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Biomedical subjects

W Armstrong

Publications and source records attributed to W Armstrong.

At least 19 recordsLinked to original sources
PubMed2006

Rhizome phyllosphere oxygenation in Phragmites and other species in relation to redox potential, convective gas flow, submergence and aeration pathways.

Underground rhizomes of emergent aquatic macrophytes are important for perennation, vegetative spread, competition and anchorage. In four species we examined the potential for the development of oxidized phyllospheres around rhizome apical buds, similar to the protective oxygenated rhizospheres around roots. Redox potentials and polarographic measurements of radial oxygen loss were recorded using platinum cathodes around the apical buds. The aeration pathway from atmosphere to phyllosphere was investigated anatomically and by applied pressurized gas flow. Redox potentials increased by +400, +45, +200 and +340 mV around rhizome apices of Phragmites australis, Oryza rhizomatis, Carex rostrata and Glyceria maxima, respectively. Radial oxygen loss from rhizome apices of Phragmites was increased by convective gas flow through the rhizome and by shoot de-submergence, and decreased by resistances applied within the aeration pathway and by shoot submergence. We conclude that oxygen passes via internal gas-space connections between aerial shoot, rhizome and underground buds and into the phyllosphere regions via scale-leaf stomata and surfaces on the buds. We suggest that oxidized phyllospheres may protect rhizome apices against phytotoxins in waterlogged soils, just as oxidized rhizospheres protect roots.

Cyperaceae↗
PubMed2003

Determination of the interconversion energy barrier of enantiomers by separation methods.

Separation methods have become versatile tools for the determination of kinetic activation parameters and energy barriers to interconversion of isomers and enantiomers in the last 20 years. New computer-aided evaluation systems allow the on-line determination of these data after separating minute amount of pure compounds or mixture of isomers or enantiomers, respectively. Both dynamic interconversion during the separation process as well as static stopped-flow techniques have been applied to determine the kinetic activation parameters and interconversion energy barriers by separation methods. The use of (1) combinations of batchwise kinetic studies with enantioselective separations, (2) a continuous flow model, (3) a comparison of real chromatograms with simulated ones, (4) stopped-flow techniques, (5) stochastic methods, (6) approximation functions and (7) deconvolution methods, for the determination of interconversion energy barriers by separation methods is summarized in detail.

Kinetics↗
PubMed2001

Pneumocystis carinii cytochrome b mutations are associated with atovaquone exposure in patients with AIDS.

This retrospective cohort study was conducted to determine whether Pneumocystis carinii cytochrome b gene mutations in patients with AIDS and P. carinii pneumonia (PCP) are associated with atovaquone exposure. Portions of the P. carinii cytochrome b genes that were obtained from 60 patients with AIDS and PCP from 6 medical centers between 1995 and 1999 were amplified and sequenced by using polymerase chain reaction. Fifteen patients with previous atovaquone prophylaxis or treatment exposure were matched with 45 patients with no atovaquone exposure. Cytochrome b coenzyme Q binding site mutations were observed in 33% of isolates from patients exposed to atovaquone, compared with 6% from those who were not (P=.018). There was no difference in survival 1 month after treatment between patients with or without cytochrome b mutations (P=.14). Thus, cytochrome b mutations are significantly more common in patients with AIDS and PCP with atovaquone exposure, but the clinical significance of these mutations remains unknown.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Pneumocystis carinii mutations are associated with duration of sulfa or sulfone prophylaxis exposure in AIDS patients.

This study was conducted to determine whether Pneumocystis carinii dyhydropteroate synthase (DHPS) gene mutations in AIDS patients with P. carinii pneumonia (PCP) are affected by duration of sulfa or sulfone prophylaxis and influence response to sulfa or sulfone therapy. The P. carinii DHPS genes from 97 AIDS patients with PCP between 1991 and 1999 from 4 medical centers were amplified, using polymerase chain reaction (PCR), and sequenced. Mutations were observed in 76% of isolates from patients exposed to sulfa or sulfone prophylaxis compared with 23% of isolates from patients not exposed (P=.001). Duration of prophylaxis increased the risk of mutations (relative risk [RR] for each exposure month, 1.06; P=.02). Twenty-eight percent of patients with mutations failed sulfa or sulfone treatment; mutations increased the risk of sulfa or sulfone treatment failure (RR, 2.1; P=0.01). Thus, an increased duration of sulfa or sulfone prophylaxis increases the chance of developing a P. carinii mutation. The majority of patients with mutations respond to sulfa or sulfone therapy.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Pneumocystis carinii mutations associated with sulfa and sulfone prophylaxis failures in immunocompromised patients.

