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Biomedical subjects

H G Haas

Publications and source records attributed to H G Haas.

At least 37 records · Page 2Linked to original sources
PubMed1986

Voltage clamp simulations for multifiber bundles in a double sucrose gap: cable complications.

A theoretical model is presented for voltage clamp of a bundle of cylindrical excitable cells in a double sucrose gap. The preparation in the test node is represented by a single one-dimensional cable (length/diameter ratio approximately) with standard Hodgkin-Huxley kinetics for transmembrane Na current. Imperfections of voltage control due to internal (longitudinal) resistivity and external (radial) resistance in series to the membrane are analysed. The electrical behavior of a fiber is described by the cable equation with appropriate boundary conditions and subsidiary equations reflecting the membrane characteristics. Membrane voltage and current distribution in response to a step command was obtained by numerical integration. The results are described in two papers. The present paper deals with the effect of internal resistivity with the external resistance being neglected. The closed loop response of a fiber displays a strong tendency to oscillate. To stabilize the system a phase lead was inserted and the gain of the control amplifier was reduced. Conditions for stability were examined by Nyquist analysis. When the Na system was activated by a command pulse below ENa, a voltage gradient developed between a depolarization (relative to the command signal) at the end where voltage was monitored and a hyperpolarization at the site of current injection. In spite of a poor voltage control the total measured current appeared to have a smooth transient. With large voltage gradients a small, second inward current was seen. At a low (high) Na conductance maximum peak inward current was larger (smaller) that the current expected from ideal space clamping.

Animals↗
PubMed1986

[PDS splint in the treatment of fractures].

Polydioxanon-splints have been used instead of Kirschner-wires in 13 cases for the treatment of fractures of the base or head of phalanges and metacarpals and also, in conjunction with intraosseous suture wires, to stabilize the bones in replantation surgery.

Bone Wires↗
PubMed1984

[Irreducible dislocations of the metacarpophalangeal joints].

Within a period of twelve years, the authors have treated twelve patients with metacarpophalangeal joint luxations of thumb and long fingers which could not be reposed by conservative treatment. The case reports are presented in order to describe the problems posed by this relatively rare injury, the reasons hindering a reposition, and the treatment methods. This study is intended to underline the importance of early diagnosis and immediate surgical treatment in order to maintain the function of the joint.

Adolescent↗
PubMed1983

Intercellular coupling in frog heart muscle. Electrophysiological and morphological aspects.

Passive electrical parameters of bullfrog atrial trabeculae were measured in a single gap arrangement. Attention was focussed on the resistance of internal longitudinal pathway. The influence of external Ca2+ depletion was tested using EGTA as chelating agent. Morphometry of trabeculae, fine structure of junctional complexes, and distribution of membrane-bound Ca were investigated by light and electron microscopic methods. The specific internal resistance to longitudinal current flow was 523 omega cm with normal Ringer as perfusing fluid and 1140 omega cm in EGTA-containing solution. These values are considered to represent the sum of myoplasmic and junctional resistivity. Morphometrical studies indicated an interstitial space of 12%, a mean cell length of 358 micron, and a mean cell diameter of 3.2 micron. In freeze-fractured preparations junctional structures were observed in the form of "atypical gap junctions" consisting of 10 nm particles arranged in a circular or linear array. The number of gap junctions was estimated to range between 20 and 50/cell which is equivalent to a junctional area of 0.01 or 0.03% of total surface area. A mean number of 55 particles/gap junction was calculated. After 20 min of exposure to EGTA the majority of junctional complexes were converted to clusters; the number of particles/gap junction was not significantly altered. The fluorescent dye CTC was used as a probe for membrane-bound Ca of isolated living cells. In normal Ringer a strong fluorescence was seen at the cell surface and in different intracellular compartments. With EGTA both superficial and internal fluorescence disappeared completely. From a combination of electrical and morphometrical data the resistance of intercellular junctions was calculated. Under normal conditions the specific resistance of junctional membrane amounted to 0.4 omega cm2 and the resistance of an individual connection was of the order of 10(11) omega. With EGTA, the respective values were increased by about 230%. The mechanism underlying this depression of junctional conductance is not clear. It seems not related to a rise of cytoplasmic free Ca2+. The EGTA-induced increase in internal resistance was reflected by a decrease of the length constant of a bundle. The nature of "atypical gap junctions" and their relation to tight junctions are discussed. It is concluded that the junctions observed in frog atrial muscle are analogous to gap junctions of insect or mammalian cells in spite of the different size and arrangement of the particles. A theoretical model is presented for the electrical behaviour of a bundle in a single gap arrangement.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1981

[Primary care of extensor tendon injuries].

Therapeutic conclusions are derived from the anatomical peculiarities of the extensor apparatus of the fingers and the extensor tendons of the metacarpus and the wrist. In open wounds primary sutures are universally possible and promising except in cases with tendon defects or with special risk of infection. Our preferred technique employs a central wire suture which is barbed to resist proximal traction, combined with fine peripheral sutures. In closed ruptures at the DIP-level conservative as well as operative treatment can be advised, whereas at the PIP-joint and in more proximal regions operative measures are preferred.

Casts, Surgical↗
PubMed1981

[Treatment outcome in de Quervain's dislocation fracture].

In De Quervains dislocation fracture pseudarthroses of the scaphoid bone following closed reduction are very common, 59% being reported in a former publication. Exact adaptation of the fragments after reduction of the perilunar dislocation is essential for healing of the fracture. In cases where this is not possible by conservative means, open reduction and screwing of the scaphoid fracture is necessary for better result with a rate of pseudarthroses of only 16%.

Bone Screws↗
PubMed1980

[Hyperparathyroidism in carcinoma of the parathyroids (author's transl)].

