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Biomedical subjects

M E Nelson

Publications and source records attributed to M E Nelson.

At least 37 records · Page 2Linked to original sources
PubMed1999

Bone mineral measurements: a comparison of delayed gamma neutron activation, dual-energy X-ray absorptiometry and direct chemical analysis.

A system in vitro consisting of a femur from a cadaver and soft-tissue equivalent material was used to test the agreement between several techniques for measuring bone mineral. Calcium values measured by delayed gamma neutron activation (DGNA) and bone mineral content (BMC) by Lunar, Hologic and Norland dual-energy X-ray absorptiometers (DXA) were compared with calcium and ash content determined by direct chemical analysis. To assess the effect of soft-tissue thickness on measurements of bone mineral, we had three phantom configurations ranging from 15.0 to 26.0 cm in thickness, achieved by using soft-tissue equivalent overlays. Chemical analysis of the femur gave calcium and ash content values of 61.83 g +/- 0.51 g and 154.120 +/- 0.004 g, respectively. Calcium measured by DGNA did not differ from the ashed amount of calcium at any of the phantom configurations. The BMC measured by DXA was significantly higher, by 3-5%, than the amount determined by chemical analysis for the Lunar densitometer and significantly lower, by 3-6%, for the Norland densitometer (p<0.001-0.024), but only 1% lower (not significant) for the Hologic densitometer. DXA instruments showed a decreasing trend in BMC as the thickness increased from 20.5 to 26.0 cm (p<0.05). However, within the entire thickness range (15.0-26.0 cm), the overall influence of thickness on BMC by DXA was very small. These findings offer insight into the differences in these currently available methods for bone mineral measurement and challenge the comparability of different methods.

Absorptiometry, Photon↗
PubMed1999

The effects of progressive resistance training on bone density: a review.

Osteoporosis is a major public health problem that is characterized by low bone mass and increased susceptibility to fractures, primarily of the hip, spine, and wrist. It is estimated to cause 1.5 million fractures annually in the United States in people aged 50 yr and older. Physical activity, particularly weight-bearing exercise, is thought to provide the mechanical stimuli or "loading" important for the maintenance and improvement of bone health, whereas physical inactivity has been implicated in bone loss and its associated health costs. Both aerobic and resistance training exercise can provide weight-bearing stimulus to bone, yet research indicates that resistance training may have a more profound site specific effect than aerobic exercise. Over the past 10 years, nearly two dozen cross-sectional and longitudinal studies have shown a direct and positive relationship between the effects of resistance training and bone density. Conversely, a handful of other studies have reported little or no effect on bone density. However, these results may be partially attributable to the study design, intensity and duration of the exercise protocol, and the bone density measurement techniques used. High-intensity resistance training, in contrast to traditional pharmacological and nutritional approaches for improving bone health in older adults, has the added benefit of influencing multiple risk factors for osteoporosis including improved strength and balance and increased muscle mass.

Aged↗
PubMed1999

Prey capture in the weakly electric fish Apteronotus albifrons: sensory acquisition strategies and electrosensory consequences.

Sensory systems are faced with the task of extracting behaviorally relevant information from complex sensory environments. In general, sensory acquisition involves two aspects: the control of peripheral sensory surfaces to improve signal reception and the subsequent neural filtering of incoming sensory signals to extract and enhance signals of interest. The electrosensory system of weakly electric fish provides a good model system for studying both these aspects of sensory acquisition. On the basis of infrared video recordings of black ghost knifefish (Apteronotus albifrons) feeding on small prey (Daphnia magna) in the dark, we reconstruct three-dimensional movement trajectories of the fish and prey. We combine the reconstructed trajectory information with models of peripheral electric image formation and primary electrosensory afferent response dynamics to estimate the spatiotemporal patterns of transdermal potential change and afferent activation that occur during prey-capture behavior. We characterize the behavioral strategies used by the fish, with emphasis on the functional importance of the dorsal edge in prey capture behavior, and we analyze the electrosensory consequences. In particular, we find that the high-pass filter characteristics of P-type afferent response dynamics can serve as a predictive filter for estimating the future position of the prey as the electrosensory image moves across the receptor array.

Animals↗
PubMed1999

Intrapulmonary cytokine accumulation following BAL and the role of endotoxin contamination.

