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Biomedical subjects

K Davis

Publications and source records attributed to K Davis.

At least 163 records · Page 9Linked to original sources
PubMed1996

Four-year follow-up of patients undergoing percutaneous balloon mitral commissurotomy. A report from the National Heart, Lung, and Blood Institute Balloon Valvuloplasty Registry.

OBJECTIVES: This study reports the long-term outcome of patients undergoing percutaneous balloon mitral commissurotomy who were enrolled in the National Heart, Lung, and Blood Institute (NHLBI) Balloon Valvuloplasty Registry. BACKGROUND: The NHLBI established the multicenter Balloon Valvuloplasty Registry in November 1987 to assess both short- and long-term safety and efficiency of percutaneous balloon mitral commissurotomy. METHODS: Between November 1987 and October 1989, 736 patients > or = 18 years old underwent percutaneous balloon mitral commissurotomy at 23 registry sites in North America. The maximal follow-up period was 5.2 years. RESULTS: The actuarial survival rate was 93 +/- 1% (mean +/- SD), 90 +/- 1.2%, 87 +/- 1.4% and 84 +/- 1.6% at 1, 2, 3 and 4 years, respectively. Eighty percent of the patients were alive and free of mitral surgery or repeat balloon mitral commissurotomy at 1 year. The event-free survival rate was 80 +/- 1.5% at 1 year, 71 +/- 1.7% at 2 years, 66 +/- 1.8% at 3 years and 60 +/- 2.0% at 4 years. Important univariable predictors of actuarial mortality at 4 years included age > 70 years (51% survival), New York Heart Association functional class IV (41% survival) and baseline echocardiographic score > 12 (24% survival). Multivariable predictors of mortality included functional class IV, higher echocardiographic score and higher postprocedural pulmonary artery systolic and left ventricular end-diastolic pressures (p < 0.01). CONCLUSIONS: Percutaneous balloon mitral commissurotomy has a favorable effect on the hemodynamic variables of mitral stenosis, and long-term follow-up data suggest that it is a viable alternative with respect to surgical commissurotomy in selected patients.

Adult↗
PubMed1996

Reversibility of T helper 1 and 2 populations is lost after long-term stimulation.

Commitment of T helper 1 (Th1) or Th2 populations developing during an immune response to a pathogen, or an inappropriate immune response to an allergen or autoantigen, may determine the difference between health and chronic disease. We show that strongly polarized Th1 and Th2 populations assessed by immunoassay are heterogeneous using flow cytometry to detect single cells producing interferon gamma (IFN-gamma) and interleukin 4 (IL-4). Th1 populations arising after 1 wk of stimulation in IL-12 plus anti-IL-4 antibodies could convert to Th2 cells when restimulated in IL-4. Th2 populations resulting from stimulation for 1 wk in IL-4 could give rise to Th1 cells upon restimulation in IL-12 plus anti-IL-4. In contrast, the cytokine profiles of long-term Th1 and Th2 populations arising originally from repeated stimulation in IL-12 or IL-4 appeared more homogeneous and were not reversible, although IL-4 dramatically reduced the number of IFN-gamma-producing Th1 cells. This may explain previous reports that Th1 cells can be converted to Th2 cells.

Allergens↗
PubMed1996

A point mutation associated with a severe phenotype of neurofibromatosis 2.

Neurofibromatosis 2 (NF2) is an autosomal dominant disease characterized by bilateral vestibular schwannomas and other nonmalignant tumors of the brain, spinal cord, and peripheral nerves. Although the average age of onset of NF2 is 20 years, some individuals may become symptomatic in childhood. We studied 5 unrelated NF2 patients who became symptomatic before age 13. All 5 had multiple tumors in addition to vestibular schwannoma, and none had a positive family history. Sequence analysis of the NF2 gene revealed identical nonsense mutation of exon 6 in 3 patients. Because this mutation destroys a restriction enzyme recognition site, genomic DNA from the 2 other children was directly tested for this change and identical alterations were detected. Although the work of our laboratory and others has not, in general, detected identical mutations in unrelated patients, this mutation seems to occur particularly frequently in the pediatric population and thus may be associated with an especially severe phenotype. Restriction analysis in children with NF2 may be a cost effective way of identifying their mutation. Further work is needed to characterize the effects of this change on the NF2 protein product and its relationship to this severe phenotype.

