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PubMed1999

Biotransformation of carbon tetrachloride by various acetate- and nitrate-limited denitrifying consortia

Fed-batch experiments were performed to determine the carbon tetrachloride (CT)-degrading ability of three denitrifying consortia cultured from sites not contaminated with CT. A mathematical model was used to quantify the rates of CT transformation by the consortia under both acetate-limiting and nitrate-limiting conditions. A rate constant for CT transformation on a cellular protein basis and the fraction of degraded CT transformed to chloroform (CF) were determined for each consortium by optimizing the model to fit the experimental data. The parameters for these experiments were statistically compared to those obtained for previous experiments with a denitrifying consortium cultured from an aquifer soil sample from the US Department of Energy Hanford site in southeastern Washington state. Results of F-test analysis indicated the rate of CT transformation and the production of CF both were functions of the limiting nutrient. Under nitrate-limited conditions, the rate constant for CT transformation for all four consortia was about 30 L/gmol/min and approximately 50% of the CT transformed was converted to CF. When acetate was the limiting nutrient, the rate constant for CT transformation was approximately 8 L/gmol/min and the CF yield decreased to about 25%. These results imply the ability to degrade CT may be inherent to some denitrifying organisms, regardless of previous exposure to CT. Copyright 1999 John Wiley & Sons, Inc.

Journal Article↗

PubMed2000

Effects of limited access to a fat option on food intake and body composition in female rats.

OBJECTIVE: The present investigation sought to determine if limiting access to an optional fatty food would induce binge-type behavior patterns in non-energy-deprived female rats. METHOD: Four groups of rats had continuous access to a commercial rodent diet throughout the 8-week study. In addition: (1) the control group had no access to vegetable shortening; (2) the high limitation group had access to shortening for 2 hr for 3 days each week; (3) the low limitation group had access to shortening for 2 hr every day; and (4) the no limitation group had continuous access to shortening. RESULTS: As access to the shortening decreased, intake during the 2-hr access period increased. Total energy intake and body weight did not differ among groups. Body fat was greatest in the rats that ate the most cumulative shortening. DISCUSSION: These results indicate that, even under non-energy-deprived conditions, limiting access to a preferred fatty food can induce binge-type behavior in female rats.

Animals↗

PubMed2001

An evaluation of the detection limits possible for competitive capillary electrophoretic immunoassays.

Using a high-affinity antibody for estradiol, thermodynamic and experimental limitations on detection limits for competitive capillary electrophoretic immunoassays were examined. Theoretical modeling of the dose-response curves for such assays allowed for optimization of experimental conditions. Through the examination of experimental and theoretical results generalizations could be made as to the ability of capillary electrophoretic immunoassays to achieve low detection limits. An experimental detection limit of 310 pM, corresponding to 2100 molecules, was achieved. A minimum theoretical detection limit for the antibody of interest was approximated to be 125-525 pM depending on the standard deviation. An overview of the optimization process is given as well as commentary on theoretical predictions.

Antibodies↗

PubMed1996

Comprehensive noninvasive assessment of cardiac involvement in limited systemic sclerosis.

OBJECTIVE: To assess cardiovascular abnormalities in patients with limited systemic sclerosis (SSc), using noninvasive cardiac techniques. METHODS: Sixty-three patients with limited SSc were prospectively evaluated with Doppler echocardiography and thallium-201 perfusion scintigraphy after a cold-stress test and radionuclide ventriculography. RESULTS: In the patients with limited SSc, there was a significantly high prevalence of abnormal left- and right-diastolic function parameters (P = 0.001 and P = 0.0002, respectively), thickening of papillary muscles (46%; P = 0.003), and mild mitral regurgitation (49%; P < 0.0001), compared with controls. Systolic pulmonary arterial hypertension was detected in 9 patients (14%), and pericardial effusion in 11 patients (18%). In 64% of patients with limited SSc, an ischemic response was detected on the thallium cold-stress scan; similarly, an ischemic response was detected in 57% of patients with primary Raynaud's phenomenon (P < 0.0001 versus controls). CONCLUSION: Although the frequency of cardiovascular symptoms was low in patients with limited SSc, a significant rate of cardiovascular abnormalities was found by noninvasive cardiac techniques.

