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Biomedical subjects

S Lehman

Publications and source records attributed to S Lehman.

18 recordsLinked to original sources
PubMed2004

14C activity and global carbon cycle changes over the past 50,000 years.

A series of 14C measurements in Ocean Drilling Program cores from the tropical Cariaco Basin, which have been correlated to the annual-layer counted chronology for the Greenland Ice Sheet Project 2 (GISP2) ice core, provides a high-resolution calibration of the radiocarbon time scale back to 50,000 years before the present. Independent radiometric dating of events correlated to GISP2 suggests that the calibration is accurate. Reconstructed 14C activities varied substantially during the last glacial period, including sharp peaks synchronous with the Laschamp and Mono Lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments. Simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14C production rate together with plausible changes in deep-ocean ventilation and the global carbon cycle during glaciation.

Journal Article↗
PubMed2001

Ischemia causes muscle fatigue.

The purpose of this investigation was to determine whether ischemia, which reduces oxygenation in the extensor carpi radialis (ECR) muscle, causes a reduction in muscle force production. In eight subjects, muscle oxygenation (TO2) of the right ECR was measured noninvasively and continuously using near infrared spectroscopy (NIRS) while muscle twitch force was elicited by transcutaneous electrical stimulation (1 Hz, 0.1 ms). Baseline measurements of blood volume, muscle oxygenation and twitch force were recorded continuously, then a tourniquet on the upper arm was inflated to one of five different pressure levels: 20, 40, 60 mm Hg (randomized order) and diastolic (69 +/- 9.8 mm Hg) and systolic (106 +/- 12.8 mm Hg) blood pressures. Each pressure level was maintained for 3-5 min, and was followed by a recovery period sufficient to allow measurements to return to baseline. For each respective tourniquet pressure level, mean TO2 decreased from resting baseline (100% TO2) to 99 +/- 1.2% (SEM), 96 +/- 1.9%, 93 +/- 2.8%, 90 +/- 2.5%, and 86 +/- 2.7%, and mean twitch force decreased from resting baseline (100% force) to 99 +/- 0.7% (SEM), 96 +/- 2.7%, 93 +/- 3.1%, 88 +/- 3.2%, and 86 +/- 2.6%. Muscle oxygenation and twitch force at 60 mm Hg tourniquet compression and above were significantly lower (P < 0.05) than baseline value. Reduced twitch force was correlated in a dose-dependent manner with reduced muscle oxygenation (r = 0.78, P < 0.001). Although the correlation does not prove causation, the results indicate that ischemia leading to a 7% or greater reduction in muscle oxygenation causes decreased muscle force production in the forearm extensor muscle. Thus, ischemia associated with a modest decline in TO2 causes muscle fatigue.

Adult↗
PubMed2001

Patient evaluation of the hotel function of hospitals.

BACKGROUND: A means of measuring patient satisfaction is essential in the effort to improve the quality of health care delivered in our nation's hospitals. Accurate feedback allows employers to better meet patients' needs and allows hospital administrators to improve service delivery. Patients are empowered by having a voice in the manner in which their health care is delivered. Moreover, improving the efficiency of the health care delivery system decreases health care costs. Hospital comparisons can be made readily available to a large audience through the Internet, resulting in empowerment of the patient and a universal improvement in hospital care. This is the first multi-institutional analysis of patient satisfaction among New York City and northern New Jersey area tertiary care hospitals. In this study, we evaluated the patient-assessed hotel function of hospitals in a single geographic region to determine whether clinically and statistically significant differences would be revealed that could provide beneficial information to stakeholders in the healthcare system. METHODS: Patients (n = 261) who had spent a night during the past year in one of eleven hospitals within 60 miles of New York City were chosen at random from doctors' waiting rooms. On average, 24 patients from each hospital were surveyed. They were asked to complete a questionnaire that rated the various departments in the hospital on qualities such as courtesy, promptness, and cleanliness. The questionnaire also rated important characteristics of the patient experience, such as the ease of parking and the taste of the food. Each item on the survey was coded on a scale of 1 to 10 with 10 being the most positive response. The 26 specific questions were divided into 14 domains. Averages in each domain were compared by gender, age, and hospital identity, attractiveness, and setting. All statistical calculations were performed using SPSS/PC, and means were compared using t-tests. RESULTS: Analysis designed to evaluate outcomes between each of the possible 54 pairs of hospitals comparisons revealed statistically significant differences as often as 44% of the time in some outcomes measures (logistics), but as rarely as 7% of the time in others (billing function). Clinically significant differences (>2 units per scale) were frequently evident, although the ranges differed dramatically depending on the domains surveyed. Although age, gender, and race/ethnicity were generally not predictive of satisfaction, non-urban setting was correlated with greater patient satisfaction. CONCLUSION: By having access to patient satisfaction comparisons among hospitals, patients are empowered to make better choices, employers can identify and adapt to patient preferences, and administrators can improve the services delivered and decrease health care costs by improving efficiency. Although our study was somewhat limited by patient selection biases, the study's results suggest that Internet-based tools of comparison will enable patients to make free and informed decisions about their health care by comparing local hospitals and voting on their impressions of the facilities from which they receive care.