STUDY OBJECTIVES: BAL induces alveolar inflammation, but its effects on intrapulmonary cytokines and the mechanisms causing inflammation are uncertain. The objectives of this study were: (1) to characterize cytokine response in the lungs to BAL, and (2) to determine whether endotoxin is introduced into the lungs during BAL, which could promote BAL-induced inflammation. DESIGN AND METHODS: We performed two BAL procedures in healthy volunteers separated by 4 (n=6), 24 (n=5), or 72 h (n=3). The initial BAL was performed in the right middle lobe (RML) and the second BAL was performed in the same location and the lingula. Concentrations of interleukin-8 (IL-8), interleukin-1 (IL-1beta), and transforming growth factor-beta were measured by enzyme-linked immunosorbent assay and tumor necrosis factor-alpha (TNF-alpha) bioactivity was determined. Endotoxin contents of saline (10 and 20 mL) infused through bronchoscopes as well as BAL fluids recovered from six subjects were assessed by limulus amebocyte assay. RESULTS: At 4 h after the initial lavage, but not at later times, BAL fluid recovered from the RML contained increased concentrations of IL-8 and IL-1beta, and increased TNF-alpha bioactivity. BAL fluid recovered from the lingula contained increased concentrations of TNF-alpha only at 4 h. All BAL samples tested contained detectable endotoxin as did all saline aliquots instilled through bronchoscopes. CONCLUSIONS: There is intrapulmonary accumulation of the cytokines TNF-alpha, IL-8, and IL-1beta in the lavaged lung within 4 h after BAL; this accumulation resolves by 24 h. Endotoxin contamination of the lungs during bronchoscopy may contribute to BAL-induced lung inflammation.

Adult↗
PubMed1998

Chronic nicotine treatment up-regulates human alpha3 beta2 but not alpha3 beta4 acetylcholine receptors stably transfected in human embryonic kidney cells.

Human nicotinic acetylcholine receptor (AChR) subtypes alpha3 beta2, alpha3 beta2 alpha5, alpha3 beta4, and alpha3 beta4 alpha5 were stably expressed in cells derived from the human embryonic kidney cell line 293. alpha3 beta4 AChRs were found in prominent 2-micrometer patches on the cell surface, whereas most alpha3 beta2 AChRs were more diffusely distributed. The functional properties of the alpha3 AChRs in tsA201 cells were characterized by whole cell patch clamp using both acetylcholine and nicotine as agonists. Nicotine was a partial agonist on alpha3 beta4 AChRs and nearly a full agonist on alpha3 beta2 alpha5 AChRs. Chronic exposure of cells expressing alpha3 beta2 AChRs or alpha3 beta2 alpha5 AChRs to nicotine or carbamylcholine increased their amount up to 24-fold but had no effect on the amount of alpha3beta4 or alpha3 beta4 alpha5 AChRs, i.e. the up-regulation of alpha3 AChRs depended on the presence of beta2 but not beta4 subunits in the AChRs. This was also found to be true of alpha3 AChRs in the human neuroblastoma SH-SY5Y. In the absence of nicotine, alpha3 beta2 AChRs were expressed at much lower levels than alpha3 beta4 AChRs, but in the presence of nicotine, the amount of alpha3 beta2 AChRs exceeded that of alpha3 beta4 AChRs. Up-regulation was seen for both total AChRs and surface AChRs. Up-regulated alpha3beta2 AChRs were functional. The nicotinic antagonists curare and dihydro-beta-erythroidine also up-regulated alpha3 beta2 AChRs, but only by 3-5-fold. The channel blocker mecamylamine did not cause up-regulation of alpha3 beta2 AChRs and inhibited up-regulation by nicotine. Our data suggest that up-regulation of alpha3 beta2 AChRs in these lines by nicotine results from both increased subunit assembly and decreased AChR turnover.

Animals↗
PubMed1998

Comparison of responses of base-specific Salmonella tester strains with the traditional strains for identifying mutagens: the results of a validation study.