Adolescent↗
PubMed1996

Neonatal damage to the rat's infraorbital nerve upregulates both galanin and neuropeptide Y in individual vibrissae-related primary afferent axons.

Previous studies in adult animals have suggested that the peptides galanin and neuropeptide Y (NPY) may be upregulated in the same primary afferent neurons after peripheral axotomy. The present study was undertaken to determine whether such upregulation occurred in vibrissae-related primary afferent neurons and their axons after damage to the infraorbital nerve [ION; the trigeminal (V) branch that innervates the vibrissae follicles]. Double-labelling experiments demonstrated that approximately 75% of axotomized V ganglion cells and the central arbors of vibrissae-related primary afferents expressed both galanin and NPY after perinatal, but not adult, nerve damage. However, additional experiments demonstrated that the sensitive periods for lesion-induced upregulation of the two peptides and the period over which they were expressed after neonatal ION transection differed substantially. Staining for both peptides was increased after ION damage on P-0 through P-14, but only galanin staining was increased in vibrissae-related primary afferents after lesions on P-21. Galanin expression was elevated in vibrissae-related primary afferents in rats killed 3, 8, and 15 days after neonatal ION transection, while increased NPY was observed at only the middle time point. The lesion-induced increases in galanin and NPY in vibrissae-related ION primary afferents suggest that these peptides may modulate central V reorganization after such damage.

Afferent Pathways↗
PubMed1996

Roberts syndrome fibroblasts showing cisplatin hypersensitivity have normal host cell reactivation of cisplatin-treated adenovirus and normal capacity of cisplatin-treated cells for adenovirus DNA synthesis.

Roberts syndrome (RS) is a rare, recessively inherited disorder characterized by growth retardation, limb reductions and craniofacial deformities. Cells from a subset of afflicted individuals, termed RS+, display unusual separation or puffing of the heterochromatic regions of their chromosomes and are hypersensitive to several DNA-damaging agents including mitomycin C (MMC) and cisplatin, both of which can induce interstrand crosslinks in DNA. For this reason, we have investigated the ability of RS+ fibroblasts to repair cisplatin-induced DNA lesions using adenoviris as a probe. Host cell reactivation of cisplatin-treated adenovirus (Ad) was significantly reduced in nucleotide excision repair (NER)-deficient xeroderma pigmentosum (XP) cells but was normal in the two RS+ fibroblast strains and the Fanconi's anemia (FA)fibroblast strain tested. The capacity of cisplatin-treated cells for Ad DNA synthesis was reduced in XP and FA cells compared to normal human cells, but was not reduced in RS+ cells. These results indicate that the hypersensitivity of RS+ cells to cisplatin is not due to a deficiency in NER nor due to a deficiency in the pathway which leads to cisplatin hypersensitivity in FA cells. It is possible that the abnormal heterochromatin organisation of RS+ cells selectively renders the heterochromatic regions of the genome more susceptible to mutagen damage and/or less available for repair.

Adenoviruses, Human↗
PubMed1996

Management of retrohepatic venous injuries with atrial caval shunts.

Retrohepatic inferior vena caval injuries resulting from blunt or penetrating abdominal trauma are rare but devastating events that remain formidable challenges to even the most experienced Level I trauma center team members. Prepackaged atrial caval shunts have improved emergency medical treatments, and prior planning and coordination by perioperative nurses allow for rapid response by surgical team members. These efforts provide an optimal level of care required to increase patient survival. This article provides a general overview of abdominal trauma and retrohepatic inferior vena caval injuries and a proactive plan to meet the needs of patients with these injuries.

Abdominal Injuries↗
PubMed1996

Vascular nurse practitioner: a collaborative practice role in the acute care setting.

