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Biomedical subjects

A Engel

Publications and source records attributed to A Engel.

At least 37 records · Page 2Linked to original sources
PubMed1991

The structural basis for the intrinsic disorder of the actin filament: the "lateral slipping" model.

Three-dimensional (3-D) helical reconstructions computed from electron micrographs of negatively stained dispersed F-actin filaments invariably revealed two uninterrupted columns of mass forming the "backbone" of the double-helical filament. The contact between neighboring subunits along the thus defined two long-pitch helical strands was spatially conserved and of high mass density, while the intersubunit contact between them was of lower mass density and varied among reconstructions. In contrast, phalloidinstabilized F-actin filaments displayed higher and spatially more conserved mass density between the two long-pitch helical strands, suggesting that this bicyclic hepta-peptide toxin strengthens the intersubunit contact between the two strands. Consistent with this distinct intersubunit bonding pattern, the two long-pitch helical strands of unstabilized filaments were sometimes observed separated from each other over a distance of two to six subunits, suggesting that the intrastrand intersubunit contact is also physically stronger than the interstrand contact. The resolution of the filament reconstructions, extending to 2.5 nm axially and radially, enabled us to reproducibly "cut out" the F-actin subunit which measured 5.5 nm axially by 6.0 nm tangentially by 3.2 nm radially. The subunit is distinctly polar with a massive "base" pointing towards the "barbed" end of the filament, and a slender "tip" defining its "pointed" end (i.e., relative to the "arrowhead" pattern revealed after stoichiometric decoration of the filaments with myosin subfragment 1). Concavities running approximately parallel to the filament axis both on the inner and outer face of the subunit define a distinct cleft separating the subunit into two domains of similar size: an inner domain confined to radii less than or equal to 2.5-nm forms the uninterrupted backbone of the two long-pitch helical strands, and an outer domain placed at radii of 2-5-nm protrudes radially and thus predominantly contributes to the outer part of the massive base. Quantitative evaluation of successive crossover spacings along individual F-actin filaments revealed the deviations from the mean repeat to be compensatory, i.e., short crossovers frequently followed long ones and vice versa. The variable crossover spacings and diameter of the F-actin filament together with the local unraveling of the two long-pitch helical strands are explained in terms of varying amounts of compensatory "lateral slipping" of the two strands past each other roughly perpendicular to the filament axis. This intrinsic disorder of the actin filament may enable the actin moiety to play a more active role in actin-myosin-based force generation than merely act as a rigid passive cable as has hitherto been assumed.

Actins↗
PubMed1991

Chiari pelvic osteotomy for osteoarthritis secondary to hip dysplasia. Indications and long-term results.

Of 142 Chiari pelvic osteotomies for osteoarthritis in dysplastic hips, most performed by Chiari himself, we were able to review 82 and obtain information about 18 by questionnaire. All patients were over 30 years of age at operation; follow-up averaged 15.5 years. Twenty hips had undergone secondary total hip replacement. The outcome was good in 75%, fair in 9% and poor in 16%. High osteotomies all gave good results, and the result also depended on adequate medialisation. Statistics were worse for patients over 44 years of age at the time of operation. For osteoarthritis secondary to hip dysplasia, the Chiari pelvic osteotomy is an alternative procedure to early hip replacement. In contrast to intertrochanteric osteotomy, it has the advantage of facilitating the implantation of an acetabular prosthesis should arthroplasty become necessary at a later stage.

Adult↗
PubMed1990

[The effect of meniscectomy on the strength of the femoral quadriceps muscle after more than 3 years].

This paper investigates the strength of the quadriceps extensor femoris following partial meniscectomy by means of arthrotomy. Measurements were carried out on 30 patients using a velocity-controlled dynamometer. Follow-up ranged from three to twelve years. On clinical examination 17 patients revealed atrophy of the quadriceps, amounting to 1 cm in 12 patients and up to 2 cm in 5 patients. The average difference in muscular strength between the operated leg and the non-operated one totalled 11% in the cases of 1 cm atrophy and 19% in the 2 cm cases. Those patients who presented with no atrophy on the operated leg had an average loss of 4% in muscular strength, which is within the normal range. In addition, an interrelationship was established between measurements carried out at different angular velocities and the extent of quadriceps atrophy. The high percentage of patients showing a weakness of the quadriceps extensor femoris after a long follow-up period is most likely due to the severing of proprioceptors during surgery and to inadequate or lacking postoperative physiotherapy.