The ability of a TA7000 series of Salmonella his- mutant tester strains to detect mutagens as classified by the traditional tester strains (TA100, TA98, TA1535, TA1537, TA97, TA102 and TA104) was evaluated using 30 coded chemicals, 5 of which were duplicates with different code numbers. The TA7000 series of tester strains were TA7001, TA7002, TA7003, TA7004, TA7005 and TA7006, each of which reverts by a specific base substitution. In addition, each chemical was tested in a mixture of the base-specific strains (the Mix), plus the traditional strains, TA98 and TA1537. A liquid version of the Salmonella mutagenicity assay was performed in microtiter plates to allow partial automation for increased throughput. The results were compared to those in the National Toxicology Program (NTP) database, which were obtained from the traditional strains in the preincubation assay. In the two strains common to both protocols, TA98 and TA1537, the agreement was 80% and 85%, respectively. When compared to the NTP results for TA100, the Mix gave a 72% concordance, while the addition of the frameshift tester strain, TA98, increased the agreement to 76%. The overall agreement on positive or negative classifications of mutagenicity was 88% for the 25 chemicals tested. There were three notable exceptions to the overall agreement. Benzaldehyde was detected as a mutagen in TA7005 in contrast to its classification as a non-mutagen in the NTP database. This does not necessarily contradict the NTP results because the base-specific strains may respond to different mutagens. Two weak mutagens in the NTP database, 1-chloro-2-propanol and isobutyl nitrite, were not detected as mutagens in the base-specific new strains in the liquid protocol. While there are a number of major differences in the two assays, it was concluded that the results from each procedure are comparable.

Mutagenicity Tests↗
PubMed1998

Losing the race to resuscitate.

Survival from in-hospital sudden cardiac death has not improved in the last 30 years. After reviewing one hospital's arrest events, their emergency response, automated external defibrillation and the current American Heart Association guidelines, a course to improve survival was initiated. Providing early defibrillation is a critical first step to improving outcomes from sudden cardiac death.

Cardiopulmonary Resuscitation↗
PubMed1998

Physical fitness: how to help older patients live stronger and longer. (1).

Most older Americans are not physically fit and do not exercise regularly. This is especially true of older women, who are weaker than men and become disabled and dependent in the later years at a much greater rate. Exercise can increase the body's metabolism and make it more efficient in burning calories. Physical fitness also makes respiration more efficient. Evidence suggests strongly that the physically fit live 2 to 3 years longer and have a better quality of life than sedentary individuals. Any time is the best time for a person of any age to start exercising. Exercise is movement--dancing, walking, lifting a weight, using the body. Older individuals tend to be willing to exercise if they are given appropriate recommendations and follow-up.

Aged↗
PubMed1998

Physical fitness: benefits of exercise for the older patient. 2.

Exercise provides important benefits for older adults in the areas of cardiovascular function, strength and muscle mass, postural stability, and psychological function. These benefits can be achieved by those who are healthy, as well as by the frail and very old. Physicians can use a simple screening test to identify patients at risk for loss of mobility and function due to muscle weakness. Exercise helps prevent hip fractures from falls by increasing bone density, coordination, balance, and muscle strength. It is also an important treatment for patients with arthritis, Parkinson's disease, stroke, and other chronic diseases of aging. Patients who exercise show improvements in depressive symptoms and sleep disorders.

Activities of Daily Living↗
PubMed1998

Determinants of channel gating located in the N-terminal extracellular domain of nicotinic alpha7 receptor.

We identified regions within the N-terminal extracellular domain of alpha7 nicotinic acetylcholine receptors that affect channel gating. By single-channel analysis of alpha7 nicotinic acetylcholine receptors currents, we show that the difference in efficacy between the two agonists acetylcholine and 1,1-dimethyl-4-phenylpiperazinium (DMPP) is due to a slower channel activation rate by DMPP. The partial efficacy of DMPP was not caused by channel block or faster desensitization of alpha7 AChRs by DMPP. In addition, the efficacy and, by inference, the activation rate were found to be voltage dependent. Using chimeras of the two closely related subunits alpha7 and alpha8, we map residues that affect channel activation rate and agonist affinity to two different regions of the extracellular domain. Residues that affect channel activation rate are within the sequence 1-179, whereas residues that affect agonist affinity are within the sequence 180-208.

Animals↗
PubMed1998

Physical fitness: exercise prescription for older adults. 3.

