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Biomedical subjects

L Todd

Publications and source records attributed to L Todd.

At least 19 recordsLinked to original sources
PubMed2001

Optokinetic reflex dysfunction in multiple sclerosis.

The aim of this study was to further investigate optokinetic reflex function in multiple sclerosis. Gaze-holding in darkness, optokinetic nystagmus, optokinetic afternystagmus and latency to circularvection were measured using electro-oculography and a rotating optokinetic drum. Gaze-holding was not significantly different between the multiple sclerosis and control groups; however, four of 23 multiple sclerosis patients exhibited eccentric gaze-evoked nystagmus. There were no significant differences in either optokinetic nystagmus frequency or latency to circularvection. However, optokinetic nystagmus slow phase velocity during rise time and amplitude during beat time were significantly reduced in the multiple sclerosis group (p < 0.05 and p < 0.0001, respectively). The time constant of optokinetic afternystagmus was also significantly reduced in the multiple sclerosis group (p < 0.005). These results indicate that optokinetic nystagmus and optokinetic afternystagmus are significantly impaired multiple sclerosis.

Adult↗
PubMed2001

Effectiveness of St John's wort in major depression: a randomized controlled trial.

CONTEXT: Extracts of St John's wort are widely used to treat depression. Although more than 2 dozen clinical trials have been conducted with St John's wort, most have significant flaws in design and do not enable meaningful interpretation. OBJECTIVE: To compare the efficacy and safety of a standardized extract of St John's wort with placebo in outpatients with major depression. DESIGN AND SETTING: Randomized, double-blind, placebo-controlled clinical trial conducted between November 1998 and January 2000 in 11 academic medical centers in the United States. PARTICIPANTS: Two hundred adult outpatients (mean age, 42.4 years; 67.0% female; 85.9% white) diagnosed as having major depression and having a baseline Hamilton Rating Scale for Depression (HAM-D) score of at least 20. INTERVENTION: Participants completed a 1-week, single-blind run-in of placebo, then were randomly assigned to receive either St John's wort extract (n = 98; 900 mg/d for 4 weeks, increased to 1200 mg/d in the absence of an adequate response thereafter) or placebo (n = 102) for 8 weeks. MAIN OUTCOME MEASURES: The primary outcome measure was rate of change on the HAM-D over the treatment period. Secondary measures included the Beck Depression Inventory (BDI), Hamilton Rating Scale for Anxiety (HAM-A), the Global Assessment of Function (GAF) scale, and the Clinical Global Impression-Severity and -Improvement scales (CGI-S and CGI-I). RESULTS: The random coefficient analyses for the HAM-D, HAM-A, CGI-S, and CGI-I all showed significant effects for time but not for treatment or time-by-treatment interaction (for HAM-D scores, P<.001, P =.16, and P =.58, respectively). Analysis of covariance showed nonsignificant effects for BDI and GAF scores. The proportion of participants achieving an a priori definition of response did not differ between groups. The number reaching remission of illness was significantly higher with St John's wort than with placebo (P =.02), but the rates were very low in the full intention-to-treat analysis (14/98 [14.3%] vs 5/102 [4.9%], respectively). St John's wort was safe and well tolerated. Headache was the only adverse event that occurred with greater frequency with St John's wort than placebo (39/95 [41%] vs 25/100 [25%], respectively). CONCLUSION: In this study, St John's wort was not effective for treatment of major depression.

Adult↗
PubMed2001

Reconciling animal and human data in a cancer risk assessment of acrylonitrile.

