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Biomedical subjects

J H Meier

Publications and source records attributed to J H Meier.

12 recordsLinked to original sources
PubMed1998

Aneurysms in the left ventricular outflow tract: clinical presentation, causes, and echocardiographic features.

We present a descriptive compendium of anatomically interrelated aneurysms and aneurysmal-like structures arising in and around the left ventricular outflow tract. Images selected from the Mayo Clinic echocardiography database illustrate classic or typical examples of each entity. Essential morphologic features of each lesion are described. Clinical presentation, causes, and diagnostic echocardiographic features taken together can improve recognition and clinical management of this diverse group of anomalies.

Aortic Aneurysm↗
PubMed1998

Extracellular potentials from active myelinated fibers inside insulated and noninsulated peripheral nerve.

A model is presented that calculates the single-fiber extracellular field and action potential (ap) of an active myelinated nerve fiber placed centrally or eccentrically inside a nerve with a cylindrical geometry, representing essentially a one-fascicle nerve. This one-fascicle nerve has the dimensions and conductivities of the rat peroneal nerve branch. The results show a wide variety of wave shapes to be measured, depending on the position of the intraneural electrode with respect to the fiber axis and to the nodes of Ranvier and depending on the presence of an isolating cuff around the nerve. Action potential shapes may range from the "classical" quasi-biphasic one, to more triphasic, or even more complicated in the case of a short insulating cuff being present around the nerve. In the latter case, when measured bipolarly, ap-wave shapes become almost monophasic.

Action Potentials↗
PubMed1995

Force recruitment during electrical nerve stimulation with multipolar intrafascicular electrodes.

Experimentally, during electrical nerve stimulation, the influence is examined of two intrafascicular anodes on the force recruitment with one intrafascicular cathode. It is found that the anodes suppress recruitment and that this effect is more pronounced when the distance of the anodes to the cathode is decreased, or when the anodal currents are increased. The measured recruitment curve patterns can be qualitatively explained by a nerve stimulation model that calculates theoretical recruitment curves for intrafascicular multi-electrode configurations. Discrepancies between the experimental and the theoretical recruitment curves are seen, but these can be understood by taking into account a non-uniform fibre distribution.

Animals↗
PubMed1995

3D neuro-electronic interface devices for neuromuscular control: design studies and realisation steps.

In order to design the shape and dimensions of new 3D multi-microelectrode information transducers properly, i.e. adapted to the scale of information delivery to and from peripheral nerve fibres, a number of studies were, and still are, being performed on modelling and simulation of electrical volume conduction inside and outside nerves, on animal experiments on stimulation and recording with single wires and linear arrays, and on new technologies for 3D micro-fabrication. This paper presents a selection of the results of these "Neurotechnology' studies at the University of Twente. The experimental and simulation results apply primarily to the peripheral motor nerves of the rat, but are also of interest for neural interfacing with myelinated nerves in man, as fascicles in man are about the same size as in the rat.

Animals↗
PubMed1994

Does omeprazole (Prilosec) improve respiratory function in asthmatics with gastroesophageal reflux? A double-blind, placebo-controlled crossover study.

Gastroesophageal reflux (GER) is common among patients with asthma, and it has been speculated that high GER may exacerbate asthma in some. This study was designed to determine if suppression of acid reflux in patients with asthma would improve pulmonary function. A double-blind, placebo-controlled crossover study design was used to determine the effect of GER suppression with omeprazole (20 mg twice daily) on pulmonary function among asthmatic patients with esophagitis. Four of 15 (27%) asthma patients with GER were shown to have a > or = 20% net improvement in pulmonary function (FEV1) after treatment for six weeks with omeprazole. These results indicate that some patients with asthma and GER will have improved pulmonary function when acid GER is treated with omeprazole.

Adult↗
PubMed1992

Simulation of multipolar fiber selective neural stimulation using intrafascicular electrodes.

A realistic, quantitative model is presented for the excitation of myelinated nerve fibers by intrafascicular electrodes. It predicts the stimulatory regions of any configuration of any number of electrodes, positioned anywhere inside the fascicle. The model has two parts. First, the nerve fiber is represented by a lumped electrical network and its response to an arbitrary extracellular potential field is calculated. Second, assuming a cylindrical geometry of the nerve bundle and its surroundings, an analytical expression for this field is derived. With realistic parameters, the model is applied to two cases: monopolar stimulation by a single cathode and stimulation by a specific tripolar configuration. It is shown that tripolar stimulation has the better spatial selectivity. Also tripolar stimulation is less sensitive to the conductivity of the medium surrounding the nerve and yields a more natural recruitment order.

Electric Conductivity↗
PubMed1991

Selectivity of intraneural prosthetic interfaces for muscular control.

Intraneural stimulation with multi-electrodes in principle offers the best possibilities to reach selectivity at motor unit level and to improve recruitment order. The selectivity of stimulation in the peroneal nerve of the rat is explored in the paper by calculations and measurements, using a linear 12-electrode array and a newly devised selectivity test method. With analytical models for potential field distributions, areas of excitation can be calculated for arbitrary electrode configurations. It is demonstrated, using tripolar electrode combinations, how selectivity can be further enhanced and recruitment order improved.

Action Potentials↗
PubMed1987

Variables associated with disrupted placement in a select sample of abused and neglected children.

The purpose of this study was to examine the placement history of 172 abused and/or neglected children who had been placed in a residential home for maltreated children. Data were collected on the child's placement history (i.e., number of placements, time in transition, and placement rate) and also on child and family characteristics. Pearson correlation coefficients were run between child and family variables and each of the three placement history variables. In addition, t-tests were also used as a method of analysis. Results indicated that children with the following characteristics or life circumstances experienced the more disruptive experience while in foster care: children having severe behavior problems; children who were very young when first removed from their natural home; and children having drug addicted and/or alcoholic parents. Implications of these findings indicate social workers and judges need to be alert to the potential for system abuse of children in foster placement, responsible long-term planning for any child in foster care is critical, and those involved in therapeutic treatment for abused/neglected children should be attentive to the child's placement history.

Adolescent↗
PubMed1983

Typology for parents of abused children.

This paper reports an effort to classify the parents of abused children with some existing and some new empirically/clinically consistent typologies, which are derived from the parents' psychopathological personality profiles. Such a classification scheme is informative and helpful for both treatment planning and permanency planning for abusive parents and abused children, whether or not the children have been separated from their parents. Several previously reported typologies for abusive parents are reviewed and then elaborated in light of the additional data and insights gained from an ongoing study of 50 abusive parents who were separated from their children due to severe child abuse. Such typological analyses based upon principal personality characteristics and dynamics promise to help in formulating both secondary and even primary child abuse prevention procedures and programs. The parent typologies which represent the more favorable prognoses, as determined by their therapist's estimate of their response to ongoing treatment, are those classified as rigid-compulsive, or experiencing identity/role crisis, or displaced abuse/violence. Parents whose child abusive behavior is a function of extremely maladaptive resolutions of major life issues fall into the hostile-aggressive, passive-dependent, and severe mental illness typologies, where the prognoses are considerably more guarded. The relatively high incidence of hostile-aggressive fathers coupled with passive-dependent mothers as abusive parents to children in a residential program for severely abused children also helps explain some of the children's psychopathology.

Adaptation, Psychological↗