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M D Siegel

Publications and source records attributed to M D Siegel.

9 recordsLinked to original sources
PubMed2001

Numerical modeling of coupled variably saturated fluid flow and reactive transport with fast and slow chemical reactions.

The couplings among chemical reaction rates, advective and diffusive transport in fractured media or soils, and changes in hydraulic properties due to precipitation and dissolution within fractures and in rock matrix are important for both nuclear waste disposal and remediation of contaminated sites. This paper describes the development and application of LEHGC2.0, a mechanistically based numerical model for simulation of coupled fluid flow and reactive chemical transport, including both fast and slow reactions in variably saturated media. Theoretical bases and numerical implementations are summarized, and two example problems are demonstrated. The first example deals with the effect of precipitation/dissolution on fluid flow and matrix diffusion in a two-dimensional fractured media. Because of the precipitation and decreased diffusion of solute from the fracture into the matrix, retardation in the fractured medium is not as large as the case wherein interactions between chemical reactions and transport are not considered. The second example focuses on a complicated but realistic advective-dispersive-reactive transport problem. This example exemplifies the need for innovative numerical algorithms to solve problems involving stiff geochemical reactions.

Diffusion↗
PubMed2001

Delirium in the intensive care unit: an under-recognized syndrome of organ dysfunction.

The intensivist should think of delirium, or acute central nervous system dysfunction, as the brain's form of "organ dysfunction.'' Delirium is extremely common in intensive care unit (ICU) patients due to factors such as comorbidity, critical illness, and iatrogenesis. This complication of hospital stay is extremely hazardous in older persons and is associated with prolonged hospital stays, institutionalization, and death. Neurologic dysfunction compromises patients' ability to be removed from mechanical ventilation or achieve full recovery and independence. Yet ICU nurses and physicians are usually unaware of the presence of hypoactive delirium and only recognize this disturbance in agitated patients (hyperactive delirium). More importantly, there are few studies that have included ICU patients in the assessment or prevention of delirium. This article reviews the definition and salient features of delirium, its primary risk factors, a newly validated instrument for delirium assessment that is being developed for ICU nurses and physicians, and pharmacological agents associated with the development of delirium and used in its management.

Journal Article↗
PubMed2000

Mechanical ventilation in chronic obstructive lung disease.

Exacerbations of COPD are a leading indication for MV in the intensive care unit. A thorough understanding of the pathophysiology of AVF in COPD is critical for physicians caring for these patients. In particular, physicians should understand DHI and use the ventilator and ancillary techniques to minimize its impact. Noninvasive positive-pressure ventilation should be considered strongly in relatively stable patients with an adequate mental status and manageable secretions. Once AVF resolves, patients should be removed from the ventilator as soon as is safe to do so to minimize the adverse effects of prolonged MV. An organized approach to weaning and identifying patients capable of independent breathing is crucial. Most patients with COPD and AVF benefit from MV and generally return to or approach their premorbid functional status. A significant subset, however, will not benefit from, or choose not to undergo, MV. Deciding upon appropriate therapeutic options for these patients relies heavily on effective communication between physician and patient. Comprehensive discussions before the development of AVF can assist decision-making after respiratory failure develops.

Acid-Base Imbalance↗
PubMed1995

Activation of the interleukin-5 promoter by cAMP in murine EL-4 cells requires the GATA-3 and CLE0 elements.

Interleukin-5 (IL-5) plays a central role in the growth and differentiation of eosinophils and contributes to several disease states including asthma. Accumulating evidence suggests a role for cAMP as an immunomodulator; agents that increase intracellular cAMP levels have been shown to inhibit production of cytokines predominantly produced by T helper (Th) 1 cells such as IL-2 and interferon gamma (IFN-gamma). In contrast, the production of IL-5, predominantly produced by Th2 cells, is actually enhanced by these agents. In this report, we have performed transient transfection experiments with IL-5 promoter-reporter gene constructs, DNase I footprinting assays, and electrophoretic mobility shift assays to investigate the key regulatory regions necessary for activation of the IL-5 promoter by dibutyryl cAMP and phorbol esters in the mouse thymoma line EL-4. Taken together, our data demonstrate the critical importance of two sequences within the IL-5 5'-flanking region for activation by these agents in EL-4 cells: one, a highly conserved 15-base pair element present in genes expressed by Th2 cells, called the conserved lymphokine element 0 (CLE0; located between -53 and -39 in the IL-5 promoter), and the other, two overlapping binding sites for the transcription factor GATA-3 (but not GATA-4) between -70 and -59. Taken together, our data suggest that activation via the unique sequence combination GATA/CLE0 results in selective expression of the IL-5 gene in response to elevated levels of intracellular cAMP.

Animals↗
PubMed1993

Advances in neonatology. View from a practicing pediatrician.

After reviewing the many problems that may be seen by the physician in follow-up care of the preterm infant and family, it is important to take a step back and evaluate the infant as a whole. In the vast majority of instances, the preterm infant will turn out to be normal. In an unfortunate minority, there may be difficult problems that the baby, parents, and caretakers must face. The pediatrician must remain diligent to attend to those problems that are correctable and to assist patients to their full potential.

Gastrointestinal Diseases↗