OBJECTIVES: Bioassays of rats exposed to acrylonitrile have consistently detected an elevated incidence of central nervous system (CNS) cancer. In contrast, epidemiologic studies have not found a statistically stable increase in CNS cancer mortality. The purpose of this paper is to examine whether or not CNS cancers predicted from the most appropriate inhalation bioassay in rats are consistent with CNS cancers observed in 3 recent, large epidemiologic studies. METHODS: A linearized multistage model was fit to dose-response data from a rat inhalation bioassay to estimate carcinogenic potency. This potency was applied to epidemiologic studies of acrylonitrile-exposed workers. After adjustment for less than complete lifetime follow-up in the epidemiologic studies, consistency was examined between CNS cancers predicted by the model fit to the animal data for the exposure levels and sample sizes of the epidemiologicy studies and the CNS cancers observed in the epidemiologic studies. RESULTS: The model predicted totals of 17.7, 3.6, and 7.6 CNS cancer deaths for the studies. These predictions were not far from the observed CNS cancer deaths (12, 6, and 6) and were well within their 95% confidence intervals of 6.9-22.3, 2.2-13.1, and 2.2-13.1, respectively. CONCLUSIONS: The CNS cancer potency estimated from the best available inhalation bioassay was consistent with the observed deaths in the epidemiologic studies as long as continuous lifetime exposure was chosen as the exposure metric. The lack of observed excess in CNS cancer among the studied workers may have been due to low exposures, insufficient follow-up times, or both.

Acrylonitrile↗
PubMed2000

Concentrated swine feeding operations and public health: a review of occupational and community health effects.

Recent industry changes in swine-management practices have resulted in a growing controversy surrounding the environmental and public health effects of modern swine production. The numerous wastes produced by intensive swine production not only pose a significant challenge to effective environmental management but also are associated with decreased air quality in confinement houses, potentially transferable antimicrobial resistance patterns, and several infectious agents that can be pathogenic to humans. Published studies have documented a variety of contaminants, microbial agents, and health effects in those occupationally exposed to swine, and these have provided the groundwork for an increasing body of research to evaluate possible community health effects. Nonetheless, several factors limit our ability to define and quantify the potential role of intensive swine-rearing facilities in occupational and community health. Our incomplete understanding and ability to detect specific exposures; the complicated nature of disease etiology; pathogenesis; and surveillance; and the inherent difficulties associated with study design all contribute to the inadequate level of knowledge that currently prevails. However; an evaluation of the published literature; and a recognition of the elements that may be compromising these studies; provides the foundation from which future studies may develop.

Air Pollutants, Occupational↗
PubMed1996

The Cardiac Arrhythmia Suppression Trial: Implications for nursing practice.

BACKGROUND: Care of patients with ventricular arrhythmia after myocardial infarction requires careful nursing management, including assisting with arrhythmia monitoring and testing. Because ventricular premature depolarization is a known risk factor for sudden cardiac death, it was hypothesized that the suppression of asymptomatic or mildly symptomatic ventricular premature depolarization would improve survival in these patients. OBJECTIVE: To review the Cardiac Arrhythmia Suppression Trial findings and provide implications for nursing practice for patients after myocardial infarction. METHODS: The Cardiac Arrhythmia Suppression Trial was a multicenter, randomized, placebo-controlled trial designed to determine whether the suppression of ventricular premature depolarizations in postmyocardial infarction patients would improve survival. Three class I antiarrhythmic drugs were used: encainide, flecainide, or moricizine. Patients for whom the drug suppressed their arrhythmia 80% or more were randomly assigned to that drug and dose or its matching placebo and were followed every 4 months (main study). Patients with 1% to 79% suppression were randomly assigned to the drug or its placebo that best treated their arrhythmia and followed every 4 months. RESULTS: Suppression of asymptomatic or mildly symptomatic ventricular premature depolarization in patients using encainide, flecainide, or moricizine failed to improve patient survival and was even harmful in some cases. CONCLUSIONS: Our results showed that in the absence of effective antiarrhythmic drug therapy, supportive nursing care and arrhythmia monitoring is important until appropriate therapy for the management of these arrhythmias in patients who have had a myocardial infarction can be found. Clinical trials are essential to provide an evaluation of therapies and direction for further studies, as well as a basis for practicing clinicians.

Aged↗
PubMed1995

Smoking cessation and arrhythmic death: the CAST experience. The Cardiac Arrhythmia Suppression Trial (CAST) Investigators.

