Perioperative cardiac evaluation for noncardiac surgery noninvasive cardiac testing

Prognostic risk stratification to identify perioperative and long-term cardiac risk in selected patients undergoing noncardiac surgery is part of good clinical practice. Exercise variables associated with significant increased risk include poor functional capacity (eg, <4 metabolic equivalents), marked exercise-induced ST segment shift or angina at low workloads, and inability to increase or actually decrease systolic blood pressure with progressive exercise. Approximately 40% of patients tested before peripheral vascular surgery will have an abnormal exercise electrocardiogram (ECG). The predictive value for a perioperative event, ie, death or myocardial infarction, ranges from 5% to 25% for a positive test and 90% to 95% for a negative test. Whereas exercise cardiac imaging is the modality of choice in patients with a noninterpretable exercise ECG, pharmacological stress imaging should be used in the 30% to 50% of patients who require perioperative noninvasive risk stratification and are unable to perform an adequate level of exercise to test cardiac reserve. Myocardial perfusion variables predictive of increased cardiac events include severity of the perfusion defect, number of reversible defects, extent of fixed and reversible defects, increased lung uptake of thallium-201, and marked ST segment changes associated with angina during the test. The reported sensitivity and specificity of dobutamine-induced echocardiographic wall motion abnormalities in patients with peripheral vascular disease is similar to myocardial perfusion scintigraphy, but the confidence limits are wider due to the smaller sample size in these more recent studies. In conclusion, noninvasive cardiac testing should be used selectively in patients undergoing noncardiac surgery; the results provide useful estimates of short- and long-term risk of cardiac events, and the magnitude of abnormal response on noninvasive testing should be used to formulate decisions regarding the need for coronary angiography and subsequent revascularization.     

Exochelin genes in Mycobacterium smegmatis: identification of an ABC transporter and two non-ribosomal peptide synthetase genes

Many strains of mycobacteria produce two ferric chelating substances that are termed exochelin (an excreted product) and mycobactin (a cell-associated product). These agents may function as iron acquisition siderophores. To examine the genetics of the iron acquisition system in mycobacteria, ultraviolet (UV) and transposon (Tn611) mutagenesis techniques were used to generate exochelin-deficient mutants of Mycobacterium smegmatis strains ATCC 607 and LR222 respectively. Mutants were identified on CAS siderophore detection agar plates. Comparisons of the amounts of CAS-reactive material excreted by the possible mutant strains with that of the wild-type strains verified that seven UV mutant strains and two confirmed transposition mutant strains were deficient in exochelin production. Cell-associated mycobactin production in the mutants appeared to be normal. From the two transposon mutants, the mutated gene regions were cloned and identified by colony hybridization with an IS6100 probe, and the DNA regions flanking the transposon insertion sites were then used as probes to clone the wild-type loci from M. smegmatis LR222 genomic DNA. Complementation assays showed that an 8 kb PstI fragment and a 4.8 kb PstI/SacI subclone of this fragment complemented one transposon mutant (LUN2) and one UV mutant (R92). A 10.1 kb SacI fragment restored exochelin production to the other transposon mutant (LUN1). The nucleotide sequence of the 15.3 kb DNA region that spanned the two transposon insertion sites overlapped the 5' region of the previously reported exochelin biosynthetic gene fxbA and contained three open reading frames that were transcribed in the opposite orientation to fxbA. The corresponding genes were designated exiT, fxbB and fxbC. The deduced amino acid sequence of ExiT suggested that it was a member of the ABC transporter superfamily, while FxbB and FxbC displayed significant homology with many enzymes (including pristinamycin I synthetase) that catalyse non-ribosomal peptide synthesis. We propose that the peptide backbone of the siderophore exochelin is synthesized in part by enzymes resembling non-ribosomal peptide synthetases and that the ABC transporter ExiT is responsible for exochelin excretion.     