Data Collection↗
PubMed2000

How animals move: an integrative view.

Recent advances in integrative studies of locomotion have revealed several general principles. Energy storage and exchange mechanisms discovered in walking and running bipeds apply to multilegged locomotion and even to flying and swimming. Nonpropulsive lateral forces can be sizable, but they may benefit stability, maneuverability, or other criteria that become apparent in natural environments. Locomotor control systems combine rapid mechanical preflexes with multimodal sensory feedback and feedforward commands. Muscles have a surprising variety of functions in locomotion, serving as motors, brakes, springs, and struts. Integrative approaches reveal not only how each component within a locomotor system operates but how they function as a collective whole.

Animals↗
PubMed2000

P-Glycoprotein inhibitor valspodar (PSC 833) increases the intracellular concentrations of daunorubicin in vivo in patients with P-glycoprotein-positive acute myeloid leukemia.

PURPOSE: The aim of the present study was to evaluate the effect of the cyclosporine derivative valspodar (PSC 833; Amdray, Novartis Pharma, Basel, Switzerland) on the concentration of daunorubicin (dnr) in leukemic blast cells in vivo during treatment. PATIENTS AND METHODS: Ten patients with acute myeloid leukemia (AML) were included. Leukemic cells from seven of the patients were P-glycoprotein (Pgp)-positive. dnr 100 mg/m(2) was given as a continuous infusion over 72 hours. After 24 hours, a loading dose of valspodar was given, followed by a 36-hour infusion of 10 mg/kg per 24 hours. Blood samples were drawn at regular intervals, and concentrations of dnr and its main metabolite, daunorubicinol, in plasma and isolated leukemic cells were determined by high-pressure liquid chromatography. RESULTS: The mean dnr concentrations in leukemic cells 24 hours after the start of infusion (before valspodar) were 18.8 micromol/L in Pgp-negative samples and 13.5 micromol/L in Pgp-positive samples. After 8 hours of valspodar infusion, these values were 25.8 and 24.0 micromol/L, respectively. The effect of valspodar was evaluated from the ratio of the area under the curve (AUC) for dnr concentration versus time in leukemic cells to the AUC for dnr concentration against time in the plasma. For the seven patients with Pgp-positive leukemia, the mean ratio increased by 52%, from 545 on day 1 to 830 on day 2 (P<.05) when valspodar was given. In the three patients with Pgp-negative leukemia, no significant difference was observed. CONCLUSION: These results strongly suggest that valspodar, by interacting with Pgp, can increase the cellular uptake of dnr in leukemic blasts in vivo.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

Factors associated with brain donation among optimally healthy elderly people.

BACKGROUND: Consent rates for brain donation were examined in 140 healthy elderly participants of the Oregon Brain Aging Study, a longitudinal study of successful aging. Subjects were initially selected for good health. The study population had a relatively high education level, a high socioeconomic status, and were predominantly white. METHODS: At each annual examination, a project physician asked participants to consider brain donation. This analysis examined variables that may affect the rate of brain donation consent: age, gender, education, socioeconomic status, marital status, religiosity, cognitive status, depression, and functional status. RESULTS: Of these variables only age was a meaningful factor. CONCLUSION: The oldest old participants (> or =85 years of age) were more likely to consent to donation than the younger participants (65-84 years of age).