Adult↗
PubMed1990

[Breast biopsy of nonpalpable lesions after mammography-guided wire localization].

Mammography is used increasingly for diagnosis and screening. Its advantage is its ability to discover very small and often nonpalpable mammary lesions. While its sensitivity in detecting pathological changes in the breast is high, differentiation between benign and malignant lesions is less precise, so biopsy is necessary. To ensure removal of the entire lesion with minimal damage to breast tissue, precise localization is mandatory. The accepted technique is the needle-wire method. 39 of 167 biopsies guided by mammography performed during 3 years for nonpalpable lesions detected by mammography were malignant. In 24 of them the histological diagnosis was atypical epithelial proliferation, considered a transition to carcinoma.

Biopsy↗
PubMed1990

[Angiologic, neurologic and orthopedic findings in vibration exposed chain saw operators].

The present study was designed to evaluate and correlate angiological, neurological and orthopaedic findings in lumberjacks, professionally exposed to vibration by chain-saws with a frequency of 40 to 120 Herz. Raynaud's phenomenon was diagnosed in 16 of 33 subjects. The nerve conduction velocity was delayed in 13 of 32 lumberjacks, the sulcus nervus ulnaris syndrome was diagnosed in 41%, the vibration threshold was abnormal in 10/32 cases. Orthopaedic examination and X-ray studies revealed spondylotic (59%) and spondyloarthritic (65%) alterations of the cervical spine; cysts in bones of the distal upper extremities were observed in 75% of cases. Frequency and severity of angiological, neurological, and orthopaedic pathological findings correlated with the total chain-saw operating time. However, there was no correlation between the presence of digital vascular hyperreactivity and the sulcus nervus ulnaris syndrome or changes in nerve conduction velocity.

Adult↗
PubMed1990

Ordered arrays of the photosystem I reaction centre after reconstitution: projections and surface reliefs of the complex at 2 nm resolution.

We present an electron microscopical analysis of the photosystem I reaction centre, the membrane complex involved in the second light-driven step of photosynthetic electron transfer in plants and cyanobacteria. To this end, ordered two-dimensional arrays were reconstituted from detergent solubilized photosystem I reaction centres and phospholipids, and studied by electron microscopy and digital image processing. Small (P1) and large (P3) hexagonal lattices obtained with reaction centres of the thermophilic cyanobacterium Phormidium laminosum had unit cell sizes of a = b = 8.8 nm and 15.8 nm, respectively. Reaction centres of a second thermophilic strain, Synechococcus sp. OD24, gave square lattices (a = b = 14.5 nm; P2(1)). Irrespective of the packing arrangement, projections of negatively stained photosystem I complexes showed elongated asymmetric shapes with a large domain at one end which was tilted with respect to a small domain forming the tip of the other end. Such features were also found in averaged projections of solubilized reaction centre trimers. Surface reliefs reconstructed from freeze-dried metal-shadowed P2(1) lattices revealed that reaction centres had a ridge of 2.5 nm height projecting from one side of the membrane while their other side was rather flat and exhibited a shallow, central indentation.

Cyanobacteria↗
PubMed1990

Imaging biological macromolecules by STM: quantitative interpretation of topographs.

Methods are discussed which permit the calibration of x-, y-, z-sensitivities, non-linearities and frequency responses of the scanning device of a scanning tunneling microscope (STM) either by interferometry or directly from STM topographs. A technique is presented to measure the frequency response of the complete STM feedback unit and to derive a maximum speed in z direction which allows one to estimate the maximum scanning speed still permitting one to track surface corrugations. The signal transfer characteristics of a STM are evaluated in a direct comparison with high resolution transmission electron microscopy on an identical specimen area. The various effects of contaminants between tip and specimen and the finite tip radius receive special attention.

Cell Wall↗
PubMed1990

Palmar hyperhidrosis CT guided chemical percutaneous thoracic sympathectomy.

Palmar hyperhidrosis or excessive sweating of the hands causes, to those affected, emotional and physical disturbance and impediment in professional and social life. The cause is unknown. Sweat glands are innervated by the sympathetic chain of the autonomous nervous system. The center of sympathetic regulation of the upper extremities is located between the segments of D.2-D.9 of the spinal cord. Accepted treatment consists of surgery aimed to excise the third thoracic sympathetic ganglion. Besides the surgical procedure as such, and its complications, there are complications inherent to the excision of the ganglion. These are Horner's syndrome, compensatory sweating in other parts of the body, and recurrence of sweating. CT guided chemical percutaneous thoracic sympathectomy presents an alternative, which in the event of failure does not prevent ensuing surgery. The preliminary experience with this procedure in 50 patients is presented and discussed.

