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Biomedical subjects

M Anliker

Publications and source records attributed to M Anliker.

At least 19 recordsLinked to original sources
PubMed1992

Monte Carlo minimization with thermalization for global optimization of polypeptide conformations in cartesian coordinate space.

A new minimization procedure for the global optimization in cartesian coordinate space of the conformational energy of a polypeptide chain is presented. The Metropolis Monte Carlo minimization is thereby supplemented by a thermalization process, which is initiated whenever a structure becomes trapped in an area containing closely located local minima in the conformational space. The method has been applied to the endogenous opioid pentapeptide methionine enkephalin. Five among 13 different starting conformations led to the same apparent global minimum of an in-house developed energy function, a type II' reverse turn, the central residues of which are Gly-3-Phe-4. A comparison between the ECEPP/2 global minimum conformation of methionine enkephalin and the apparent one achieved by the present method shows that minimum-energy conformations having a certain similarity can be generated by relatively different force fields.

Amino Acid Sequence↗
PubMed1992

Fluorescence spectroscopy for identification of atherosclerotic tissue.

OBJECTIVE: Vessel perforation and limited steerability of the laser light are the major limitations of laser angioplasty. To improve steerability fluorescence spectroscopy has been proposed for identification of atherosclerotic plaques. The aim was to investigate this. METHODS: Fluorescence spectroscopy with three different excitation wavelengths (325 nm, 380 nm, 450 nm) was tested in an emission range of 400 nm to 600 nm. Intensity ratios at 480/420 nm were determined in different types of blood vessels. Necropsy material from 40 patients (punch biopsies of 4 mm diameter from the coronary and carotid artery as well as from the ascending and descending aorta) was studied spectroscopically. Histological alterations of the vessel wall were assessed by a semiquantitative score (0 to 10 points): (a) normal tissue, 0 to 2 points (mean = 0.25; n = 38); (b) mild atherosclerotic lesions, 3 to 5 points (mean = 3.35; n = 39); (c) severe atherosclerotic lesions, greater than or equal to 6 points (mean = 6.75; n = 43). RESULTS: Best spectroscopic results were obtained with an excitation wavelength of 325 nm. In samples with severe atherosclerotic lesions the fluorescence spectra showed a significant reduction of the emitted wavelength intensities when compared to normal tissue. There was a clear separation of the fluorescence spectra between normal and mild as well as between normal and severe atherosclerotic lesions; normal tissue showed an increased intensity in the range from 420 nm to 540 nm, whereas atherosclerotic lesions had no or only a small peak at 480 nm. There was a significant correlation between the semiquantitative score (n = 120) and the fluorescence ratio at 480/420 nm (excitation wavelength 325 nm) with a correlation coefficient of 0.87. The spectroscopic results showed no differences between the samples taken from different types of vessels. CONCLUSIONS: Fluorescence spectroscopy allows a reliable identification of normal and atherosclerotic lesions. The close correlation between the emitted light intensity ratio at 480/420 nm and the histological alterations of the vessel wall suggests a relationship between vessel wall fluorescence and the atherosclerotic alterations of the wall.

Adolescent↗
PubMed1979

Loss and recovery of trabecular bone in the distal radius following fracture--immobilization of the upper limb in children.

Computed tomography of the human radius is performed using a special purpose scanning device which incorporates a radionuclide (125I) as radiation source. Parameters decribing the trabecular bone and the compact bone are determined at a distal and a diaphyseal measuring site respectively. Using this measurement technique changes in bone mineralization in the radius were studied in a group of 23 children following immobilization of an upper limb for fracture healing. An immobilization period of between three to six weeks resulted in a reduction of the relevant parameter value of up to 44% (mean 16%) in the distal part of the radius, whereas no significant change could be seen in the diaphyseal part of the same bone. Rapid remineralization of trabecular bone is indicated by the increase of the corresponding parameter value at a rate of up to several percent per week. However, in some of the patients studied complete normalization was not attained during the first six months following cast removal.

Bone Regeneration↗
PubMed1979

Blood pressure fluctuations in human nailfold capillaries.

Dynamic blood pressure was measured in 33 human finger nailfold capillaries after direct cannulation with glass micropipettes by means of a resistance servo-nulling pressure measuring method. ECG, finger pulsations, and respiratory thorax excursions were monitored simultaneously. All recordings exhibited pulsatile oscillations related to the cardiac rhythm. These oscillations resembled the wave forms of arterial pulsations with steep upstroke and dicrotic notch when the pressure amplitudes were above 10 mmHg. There was no apparent dependence on respiration. In 12 instances, pressure fluctuations with frequencies ranging from 0.2 down to 0.07 Hz were observed in both the arteriolar and venular limb. Blood pressure in human skin capillaries is pulsatile and subject to remarkable fluctuations in the arteriolar as well as in the venular limb, systolic pressure values ranging from 14 to 71 mmHg and from 11 to 52 mmHg, respectively.