A collaborative practice model was initiated in a 440-bed university teaching hospital to trial the appropriateness and effectiveness of placing a nurse practitioner (NP) in the acute-care setting with a group of vascular surgeons. The vascular NP and three physicians collaborated as providers of patient care in both ambulatory and hospital settings. The NP managed and coordinated patient care. After orientation, the NP used a data-tracking form to record daily work activities categorized as direct care, indirect care, administration, education, and research. Satisfaction surveys were distributed to patients, nurses, and physicians to measure key elements of the NP's job responsibilities as they related to each group. The NP's data were independently analyzed, implications were discussed, and results were collated for presentation. The data were also used to guide future practice. The data reflected the vascular NP's unique acute care role within a specialty service.

Humans↗
PubMed1996

Comparison of volume control and pressure control ventilation: is flow waveform the difference?

OBJECTIVE: To examine the hypothesis that a decelerating inspiratory flow waveform is responsible for improvements in gas exchange during pressure control ventilation for acute lung injury. DESIGN: Prospective, controlled, crossover study. MEASUREMENTS AND MAIN RESULTS: Twenty-five patients with acute lung injury requiring mechanical ventilation with a positive-end expiratory pressure > or = 10 cm H2O, ventilator frequency of > or = 8 bpm, inspired oxygen concentration of > or = 0.50, peak inspiratory pressure > or = 40 cm H2O, and requiring sedation and paralysis were studied. Patients were ventilated at a tidal volume of 10 mliters/kg, respiratory frequency was set to maintain a pH > 7.30 and PaCO2 < 50 mm Hg, and positive end-expiratory pressure (PEEP) set to maintain Pao2 > 70 mm Hg or Sao2 > 93% with an Fio2 < or = 0.50. In random sequence, ventilator mode was changed from volume control with a square flow waveform, pressure control ventilation with a decelerating flow waveform, or volume control ventilation with a decelerating flow waveform. Tidal volume, minute ventilation, and airway pressures were continuously measured at the proximal airway. After 2 hours of ventilation in each mode, arterial and mixed venous blood gases were drawn and cardiac output determined by thermodilution. Dead space to tidal volume ratio was determined from mixed expired gas concentrations and Paco2. During volume control ventilation with a square flow waveform, Pao2 was decreased (75 +/- 11 mm Hg vs. 85 +/- 9 mm Hg and 89 +/- 12 mm Hg), p < 0.05, and peak inspiratory pressure was increased (50 +/- 9 cm H2O vs. 42 +/- 7 cm H2O and 39 +/- 9 cm H2O) p < 0.05 compared to volume control with a decelerating flow waveform and pressure control ventilation. Mean airway pressure was also lower with volume control with a square flow waveform (17 +/- 4 cm H2O vs. 20 +/- 4 cm H2O and 21 +/- 3 cm H2O) compared to volume control with a decelerating flow waveform and pressure control ventilation. There were no differences in hemodynamic parameters. CONCLUSIONS: Both pressure control ventilation and volume control ventilation with a decelerating flow waveform provided better oxygenation at a lower peak inspiratory pressure and higher mean airway pressure compared to volume control ventilation with a square flow waveform. The results of our study suggest that the reported advantages of pressure control ventilation over volume control ventilation with a square flow waveform can be accomplished with volume control ventilation with a decelerating flow waveform.

Adult↗
PubMed1996

Long-term tacrine (Cognex) treatment: effects on nursing home placement and mortality, Tacrine Study Group.

OBJECTIVE: To assess the possible association between tacrine (Cognex, manufactured by Parke-Davis, Morris Plains, NJ) dose and likelihood of nursing home placement (NHP) or death in patients with AD. DESIGN: A 30-week, randomized, double-blind, placebo-controlled, parallel-group multicenter clinical trial involving 663 patients, after which patients were treated openly and followed up a minimum of 2 years later. PATIENTS: At baseline, outpatients were at least 50 years of age, met criteria for probable AD, with baseline Mini-Mental State Examination scores between 10 and 26 (inclusive), were otherwise healthy, and had a caregiver who could provide assessments and ensure medication compliance. INTERVENTIONS: mandomized assignment to placebo or one of three ascending dosage regimens of tacrine over 30 weeks, followed by open label treatment for all patients who began the double-blind trial. OUTCOME MEASURES: NHP and death were examined using logistic regression. RESULTS: PATIENTS who remained on tacrine and were receiving doses > 80 mg/d or > 120 mg/d were less likely to have entered a nursing home than patients on lower doses (odds ratios > 2.7,2.8, respectively.) There was a trend for lower mortality for patients receiving > 120 mg/d (p = 0.063). CONCLUSIONS: Treatment with tacrine at doses > 80 mg/d was associated with a reduced likelihood of NHP. These data demonstrate that tacrine's 30-week effects on cognitive function and clinicians' global ratings may generalize to effects on a major milestone of AD. Future studies should attempt to replicate these findings prospectively.