Patients age 50 and older who are seen by primary care doctors are in various stages of wellness, ranging from healthy to frail. Because of this diversity, exercise prescription needs to be individualized, based on many of the same principles as drug prescription. Fitness programs typically include exercises to improve posture, aerobics, flexibility, strength, and balance. Exercising for 5 minutes a day is a good starting point, with sessions increasing gradually to 20 to 30 minutes. Trunk strengthening exercise can help patients stand from soft, low chairs. Ankle exercises can reduce the risk of falls and hip fractures. Weight training is safe and effective exercise for older patients.

Aged↗
PubMed1998

Understanding the needs of children following large-scale disasters and the role of government.

No one who experiences a disaster is untouched by it. Children and their families are often among the most affected. This article explains how mental health and medical professionals can assist families and communities in dealing with common disaster-related stress reactions in children. An overview of disaster research and examples of special concerns about children are given. In addition, an overview of the role of local, state, and federal governments, as well as other organizations, is provided.

Adolescent↗
PubMed1997

Characterization and modeling of P-type electrosensory afferent responses to amplitude modulations in a wave-type electric fish.

The first stage of information processing in the electrosensory system involves the encoding of local changes in transdermal potential into trains of action potentials in primary electrosensory afferent nerve fibers. To develop a quantitative model of this encoding process for P-type (probability-coding) afferent fibers in the weakly electric fish Apteronotus leptorhynchus, we recorded single unit activity from electrosensory afferent axons in the posterior branch of the anterior lateral line nerve and analyzed responses to electronically generated sinusoidal amplitude modulations of the local transdermal potential. Over a range of AM frequencies from 0.1 to 200 Hz, the modulation transfer function of P-type afferents is high-pass in character, with a gain that increases monotonically up to AM frequencies of 100 Hz where it begins to roll off, and a phase advance with a range of 15-60 degrees. Based on quantitative analysis of the observed gain and phase characteristics, we present a computationally efficient model of P-type afferent response dynamics which accurately characterizes changes in afferent firing rate in response to amplitude modulations of the fish's own electric organ discharge over a wide range of AM frequencies relevant to active electrolocation.

Action Potentials↗
PubMed1997

Rapid lung cytokine accumulation and neutrophil recruitment after lipopolysaccharide inhalation by cigarette smokers and nonsmokers.

Inhalation of lipopolysaccharide (LPS) by humans rapidly recruits neutrophils to alveolar structures. Recruitment of neutrophils may be mediated in part by intrapulmonary release of cytokines such as tumor necrosis factor-alpha, interleukin (IL)-1beta, and IL-8, although the kinetics of cytokine accumulation and neutrophil recruitment to the lungs after LPS inhalation have not been determined. Release of some cytokines in response to LPS is reported to be decreased in smokers' alveolar macrophages compared with nonsmokers', suggesting responses to LPS may differ in smokers (S) and nonsmokers (NS). To assess the kinetics of early cytokine accumulation after LPS inhalation and to compare inflammation induced in LPS-exposed S and NS, we performed bronchoalveolar lavage (BAL) in 28 subjects (14 NS and 14 S) at 90 or 240 minutes after inhalation of aerosolized LPS (30 microg). BAL performed at 90 and 240 minutes after LPS inhalation recovered increased numbers of neutrophils and lymphocytes in both NS and S compared with an unexposed control group (10 NS, 10 S), with greater recovery of neutrophils in S than NS (p < 0.001). BAL fluid supernate concentrations of IL-8, IL-1beta, and tumor necrosis factor-alpha at 90 minutes were increased in S and NS compared with an unexposed control group. IL-8 and tumor necrosis factor-alpha concentrations were similar in S and NS; however, IL-1beta concentrations were greater in S (p < 0.005). BAL fluid concentrations of IL-1beta and IL-8 at 90 minutes correlated with absolute neutrophil recovery in S and NS. These findings suggest that the rapid accumulation of cytokines, particularly IL-1beta and IL-8, contributes to lung neutrophil recruitment after LPS inhalation. In addition, parameters of pulmonary inflammation present in S after LPS inhalation are similar to or increased compared with those present in NS.

Administration, Inhalation↗
PubMed1997

A multi-center comparison of dual energy X-ray absorptiometers: in vivo and in vitro soft tissue measurement.

