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M L Olson

Publications and source records attributed to M L Olson.

12 recordsLinked to original sources
PubMed2006

Propagation of the cardiac impulse in the diabetic rat heart: reduced conduction reserve.

Diabetes mellitus is a growing epidemic with severe cardiovascular complications. Although much is known about mechanical and electrical cardiac dysfunction in diabetes, few studies have investigated propagation of the electrical signal in the diabetic heart and the associated changes in intercellular gap junctions. This study was designed to investigate these issues, using hearts from control and diabetic rats. Diabetic conditions were induced by streptozotocin (STZ), given i.v. 7-14 days before experiments. Optical mapping with the voltage-sensitive dye di-4-ANEPPS, using hearts perfused on a Langendorff apparatus, showed little change in baseline conduction velocity in diabetic hearts, reflecting the large reserve of function. However, both the gap junction uncoupler heptanol (0.5-1 mM) and elevated potassium (9 mM, to reduce cell excitability) produced a significantly greater slowing of impulse propagation in diabetic hearts than in controls. The maximal action potential upstroke velocity (an index of the sodium current) and resting potential was similar in single ventricular myocytes from control and diabetic rats, suggesting similar electrical excitability. Immunoblotting of connexin 43 (Cx43), a major gap junction component, showed no change in total expression. However, immunofluorescence labelling of Cx43 showed a significant redistribution, apparent as enhanced Cx43 lateralization. This was quantified and found to be significantly larger than in control myocytes. Labelling of two other gap junction proteins, N-cadherin and beta-catenin, showed a (partial) loss of co-localization with Cx43, indicating that enhancement of lateralized Cx43 is associated with non-functional gap junctions. In conclusion, conduction reserve is smaller in the diabetic heart, priming it for impaired conduction upon further challenges. This can desynchronize contraction and contribute to arrhythmogenesis.

Animals↗
PubMed2006

Atmospheric mercury speciation in Yellowstone National Park.

Atmospheric concentrations of elemental mercury (Hg(0)), reactive gaseous Hg (RGM), and particulate Hg (pHg) concentrations were measured in Yellowstone National Park (YNP), U.S.A. using high resolution, real time atmospheric mercury analyzers (Tekran 2537A, 1130, and 1135). A survey of Hg(0) concentrations at various locations within YNP showed that concentrations generally reflect global background concentrations of 1.5-2.0 ng m(-3), but a few specific locations associated with concentrated geothermal activity showed distinctly elevated Hg(0) concentrations (about 9.0 ng m(-3)). At the site of intensive study located centrally in YNP (Canyon Village), Hg(0) concentrations did not exceed 2.5 ng m(-3); concentrations of RGM were generally below detection limits of 0.88 pg m(-3) and never exceeded 5 pg m(-3). Concentrations of pHg ranged from below detection limits to close to 30 pg m(-3). RGM and pHg concentrations were not correlated with any criteria gases (SO(2), NO(x), O(3)); however pHg was weakly correlated with the concentration of atmospheric particles. We investigated three likely sources of Hg at the intensive monitoring site: numerous geothermal features scattered throughout YNP, re-suspended soils, and wildfires near or in YNP. We examined relationships between the chemical properties of aerosols (as measured using real time, single particle mass spectrometry; aerosol time-of-flight mass spectrometer; ATOFMS) and concentrations of atmospheric pHg. Based on the presence of particles with distinct chemical signatures of the wildfires, and the absence of signatures associated with the other sources, we concluded that wildfires in the park were the main source of aerosols and associated pHg to our sampling site.

Aerosols↗
PubMed1998

Transposon tagging and the study of root development in Arabidopsis.

The maize Ac-Ds transposable element family has been used as the basis of transposon mutagenesis systems that function in a variety of plants, including Arabidopsis. We have developed modified transposons and methods which simplify the detection, cloning and analysis of insertion mutations. We have identified and are analyzing two plant lines in which genes expressed either in the root cap cells or in the quiescent cells, cortex/endodermal initial cells and columella cells of the root cap have been tagged with a transposon carrying a reporter gene. A gene expressed in root cap cells tagged with an enhancer-trap Ds was isolated and its corresponding EST cDNA was identified. Nucleotide and deduced amino acid sequences of the gene show no significant similarity to other genes in the database. Genetic ablation experiments have been done by fusing a root cap-specific promoter to the diphtheria toxin A-chain gene and introducing the fusion construct into Arabidopsis plants. We find that in addition to eliminating gravitropism, root cap ablation inhibits elongation of roots by lowering root meristematic activities.

Arabidopsis↗
PubMed1993

Utility of slide centrifuge gram's stain versus quantitative culture for diagnosis of urinary tract infection.

