Sorted averaging--application to auditory event-related responses

To isolate event-related potentials (ERPs) from the biological background noise, averaging of stimulus-locked electroencephalogram (EEG) epochs is needed. Recordings with patients often reveal a noisy background EEG, i.e., a high amplitude and multiple artifacts. Research studies have to deal with a limited number of available epochs. Therefore, averaging and efficient artifact rejection algorithms are needed. This paper focuses on the sorted averaging algorithm which was developed for the recording of auditory brainstem responses. We demonstrate the applicability of sorted averaging on ERPs by comparing three different averaging algorithms on a classical mismatch negativity (MMN) paradigm, recorded at 10 normal hearing volunteers. The resulting estimated signal-to-noise ratio (SNR) of the ERP waveforms was significantly increased compared to established averaging algorithms. Thus, the sorted averaging algorithm provides an improvement of the SNR in recordings with poor SNR (e.g., the MMN) or noisy background EEG (e.g., at Cochlear Implant users).     

Zur Wirkungsweise der Sulfonamide

Ohne Zusammenfassung     

Synthesis, biodistribution and renal handling of various chelate-somatostatin conjugates with metabolizable linking groups

A series of DTPA-octreotide conjugates, with various linking groups, were synthesised to investigate the effect of different metabolizable linkers on the renal retention of radioactivity. All these newly synthesised octreotide conjugates retained the high binding affinity of octreotide for the somatostatin (SRIF) receptors either when unlabeled or radiolabeled with ¹¹¹In. Some of the metabolizable linkers were rapidly degraded in vitro when incubated with a kidney homogenate. However, in vivo, all these conjugates displayed a significantly lower uptake in SRIF receptor-positive tissue compared to two conjugates with short, stable linkers. Additionally, the compounds with a potentially metabolizable linker had a higher whole-body retention of activity as opposed to the three metabolically stable compounds. Several of the linkers gave evidence of cleavage while in circulation in the blood, and it is probable that the lower tumour accumulation of most of the compounds tested was low due to the high enzymatic nature of the exocrine pancreatic tumour model used. In short, no increase in the tumour-to-kidney ratio was achieved with the analogues containing a metabolizable linker. The highest target-to-nontarget tissue ratios were obtained for the DTPA-octreotide conjugates that had short, metabolically stable linkers.     

Pedal arterial bypass for limb salvage in patients with diabetes mellitus.

OBJECTIVE: to evaluate pedal bypass grafting in patients with diabetes mellitus with critical limb ischaemia. PATIENTS AND METHOD: from 1994 to 1999, 49 consecutive pedal bypass grafts were performed in 46 patients with a median age of 69 years (range 37-85 years). The incidence of insulin-dependent diabetes mellitus was 87%. The distal anastomosis was located at the dorsalis pedis artery in 36, at the inframalleolar posterior tibial artery in 9 and at the plantar artery in 4 cases, respectively. RESULTS: one patient died perioperatively. Two bypass occlusions and one major amputation accounted for a primary patency rate of 96% and a limb salvage rate of 98% at 30 days, respectively. During a median follow-up of 28 months (range 1-70 months), 21 patients died of nonrelated causes. Three additional graft occlusions and 4 major amputations were noted resulting in a primary patency rate of 89% and a limb salvage rate of 87% at 48 months, respectively. CONCLUSION: Pedal bypass grafting utilising the greater saphenous vein with in-situ technique is a reliable and effective procedure to achieve durable limb salvage in patients with diabetes mellitus.     

Detection of central pulmonary artery thromboemboli by transesophageal echocardiography in patients with severe pulmonary embolism.

Transthoracic echocardiography generally provides only indirect signs of pulmonary embolism. In contrast, with transesophageal echocardiography the thromboembolus itself can be visualized in the central parts of the pulmonary artery. The aims of our study were to evaluate, first, the incidence of central pulmonary artery thromboemboli in patients with severe pulmonary embolism, and second, the accuracy of the echocardiographic diagnosis. Our study group comprised 60 patients with proved severe pulmonary embolism. All patients were examined by transthoracic and transesophageal echocardiography. The echocardiographic findings concerning the absence or presence of central pulmonary artery thromboemboli were compared with the results of different reference methods. Central pulmonary thromboemboli were found in 35 patients (58.3%) by echocardiography. Two types of thrombus were differentiated. Type A is a long, highly mobile thrombus, and type B is an immobile wall-adherent thrombus. In comparison with the reference methods, we determined a sensitivity of 96.7% and a specificity of 88% for the echocardiographic detection of central pulmonary artery thromboemboli in patients with severe pulmonary embolism. Transesophageal echocardiography seems to be a useful method for the diagnosis of severe pulmonary embolism. In our series, central pulmonary artery thromboemboli were present in more than half of the patients. In these cases, transesophageal echocardiography can clarify the diagnosis within a few minutes without further invasive diagnostic procedures.     

High-resolution, spin-echo BOLD, and CBF fMRI at 4 and 7 T.

With growing interest in noninvasive mapping of columnar organization and other small functional structures in the brain, achieving high spatial resolution and specificity in fMRI is of critical importance. We implemented a simple method for BOLD and perfusion fMRI with high spatial resolution and specificity. Increased spatial resolution was achieved by selectively exciting a slab of interest along the phase-encoding direction for EPI, resulting in a reduced FOV and number of phase-encoding steps. Improved spatial specificity was achieved by using SE EPI acquisition at high fields, where it is predominantly sensitive to signal changes in the microvasculature. Robust SE BOLD and perfusion fMRI were obtained with a nominal in-plane resolution up to 0.5 x 0.5 mm(2) at 7 and 4 Tesla, and were highly reproducible under repeated measures. This methodology enables high-resolution and high-specificity studies of functional topography in the millimeter to submillimeter spatial scales of the human brain.     