Adult↗

PubMed2005

Arthritis onset and worsening self-rated health: a longitudinal evaluation of the role of pain and activity limitations.

OBJECTIVE: To longitudinally explore the hypothesized role of worsening pain and development of activity limitations as mediators in the relationship between arthritis onset and worsening self-rated health (SRH). METHODS: Data was obtained from the 1998/1999 and 2000/2001 cycles of the population-based Canadian longitudinal National Population Health Survey (n = 10,859; ages > or = 18; response rate: time 1 = 81.6%, time 2 = 89.2%). Respondents were asked about chronic conditions, pain, activity limitations, and self-perceived health; change over time was assessed. Change in effect of arthritis onset on worsening SRH upon considering potential mediators was assessed through multivariate logistic regression, controlling for sociodemographic characteristics and onset of other conditions. RESULTS: Worsening pain fully explained the effect of arthritis onset on worsening SRH; a portion of the effect of worsening pain was mediated by the development of activity limitation. Residual direct effect of arthritis onset was statistically insignificant. Worsening pain and development of activity limitations also mediated a portion of the effects of onset of other chronic conditions but to a lesser extent than arthritis onset. CONCLUSION: This is the first study to examine these relationships longitudinally. Identifying the role of mediators is necessary if target areas of prevention and/or management are sought, either at the individual or population level. Our results indicate that the development of arthritis has a significant impact on worsening SRH. Pain and development of activity limitations fully account for the relationship between arthritis onset and worsening SRH. High priority should be placed on prevention and management strategies for pain among people with arthritis.

Activities of Daily Living↗

PubMed2005

Risk factors for functional limitations in patients with long-standing ankylosing spondylitis.

OBJECTIVE: To identify risk factors for functional limitations in patients with ankylosing spondylitis (AS) of at least 20 years' duration. METHODS: Patients with AS for > or =20 years were enrolled in the cross-sectional component of the Prospective Study of Outcomes in AS. All patients had clinical evaluations and completed questionnaires on functional limitations and potential risk factors. Functional limitations were assessed using the Bath Ankylosing Spondylitis Functional Index (BASFI; score range 0-100, higher scores indicate more limitations) and the Health Assessment Questionnaire for the Spondylarthropathies (HAQS). Risk factors included demographic characteristics, duration of AS, smoking status, number of comorbid medical conditions, recalled level of recreational activity in teens and twenties, occupational physical activity throughout life (rated 1 = little, 2 = moderate, 3 = heavy, and weighted by the number of years in each job), and history of AS in a first-degree relative. RESULTS: The 326 patients (74% men) had a mean +/- SD age of 55.0 +/- 10.7 years, a mean duration of AS symptoms of 31.7 +/- 10.2 years, and a mean BASFI score of 40.7 +/- 25.6. BASFI scores increased with higher lifetime occupational physical activity (r = 0.31; P < 0.0001), the number of comorbid conditions (r = 0.25; P < 0.0001), and the duration of AS (r = 0.12; P = 0.04). BASFI scores were higher among current smokers compared with former/nonsmokers (55.5 versus 38.9; P = 0.0002), and among nonwhites compared with whites (49.9 versus 39.3; P = 0.02). In multivariable analyses, lifetime occupational physical activity, current smoking, education level, number of comorbid conditions, and family history were significantly associated with BASFI scores. The same risk factors were associated with the HAQS. CONCLUSION: Functional limitations in patients with AS for >/=20 years are greater among those with a history of more physically demanding jobs, more comorbid conditions, and among smokers, and are less severe among those with higher levels of education and a family history of AS.

Age of Onset↗

PubMed2006

Projections of US prevalence of arthritis and associated activity limitations.

