[Replacement of the descending aorta sparing the aortic valve: the David's operation]. / Le cas clinique du mois. Remplacement de l'aorte ascendante et conservation de la valve aortique: opération de David.

We report the case of an ascending aortic aneurysm involving the aortic root, with a functionally competent bicuspid aortic valve, treated by the David's operation. This operation allows to fix the aortic root pathology, whilst preserving the native aortic valve. The technical aspects, surgical indications, and potential benefits of this operation are reviewed.

Crural artery bypass with the autogenous greater saphenous vein.

OBJECTIVE: To evaluate the long-term outcome of greater saphenous vein (GSV) infrapopliteal revascularisation in a single centre over a 10 year period. MATERIAL AND METHODS: Fourty-one variables relating to a consecutive series of 90 crural artery GSV(76% in situ) bypasses in 81 patients (1990-2000) were analysed. The mean age of the 47 men and 34 women was 70 years. Limb-threatening ischaemia was present in 96% of cases, claudication in four patients. In 18 patients, surgery was 'redo'. RESULTS: The perioperative mortality was 3% (n=3). Patient survival was 54% at 4 years. Independent risk factors affecting survival were chronic renal insufficiency (p=0.04), hypertension (p=0.02), and ischaemic heart disease (p=0.01). Four bypasses thrombosed within 30 days. Three of them could be successfully reopened. Mean follow-up was 39 months. The primary patency rate at 4 years was 80%. Chronic renal insufficiency revealed to be the single independent risk factor for graft thrombosis (p=0.03, RR=12.4). The 4-year limb salvage rate was 88%. No independent risk factor affecting the limb salvage could be identified. CONCLUSION: Crural artery revascularisation is a valuable option for the management of limb threatening infrapopliteal arterial occlusive disease.

[Prevention of lower limb necrosis and amputation by femoro-crural bypass: indications, techniques and results]. / Prévention de la nécrose des membres inférieurs et de l'amputation par pontages fémoro-tibiaux: indications, technique et résultats.

Limb threatening ischemia is a challenge for the vascular surgeon. Recent progress in revascularization procedures allow to minimize the primary amputation rate in the management of chronic critical limb ischemia. The authors discuss the prevalence and causes of chronic critical limb ischemia, with a special interest for diabetic arteriopathy. The technique of crural and pedal vessel revascularization is described, as well as the innovative tourniquet technique for distal bypass surgery. A review of published series of infrapopliteal bypass surgery is made. The experience of the authors during last decade with crural and pedal bypass surgery is analyzed.

A faster way to characterize by triple-quantum-filtered (17)O NMR water molecules strongly bound to macromolecules in solution.

The simultaneous use of transverse and longitudinal relaxation rates, together with a transverse triple-quantum-filtering NMR sequence, was estimated for the adequate characterization of (17)O-water relaxation behavior in protein solutions. A complementary contribution to transverse relaxation was found, which was interpreted as chemical exchange of (17)O-water between different sites of the proteins. This contribution was estimated via calibration measurements. Then, for other similar samples, faster experiments could be performed. The analysis of the results obtained in this way gave adequate values of the relaxation rate of water in fast motion, of the fraction of water in slow motion, and of its correlation time. Hence, it permitted the complete characterization of the sample in a reasonable experimental time.

Characterisation by triple-quantum filtered 17O-NMR of water molecules buried in lysozyme and trapped in a lysozyme-inhibitor complex.

Triple-quantum filtering NMR sequences were used to study the multiexponential relaxation behaviour of H2 17O in the presence of hen egg white lysozyme. By this means, the fraction and the correlation time of water were determined in slow motion, as well as the relaxation time of water in the extreme narrowing limit. The small number of water molecules in slow motion, which is between four and five per lysozyme, seems to correspond to the 'integral' water, buried or in the cleft inside the protein, whereas water in fast motion corresponds to all other water molecules, interacting or not with the macromolecules. The same experiment was performed after addition of the inhibitor tri-N-acetylglucosamine (NAG)3. For solutions of sufficient viscosity, there were approximately three supplementary water molecules in slow motion per lysozyme, probably trapped between the protein and the inhibitor. The correlation time of these water molecules was estimated at 2 ns, which should correspond to their residence time in the complex.

Off-resonance irradiation effect in steady-state NMR saturation transfer.

The off-resonance irradiation effect (spill-over effect), occurring in steady-state NMR saturation-transfer experiments, is studied theoretically and experimentally for a two-spin system in chemical exchange, when a contralateral irradiation is applied to record the reference spectrum. The relevant parameter chosen for this study is the saturation-transfer ratio. It is defined as the ratio between the value of one exchanging magnetization, obtained when saturating the other, and that of the same magnetization measured when applying a contralateral irradiation. The theoretical study is carried out via a model based on the Bloch equations modified for chemical exchange and expressed in a doubly tilted single rotating frame. The saturation-transfer ratio is expressed as a function of the saturating RF field magnitude. It is shown that the RF field applied off-resonance during the acquisition of the reference spectrum does not correct the experimental saturation-transfer ratio for the spill-over effect. In fact, the saturation-transfer ratio increases with the magnitude of this field. This result is qualitatively explained by the consequence of the effective magnetic fields' relative orientations upon the amount of exchanged magnetization. The validity of the theoretical description is tested experimentally with a solution of N,N-dimethylacetamide in which chemical exchange arises from internal hindered rotation. An experimental protocol is proposed to detect spill-over and correct it when necessary. The way to describe spill-over theoretically when more than two spins interact by chemical exchange and/or dipolar coupling is also given.

Determination of the Bound Water Fraction in Cells and Protein Solutions Using 17O-Water Multiple-Quantum Filtered Relaxation Analysis

Multiple-quantum filtering NMR sequences were used to study the multiexponential relaxation behavior of H217O in the presence of macromolecules. By this means, the fraction and the correlation time of water in slow motion, or "bound" water, were determined, as well as the relaxation time of bulk water in the extreme-narrowing limit. Aqueous solutions of bovine serum albumin and intact human red blood cells were studied. The small fraction of bound water of less than 1% appeared to correspond to "strongly bound" water, whereas the behavior of bulk water was different from pure water and was interpreted as being due to weak (or transient) interactions with macromolecules. The experiments and the data analysis appeared to be reproducible, which suggests that diverse samples might be studied this way and thus help define the properties of water in these systems.