Alkane isomers: presence in petroleum ether and complexity.

The presence and absence of alkane isomers in petroleum and petroleum derivatives depend on the complexity of these structures. It was assumed that the more complex the structure is the less probable it is that that the molecule can be detected in any petroleum derivative. Complexity is a vague concept, which has not been defined in quantitative terms yet, and therefore there is no experimental method, which could be used to determine 'complexity'. Mass spectrometry and infrared spectroscopy in combination with gas chromatography were used to identify the various structural isomers of alkanes in petroleum ether. The isomers were categorised in quantitative terms by using topological indices and linear discriminant analysis. It was found that alkanes possessing a more complex, highly branched structure are less probable to be detected in petroleum ether than isomers with a simpler backbone structure. It was proposed that the experimental 'measure' of the complexity of isomer(i) should be proportional to 1/C(i), where C(i), denotes the concentration of isomer(i) in a (primary) petroleum derivative.

Vibrational spectra of partially oriented molecules having two conformers in nematic and isotropic solutions: furfural and 2-chlorobenzaldehyde.

Vibrational analysis of the two conformers of furfural and 2-chlorobenzaldehyde has been carried out on the basis of their IR and Raman spectra measured in isotropic and anisotropic (nematic liquid crystalline) solvent. The average orientation of the individual conformers in the nematic solvent has been determined by means of a recently developed approach for low symmetry planar molecules using DFT calculations of the vibrational transitions moments. The complex shape of the carbonyl band additionally split into several components is interpreted as an effect of Fermi resonance.

Prophylactic urgent revascularization of the internal carotid artery in the symptomatic patient.

BACKGROUND: The symptomatic patient showing a string sign or ulcerative stenosis of the internal carotid artery (ICA) is subject to a high risk of arterial thrombosis or persisting intracranial embolization during the waiting period before operative revascularization. PATIENTS AND METHODS: During one year 186 operative revascularization procedures of the ICA were performed on the symptomatic patient. 26 of them fulfilled the prophylactic urgency criteria: symptoms of the cerebrovascular insufficiency and a string sign or ulcerative stenosis of the ICA with ulceration greater than 2 mm in depth. These results were compared to the control group of the 157 procedures under elective circumstances. RESULTS: Mean clamping time of the urgency and the elective patients were 23.8 min vs. 24.5 min and operation time 50.1 min vs. 54.3 min. None of our urgency patients presented new neurological defects in the postoperative phase, while this occurred in 3.8% in the elective group. Mortality rate in the elective group was 2.7% and 0% in the urgency group. Furthermore, there were fewer local complications in the urgency group. CONCLUSION: The urgent indication for the desobliteration of the ICA showing a symptomatic string sign or ulcerative stenosis can be recommended. Early thrombosis or neurological defects during the waiting period may be prevented without increasing complication rates.

Eversion endarterectomy versus open thromboendarterectomy and patch plasty for the treatment of internal carotid artery stenosis.

OBJECTIVE: in 1996 we changed our treatment for stenosis of the internal carotid artery (ICA) from open thromboendarterectomy and PTFE-patch plasty (TEA) to eversion endarterectomy (EEA). DESIGN: retrospective study. METHODS: a total of 475 EEAs of the ICA were performed between 2/96 and 11/96. These results were compared to the results of TEA carried out between 2/94 and 11/94 (n=388). RESULTS: clamping and operation time were significantly shorter for EEA. Neurological complications included transient ischaemic attacks in 1. 0% in the EEA group versus 1.3% after TEA (p=0.72), minor strokes (0. 6% vs. 1.8%, p=0.10) and major strokes in 1.5% versus 1.1% (p=0.59). The rate of restenosis >50% was 2.5% after EEA and 10.2% after TEA. The only detectable difference of statistical significance in complication rates was in the lesions of the hypoglossal nerve (5.3% vs. 2.6%, p=0.04). CONCLUSIONS: EEA of the ICA is a safe procedure for carotid reconstruction with the additional advantages of short clamping time, possibility of simultaneous shortening of an elongated ICA, and no requirement for patching.

Atherosclerosis in amputated legs of patients with and without diabetes mellitus.

BACKGROUND: The aim of this study was to compare the histomorphologic appearance of atherosclerosis in amputated legs of diabetic and non-diabetic patients. METHODS: Twenty-eight legs amputated below the knee for chronic ischaemia were studied. Fourteen legs were amputated in patients with diabetes (10 Type II, 4 nonclassified) and 14 in non-diabetics. The mean age of patients at the time of the amputation was 63.3 years in diabetics and 63.9 years in non-diabetics. Samples were taken from the main arteries at the following levels: the midleg, 5 cm above the ankle, 3 cm below the ankle and 10 cm below the ankle. Cross-sections of the arteries were examined with light microscopy and the severity of the occlusive disease determined using morphometric analysis. Medial calcification and chronic inflammation were assessed semiquantitatively. RESULTS: Arteries at 5 cm above the ankle were more severely stenotic in diabetics than in non-diabetics (p<0.05). In both diabetics and non-diabetics the posterior tibial and plantar arteries appeared to be the most stenotic. Medial calcification tended to be more prominent in diabetics than in non-diabetics. Chronic inflammation in the arterial wall occurred at the same degree in diabetics and non-diabetics. In non-diabetics chronic inflammation was more severe in the posterior tibial and plantar arteries than in the anterior tibial and dorsalis pedis arteries (p<0.04). Chronic arterial inflammation correlated with the severity of chronic arterial occlusive disease (p<0.0002). CONCLUSIONS: In diabetics occlusive disease in amputated legs is more severe in arteries above the ankle than in non-diabetics. However, no difference was demonstrated in this series in arteries of the ankle and foot. Diabetics are likely to have more medial calcification in the arteries than non-diabetics. Chronic inflammation in the arterial wall is associated with more severe stenosis.