OBJECTIVE: To update the projected prevalence of self-reported, doctor-diagnosed arthritis and arthritis-attributable activity limitations among US adults ages 18 years and older from 2005 through 2030. METHODS: Baseline age- and sex-specific prevalence rates of arthritis and activity limitation, using the latest surveillance case definitions, were estimated from the 2003 National Health Interview Survey, which is an annual, cross-sectional, population-based health interview survey of approximately 31,000 adults. These estimates were used to calculate projected arthritis prevalence and activity limitations for 2005-2030 using future population projections obtained from the US Census Bureau. RESULTS: The prevalence of self-reported, doctor-diagnosed arthritis is projected to increase from 47.8 million in 2005 to nearly 67 million by 2030 (25% of the adult population). By 2030, 25 million (9.3% of the adult population) are projected to report arthritis-attributable activity limitations. In 2030, >50% of arthritis cases will be among adults older than age 65 years. However, working-age adults (45-64 years) will account for almost one-third of cases. CONCLUSION: By 2030, the number of US adults with arthritis and its associated activity limitation is expected to increase substantially, resulting in a large impact on individuals, the health care system, and society in general. The growing epidemic of obesity may also significantly contribute to the future burden of arthritis. Improving access and availability of current clinical and public health interventions aimed at improving quality of life among persons with arthritis through lifestyle changes and disease self-management may help lessen the long-term impact.

Adolescent↗

PubMed1990

Approach to the limit of counterion condensation.

According to counterion condensation theory, one of the contributions to the polyelectrolyte free energy is a pairwise sum of Debye-Hückel potentials between polymer charges that are reduced by condensed counterions. When the polyion model is taken as an infinitely long and uniformly spaced line of charges, a simple closed expression for the summation, combined with entropy-derived mixing contributions, leads to the central result of the theory, a condensed fraction of counterions dependent only on the linear charge density of the polyion and the valence of the counterion, stable against increases of salt up to concentrations in excess of 0.1 M. Here we evaluate the sum numerically for B-DNA models other than the infinite line of B-DNA charges. For a finite-length line there are end effects at low salt. The condensation limit is reached as a flat plateau by increasing the salt concentration. At a fixed salt concentration the condensation limit is reached by increasing the length of the line. At moderate salt even very short B-DNA line-model oligomers have condensed fractions not far from the infinite polymer limit. For a long double-helical array with charge coordinates at the phosphates of B-DNA, the limiting condensed fraction appears to be approached at low salt. In contrast to the results for the line of charges, however, the computed condensed fraction varies strongly with salt in the range of experimentally typical concentrations. Salt invariance is restored, in agreement with both the line model and experimental data, when dielectric saturation is considered by means of a distance-dependent dielectric function. For sufficiently long B-DNA line and helical models, as typical salt concentrations, the counterion binding fraction approaches the polymer limit as a linear function of 1/P, where P is the number of phosphate groups of B-DNA.

Animals↗

PubMed2003

Pulsed addition of limiting-carbon during Aspergillus oryzae fermentation leads to improved productivity of a recombinant enzyme.

Fungal morphology in many filamentous fungal fermentations leads to high broth viscosity which limits oxygen mass transfer, and often results in reduced productivity. The objective in this study was to determine if a simple, fed-batch, process strategy-pulsed addition of limiting-carbon source-could be used to reduce fungal broth viscosity, and increase productivity of an industrially relevant recombinant enzyme (glucoamylase). As a control, three Aspergillus oryzae fed-batch fermentations were carried out with continuous addition of limiting-carbon. To determine the effect of pulse-feeding, three additional fermentations were carried out with limiting-carbon added in 90-second pulses, during repeated five-minute cycles. In both cases, overall carbon feed-rate was used to control dissolved oxygen concentration, such that increased oxygen availability led to increased addition of limiting-carbon. Pulse-fed fermentations were found to have smaller fungal mycelia, lower broth viscosity, and improved oxygen mass transfer. As a result, more carbon was added to pulse-fed fermentations that led to increased enzyme productivity by as much as 75%. This finding has significant implications for the bioprocessing industry, as a simple process modification which is likely to cost very little to implement in most production facilities, has the potential to substantially increase productivity.