Controlling signaling with a specifically designed Gi-coupled receptor

We are developing a system to control G protein signaling in vivo to regulate a broad range of physiologic responses. Our system utilizes G protein-coupled peptide receptors engineered to respond exclusively to synthetic small molecule ligands and not to their natural ligand(s). These engineered receptors are designated RASSLs (receptor activated solely by a synthetic ligand). We have made two prototype RASSLs that are based on the human kappa opioid receptor. Small molecule drugs that activate the kappa receptor are nonaddictive and safe to administer in vivo. Binding and signaling assays reveal 200-2000-fold reductions in the ability of our RASSLs to bind or be activated by dynorphin, an endogenous peptide ligand of the kappa opioid receptor. In a high-throughput signaling assay, these prototype RASSLs expressed in Chinese hamster ovary K1 cells showed little or no response to a panel of 21 opioid peptides but still signaled normally in response to small molecule drugs such as spiradoline. Activation of a RASSL by spiradoline also caused proliferation of rat-1a tissue culture cells. These data provide evidence that G protein-coupled receptors can be made into RASSLs. The potential in vivo applications for RASSLs include the positive enrichment of transfected cells and the development of new animal models of disease.     

Issues in the design and interpretation of studies to evaluate the impact of community-based interventions

Increasingly, epidemiologists are faced with the need to evaluate the impact of an intervention that is delivered at the level of a community or cluster of individuals, rather than at the individual level. This has profound implications for the design and interpretation of a study to evaluate its impact. We start by discussing the issues arising in the extension of the randomized double-blind controlled trial methodology to the evaluation of interventions delivered to clusters of individuals, or to whole communities, where the unit of randomization is a cluster of individuals rather than an individual. We then consider alternative approaches to design, discuss their relative strengths and weaknesses and present a framework of design options. Finally we propose a pragmatic approach to evaluation design in this setting. We believe that the answer lies in the judicious selection of different design elements, combined in such a way that when the evidence from each is presented together, a clear picture of the impact of the intervention emerges. We illustrate this using an example from the recent literature.     

Differential effect of steady versus oscillating flow on bone cells

Loading induced fluid flow has recently been proposed as an important biophysical signal in bone mechanotransduction. Fluid flow resulting from activities which load the skeleton such as standing, locomotion, or postural muscle activity are predicted to be dynamic in nature and include a relatively small static component. However, in vitro fluid flow experiments with bone cells to date have been conducted using steady or pulsing flow profiles only. In this study we exposed osteoblast-like hFOB 1.19 cells (immortalized human fetal osteoblasts) to precisely controlled dynamic fluid flow profiles of saline supplemented with 2% fetal bovine serum while monitoring intracellular calcium concentration with the fluorescent dye fura-2. Applied flows included steady flow resulting in a wall shear stress of 2 N m(-2), oscillating flow (+/-2 Nm(-2)), and pulsing flow (0 to 2 N m(-2)). The dynamic flows were applied with sinusoidal profiles of 0.5, 1.0, and 2.0 Hz. We found that oscillating flow was a much less potent stimulator of bone cells than either steady or pulsing flow. Furthermore, a decrease in responsiveness with increasing frequency was observed for the dynamic flows. In both cases a reduction in responsiveness coincides with a reduction in the net fluid transport of the flow profile. Thus. these findings support the hypothesis that the response of bone cells to fluid flow is dependent on chemotransport effects.     

Investigation of the selenium status of aborted calves with cardiac failure and myocardial necrosis

Lesions of heart failure, specifically cardiac dilation or hypertrophy along with a nodular liver (chronic passive congestion) and ascites, have been found in 4-5% of aborted bovine fetuses. In this study, a group of 22 such fetuses was compared with groups of aborted fetuses without lesions of heart failure and with nonaborted fetuses obtained from a slaughterhouse. The fetuses were necropsied, tissues were taken for histopathology, and samples were collected for routine bacteriologic and virologic examinations. Liver and kidney tissue was saved for selenium analysis. Histopathologic examinations of myocardium of fetuses with cardiac failure revealed myocardial necrosis and mineralization in 7 fetuses, lymphocytic myocarditis in 5 fetuses, myocardial fibrosis in 5 fetuses, or no microscopic lesions in 5 fetuses. Mean liver selenium levels were 5.5 mumol/kg in the fetuses with heart lesions, 6.5 mumol/kg in the fetuses without heart lesions and 7.5 mumol/kg in fetuses from the slaughterhouse; these differences were statistically significant. The results suggest that selenium deficiency in bovine fetuses may cause myocardial necrosis and heart failure. This study also provides data on normal liver and kidney selenium levels in bovine fetuses from the analyses of 19 nonaborted fetuses.