Recent studies have shown that mutations in two amino acid positions of the Pneumocystis carinii dihydropteroate synthase gene are significantly more common in immunocompromised patients with P. carinii pneumonia who fail sulfa or sulfone prophylaxis. This paper reviews the studies that suggest that these mutations may be responsible for some failures of prophylaxis in P. carinii.

Anti-Infective Agents↗
PubMed1998

Pharyngoesophageal reconstruction with the ulnar forearm flap.

OBJECTIVE: To evaluate the use of a generous fasciocutaneous ulnar forearm free flap in pharyngoesophageal reconstruction. DESIGN: Tertiary referral center. SETTING: Private practice. PATIENTS: From September 1, 1991, to October 30, 1996, 20 ulnar forearm free flaps were used to reconstruct the pharyngoesophagus in 19 patients after surgery for squamous cell carcinoma. There were 13 circumferential defects and 7 near-circumferential defects (<2 cm of mucosa remaining). The reconstructions were performed primarily (at the time of tumor resection) in 16 cases and secondarily in 4 cases. INTERVENTION: A generous fasciocutaneous ulnar forearm flap with a minimum dimension of 9 x 22 cm was harvested to reconstruct the pharyngoesophagus. A 2-layer closure was performed in flap tailoring and proximal (pharynx to flap) and distal (flap to esophagus) anastomoses to minimize the risk of leakage. Also, portions of the flap were used to monitor flap viability, to cover cervical vessels, to obliterate dead space, and as skin coverage when the skin flaps were deficient. RESULTS: Nineteen of the 20 flaps transferred were successful. Swallow function was restored in 18 cases, and voice was rehabilitated in all the patients using either tracheoesophageal puncture and a voice device or an electrolarynx device. There was 1 perioperative mortality. Three fistulas occurred, all of which healed with nonsurgical treatment. One stricture developed that required intermittent dilatation. The donor site morbidity was minor. CONCLUSIONS: This versatile technique achieves excellent results with a decreased complication rate compared with other methods currently available in pharyngoesophageal reconstruction.

Adult↗
PubMed1998

Recommendations for training in performance and interpretation of stress echocardiography. Committee on Physician Training and Education of the American Society of Echocardiography.

Stress echocardiography has emerged as a clinically useful procedure in the management of patients with ischemic heart disease and other conditions. However, the accuracy of this test relies on the ability of those who carry out the technical aspects of the test and depends critically on proper interpretation of the images. Appreciation of wall motion abnormalities is generally acknowledged as one of the most difficult skills to master in echocardiography. There is consensus that this is also one of the most difficult skills to teach. Appreciating stress-induced changes in wall motion, which sometimes are subtle, requires a significant commitment to initial training in this skill and its maintenance. This document provides recommendations for physician training in stress echocardiography.

Cardiology↗
PubMed1998

Illusions of control, underestimations, and accuracy: a control heuristic explanation.

The illusions of control area is reviewed, and 5 conditions that influence control judgments are identified: skill-related factors, success or failure emphasis, need for the outcome, mood, and the intrusion of reality. It is proposed that individuals use a control heuristic that includes perceptions of intentionality and connection. Judgments of intentionality are based on foreseeability, ability to produce the effect, and valence of the outcome. Judgments of connection are based on the perceived association between the action and the outcome, which includes temporal, shared meaning, and predictive association. Effects of motives to overestimate, underestimate, and have accurate assessments of control are explained, using the concepts of hindsight bias, connection, and counterfactuals. In addition, the relation between the control heuristic and illusory correlation research and applications of the control heuristic to coping with chronic illness are explored.

Humans↗
PubMed1998

Preoperative echocardiographic evaluation of patients referred for lung volume reduction surgery.

BACKGROUND: The most efficient preoperative assessment for lung volume reduction surgery (LVRS) in patients with advanced emphysema is undefined. This study analyzed the preoperative assessment of patients by surface echocardiography (without and with dobutamine infusion), the results of which were used to exclude patients with significant pre-existing cardiac disease, a contraindication to LVRS, from the surgery. SETTING: A university-based, tertiary care referral center. METHODS: Patients with emphysema who met initial LVRS screening criteria underwent resting and stress surface echocardiography with Doppler imaging. Patients were evaluated prospectively for perioperative cardiac complications. RESULTS: Between July 1994 and December 1996, 503 candidates for LVRS were evaluated. Of these, 207 patients (81.8%) who had echocardiography performed at our institution formed the primary study group. Images were adequate for the analysis of chamber sizes and function in 206 patients (99.5%) undergoing resting echocardiography, and the images were adequate for wall motion analysis in 172 of 174 patients (98.9%) undergoing functional testing. Right heart abnormalities were common (40.1%). Significant pulmonary hypertension (> 35 mm Hg) was uncommon (5 patients, 5.4%) among the 92 patients who subsequently underwent right heart catheterization. Occult ischemia, left ventricular dysfunction, and valvular abnormalities also were uncommon. Thus, although Doppler imaging estimates of right ventricular systolic pressure were imperfect, echocardiographic findings of normal right heart anatomy and function excluded significant pulmonary hypertension. Ninety patients (43%) eventually underwent LVRS (70 bilateral and 20 unilateral). A total of 13 perioperative cardiac events occurred in 10 patients, 6 of whom had undergone preoperative echocardiography. No patient suffered acute myocardial infarction or cardiac death. CONCLUSIONS: Despite potential limitations due to severe obstructive lung disease, surface echocardiographic imaging is a feasible, noninvasive tool in this patient population to identify patients with evidence of cor pulmonale that suggests pulmonary hypertension. The routine use of surface resting and stress echocardiography for preoperative screening obviates the need for invasive right heart catheterization in many patients and results in a low incidence of significant perioperative cardiac complications.