Aspergillus oryzae↗

PubMed2001

Limited adhesion of biodegradable microspheres to E- and P-selectin under flow.

In a variety of disease settings the expression of the endothelial selectins E- and P-selectin appears to be increased. This feature makes these molecules attractive targets around which to design directed drug-delivery schemes. One possible approach for achieving such delivery is to use polymeric biodegradable microspheres bearing a humanized monoclonal antibody (MAb) for E- and P-selectin, MAb HuEP5C7.g2. Perhaps the simplest technique for "coupling" HuEP5C7.g2 to the microspheres is via nonspecific adsorption. Previous studies suggest, however, that the adsorption of proteins onto microspheres fabricated in the presence of a stabilizer such as poly(vinyl alcohol) (PVA) is limited. It is unclear to what extent this limited level of adsorbed HuEP5C7.g2 would be able to support adhesion to E- and P-selectin under flow conditions. To explore this issue, we prepared microspheres from the biodegradable polymer, poly(epsilon-caprolactone) (PCL), using a single emulsion process and PVA as a stabilizer. We then incubated the PCL microspheres with HuEP5C7.g2 and studied the adhesion of the resulting HuEP5C7.g2 microspheres to E- and P-selectin under in vitro flow conditions. We found that the HuEP5C7.g2 PCL microspheres exhibit specific adhesion to Chinese hamster ovary cells stably expressing P-selectin (CHO-P) and 4-h IL-1beta-activated human umbilical vein endothelial cells (HUVEC). In contrast, HuEP5C7.g2 PCL microspheres exhibit little adhesion to parental CHO cells or unactivated HUVEC. The attachment efficiency to the selectin substrates was quite low, with appreciable attachment occurring only at low shear (0.3 dyn/cm(2)). Other supporting data strongly suggest that the limited attachment efficiency is due to a low level of HuEP5C7.g2 adsorbed to the PCL microspheres. Although the attachment was limited, a significant percentage of the HuEP5C7.g2 PCL microspheres were able to remain adherent at relatively high shear (8 dyn/cm(2)). Combined, our data suggest that HuEP5C7.g2 PCL microspheres exhibit selective limited adhesion to cellular substrate expressing E- and P-selectin.

Adsorption↗

PubMed1978

Analysis of double-substrate limited growth.

Mathematical models which relate the growth rate of a microorganism to a single limiting substrate concentration have long been established. In recent years, it has become apparent that, under certain conditions, the growth rate of an organism may be simultaneously limited by two or more substrates. Mathematical models of double-substrate limitation fall into two categories: interactive and noninteractive models. A discussion of both types of models is presented in both conceptual and mathematical terms. An analogous case of an enzyme which requires two different substrates to produce a single product is presented. This enzyme analog indicates that both types of double-substrate limitation models appear to be feasible under certain conditions. Based upon stoichiometry and specific growth rate-substrate concentration contour plots, a method for determining the operational conditions which will lead to double-substrate limitation is presented.

Bacteria↗

PubMed2003

Right coronary arteriography: experience with standard-torque and limited-torque techniques in children and young adults.

Coronary spasm and intimal injury may occur during selective right coronary arteriography. The safety and efficacy of right coronary arteriography in children and young adults were retrospectively reviewed for this report. Right coronary arteriography was performed in 200 patients. A standard-torque technique was used in 150 patients, a limited-torque technique was used with a reshaped left coronary catheter in 53 patients. The standard-torque technique was associated with proximal coronary spasm in nine patients, nonsustained ventricular tachycardia in one patient, and ST segment changes in one patient. The limited-torque technique was associated with no complications. The standard-torque technique was effective in one patient when the limited-torque technique failed to define distal coronary branches clearly. The limited-torque technique was effective in nine patients when the right coronary artery could not be engaged while attempting the standard-torque technique. In conclusion, right coronary arteriography may be performed in a safe and potentially more effective manner using a new catheter design and a limited-torque technique.