OBJECTIVES: This study was performed to assess the effect of cigarette smoking cessation on overall mortality and the incidence of arrhythmic death in the population of the Cardiac Arrhythmia Suppression Trial (CAST). BACKGROUND: Cigarette smoking is a known risk factor for sudden cardiac death. Some of the adverse effects of smoking have been shown to dissipate with smoking cessation, but the time frame over which these changes occur and the population that stands to benefit have not been well delineated. CAST was a multicenter double-blind placebo-controlled study to determine whether suppression of ventricular ectopic activity by means of antiarrhythmic drugs in patients with left ventricular dysfunction after acute myocardial infarction would reduce the incidence of arrhythmic death. METHODS: Of 2,752 patients randomized to blinded therapy, 1,026 were smoking at the time of their baseline examination and completed a 4-month follow-up visit. Of these, 517 stopped smoking by the time of this visit ("quitters") and 509 continued to smoke ("smokers"). RESULTS: Over a mean follow-up period of slightly < 16 months, there were 17 arrhythmic deaths and 32 total deaths among the quitters versus 30 and 45, respectively, among the smokers; these differences were of marginal statistical significance. Most of the fatal events occurred in a group at high risk of ongoing ischemia: the 558 patients who did not have thrombolysis or undergo revascularization after their qualifying myocardial infarction. In this high risk cohort, smoking cessation greatly reduced the incidence of arrhythmic death and was associated with a statistically significant benefit in survival. CONCLUSIONS: Smoking cessation was accompanied by a marked reduction in arrhythmic death and overall mortality that achieved statistical significance in a high risk cohort. These data imply that smoking cessation is important in risk factor reduction in patients with advanced ischemic heart disease.

Aged↗
PubMed1995

Evaluation of an infrared open-path spectrometer using an exposure chamber and a calibration cell.

This study evaluated the use of a controlled exposure chamber and calibration cell to investigate the performance of open-path remote sensing instruments for workplace monitoring of pollutants. An open-path infrared spectrometer was deployed in a chamber, and a range of homogeneous air concentrations were generated using the tracer gas sulfur hexafluoride (SF6). Open-path measurements were compared with point-sample measurements taken along the beam and analyzed using an infrared (IR) and electron capture detector (ECD). A five-compartment calibration cell placed in the optical path was used to simulate heterogeneous concentrations of pollutants. Fifteen concentration patterns were created by injecting different volumes of SF6 into each compartment. Open-path spectrometer measurements were compared with compartment concentrations measured using an ECD. Results indicated that stable homogeneous and heterogeneous concentrations of SF6 were generated in the controlled exposure chamber and five-compartment calibration cell, respectively. Overall, individual open-path measurements were within 20% of point samples measured with the IR and ECDs. The open-path spectrometer measurements had a consistent positive bias of about 12%. Exposure chamber experiments uncovered remote sensing instrument design aspects that could adversely impact its use for indoor monitoring. The weight and size of the instrument make it useable only in a fixed position, thus limiting spatial coverage of the beam in a room. The instrument components were not air-tight, resulting in overestimation of some open-path concentrations. A controlled test chamber and a long calibration cell placed in the optical path are useful tools for evaluating a variety of open-path spectrometer instrument performance issues relevant to industrial hygiene monitoring.

Air Pollutants, Occupational↗
PubMed1994

Evaluation of optical source-detector configurations for tomographic reconstruction of chemical concentrations in indoor air.

This article reports on numerical studies to evaluate and compare optical remote sensing configurations for tomographically reconstructing pollutant concentrations in indoor air. With a remote sensing/computed tomography system, two-dimensional maps of pollutant concentrations with good spatial resolution can be created for an entire room. The successful use of such a system for exposure assessment, ventilation assessment, or source monitoring depends on the remote sensing configuration. A systematic method was developed to evaluate the performance of 10 configurations. One hundred and twenty test maps were reconstructed with an algebraic reconstruction method using all 10 configurations; reconstruction quality was evaluated using 4 criteria. Reconstruction quality was related to the number and location of detectors in the room and the complexity of the test maps. Configurations using the same number of detectors placed in different locations resulted in reconstructions that differed in quality. The effect of reducing the number density of rays on reconstruction quality was studied. Based on these simulations, two configurations that used four detectors to scan the room were selected, and their performance was evaluated in the presence of various levels of measurement noise. Two configurations that used four detectors were most suited for exposure assessment. It was found that when designing a configuration, the number and independence of rays should be maximized. Results underscored the need to thoroughly test configurations through numerical studies prior to field implementation; a wide variety of concentration maps, relevant to the application, should be tested under both ideal and nonideal sampling conditions.