Aged↗
PubMed1997

Lateral arm microvascular flap in head and neck reconstruction.

OBJECTIVES: To report our results of a study of 28 patients who underwent sequential reconstructions of the head and neck using the lateral arm flap. To discuss the situations where we have found the procedure useful, report the complication rates, and delineate the advantages and disadvantages of using this flap. DESIGN: A clinical series of patients was followed up prospectively. The swallowing function of a subgroup that underwent oropharyngeal reconstruction was compared with that of a simultaneous control group that underwent reconstruction with the pectoralis major flap. SETTING: University medical center. PARTICIPANTS: Patients with malignant neoplasms of the head and neck who underwent resections and reconstruction with the lateral arm flap. INTERVENTIONS: Twenty-eight patients underwent head and neck reconstruction using lateral arm flaps. In 17 patients, the lateral arm flaps were used for pharyngeal and posterior oral cavity defects. Thirteen of these patients underwent reinnervation. Nine combined palatal and midfacial defects were reconstructed, and 1 lateral facial defect was reconstructed. Most cases were advanced malignant neoplasms and represented a selected minority of similar resections performed at our institutions. Three maxillary reconstructions were performed secondarily. All other reconstructions were performed at the time of tumor ablation. MAIN OUTCOME MEASURES: Data were collected regarding flap survival, return of sensation in flaps, complication rates, and the ability to feed orally. RESULTS: All flaps survived in their entirety. Of 7.5 tested flaps acquired sensation. Of 14 patients with large oropharyngeal defects, 8 resumed early oral feeding and all survivors eventually obtained nutrition orally. The ability to swallow was superior to the results obtained in a retrospective analysis of a group reconstructed using pectoralis major flaps. CONCLUSIONS: A unique feature of this flap is that it incorporates both thin skin from the proximal forearm and thicker skin from the upper arm. This is ideal for an oropharyngeal defect, where the thin malleable portion can be used in the posterior oral cavity or pharyngeal wall and the thicker portion in the tongue base. Either portion can be used alone as well. The availability of intermediate tissue bulk can also be advantageous for midfacial reconstruction. Sensation can be reliably reconstituted with this flap. We think that the lateral arm flap is versatile and has particularly low donor-site morbidity.

Adult↗
PubMed1997

De novo chronic graft-versus-host disease presenting as hemolytic anemia following partially mismatched related donor bone marrow transplant .

Chronic graft-versus-host disease (cGVHD) is a disease of immune dysregulation that resembles an autoimmune disease. It usually involves the skin, mucosal and serosal surfaces and, less commonly, the hematopoietic system. We report hemolytic anemia (HA) as the primary manifestation of de novo cGVHD in recipients of partially mismatched related donor transplants. Five of 40 eligible patients developed HA at a median of 168 days post-transplant. Recipients were mismatched for one to three major HLA antigens. Conditioning therapy consisted of total body irradiation, etoposide, Ara-C, cycle-phosphamide and steroids. GVHD prophylaxis included partial T cell depletion, using anti alpha/beta CD3 antibody (T10B9) and complement, in addition to post-transplant immunosuppression. At presentation, all patients were receiving cyclosporine with or without low-dose steroids. Along with a mean Hb of 7.1 g%, patients had an increased reticulocyte count, a mild raised lactic dehydrogenase and a positive Coombs' test (in 2/5 patients). Four patients had also demonstrated a decrease in platelet count. Treatment was initiated with high-dose steroids and intravenous gamma globulin and response was observed within 1 week. Awareness of this presentation of cGVHD and early therapeutic intervention can result in successful reversal of presumed immune-mediated red cell and platelet destruction.

Adrenal Cortex Hormones↗
PubMed1996

Breast cancer in New Zealand: trends, patterns, and data quality.