Adolescent↗

PubMed1982

Limiting dilution analysis of human peripheral blood mononuclear leukocytes that react to human amnion cells and protect these against viral challenge.

Human peripheral blood mononuclear leukocytes (PBL) cocultured with WISH human amnion cells rapidly produced alpha-type interferon (IFN-alpha) and in an IFN-dependent manner protected the WISH cells against the cytopathic effects caused by vesicular stomatitis virus. When the number of PBL per WISH cell monolayer culture was diluted out using multiple WISH microtiter plate cultures for each PBL dilution, the protection of the WISH cultures appeared as an all-or-none phenomenon. Thus, at one small mean number of PBL per culture, some cultures were protected against the virus, while others were not. Limiting dilution analysis, with plot of the logarithm of the fraction of nonprotected WISH cell cultures at each PBL dilution against the mean number of PBL per culture, yielded straight lines with an intercept on the ordinate close to 1. This indicated a single-hit event due to the function of a single type of limiting "protecting unit". The frequency of this limiting unit in the PBL population could reproducibly be determined for an individual blood donor. For a limited number of different blood donors it ranged from 1/400 to 1/3000. These minimal frequency estimates were considerably increased (40-300%) after 3 h preincubation of PBL with IFN-alpha. Two major alternatives were considered with regard to the nature of the limiting protecting units. They were either IFN-producing cells operating alone, or they were inducer-type cells that possibly used IFN as a mediator to activate protecting cells present in excess in the coculture system. The second possibility was favored, and the relation of the protecting cell type to the natural killer cell system is discussed herein.

Amnion↗

PubMedDate not supplied

Effect of albumin binding on extraction of sulfobromophthalein by perfused elasmobranch liver: evidence for dissociation-limited uptake.

We investigated the role of serum albumin in the hepatic uptake of organic anions by determining the effect of added bovine albumin on sulfobromophthalein (BSP) uptake in skates, an animal which naturally lacks this protein. A single-pass perfused liver model was used to determine steady-state net uptake rates as the BSP or BSP and albumin concentrations were systematically varied. Results indicated that two different steps in the uptake process are capable of limiting the uptake rate depending on the albumin and BSP concentrations selected. At higher rates of uptake corresponding to higher BSP concentrations (up to 112 microM), saturation kinetics were observed as the BSP concentration was varied, with apparent Km and Vmax values which were independent of the albumin concentration (0.05 to 0.75%). These data suggest that under these conditions uptake is limited by a saturable step intrinsic to the liver. In contrast, for lower BSP concentrations and albumin concentrations below about 0.5%, a different kinetic pattern was seen which suggested that the rate-limiting step in uptake was transfer of BSP from albumin to the liver. The latter data were found to be consistent with a model in which the limiting step in the transfer process is spontaneous dissociation of the BSP from binding sites on albumin within the sinusoid. These results suggest that skate liver clears BSP from albumin solutions by a two-step mechanism in which dissociation from albumin is followed by a saturable process consistent with carrier-mediated transport. The albumin concentration and uptake velocity are important factors in determining which of these steps limits the uptake rate. Clearance is efficient and irreversible even though elasmobranch liver lacks high-affinity cytosolic binding proteins for BSP, and elasmobranch plasma does not normally contain albumin.

Animals↗

PubMed2002

Scatter-limited phototherapy: a model for laser treatment of skin.

BACKGROUND AND OBJECTIVES: To effectively deliver laser light into the skin for non-ablative resurfacing, hair removal, and other applications, one must account for scatter, absorption, and thermal diffusion. A novel method to control the penetration of laser light into tissue is proposed. This method uses the incident beam diameter, the pulse duration, and the intrinsic light scattering of tissues such as skin to limit the laser light penetration and thermal damage. We term this innovative laser delivery concept 'scatter-limited phototherapy'. STUDY DESIGN/MATERIALS AND METHODS: This study demonstrates how the delivery mechanism simplifies the non-ablative treatment of sun-damaged skin. Calculations are based upon Gaussian scatter of light and isotropic thermal diffusion. Calculations of light distribution and profiles of temperature increase are created. RESULTS: Using an optical fiber delivery system with the appropriate diameter, coupled with skin surface protection, one can create thermal damage at a given depth with preservation of the epidermis. CONCLUSIONS: Scatter-limited phototherapy is a predictive model, allowing one to design better laser delivery systems. Scatter-limited phototherapy should also be applicable to other fields of dermatologic surgery, such as hair removal and the treatment of vascular lesions. Additionally, other medical specialties will be able to use the concept of scatter-limited phototherapy to predict and better understand laser-tissue interactions.

