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Biomedical subjects

G Arnold

Publications and source records attributed to G Arnold.

At least 181 records · Page 10Linked to original sources
PubMed1977

[Biomechanical investigations of the liver capsule (author's transl)].

The strain properties of geometrically defined specimens of human, pig, and bovine liver capsule were analysed in vitro by applying histomechanical procedures. The dynamic relaxation correlates with the static relaxation under sinus shaped strain process after previous additional predetermined increase in length. If such a process occurs in the linear region of the stress-strain curve, the relaxation process continues on a new level even if the amplitude of the sinus length-time input function is augmented. The same experiment causes in the lower non-linear region of the stress-strain relation the so-called asymmetric amplitude phenomenon. Further histomechanical features of the liver capsule obtained after defined length-time input functions such as relaxation, static isorheological line, dynamic isorheological curve, increase of the vertices of the dynamic force-time function after static relaxation and dynamic force recovery curve are shown. The phase shift between force and lenth is pointed out. The significance of the biomechanical properties of the liver capsule under physiological and pathological conditions is discussed.

Animals↗
PubMed1977

On the biomechanical function of the liver capsule.

UNLABELLED: We have carried out histomechanical studies on the human bovine liver caps-le under tension loading. RESULTS: Nonlinear force-time curve under extension with constant speed, initial upper and lower summit decrease of the dynamic relaxation curve, amplitude diminution phenomenon of the dynamic relaxation in the lower nonlinear part of the extension-time curve, dynamic (cyclic) force recovery.

Animals↗
PubMed1977

Light and electron-microscopic studies on guinea pig hearts after perfusion with nitro-blue tetrazolium (NBT).

Guinea pig hearts isolated by the Langendorff technique were perfused with a nitro-blue tetrazolium salt solution. In spite of a homogeneous dark-blue staining at the macroscopic examination, light-microscopic studies showed a spotty staining of the myocardial fibers. Since no microscopic alterations were found which could explain the unstained areas, ultramicroscopic studies were undertaken. At ultrastructural level, striking alterations of myocardial cells were observed. They consisted of mitochondrial lesions, alterations of the transversal tubuli, and intercalated discs. Arteriolar narrowing and capillary edema were found, suggesting that pathological changes in the microcirculation could be a possible reason for the spotty staining of the myocardial fibers. Some speculations on the nature and localization of the formazan granules are also reported.

Animals↗
PubMed1977

[Experimental studies of the historheology of the liver capsule (author's transl)].

We have performed histomechanical experiments with historheological methods on the liver capsule of men and cattle. The liver capsule is a non linear viscoelastic tissue. The force-extension diagram or the force-time curve under increase in length shows a flat initial part with a large strain reserve, then an arched domain and subsequently a steep increase in force with a coordination of a small increase in length. The hysteresis loop is represented. When the tissue is in a viscoelastic steady state (preconditioned), the force-extension curves respectively the force-time curves are identical one with another and under certain presuppositions reproducible. This is also the case with the static relaxation curve and the force recovery curve (inverse relaxation). With a ramp shaped extension time input function and an additional, superimposed sinus length-time input function we can observe the following dynamical force-time output functions: Non linear dynamical force increase, amplitude increment phenomenon, dynamical force recovery (dynamical inverse relaxation). Various dynamical-statical transients are demonstrated in diagrams. The mechanical properties of the liver capsule are interacting with the ligaments of the liver, with the intrahepatic connective tissue, and with the liver parenchyma. Aspects of the functional anatomy and the tension of the capsule in an acute increase of he liver parenchyma are discussed.

Animals↗
PubMed1977

[Tissue mechanical behavior of tendinous fibers under statistical and dynamic requirements].

With a device for dynamical processes tension tests were performed on bundles of collagen fibres of human and bovin origin. Part of the studies were performed under statical condition with an universal materials testing machine, equipped with a closed loop feed back control system. If the force is to be kept constant subsequently to a strain process on a collagen fiber bundle (isotonic condition), the fiber length must increase (creep phenomenon, retardation). The force decreases under constant length after a preceding strain process (relaxation). In analogy to the statical relaxation, statical isorheological line, and statical force recovery curve the dynamical (cyclic) relaxation, dynamical (cyclic) isorheological curve, and dynamical (cyclic) force recovery curve are described. The mechanical-rheological properties collagen fiber bundles are discussed in relation to functional anatomy.

Biomechanical Phenomena↗
PubMed1977

[An accessory muscle and additional variants of the forearm].

A report is given on an accessory muscle of the forearm. The muscle originates from the medial epicondyle and the fascia of the forearm and inserts into the pisiform bone and retinaculum. The accessory muscle has a great similarity with the flexor carpi ulnaris muscle.

Forearm↗
PubMed1976

Microperoxisome distribution in the central nervous system of the rat.

The distribution of microperoxisomes was studied in areas of the central nervous system having high concentrations of catecholaminergic neurons and in areas lacking this neuron type, using the alkaline DAB cytochemical method for catalase. Substantial numbers of microperoxisomes are found in neurons in the locus coeruleus and in nucleus A1 of the medulla, as well as in the substantia nigra, whereas few catalase-reactive bodies are seen in neurons of the cerebrum and cerebellum. The number of catalase-reactive microperoxisomes per unit area in the catecholaminergic neurons of the CNS is comparable to the number seen previously in neurons of the peripheral cervical sympathetic ganglia. Some spinal cord neurons also contain reactive microperoxisomes. Catalase-reactive microperoxisomes are numerous in oligodendrocytes of all areas studied, and in ependymal cells bordering the third and fourth ventricles. Astrocytes contain few reactive structures in the cytoplasm near the nucleus, but they are readily found in astrocytic processes and end-feet.

Animals↗
PubMed1976

[Mechanisms in the group effect of honeybees].

We consider the group effect on the mortality rate of honeybees and on the development of certain of their organs the mortality rate isolate honeybee varies according to the time of year, which leads us to believe that the group effect has an alimentary origin, at least at the outset. A sensory and perhaps pheromonal origin is equally demonstrated. Moreover, there is a group effect on most of the organs studied.

Animals↗
PubMed1976

[Biomechanics of human tendons: connection between stress relaxation and stress recovery (author's transl)].

108 tendons of the m. extensor hallucis longus were examined with a tensile testing machine within 36 h after death. The specimen were kept at a resting length of 20 mm. After the "steady state" was reached by cyclic loading, the tendons were stretched up to a maximum load of 18 kp, then deloaded to a certain level and after that the elongation was kept constant. At high loading level the tension of the tendon decreases with time (relaxation). At medium and low loading level the tension increases slightly (mechanical recovery). Between that two regions there is a certain load, where the tension will not change with time (isorheological point). The position of the isorheological point depends on the velocity of the elongation. At low velocity (2 mm/min) the isorheological point is situated at 70%, at high velocity (12 mm/min) at 60% of the maximum load. One will find the maximum relaxation, when no deloading occurs. The mechanical recovery, however, has its maximum at 5--25% of the maximum load. But when the tendon is totally deloaded, there seems to occur no recovery. The maximum relaxation is 5 to 6 times larger than the maximum recovery. Supposingly the relaxation- and recovery-processses will happen at the same time but with different intensity depending on the loading level. At least the relaxation-process consists of different relaxation components with different relaxation times. This will explain the phenomenon of a "secondary relaxation": After a long time of registration the recovery will turn into a slight relaxation.

Adolescent↗