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Biomedical subjects

D Halpern

Publications and source records attributed to D Halpern.

10 recordsLinked to original sources
PubMed1992

Gas dispersion in volume-cycled tube flow. I. Theory.

A mathematical theory is derived for the dispersion of a contaminant bolus introduced into a fully developed volume-cycled oscillatory pipe flow. The convection-diffusion equation is solved for a tracer gas bolus by expressing the local concentration field as a series expansion of derivatives of the area-averaged concentration. The local, as well as the area-averaged, concentration is determined for a uniform initial slug or Gaussian bolus. The effect of various flow parameters such as Womersley parameter, Schmidt number, and tidal volume is investigated. The overall dispersion is characterized by a time-averaged effective diffusion coefficient, which for long duration coincides with previous dispersion theories based on a constant linear axial concentration profile. The effective diffusion coefficient can be determined from the local time history of concentration, independent of the spatial location or the initial tracer bolus. Furthermore the local peaks of the concentration-time curve follow a decaying curve dictated by the time-averaged effective diffusion coefficient. Thus the theory is directly applicable for dispersion measurements in oscillatory tube flows, a basis for the pulmonary airways application, as shown by Gaver et al. (J. Appl. Physiol. 72: 321-331, 1992).

Bronchi↗
PubMed1991

Gel electrophoresis of polystyrene particles in glutaraldehyde crosslinked polyvinyl alcohol.

Polystyrene sulfate and carboxylate particles (19-189 nm radius) were subjected to electrophoresis in glutaraldehyde crosslinked polyvinyl alcohol of molecular weight 25.000 and 650.000 Da at various concentrations. The degree of crosslinking is severely limited by the mechanical properties of the gels that deteriorate beyond a glutaraldehyde concentration which decreases with increasing polyvinyl alcohol chain length. The effective fiber radius of the short-chain and long-chain polymer fiber was 45 +/- 25 and 131 +/- 47 nm, respectively. Thus, these media do not significantly exceed the apparent fiber thickness of agarose, are more difficult to prepare--but are well-defined synthetic products rather than natural ones, and have the advantage of carrying no net charge and can therefore be expected to exhibit no electroendosmosis.

Cross-Linking Reagents↗
PubMed1991

Leech therapy: when once is not enough.

Venous congestion is a constant threat in the survival of free flaps, pedicled flaps, tissue replantations and traumatized tissue. Leech therapy has proved effective in salvaging much of these compromised tissues. To be effective, leeches must be both readily available and hungry, requirements not always easily met. Our investigation seeks to establish a means to return sated leeches to their previous unfed, hungry state for reuse. Sated leeches were purged of their blood meals by placement in 3% hypertonic saline or by gentle finger pressure, then exposed to serotonin 0 microM (control), 10 microM, 30 microM or 90 microM for 20 min. Subsequent rebiting/refeeding was observed and analysed. Leeches bathed in serotonin rebit or reattached at nearly four times the rate of unexposed leeches; 30% vs 8% respectively. Biting, however, is not refeeding. Overall, 41 leeches were treated with serotonin with four (10%) refeeding. Those that refed consumed a significantly smaller blood meal than the initial feeding; 50% +/- 47% SD vs 348% +/- 143% SD of original body weight. None of the control group refed. As a method for routinely reusing leeches, serotonin bathing cannot be recommended. In the immediate postoperative period with the sudden emergence of venous congestion requiring leech therapy, but with an inadequate number available, this 20% [corrected] refeed rate after 10 microM serotonin exposure could potentially determine the success or failure of the flap/replantation until fresh leeches are made available.

Animals↗
PubMed1979

Muscular hypertonia: quantitative analysis.

By a statistical method of analysis, the force applied to move a limb passively can be translated into physiologically relevant parameters relating to the muscle. The parameters identified and measured are the dynamic and static activity of the muscle and their interactions with the varying length of the muscle during stretch. This method of analysis has been shown to be of assistance in evaluating the reflex status of persons with central nervous system disorders in preparation for treatment and in measuring the effects of treatment.