Age Factors↗
PubMed1998

High single dose of mitoxantrone and cytarabine in acute non-lymphocytic leukemia: a pharmacokinetic and clinical study.

In a phase I-II study, the authors evaluated the intracellular pharmacokinetics, toxicity, and efficiency of a high dose of mitoxantrone given as first induction in acute non-lymphocytic leukemia. Twenty-two patients with previously untreated de novo ANLL were included and received 30 or 40 mg/m2 mitoxantrone on day 1 by intravenous infusion over 1 hour and 500 mg/m2 ara-C twice a day for 5 days. If there was no complete remission (CR), a second induction with ara-C, etoposide, and amsacrine was given. The CR rate after two courses with this regimen was 77%. Median duration of severe neutropenia was 18 days in the 30-mg/m2 group and 25 days in the 40-mg/m2 group. Two patients had fatal lung complications probably unrelated to mitoxantrone. A third patient had a possible mitoxantrone-induced reversible lung complication. In the leukemic cells, we found a high accumulation of mitoxantrone which, in contrast to the plasma concentration, remained stable during the 48 hours studied. Compared with previous results with 12 mg/m2 mitoxantrone, the AUC for intracellular concentrations versus time for the first 20 hours studied was increased by 150% to 0.638 nmol/mg cell protein x hour with 30 mg/m2 mitoxantrone and by 260% to 1.103 nmol/mg cell protein x hour with 40 mg/m2 mitoxantrone. In conclusion, a high dose of mitoxantrone results in a high intracellular exposure of the leukemic cells, which may be an advantage in improving survival of these patients.

Adult↗
PubMed1997

Talking while walking: the effect of a dual task in aging and Alzheimer's disease.

We determined the effects of distraction on gait in healthy elderly subjects and Alzheimer's disease (AD) patients. The effects of simultaneous performance of a verbal fluency task (effect of reciting male or female names) on the time and number of steps taken to walk 30 feet were compared using a repeated-measures design with between-group comparison between community-dwelling healthy old old (oOld; n = 20; mean age +/- SD, 86 +/- 4.4), healthy young old (yOld; n = 23; mean age +/- SD, 72 +/- 3.6), and probable AD subjects without parkinsonism (n = 15; mean age +/- SD, 74 +/- 13). AD patients slowed more than the yOld (p = 0.005) and the oOld (p = 0.002). The yOld and oOld did not differ from each other (p = 0.68). Mean (+/-SD) differences in time were as follows: yOld, -2.2 +/- 1.9; oOld, -1.6 +/- 2.0; AD, -7.1 +/- 9.2 seconds. The change in steps did not differ between groups. Walking speed of AD patients slowed more than that of elderly subjects during the dual task. This may contribute to the risk of falls in AD.

Aged↗
PubMed1997

Establishment of behavioral parameters for the evaluation of osteopathic treatment principles in a rat model of arthritis.

Unilateral arthritis was produced in rats by use of methylated bovine serum albumin in a model of antigen-induced arthritis. The progression of arthritis was measured by computerized motion analysis, bilateral joint circumference, voluntary extension force of the hindlegs, and length of ankle extension. Animals with induced arthritis were assigned to treated and untreated groups on the basis of approximately equal deficits by the parameters measured. A third group of rats, which did not have arthritis induced and received no treatment, served to establish mean normal parameters. Modified techniques of muscle energy, passive movement of the ankle and knee, and passive myofascial stretch were applied to the animals, and the animals were exercised in a mechanized exercise wheel. Parameters associated with gait were examined by computerized motion analysis of walking. Animals treated with manipulation and exercise improved significantly relative to untreated animals with antigen-induced arthritis in vertical ankle lift, ankle-based and foot-based stride lengths, knee circumference, and normalized extension of the ankle. The results demonstrate that the parameters identified can be used to detect functional deficits and significant improvement from those deficits can be derived from a nonpharmacologic treatment paradigm that includes osteopathic manipulation and exercise in an animal model of arthritis. These parameters may be useful in the identification of the relative benefits of independent treatment variables including frequency of osteopathic manipulation and exercise and the relative benefits of each in this model. Also, they may elucidate how these treatments produce their beneficial effects clinically.