Hair Removal↗

PubMed2002

Assessment of inspiratory flow limitation in children with sleep-disordered breathing by a nasal cannula pressure transducer system.

A nasal cannula pressure transducer system identifies inspiratory flow limitation and increased upper airway resistance in adults with sleep-disordered breathing (SDB). The purpose of this study was to evaluate whether nasal cannula pressure (NCP) detects apneas and hypopneas as well as additional flow-limited events associated with increased airway resistance in children. We studied NCP in 47 patients (ages 2-14 years) referred for SDB to a university-based sleep disorders program during nocturnal polysomnography (NPSG). During NPSG, airflow was assessed simultaneously by thermistor and NCP. There was a high correlation between apneas assessed by thermistor (T) and NCP (r = 0.90, P < 0.0001), and for hypopneas using these two methods (r = 0.94, P = 0.0001). Respiratory driving pressure was indirectly measured with an esophageal pressure catheter. Flow-limited (flattened) NCP waves were associated with significantly higher driving pressure, indicating elevated upper airway resistance, compared to nonflow-limited (rounded) waves during nonrapid eye movement (NREM) (P = 0.05) and rapid eye movement (REM) (P = 0.01) sleep. Patients were classified as either having obstructive sleep apnea syndrome (OSAS) or primary snoring, based on standard NPSG criteria. NCP identified additional respiratory events with a flattened contour (FC) not detected by thermistor. NCP is a noninvasive device that identifies obstructive apneas and hypopneas as well as additional respiratory events associated with flow limitation in children.

Adolescent↗

PubMed1995

Decision and detection limits for linear homoscedastic assays.

This paper focuses on the effect of estimating the calibration parameters on the decision and detection limits for linear homoscedastic assays. Assay decision and detection limits are defined. For linear homoscedastic assays expressions for these limits are derived when the calibration parameters are known and unknown. These expressions, together with others previously reported in the literature, are used to calculate limits for a particular example of a cyclic AMP assay. The various methods of computing decision and detection limits are compared in a simulation study. The results demonstrate the importance of taking into consideration the variation in the estimators of the calibration parameters.

Chemistry, Clinical↗

PubMed1988

Metabolic responses of Saccharomyces cerevisiae CBS 8066 and Candida utilis CBS 621 upon transition from glucose limitation to glucose excess.

When chemostat cultures of Saccharomyces cerevisiae CBS 8066 and Candida utilis CBS 621, grown under glucose limitation, were pulsed with excess glucose, both organisms initially exhibited similar rates of glucose and oxygen consumption. However, striking differences were apparent between the two yeasts with respect to the production of cell mass in the culture and metabolite excretion. Upon transition from glucose limitation to glucose excess, S. cerevisiae produced much ethanol but the growth rate remained close to that under glucose limitation. C. utilis, on the other hand, produced little ethanol and immediately started to accumulate cell mass at a high rate. This high production rate of cell mass was probably due to synthesis of reserve material and not caused by a high rate of protein synthesis. Upon a glucose pulse both yeasts excreted pyruvate. In contrast to C. utilis, S. cerevisiae also excreted various tricarboxylic acid cycle intermediates, both under steady-state conditions and after exposure to glucose excess. These results and those of theoretical calculations on ATP flows support the hypothesis that the ethanol production as a consequence of pyruvate accumulation in S. cerevisiae, occurring upon transition from glucose limitation to glucose excess, is caused by a limited capacity of assimilatory pathways.

Adenosine Triphosphate↗