Adult↗
PubMed1979

Bone densitometry using computed tomography. Part I: selective determination of trabecular bone density and other bone mineral parameters. Normal values in children and adults.

Gamma-ray computed tomography (gamma-ray CT), using a special purpose scanner, enables in-vivo quantitative analysis of bone mineralization. Trabecular bone density (TBD), the relative amount of compact bone (bone density, BD) and the total absorption (TA) for a cross-section of the radius are determined from measurements of local linear absorption coefficients. A preliminary study of normal children (n = 49) and adults (n = 34) indicated that TBD is independent of age and sex in the age range 4 to 40 years. DB remains constant throughout childhood but increases after puberty in both women and men. TA is higher for adults than for children, and also higher for men than for women. A correlation between TA and parameters relating to body size indicates a relationship between body weight and bone mass.

Adolescent↗
PubMed1979

Bone densitometry using computed tomography. Part II: increased trabecular bone density in children with chronic renal failure.

The method of gamma-ray computed tomography (gamma-ray CT) bone densitometry described in the preceding article provides selective determination of trabecular bone density (TBD), the relative amount of compact bone (bone density, BD), and the total absorption (TA) within a bone cross section. Seven of nine children with chronic renal failure (CRF), and selected only on the basis of their serum creatinine value (greater than 5 mg/100 ml), had increased TBD values above the normal range, whereas the other bone mineral parameters were normal. Radiographic signs of secondary hyperparathyroidism (subperiosteal erosions, cysts) were reported in the five patients with the highest TBD values, whereas the subjective diagnosis of osteosclerosis reported in three of these five and in one other patient correlated less well with the TBD increases. However, this is the first report of an objective, non-invasive documentation of the radiological finding of osteosclerosis in CRF. It also explains why methods for bone mineral measurements used previously, such as a photon absorptiometry which provides only a parameter equivalent to TA, failed to reveal increases in bone mineral content in renal osteodystrophy even when signs of osteosclerosis were present. Thus, gamma-ray CT helps to document objectively the degree of osteosclerosis and its location.

Adolescent↗
PubMed1979

Computed tomography reconstruction from hollow projections: an application to in vivo evaluation of artificial hip joints.

The long-term mechanical stability of total hip arthroplasties limits the application of this widely used surgical procedure in cases of severe coxarthroses. A noninvasive method of assessing the tissue distribution in the vicinity of the implant--bone interface is needed to identify early signs of implant loosening and to evaluate new prosthetic solutions. In order to develop such a method, a modified computed tomography technique has been devised that yields cross-sectional images without the usual artifacts caused by metallic implants. This technique provides information on bone mineral and bone cement distributions as well as on the precise position and orientation of the implant within the femur shaft. Results obtained from excised human femurs and preliminary data from measurements on patients made 3 months postoperatively reveal that the bone cement distribution is much less favorable than is indicated by radiographs.

Aged↗
PubMed1977

Changes in phasic femoral artery flow induced by various stimuli: a study with percutaneous pulsed Doppler ultrasound.

Transcutaneous blood flow measurements were performed by means of pulsed Doppler ultrasound flowmeter in the femoral artery of healthy subjects. The pulsatile flow pattern was changed characteristically from resting state by postocclusive reactive hyperaemia, by the application of amyl nitrite, xanthinol nicotinate, and angiotensin amide. During reactive hyperaemia systolic flow was increased, diastolic reverse flow was abolished, and the forward flow continued throughout diastole. Amyl nitrite augmented thenegative flow phase and reduced mean flow, while xanthinol nicotinate decreased the negative component and augmented mean flow. Angiotensin amide produced enhancement of the average flow by elevating systolic and diastolic flow equally over the base line. In each of these interventions the changes in flow were determined mainly by variations during the diastolic flow phase.

Adult↗
PubMed1976

Quantification of bone mineralization using computed tomography.

Computed tomography was used to find a sensitive parameter for bone mineralization. A precision scanning instrument was constructed for determination of the mineral distribution in sections of the forearm. The quality of the reconstructed images allows separate quantification of compact and spongy bone even when gamma rays are used. Computer simulation and measured of models and macerated human bones showed that under clinical conditions it is possible to quantify spongy bone density within an accuracy of +/-2%.

Adolescent↗
PubMed1975

[Proceedings: Determination of the severity of aortic insufficiency with pulsed Doppler-ultrasound in the common carotid artery].

The severity of aortic incompetence can be assessed by quantifying the alteration of blood flow in the common carotid artery. The use of a pulsed multichannel ultrasonic Doppler device in 41 patients with aortic valve disease yielded a satisfactory correlation between the ultrasonic parameters and the maximal aortic regurgitation distance. Correlations between Doppler parameters and regurgitation (thermodilution) were less strict.

Adult↗