The slide centrifuge (cytospin) Gram's-stain technique has been shown in previous studies to be a sensitive technique for detecting bacteriuria when compared to culture. The method concentrates urine sediment in a small defined area on a glass slide for Gram's staining. A positive test provides morphologic information about suspected pathogens. This study evaluated the cytospin technique using 788 urine specimens, on which routine culture was simultaneously performed, and compared both with clinical evidence for urinary tract infection. One hundred twelve of these specimens, which were cytospin positive and had a culture growing more than 100,000 CFU/mL, were assumed, by definition, to represent true urinary tract infection. Five hundred twenty-six specimens had negative cytospin and negative culture results (less than 1,000 CFU/mL) and were assumed, by definition, to rule out the diagnosis of urinary tract infection. Clinical data were evaluated for 56 cytospin-positive specimens in which culture results were less than 100,000 CFU/mL. Of these specimens, 37 were false positive (no clinical evidence of urinary tract infection), 9 had clinical evidence of urinary tract infection, and for the remaining 10, data regarding clinical status could not be interpreted. Seventy-one specimens were cytospin negative, with cultures growing more than 1,000 CFU/mL. Of these, only one patient had clinical evidence of a urinary tract infection, and his culture result was less than 10,000 CFU/mL. The predictive value of a negative cytospin test was 99.8% compared to clinical information, whereas the predictive value of a negative culture (less than 100,000 CFU/mL) was 98.4%.

Cells, Cultured↗
PubMed1991

The slide centrifuge gram stain as a urine screening method.

A slide centrifuge Gram stain procedure was performed to screen for bacteriuria 4161 urine specimens submitted in urine preservative tubes for routine culture. For slide centrifuge Gram staining, each urine sample was mixed well. Thereafter, 0.2 mL of each sample was placed, using a pipette, into a slide centrifuge chamber and centrifuged at 2,000 rpm for 5 minutes. The slides were heat fixed, Gram stained, and read by laboratory personnel who scanned 12 consecutive oil-immersion fields using a set pattern. The presence of the same organism in six or more fields was defined as a positive urine screen. Urine samples were cultured using a 0.001-mL loop and a comparison of culture growth with slide centrifuge screening was made. When growth of 100,000 or more colony-forming units per milliliter (CFU/mL) was the reference for comparison, the screen had a sensitivity rate of 98%, a specificity rate of 90%, a negative predictive value of 99%, and a positive predictive value of 65%. When a lower colony count of 10,000 or more CFU/mL was the reference for comparison, the screen had a sensitivity rate of 88%, a specificity rate of 95%, a negative predictive value of 96%, and a positive predictive value of 84%. The slide centrifuge Gram stain is a very sensitive screening method to detect bacteriuria in an adult male population.

Adult↗
PubMed1984

Use of a needle valve variable resistor to improve invasive blood pressure monitoring.

Inaccurate measurements using in-line systems are partly due to the resonance frequency. A variable acoustic resistor designed to change the damping coefficient of these monitoring systems was evaluated under clinical conditions. The device improved pressure transmission characteristics in measurements on 12 of 13 patients. Use of the device and of the bedside step-impulse test for calibration should improve the reliability of in-line blood pressure monitoring.

Blood Pressure Determination↗
PubMed1981

Methemoglobinemia induced by local anesthetics.

A case of methemoglobinemia secondary to topical local anesthetic agents is reported. A 28-year-old, 80-kg white man was admitted to a hospital for respiratory distress two days after an accident. During intubation, Cetacaine (benzocaine, butamben, and tetracaine) spray and Americaine (benzocaine) ointment were used topically for local anesthesia. Ninety minutes later, the patient was cyanotic despite ventilation, and an arterial blood sample was chocolate-brown and contained 29 d/dl methemoglobin (normal less than 1.7 g/ dl). Methylene blue, 80 mg as a 1% solution in 5% dextrose in water, was infused over 20 minutes, and hte patient's cyanosis disappeared within the next 30 minutes. The following afternoon, the patient was reintubated, using 4% lidocaine and benzocaine as local anesthetics. He again developed cyanosis. Methylene blue again cleared the cyanosis. Abnormal hemoglobin variants and NADH-methemoglobin reductase deficiency were ruled out as sources of methemoglobinemia. A discussion of methemoglobinemia, including biochemistry, pathogenesis, symptomatology, and management, is presented. If cyanosis occurs following application of local anesthetics, methemoglobinemia secondary to these drugs should be considered in the differential diagnosis.

4-Aminobenzoic Acid↗
PubMedDate not supplied

Disability and rehabilitation in head and neck cancer patients after treatment.

In an effort to obtain quantitative and qualitative information regarding the extent of disability sustained following definitive treatment for head and neck cancer, 51 patients--28 who had had laryngectomy and 23 who had had other major surgery--were interviewed. Also examined were the types of rehabilitation measures taken. In all cases, the following areas in which disability could occur were identified and explored: physical appearance, speech, deglutition, mastication, salivation, sensory deficits, cranial motor-nerve deficits, pain, nutrition, activities of daily living, psychosocial functioning, vocational status, environmental parameters, and delayed complications. Where appropriate, ratings and delineations of severity were compiled. Nine methods of rehabilitation were assessed with regard to frequency of utilization: surgical reconstruction, dental-maxillofacial prosthetics, speech therapy, physical therapy, rehabilitation nursing, occupational therapy, vocational rehabilitation, rehabilitation counseling, and social service. Our conclusions were that half of the patients studied had sustained significant disability in three to four areas, while 43% had moderate or severe disability in five to nine areas. Additionally, the head and neck surgeon was found to have used surgical reconstruction and dental-maxillofacial prosthetic measures, as well as the services of seven categories of allied health professionals, to provide rehabilitation.

Deglutition↗