Humans↗
PubMed1979

Intramuscular neurolysis for spasticity in children.

Intramuscular neutrolysis with phenol has been used for 10 years in the management of spasticity in children. Best results depend on fastidious technique and realistic use of the procedure. Sedation or anesthesia was used in all cases -- 5% phenol in water was used for all procedures. The main indications were spasticity which interfered with function, either actual or potential, or with care. Where uninhibited vestibular or tonic neck reflexes affect muscle tone, or there is dystonia or athetosis, the procedure is less effective than where spasticity alone is present. Duration of relief of spasticity ranged from 1 month to more than 2 years. About one half of the lower extremity muscle treated required tenotomy later. Generally training was required after the procedure to obtain improved function. A representative sample of muscles treated, repeat procedures, and later surgery is discussed. The procedure is recommended for use in the management of spasticity in children as a way of improving function and/or care.

Adolescent↗
PubMed1978

Electromyographic feedback and physical therapy for neuromuscular retraining in hemiplegia.

Electromyographic feedback was compared with physical therapy for its relative effectiveness in training motor activity in patients with hemiplegia. A cross over design was used, so that each patient served as his own control. Strong reinforcement for attentional direction and for successful response to established criteria was used with both modalities. Electromyography through auditory and visual display was found effective in improving electromyographic activity, but more limited in training effective function as measured by active range of motion. In some cases it was counterproductive. Using an instrumental modality permits attention to only a limited number of motor elements involved in a motion, and is even more limited with respect to the interplay of activation and inhibition of those components. The activity of physical therapy, using tactile, proprioceptive, visual and communicative modalities, has the capacity for attending and drawing attention to many motor elements, as well as to the complexities of activation of some components concomitantly with the inhibition of others during the training process. Electromyographic feedback was felt to be especially useful in its ability to enhance figure-background discrimination and bypass possible areas of sensory obtundation.

Aged↗
PubMed1978

The training of coordination.

The training of coordination is generally considered a volitional activity, during which, by trial and perception of results, an individual selects the muscular activity resulting in the desired performance. This concept of volitionally directed complex coordination of multiple muscles with speed, skill, and strength does not stand the test of thorough evaluation. Attention is limited to 1 activity at a time, with the ability to shift attention not more frequently than 3 times per second. Only under special conditions can activity be limited to specific muscles during an untrained contraction without cocontraction of other muscles. However, with repeated practice of the desired activity, a pattern of performance is developed which can be carried out rapidly and forcefully without activation of other muscles. At that time, the consciousness is no longer directing the components of the activity but merely starting, maintaining, and stopping the performance. The development of these patterns, or engrams, by practice develops the capacity to automatically inhibit muscles that do not contribute to the performance of the desired pattern. The capacity for inhibition results in coordinated activation of the muscles contributing to the performance desired. Investigation of the development of coordination in many types of normal activities, as well as in neuromuscularly impaired patients, shows that engrams develop progressively by slow, precise practice of simple patterns, combined as they develop into more and more complex patterns, until the final skill is attained.

Attention↗
PubMed1977

Histologic studies in animals after intramuscular neurolysis with phenol.

The histologic effects of the intramuscular injection of phenol concentrations ranging from 1% ot 7% were studied in rats and dogs at from one day to ten months after injection. The sites within the muscle localized by a standardized technique for electrical stimulation proved to be intramucular nerves, either near the terminal innervation band, or more proximally, mixed nerves running in the neurovascular bundle in the interfascicular regions of the muscle. The latter was by far the more frequent site of localization. The procedure is therefore identified as "intramuscular neurolysis" rather than motor end-plate or motor point block. Phenol causes nerve destruction with secondary denervation and atrophy, and muscle necrosis, Both nerve and muscle show regeneration which is well established by two months, and almost complete in three months.

Animals↗