Animals↗
PubMed1994

Sensitivity functions of a human head movement model.

With time as the criterion to be optimized, the divergences from optimal head movements show systematic differences of their control signal variables with respect to single behaviours. To clarify these relationships, this study uses manipulation and mathematical analysis of the 6th order nonlinear head movement model, i.e. the threefold approach of sensitivity analysis. In addition to sensitivity coefficients, graphs and trajectories sensitivity functions have been analysed. This is the sensitivity of a nominal head movement to changes of the model parameters during the time course of the movement. This demonstrated both the specific change of the visco-inertial properties of the head movement model during the movement and also the potential pathological deficits that may occur.

Computer Simulation↗
PubMed1993

Human studies to measure the effect of antibiotic residues.

This epidemiological study compares the frequency of resistant bacteria in stool microflora among vegetarians and nonvegetarians over a 12 month period. Two well characterized vegetarian populations (one in Boston, MA and the other in Loma Linda, CA) as well as appropriate controls were studied. No apparent differences in the prevalence of antibiotic resistance in the microflora were noted; however, vegetarians had a significantly greater incidence of multi-antibiotic resistance. E. coli of the same API biotype had the same frequency of antibiotic resistance in both vegetarians and nonvegetarians. Quantitative studies showed similar percents of tetracycline resistant facultative isolates and of "bacteroides." Klebsiella were more common in the stool of the nonvegetarians. As shown in previous studies, exposure to animal products either as meat eaters or production workers in a poultry abattoir was not associated with an increased incidence of resistant bacterial flora or infections caused by resistant strains.

Anti-Bacterial Agents↗
PubMed1992

Sensitivity coefficients, trajectories and graphs of a human head-movement model.

With time as the criterion to be optimized, the divergences from optimal head movements show systematic differences in their control signal variables with respect to single behaviours. To clarify these relationships, this study applies manipulation and mathematical analysis of the 6th-order nonlinear head movement model, using the three-fold approach of sensitivity analysis. The sensitivity analysis of the improved and refined head movement model explains the different tasks of the control parameters and their relation to the plant. It shows that width more than height of the agonistic and antagonistic pulses dominate the important behaviours of the movement: acceleration, magnitude and duration.

Head↗
PubMed1988

Regional differentiation in the stomach of the green anole.

The stomach of Anolis carolinensis (Reptilia: Iguanidae) has four histologically and histochemically distinct regions. The gastroesophageal junction has an acidic surface mucin and no glands. The cardia has an acidic surface mucin and mucous glands. This acidic mucin appears to contain neither sulfates nor sialic acid. The fundus has a neutral surface mucin and mucoserous glands. The pylorus has a neutral surface mucin and mucous glands.

Animals↗
PubMed1981

Simulation of head movement trajectories: model and fit to main sequence.

A sixth order nonlinear model for horizontal head rotations in humans is presented and investigated using experimental results on head movement trajectories and neck muscle EMG. The controller signals, structured in accordance with time optimal control theory, are parameterized, and controller signal parameter variations show a dominating influence on different aspects of the head movement trajectory. The model fits the common head acceleration types over a wide range of amplitudes, and also less common (dynamic overshoot) trajectories.

Electromyography↗
PubMed1981

Sensitivity analysis and optimization for a head movement model.

A sixth order nonlinear model for horizontal head rotations in humans is analyzed using an extended parameter sensitivity analysis and a global optimization algorithm. The sensitivity analysis is used in both the direct sense, as a model fitting tool, and in the indirect sense, as a guide to experimental design. Resolution is defined in terms of the sensitivity table, and is used to interpret the sensitivity results. Using sensitivity analyses, the head and eye movement systems are compared and contrasted. Controller signal parameters are the most influential. Their variations and effects on head movement trajectories and accelerations are investigated, and the conclusions are compared with clinical neurological findings. The global optimization algorithm, in addition to automating the fitting of various types of data, is combined with time optimality theory to give theoretical time-optimal inputs to the model.

Computers↗