Air Pollutants↗
PubMed1994

Evaluation of algorithms for tomographic reconstruction of chemical concentrations in indoor air.

Numerical studies were performed to evaluate and compare four different algorithms for tomographically reconstructing pollutant concentrations in indoor air measured with an optical remote sensing system. With a remote sensing/computed tomography system, two-dimensional maps of air concentrations can be created for an entire room with good spatial and temporal resolution. The success of such a system for characterizing the flow of contaminants in air, exposure assessment, and leak detection depends on the choice of tomographic reconstruction algorithm. A systematic method was developed to evaluate the performance of four algorithms: ART, ART3, SIRT, and SART. One hundred and twenty test maps were reconstructed by each algorithm under ideal and nonideal sampling conditions, and image quality was evaluated using four criteria. The nonideal sampling conditions included simulation of measurement noise and reduction in the number density of rays. Performance of the algorithms was found to be intimately related to the number of peaks in the test maps. The importance of using multiple measures of image quality was underscored by the fact that for some sampling conditions simulated, performance of the algorithms was judged differently depending on the evaluation criteria. Results indicated that using numerical studies is successful for evaluating such algorithms.

Air Pollutants, Occupational↗
PubMed1990

Resistance between stages of the tick Rhipicephalus appendiculatus (Acari: Ixodidae).

The ability of one stage of Rhipicephalus appendiculatus Neumann to induce resistance in a host to the feeding of the next stage in the life cycle was studied using Bos taurus cattle and rabbits. Simple resistance within a stage and cross-resistance between stages was generally less than 50%. The cumulative effect of simple resistance and cross-resistance over the whole life cycle in this experiment was estimated at 97% resistance measured as reduction in engorgement mass, numbers detached, and survival. Potential antigens in salivary glands of the three stages were compared by microscopy and electrophoresis and found closely similar. Production of serum antibodies against salivary antigens was examined by Western blotting of the electrophoretically separated salivary peptides. Cross reactions occurred but with little consistency. Hypersensitivity reactions were observed directly and tested immunologically. Only delayed hypersensitive reactions were directly involved in simple resistance and cross-resistance. These results can be applied in the selection of cattle for resistance to ticks, and this is discussed.

Animals↗
PubMed1985

Pulmonary toxicity of monocrotaline differs at critical periods of lung development.

We injected 3-day-old (neonatal), 8-day-old (infant), and 8-wk-old (adult) Sprague-Dawley rats with monocrotaline to examine the effect of a toxic agent at various stages of lung development. Two and four weeks after injection the rats were killed and the heart and lungs removed: the right and left ventricles were separated and weighed, the pulmonary artery was injected with barium-gelatin, and the lung was fixed in the inflated state. Morphometric techniques were applied to assess lung volume, alveolar size and number, and arterial size, muscularity, and concentration relative to alveolar. Rats injected with monocrotaline in the neonatal period did not survive to 3 wk. After 2 wk, there was no significant right ventricular hypertrophy and pulmonary vascular changes were no worse than in the other rat groups injected with monocrotaline, but alveolar development was severely impaired; less than one-third the normal number was present. Rats injected with monocrotaline in infancy had normal alveolar development. After 2-wk, the arterial changes, i.e. extension of muscle into peripheral arteries, medial hypertrophy of muscular arteries, and decreased arterial concentration relative to alveolar were similar to those observed in adult rats. After 4 wk, there was a decrease in medial hypertrophy associated with growth in artery size and only a lack of regression of right ventricular weight. In adult rats, after 4 wk medial hypertrophy became progressively more severe, the arterial concentration relative to alveolar decreased further, and right ventricular hypertrophy developed.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