Factors influencing preoperative stress response in coronary artery bypass graft patients

BACKGROUND: In many studies investigating measures to attenuate the hemodynamic and humoral stress response during induction of anaesthesia, primary attention was paid to the period of endotracheal intubation since it has been shown that even short-lasting sympathetic cardiovascular stimulation may have detrimental effects on patients with coronary artery disease. The aim of this analysis was, however, to identify the influencing factors on high catecholamine levels before induction of anaesthesia. METHODS: Various potential risk factors that could impact the humoral stress response before induction of anaesthesia were recorded in 84 males undergoing coronary aortic bypass surgery, and were entered into a stepwise linear regression analysis. The plasma level of norepinephrine measured immediately after radial artery canulation was chosen as a surrogate marker for the humoral stress response, and it was used as the dependent variable in the regression model. Accordingly, the mean arterial blood pressure, heart rate and the calculated pressure-rate product were taken as parameters of the hemodynamic situation. RESULTS: Stepwise regression analysis revealed that the oral administration of low-dose clonidine (mean dose 1.75 μg.kg-1) on the morning of surgery was the only significant predictor (p = 0.004) of the high variation in preoperative norepinephrine plasma levels. This intervention decreased norepinephrine levels by more than 40% compared to no clonidine administration, from 1.26 to 0.75 nmol.l-1. There was no evidence for dose-responsiveness of clonidine. All other potential predictors were removed from the model as insignificant (p > 0.05). The use of beta-blocker, ace-inhibitors, ejection fraction, and body mass index were significant determinants for the hemodynamic situation (heart rate, mean arterial pressure, pressure rate product) of the patient during the pre-induction period. CONCLUSION: The oral administration of clonidine is the only significant predictor for the observed variation of norepinephrine levels during the preoperative period. Lack of significant dose responsiveness suggests that even a low dose of the drug can attenuate the preoperative stress response and thus is recommended in cardiovascular high risk patients.     

Coronary pressure and FFR predict long-term outcome after PTCA

Although coronary stents have been the most important improvement in percutaneous coronary interventions in the last 10 years, it is well known to interventionalists that many patients after percutaneous transluminal coronary angioplasty (PTCA) have a favourable outcome without stenting. Coronary angiography, however, is not sensitive enough to identify those particular patients and it has been suggested that a combination of angiographic and functional criteria would be more suitable to distinguish patients with a low restenosis chance after plain balloon angioplasty. In the present study, the authors investigated the value of coronary pressure measurement for conditional stenting in 85 patients. It was demonstrated that in patients in whom a high fractional flow reserve (FFR) was present (> 0.90), the incidence of coronary events at two-year follow-up was almost three times lower than in those patients with an FFR below 0.90. Such high FFRs could be obtained in approximately 45% of all patients. In an additional group of patients, it was demonstrated by intravascular ultrasound (IVUS) studies that the mechanism of a high FFR after plain balloon angioplasty is most likely the result of a larger lumen compared with patients with a suboptimal FFR. This means that, in patients in whom both the angiographic and the functional result after PTCA is optimal, a restenosis rate is achieved similar to that achieved by stenting. Obviously, in such patients, additional stenting and a number of problems in the long-term possibly related to stenting can be avoided. Therefore, coronary angiography and coronary pressure measurement have a complementary value in the evaluation of PTCA results and such information can be easily obtained by using a pressure wire instead of a regular guidewire.     

The Diatom Flora of Bethany Boǵ

The results of these studies indicate that the first diatom flora developed at the 13-meter level. The flora at 12 meters increased. At the 11- and 9-meter levels the lake became increasingly eutrophic. Both plankton and benthic forms were present. At the 8- and 7-meter levels the lake was in a transitional stage from lake to bog conditions. From 6 meters to the surface bog conditions were present.     

Design of reference populations for genomic selection in crossbreeding programs

Background

In crossbreeding programs, genomic selection offers the opportunity to make efficient use of information on crossbred (CB) individuals in the selection of purebred (PB) candidates. In such programs, reference populations often contain genotyped PB animals, although the breeding objective is usually more focused on CB performance. The question is what would be the benefit of including a larger proportion of CB individuals in the reference population.

Methods

In a deterministic simulation study, we evaluated the benefit of including various proportions of CB animals in a reference population for genomic selection of PB animals in a crossbreeding program. We used a pig breeding scheme with selection for a moderately heritable trait and a size of 6000 for the reference population.

Results

Applying genomic selection to improve the performance of CB individuals, with a genetic correlation between PB and CB performance (r_PC) of 0.7, selection accuracy of PB candidates increased from 0.49 to 0.52 if the reference population consisted of PB individuals, it increased to 0.55 if the reference population consisted of the same number of CB individuals, and to 0.60 if the size of the CB reference population was twice that of the reference population for each PB line. The advantage of using CB rather than PB individuals increased linearly with the proportion of CB individuals in the reference population. This advantage disappeared quickly if r_PC was higher or if the breeding objective put some emphasis on PB performance. The benefit of adding CB individuals to an existing PB reference population was limited for high r_PC.

Conclusions

Using CB rather than PB individuals in a reference population for genomic selection can provide substantial advantages, but only when correlations between PB and CB performances are not high and PB performance is not part of the breeding objective.     

Seeing the Past: Visual Media in Archaeology

As digital media become increasingly affordable and accessible, visual representation in archaeology is expanding across several dimensions. In this essay, I examine some emerging forms of visual media in archaeology, including online documentaries, maps and photographs, hypermedia, experimental films, and peripatetic video. Visual media offer powerful opportunities for engagement with the public. In addition, archaeologists are finding new ways to use the visual in interpretation, analysis, and critique. Experimental visual works often are self-consciously reflexive, questioning and exposing the ways archaeological knowledge is constructed, represented, and disseminated.