intake problems observed with Zn sulfate. Use of either Zn gluconate or Zn acetate as a standard in assays or use of MT synthesis as a bioavailability criterion will probably not be useful to improve accuracy of the estimates.