AIMS: To determine if incidence of cancer of the female breast in New Zealand is changing by age, ethnic group, and geographic region, and if there are differences in rates for stage of tumour by urban and rural residence. METHODS: Age-adjusted incidence rates for Maori and nonMaori were computed from all primary cancers of the breast registered in the National Cancer Registry, 1978-92. Analyses of time trends and geographic variations were conducted using standard statistical methods. RESULTS: There were steady, but nonsignificant, increases in the Maori and nonMaori incidence rates between 1978-92 which represents important increases in case numbers. The age-specific rates increased sharply from age 20, levelled out at age 45 and slowly increased through 85 years and older. There was a significant trend over time for the rate of "not staged" cases which was due to an artifact. No statistically significant variations in the age-adjusted rates by area (14 area health board districts, 4 regional health authorities), or by stage of tumour in three urban-rural groups were found. Maori women showed less shift in incidence rates from regional to local stage of tumour than nonMaori. The proportion of tumours reported without stage increased in the period 1988-92. A large proportion of cases had nonspecific morphology codes. CONCLUSIONS: There are small differences between rates of breast cancer in rural and urban residences in New Zealand, as compared to some other countries. The quality of the Cancer Registry as a basis for evaluating the planned breast cancer screening programme is adversely affected by the high proportion of cases found with no reported stage of tumour. The proportion of nonspecific morphologies in these data is also of concern. The recent passing of the Cancer Registry Act should ensure better reporting of morphologies.

Adult↗
PubMed1992

Improved stenosis geometry by quantitative coronary arteriography after vigorous risk factor modification.

This study is a randomized, controlled, blinded, arteriographic trial to determine the effects of a low-cholesterol, low-fat, vegetarian diet, stress management and moderate aerobic exercise on geometric dimensions, shape and fluid dynamic characteristics of coronary artery stenoses in humans. Complex changes of different primary stenosis dimensions in opposite directions or to different degrees cause stenosis shape change with profound effects on fluid dynamic severity, not accounted for by simple percent narrowing. Accordingly, all stenosis dimensions were analyzed, including proximal, minimal, distal diameter, integrated length, exit angles and exit effects, determining stenosis shape and a single integrated measure of stenosis severity, stenosis flow reserve reflecting functional severity. In the control group, complex shape change and a stenosis-molding characteristic of statistically significant progressing severity occurred with worsening of stenosis flow reserve. In the treated group, complex shape change and stenosis molding characteristic of significant regressing severity was observed with improved stenosis flow reserve, thereby documenting the multidimensional characteristics of regressing coronary artery disease in humans.

Adult↗
PubMed1991

A biotin-containing compound N-(2-aminoethyl)biotinamide for intracellular labeling and neuronal tracing studies: comparison with biocytin.

The hydrochloride salt of a new, small molecular weight (M.W. = 286) biotin-containing compound referred to as biotinamide (N-(2-aminoethyl)biotinamide) was compared with biocytin (M.W. = 372) for its use in intracellular labeling of neurons and in neuronal tracing experiments using avidin conjugates for histochemical detection. The DC resistance and current passing ability of electrodes filled with 1-2 M potassium chloride, potassium acetate or potassium methylsulfate and containing 1-4% of these compounds were compared. Although differences were observed due to the electrolyte, with KCl electrodes being the least resistant, no electrode differences could be attributed to the concentration or type of tracer. However, whereas biocytin could be electrophoresed with either positive or negative current with roughly similar facility, biotinamide was selectively ejected with positive current. This would be beneficial to electrophysiologists using hyperpolarizing current to stabilize the membrane potential of neurons prior to recording. In addition, biotinamide-HCl could be dissolved at concentrations of 2-4% in either 1 or 2 M salt without precipitation, whereas biocytin precipitated in some of these solutions. Both compounds were equally useful for neuronal tracing experiments with survival times of 2 days, but labeling was much weaker with longer survival times. There was also little difference in the ability to histochemically localize these compounds using avidin conjugates, including avidin-biotin-horseradish peroxidase complex. In conclusion, biotinamide shares many of the useful features of biocytin, but can be selectively electrophoresed with positive current and can be dissolved at higher concentrations with little detriment in the electrical properties of the recording electrode.

Animals↗
PubMed1990

Increased rate of base substitution in a hamster mutator strain obtained during serial selection for gene amplification.

The pattern of mutations produced by a mutator gene (obtained during serial selection for amplification of the dihydrofolate reductase [dhfr] locus) shows a pronounced shift from that found in wild-type cells. The rate of certain types of base substitutions (particularly transitions) is dramatically increased, while gene rearrangements constitute a lower proportion of mutations. These data suggest a lower fidelity of the replication process in the mutator strain.

Animals↗