Parathyroid carcinoma as the cause of primary hyperparathyroidism was found in 3 out of 102 patients. The diagnosis was based on the findings of markedly increased serum calcium and parathormone values, definite infiltration of the tumour into the surrounding tissue, mitoses, wide connective tissue septa in the tumour as well as rupture of the capsule and penetration of vessels. The diagnosis can only be made after close cooperation between endocrinologists, surgeons and pathologists.

Adult↗
PubMed1980

Polyendocrine deficiency syndrome. Occurrence in a patient with depressed IgA titers receiving phenytoin.

A 35-year-old woman had an addisonian crisis and primary adrenal, ovarian, and thyroid failures were detected. Antibodies against the adrenal glands and the thyroid were found, together with consistently low IgA levels. The patient had been receiving phenytoin, a drug known to induce an IgA deficiency, for 20 years. The question arises as to whether this substance was responsible for an immunological defect leading to an autoimmune process that damaged the adrenal glands, the ovaries, and the thyroid.

Addison Disease↗
PubMed1980

Influence of intercellular clefts on potential and current distribution in a multifiber preparation.

A theoretical model is presented for current and voltage clamp of multifiber bundles in a double sucrose gap. Attention is focused on methodological errors introduced by the intercellular cleft resistance. The bundle is approximated by a continuous geometry. Voltage distribution, as a function of radial distance and time, is defined by a parabolic partial differential equation which is specified for different membrane characteristics. Assuming a linear membrane, analytical solutions are given for current step and voltage step conditions. The theoretical relations (based on Bessel functions) may be used to calculate membrane conductance and capacity from experimental clamp data. The case of a nonlinear membrane with standard Hodgkin-Huxley kinetics for excitatory Na current is treated assuming maximum Na conductances (gNa) of 120, 10, and 1 mmho/cm2. Numerical simulations are presented for potential and current distribution in a bundle of 60 microns diameter during depolarizing voltage steps. Adequate voltage control is restricted to the peripheral fibers of the bundle whereas the membrane potential of the inner fibers deviates from the command level during early inward current, tending to the Na equilibrium potential. In the peak current-voltage diagram the loss of voltage control is reflected by an increased steepness of the negative region and a decreased slope conductance of the positive region. With gNa = 120 mmho/cm2, the positive slope conductance is approximately 25% of the slope expected from ideal space clamping. With the lower values of gNa, the slope conductance ratio is in the order of 50%. Implications of the results for an experimental voltage clamp analysis of early inward current on multifiber preparations are discussed.

Animals↗
PubMed1980

Tumoral calcinosis. Observations during six years.

Findings of a 56 year old woman suffering from tumoral calcinosis, who was treated for 6 years, are presented. Under conditions known to lead to negative calcium-phosphorus balance, a reduction in tumor size was seen. Transient hypercalcemia was attributed to immobilization. The process of tumor reduction was not definitely accelerated by treatment with ethane-hydroxy-diphosphonate (EHDP; 500 mg/day for 20 months). Nephrotic syndrome as a consequence of amyloidosis developed. Amyloidosis seems to have resulted from the aseptic histiocytic inflammatory process in the tumors. The possible importance of high cholesterol in very low density lipoproteins in the serum of the patient is discussed.

Amyloidosis↗
PubMed1979

[Primary hyperparathyroidism--bone turnover and osteitis fibrosa assessed by x-ray (author's transl)].

1. In primary hyperparathyroidism an increased bone turnover is seen, accompanied by osteitis fibrosa (= fibroosteoclasia, FO) in severe forms of the disease. Both types of bone reaction may be detected by microradioscopy X-rays of the hand, extensive striation of metacarpal cortical bone indicating increased bone turnover and subperiosteal resorption of phalanges pointing to FO. 2. In the present study 65 patients with proven PHPT were evaluated before and 39 after operation. Microradioscopy was combined with biochemical assessment of hyperparathyroidism including alkaline serum phosphatase (aPh) as an index of osteoblastic activity, hydroxyprolin excretion (HyPro) reflecting bone turnover, immunoreactive parathyroid hormone levels (PTH), serum calcium (SCa), urinary calcium (UCa), serum inorganic phosphorus (SP) and clearance of phosphate (Cp). A comparison was made with the incidence of renal stone disease and the degrees of metacarpal striation (StG) and subperiosteal resorption (UG) were followed after operation. 3. Preoperative X-rays of 60% of the PHPT subjects showed increased StG and/or UG, and in 41,5% the diagnosis of PHPT was possible from the X-ray findings only. There existed a significant correlation between StG and UG on one hand and aPh, HyPro and PTH on the other. No correlation, either positive or negative, was seen between FO and the incidence of renal stones. After surgery, subperiosteal bone lesions disappeared in all patients, while intracortical striations persisted in half of the subjects despite the normalised bone turnover. Thus, primary hyperparathyroidism may not only lead to endosteal bone loss but to an irreversible intracortical bone deficit as well.

Adolescent↗
PubMed1979

Tumoral calcinosis: accumulation of bone-seeking tracers in the calcium deposits.

Rapid and preferential uptake of 47 calcium 87m Strontium by the multinodular calcareous masses was seen in a patient with tumoral calcinosis. Using 87m Strontium, scintigraphic imaging of the tumors was achieved, while the skeleton was barely visible. More intense accumulation of 87m Sr. in one tumor suggested a higher rate of calcium depostion. This was in agreement with the observation that this tumor showed less tendency to decrease in size during calcium and phosphorus deprivation therapy. Quantitative measurements of the uptake of bone seeking tracers by the tumors may be of value in estimating calcium turnover in the calcified masses.

Calcinosis↗