Evaluation of the healing of precoated vascular dacron prostheses

Summary Knitted and woven Dacron grafts commercially coated with bovine collagen, gelatin and human albumin were implanted end-to-side between the infrarenal aorta and the bifurcation in 35 growing pigs. Grafts were explanted after 4, 8 and 12 weeks and compared to 6 uncoated knitted prostheses preclotted with blood that served as a control. Uncoated grafts rapidly developed a firmly attached neointima lined with endothelium. Compared with coated grafts the thrombus-free area of uncoated grafts was significantly larger (P < 0.05). The slow resorption of albumin resulted in a delayed and incomplete neointimal healing and failing graft incorporation. Although the bovine collagen was only minimally cross-linked by formaldehyde, healing of the neointima was compromised in a thin woven graft that demonstrated peeling of the inner capsule even after 12 weeks. The identical collagen as well as bovine gelatin were quickly degraded in knitted grafts and both types showed transprosthetic infiltration at 4 weeks. All knitted grafts coated with either collagen or gelatin, however, were occluded after 8 and 12 weeks. Light microscopy revealed hyperplasia of smooth-muscle cells within the thickened distal anastomotic region. These results demonstrate that a timely return of porosity is mandatory for the development and maintenance of an intact neointima. Both the structure of the fabric as well as the method of preparing the coating are crucial variables to determine the rate of biodegradation.

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Untersuchung zur Einheilung vorbeschichteter Dacrongefaäßprothesen

Zusammenfassung Gestrickte und gewebte Dacronprothesen mit kommerzieller Vorbeschichtung aus bovinem Kollagen, Gelatine oder humanem Albumin wurden bei 35 Schweinen End-zu-Seit zwischen infrarenaler Aorta und der Bifurkation implantiert. Die Prothesen wurden nach 4, 8 und 12 Wochen explantiert und mit 6 unbeschichteten gestrickten Dacronprothesen verglichen. Unbeschichtete Dacronprothesen entwickelten rasch eine fest haftende Neointima mit Endothelauskleidung, wobei die thrombusfreie Fläche gegenüber beschichteten Prothesen signifikant größer war (P<0,05). Die verlangsamte Albuminresorption führte zu einer verzögerten und inkompletten Neointimaausbildung sowie zu einer ausbleibenden Protheseneinheilung. Obwohl das bovine Kollagen nur schwach vernetzt war, war auch bei gewebten beschichteten Dacronprothesen die Neointimaausbildung verzögert, wobei noch nach 12 Wochen die Neointima nur locker mit der Prothese verbunden war. Das identische Kollagen sowie die bovine Gelatine waren bei gestrickter Prothesenstruktur bereits nach 4 Wochen resorbiert und die Prothesen waren komplett eingeheilt. Diese beiden Prothesentypen zeigten jedoch nach 8 bzw. 12 Wochen konstant einen organisierten thrombotischen Verschluß. Hier wies die Histologic eine Hyperplasie glatter Muskelzellen innerhalb der verdickten distalen Anastomosenregion nach. Diese Ergebnisse zeigen, daß die zeitgerechte Wiederkehr der Porosität unverzichtbar ist für die regelrechte Entwicklung sowie für die Aufrechterhaltung einer intakten Neointima. Hier sind sowohl die Struktur der Prothese als auch die Art der Beschichtungsverarbeitung entscheidende Parameter, die die Resorptionsrate der Imprdgnierung beeinflussen.

     

Surgical therapy of thoracic aortic dissection]

Considerable surgical progress of treating aortic dissection has been achieved during the past decade. The emergency indication for acute dissection of the ascending aorta (type A according to the Stanford classification) is unquestioned while surgical treatment for acute dissection of the descending aorta (type B dissection) is mainly reserved for complicated cases. The major complication of acute operations--fatal hemorrhage from the suture line and secondary multi-organ failure--have been successfully reduced by a progress of cardiopulmonary bypass techniques, the introduction of cold cardioplegic myocardial protection, the development of modern suture materials and glues and last not least by a continuous intensive monitoring. Especially the introduction of the so-called french glue safely enabled both the closure of the false lumen as well as the strong reinforcement of the diseased aortic wall and seems to offer a reliable alternative to the application of multi-layered teflon strips. Since the principle of all reconstructive approaches in case of dissection consists of closure of dissected layers and the limited replacement of the segment that is susceptible to a rupture the exact readaptation and reinforcement of the diseased aortic wall represents a fundamental operative step. In type A operations the supracoronary aortic prosthetic replacement or the combined replacement of ascending aorta plus aortic valve followed by the reattachment of coronary arteries has become the standard operative technique. In fact, independently from the location of the primary intimal tear the operation has been traditionally limited to replace the ascending aorta in order to remove an aortic segment that is most likely to rupture. Yet an increasing number of follow-up investigations has demonstrated recurrence of dissection or an aneurysmatical dilatation of the false lumen in about 20% of patients treated with ascending aortic replacement. Consequently, repair of the aortic transverse arch and the radical elimination of the intimal entry is now favoured by an increasing number of surgeons. In addition to these various perioperative and intraoperative adjuncts the introduction of new imaging techniques, especially computerized tomography, magnetic resonance imaging and transesophageal echocardiography allowed to establish adequate therapeutical concepts on a more rational basis. Transesophageal echocardiography as a mobile diagnostic device enables investigators to perform a bed-side dynamic visualization of both the location and extent of a dissection, the evaluation of ventricular performance and aortic competence. Treatment of acute type B dissection is mainly conservative unless complications like intractable pain, aneurysmatic enlargement of the false lumen, ischemia of visceral organs or even rupture occur.(ABSTRACT TRUNCATED AT 400 WORDS)