OBJECTIVE: To assess intra- and inter-site soft tissue variability by dual energy X-ray absorptiometry (DXA). DESIGN: Cross-sectional trial. SETTING: Three medical research institutions. SUBJECTS: Five humans (in vivo) and four phantoms (in vitro), configured from two whole body phantoms with artificial skeletons and thickness overlays. INTERVENTIONS: Duplicate total-body DXA scans were performed on all subjects at each institution within a 15 d period. RESULTS: All intra-site coefficients of variation (CV) were < 0.5% for total tissue mass, but in vitro and in vivo Cvs were 7.2% and 2.3% for fat mass (FM) and 2.5% and 0.9% for lean mass (LM), respectively. Several total-body and regional FM and LM measurements were significantly different between sites (P < 0.05), with percent differences between sites ranging from 2.6-13.3% for FM and from 1.6-13.6% for LM. Site 2 was consistently lower for FM and Site 3 was consistently lower for LM. CONCLUSIONS: These results stress the need for both rigorous and standardized cross-calibration procedures for soft tissue measurement by DXA.

Absorptiometry, Photon↗
PubMed1996

A multicenter comparison of dual-energy X-ray absorptiometers: in vivo and in vitro measurements of bone mineral content and density.

As part of a multicenter research project, we compared dual-energy X-ray absorptiometry (DXA) instruments at three research centers (sites 1, 2 and 3) to determine both intra- and intersite variability of bone mineral content (BMC), bone mineral density (BMD), and bone area (BA). Scans of the total body and lumbar spine were performed in duplicate on five humans (in vivo), and scans of the total body were performed on two whole body phantoms with artificial skeletons and thickness overlays (in vitro) at all sites over 15 days. The average intrasite variability in two consecutive total body BMD measurements, expressed as a percent difference, was significantly higher in vitro, 1.74 +/- 1.97%, than in vivo, 0.71 +/- 0.38% (p < 0.05). Average intrasite variability of the in vivo lumbar spine BMD was 1.08 +/- 1.12%. The intersite coefficients of variation for all BMD, BMC, and BA measurements were < 2.0%. The total body BMD from site 2 was systematically lower than at sites 1 and 3 both in vivo and in vitro (p < 0.05) with no differences in BMC and BA. Although significant, the total body BMD differences between sites were small (< 1.2%) in vivo compared with in vitro (< 2.6%) and are encouraging for the comparison and pooling of human data from multicenter trials, provided that appropriate standardized cross-calibration and analysis procedures are applied.

Absorptiometry, Photon↗
PubMed1996

Alveolar macrophages accumulate iron and ferritin after in vivo exposure to iron or tungsten dusts.

Extracellular iron present in alveolar structures may contribute to oxidative lung injury induced by toxic mineral dusts by enhancing dust-induced generation of hydroxyl radicals. Alveolar macrophages (AMs) can sequester iron within ferritin and limit generation of hydroxyl radicals. In the current study we sought to assess whether AMs accumulate iron and ferritin after in vivo exposure to a dust with high iron content, to iron oxide, or to an inflammatory dust, calcium tungstate. We performed lung lavage 1, 7, 14, 28, 42, and 56 days after intratracheal instillation of mineral dust in saline solution or instillation of saline solution alone and quantitated cell recovery and AM content of iron and ferritin. Instillation of iron oxide increased neutrophil recovery only on a day 1 when compared with results in controls, whereas calcium tungstate increased neutrophil recovery through day 14. AMs recovered after instillation of iron oxide contained increased amounts of iron and ferritin, beginning on day 1 and progressing through day 56 after treatment (7.57 +/- 0.38 microgram iron per 10(6) AMs vs 1.54 +/- 0.28 microgram iron per 10(6) AMs for controls, p < 0.001; and 5908 +/- 768 ng ferritin per 10(6) AMs vs 395 +/- 20 ng ferritin per 10(6) AMs, p < 0.001). AMs recovered after calcium tungstate instillation also contained increased amounts of iron and ferritin beginning 14 days after treatment, with greatest content 42 days after treatment (4.85 +/- 0.68 microgram iron per 10(6) AMs, p < 0.001, and 2274 +/- 736 ng ferritin per 10(6) AMs, p < 0.001). Tumor necrosis factor, which can enhance iron accumulation by macrophages, was spontaneously released by AMs recovered from tungsten-treated rats. These studies indicate that AMs accumulate iron and ferritin in response to both iron loading of the lungs with iron oxide exposure and lung inflammation induced by calcium tungstate exposure.

Adult↗