Adolescent↗
PubMed1990

Invasive lobular carcinoma. Mammographic pattern.

A retrospective study was done on 107 histologically proven cases of invasive lobular carcinoma which represent about 11.5% of the total of 934 cases of cancer of the breast. Age, breast parenchyma pattern and morphology, and radiological signs of malignancy were tabulated and correlated with the same data in ductal carcinoma. The number of false negative cases was almost twice as high as in ductal carcinoma type (19% versus 10%). In the majority of cases the patients presented a glandular or dense type of parenchyma pattern, which reduced the internal visibility. Besides spiculated masses, relatively subtle signs of malignancy, as asymmetric density and architectural distortion were relatively more frequently represented than in the ductal type of breast carcinoma. No clear-cut radiological criteria could be found pointing toward the underlying histology. Discreet clinical signs in younger patients with glandular or dense breast should alert the radiologist to the possible presence of this type of carcinoma. Due attention should be warranted to these less conspicuous signs of malignancy such as asymmetric density and architectural distortion.

Adult↗
PubMed1990

Correlation between structure and mass distribution of the nuclear pore complex and of distinct pore complex components.

Nuclear pore complexes (NPCs) prepared from Xenopus laevis oocyte nuclear envelopes were studied in "intact" form (i.e., unexposed to detergent) and after detergent treatment by a combination of conventional transmission electron microscopy (CTEM) and quantitative scanning transmission electron microscopy (STEM). In correlation-averaged CTEM pictures of negatively stained intact NPCs and of distinct NPC components (i.e., "rings," "spoke" complexes, and "plug-spoke" complexes), several fine structural features arranged with octagonal symmetry about a central axis could reproducibly be identified. STEM micrographs of unstained/freeze-dried intact NPCs as well as of their components yielded comparable but less distinct features. Mass determination by STEM revealed the following molecular masses: intact NPC with plug, 124 +/- 11 MD; intact NPC without plug, 112 +/- 11 MD; heavy ring, 32 +/- 5 MD; light ring, 21 +/- 4 MD; plug-spoke complex, 66 +/- 8 MD; and spoke complex, 52 +/- 3 MD. Based on these combined CTEM and STEM data, a three-dimensional model of the NPC exhibiting eightfold centrosymmetry about an axis perpendicular to the plane of the nuclear envelope but asymmetric along this axis is proposed. This structural polarity of the NPC across the nuclear envelope is in accord with its well-documented functional polarity facilitating mediated nucleocytoplasmic exchange of molecules and particles.

Animals↗
PubMed1990

The effect of intra-articular gadolinium-DTPA on synovial membrane and cartilage.

This investigation evaluated the potential effect of gadolinium (Gd)-DTPA-dimeglumine on synovial membrane and joint cartilage, using macroscopic, microscopic, and x-ray fluorescent spectroscopic techniques. Thirteen New Zealand white rabbits (26 knees) were used in this study, ten receiving 500 micromolar injections of Gd-DTPA-dimeglumine in their right knees; the remainder of the knees served as controls. One injected knee had minimal joint effusion and one had mild hyperemia. Microscopically four knees exhibited mild focal hyperplasia of the synovium, another three minimal focal mononuclear cell infiltration. X-ray fluorescent spectroscopy demonstrated no evidence of Gd-DTPA-dimeglumine in the synovium or articular cartilage. Neither macroscopic nor microscopic evaluation detected any Gd-DTPA-dimeglumine related effects. Gd-DTPA-dimeglumine was found to be safe for intra-articular injection in this animal model.

Animals↗
PubMed1990

First description of mechanoreceptors in the corpus adiposum infrapatellare of man.

The sensory innervation of the corpus adiposum infrapatellare of the human knee joint was studied by light microscopy. Small lamellated corpuscles (pacinian corpuscles) were found in the adipose tissue of the corpus adiposum infrapatellare. The lamellated corpuscles measured about 20 microns and consisted of 3-4 lamellae. It is discussed whether the corpus adiposum infrapatellare might perform a sensory function, influencing the muscle tone via polysynaptic reflexes.

Adipose Tissue↗
PubMed1990

Injury of the Achilles tendon: diagnosis with sonography.