Aged↗
PubMed1996

Methods for microelectrode-guided posteroventral pallidotomy.

Methods for localizing the posteroventral globus pallidus intermus are described. The authors' techniques include the use of microelectrodes to record single-unit activity and to microstimulate in human pallidum and its surrounding structures. This technique allows a precise determination of the locations of characteristic cell types in sequential trajectories through the external and internal segments of the pallidum. The location of the optic tract can be determined from microstimulation-evoked visual sensations and recordings of flash-evoked potentials. In addition, microstimulation-evoked motor and sensory responses allow the internal capsule to be identified. The data collected using this technique are an important adjunct to selecting optimum sites to place electrocoagulation lesions for stereotactic posteroventral pallidotomy for refractory Parkinson's disease.

Catheter Ablation↗
PubMed1996

Karlene Davis.

Explore the source record for details and available documents.

Humans↗
PubMed1995

Heterogeneity of intracellular cytokine synthesis at the single-cell level in polarized T helper 1 and T helper 2 populations.

CD4+ T helper (Th) cells can be classified into different types based on their cytokine profile. Cells with these polarized patterns of cytokine production have been termed Th1 and Th2, and can be distinguished functionally by the production of IFN-gamma and IL-4, respectively. These phenotypes are crucial in determining the type of immune response that develops after antigen priming. There are no surface markers that define them, and cytokine immunoassay or mRNA analysis both have limitations for characterization of single cells. Using immunofluorescent detection of intracellular IFN-gamma and IL-4, we have studied the emergence of Th1 and Th2 cells in response to antigen exposure and the patterns of cytokine synthesis in established T cell clones. IFN-gamma production by Th1 clones was detectable in almost all cells by 4 h, and it continued in most cells for > 24 h. IL-4 production in Th2 cells peaked at 4 h, but declined rapidly. In Th0 cells containing both cytokines, fewer cells produced IFN-gamma, which did not appear until IL-4 synthesis declined. Cocultivation of clones showed no such cross-regulation. Antigen stimulation of transgenic T cells expressing an ovalbumin-specific T cell receptor generated Th2 cells, probably as a result of endogenous IL-4 production. Addition of IL-12 and/or anti-IL-4 caused Th1 cells to develop, while some Th0 cells were seen when IL-12 alone was added. These results show that stimulation in the presence of polarizing stimuli results in cells producing either IFN-gamma or IL-4, but that coproduction can occur in rare cells under defined conditions.

Animals↗
PubMed1995

Rapid construction of integrated maps using inner product mapping: YAC coverage of human chromosome 11.

Inner product mapping (IPM) has been proposed as a hybridization-based method for achieving low-cost, high-throughput, high-resolution radiation hybrid (RH) mapping of clones. Using Alu-PCR products of chromosome 11-specific clones, we serially hybridized a set of RHs against gridded filters of YACs having an average size of 350 kb. We then combined these hybridization data with preexisting RH map data to build an inner product map. This binning of 865 YACs provides the first high-resolution large-scale (> twofold redundancy) clonal coverage of human chromosome 11 and is the first inner product map ever constructed. We verified the accuracy and precision of this chromosome 11 map by performing a novel likelihood analysis on independent YAC hybridization data. These results establish that IPM is a highly rapid, inexpensive, accurate, and precise large-scale long-range mapping method, particularly when preexisting RH maps are available, and that IPM can replace or complement more conventional short-range mapping methods. IPM may enable the rapid construction of sequence-ready maps and the binning of expressed sequences.

Chromosome Mapping↗