We determined the diagnostic accuracy of sonography for the assessment of injury to the Achilles tendon. After anatomic investigations in three human cadavers, we performed a clinical study in 24 healthy volunteers and 73 symptomatic patients referred for achillodynia or signs of heel thickening or both in whom a clinical diagnosis of acute total rupture was excluded. High-resolution real-time sonography was performed and the results were compared with final clinical diagnoses (55 patients) and surgical findings (18 patients). Fifty-two of the patients had been involved in various sporting activities (long-distance runners, jumpers, and basketball players), three patients had familial hypercholesterolemia, five patients had systemic inflammatory disease, and 13 patients had no known underlying cause. Anatomic investigation demonstrated accurate assessment of tendon structure and thickness. Sonograms were abnormal in 53 patients (sensitivity, 0.72; specificity, 0.83), and the extent of structural disorders of the tendon could be assessed properly. Abnormalities occurred in the form of tendon swelling (45%), abnormal tendon structure (42%), rupture (15%), and peritendinous lesions (47%). No changes were detected in low-grade disease of short duration, which suggests symptoms caused by functional disorders. Sonography is valuable in the diagnosis of various lesions of the Achilles tendon and its surrounding tissue. Furthermore, it can be used to estimate the degree of tendon abnormality and to differentiate between functional and morphologic conditions.

Achilles Tendon↗
PubMed1990

[Isokinetic measurements of the stretch strength of the femoral quadriceps muscle in surfers in comparison to healthy, untrained persons].

The strength of the quadriceps muscle of twelve male surfers who practice their sport for more than 10 years was compared with results of 15 male untrained persons. The concentric peak torque of knee extensors was measured every 10 degrees in a range from 90 to 20 degrees isometrically and dynamically with a constant angle velocity of 10 degrees/sec. The difference in torque between the left and the right leg is not significant, but there is a slight dominance in favour of the standing leg. The body weight related strength of the surfers was 3.2 Nm/kg indicating a higher strength characteristic compared to 2.7 Nm/kg of untrained subjects. Moreover the strength values of our group of athletes were above the value of 3 Nm/kg, which is referred to in the literature as representing a good training status. In view of these results it can be concluded that a long-lasting specific training like surfing will change the strength characteristics of the quadriceps muscles, although none of the surfers had undertaken an extensive strength training for the lower extremity.

Adult↗
PubMed1990

Magnetic resonance knee arthrography. Enhanced contrast by gadolinium complex in the rabbit and in humans.

This study contains the fundamentals and the technique of the intraarticular application of an MRI contrast agent in connection with magnetic resonance imaging (MRI arthrography). It also presents the resulting clinical relevance for knee joint diagnostics. The significance of MRI arthrography is linked above all to the central question of whether or not it is possible to depict the hyaline cartilage, its surface and its thickness with the help of MRI arthrography. MRI arthrography was used for in vitro examinations of rabbit knee joint cartilage and human joint cartilage. The in vivo application was carried out in 73 patients. Apart from the metric evaluation and the assessment of the information content of the MRI image, the corresponding histologic sections were made in 20 knee joints in order to compare the cartilage surface and the thickness of the cartilage with the results in the MRI image. The optimum amount of contrast agent for visualization was determined, the uptake and clearance of the contrast agent from the cartilage were assessed, and trace elements from the cartilage were also analyzed. The examination showed that the molecular structure of the contrast agent (gadolinium-DTPA) does not prevent the uptake of the contrast agent into the matrix of the hyaline cartilage. But this process is reversible. Thus, 14 hours after the intraarticular application of the contrast agent no measurable traces of gadolinium-DTPA could be established. The intraarticular application of the contrast agent also made it possible to achieve a constant and reproducible visualization of all joint structures. This affected mainly the surface of the hyaline cartilage. The best imaging quality was achieved with intraarticular application of 30 to 40 mL of a 2 mmolar solution of gadolinium-DTPA. The technique used for the intraarticular application is the same as for the common procedures of knee joint aspiration. The clinical importance of MRI arthrography lies in the fact that a very detailed assessment can be made for therapy planning and furthermore in the possibility to provide the surgeon with answers to specific questions concerning the therapy. Examples are the extent and location of chondromalacia in a patient and the question whether a cartilage fracture has already occurred in osteochondrosis dissecans or not. The evaluation of cartilage together with the possibility to assess all other structures in the knee joint is a special feature of MRI arthrography. The high sensitivity and specificity of this method makes it superior to the examination without contrast agent and comparable to diagnostic arthroscopy.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