Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Limitations”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43Linked to original sources

Bronchial hyperresponsiveness, airway inflammation, and airflow limitation in endurance athletes.

BACKGROUND: Whereas a high prevalence of bronchial abnormalities has been reported in endurance athletes, its underlying mechanisms and consequences during exercise are still unclear. STUDY OBJECTIVES: The purpose of this study was to assess the following: (1) bronchial responsiveness to methacholine and to exercise; (2) airway inflammation; and (3) airflow limitation during intense exercise in endurance athletes with respiratory symptoms. DESIGN: Cross-sectional observational study. SETTING: Lung function and exercise laboratory at a university hospital. PATIENTS AND MEASUREMENTS: Thirty-nine endurance athletes and 13 sedentary control subjects were explored for the following: (1) self-reported respiratory symptoms; (2) bronchial hyperresponsiveness (BHR) to methacholine and exercise; (3) airflow limitation during intense exercise; and (4) bronchial inflammation using induced sputum and nitric oxide (NO) exhalation. RESULTS: Fifteen athletes (38%) showed BHR to methacholine and/or exercise in association with bronchial eosinophilia (mean [+/- SD] eosinophil count, 4.1 +/- 8.5% vs 0.3 +/- 0.9% vs 0%, respectively), higher NO concentrations (19 +/- 10 vs 14 +/- 4 vs 13 +/- 4 parts per billion, respectively), a higher prevalence of atopy, and more exercise-induced symptoms compared with non-hyperresponsive athletes and control subjects (p < 0.05). Furthermore, airflow limitation during intense exercise was observed in eight athletes, among whom five had BHR. Athletes with airflow limitation reported more symptoms and had FEV1, FEV1/FVC ratio, and forced expiratory flow at midexpiratory phase values of 14%, 9%, and 29%, respectively, lower compared with those of nonlimited athletes (p < 0.05). CONCLUSION: BHR in endurance athletes was associated with the criteria of eosinophilic airway inflammation and atopy, whereas airflow limitation during exercise was primarily a consequence of decreased resting spirometric values. Both BHR and bronchial obstruction at rest with subsequent expiratory flow limitation during exercise may promote respiratory symptoms during exercise in athletes.

Adult↗

Cerebrospinal fluid tau and Abeta42 concentrations in healthy subjects: delineation of reference intervals and their limitations.

Many limitations and conflicting results have cast serious doubts on the validity of cerebrospinal fluid tau and Abeta42 levels for the biological diagnosis of Alzheimer's disease, particularly extreme variations of the reference limits found by unrelated groups as a consequence of different reference populations used. In this study, we addressed the issue of defining reference limits for cerebrospinal fluid tau and Abeta42 in healthy adult individuals. One hundred and five neurologically intact subjects were enrolled according to strict inclusion criteria, 10 of them with autopsy confirmation of brain integrity. All cerebrospinal fluid samples were similarly and optimally processed as were the dosage methods used and the statistical analyses performed. A robust correlation with age was demonstrated for Abeta42 but not for tau. For tau, we found that an upper cut-off value of 443 ng/l allowed 95% of the subjects to be correctly classified as normal. For Abeta42, a lower cut-off value of 90 ng/l allowed a correct classification of 90% of the subjects. However, a large variance of the reference values, partly explained by the potential contamination of the reference population with presymptomatic dementia patients, may limit the use of reference limits based on living subjects. We propose that the issue of defining reference limits for both cerebrospinal fluid tau and Abeta42 may ultimately be settled by studying large numbers of autopsy-proven neurologically intact individuals only.

Adult↗

[Assessment of occupational exposures to industrial hazardous substances. IV. A proposed method based on one-sided tolerance limits].

Occupational exposures to potentially hazardous substances may vary considerably because of interday environmental behavioral fluctuations in the contaminant concentration. Such occupational exposures including those of non-monitored days can be theoretically evaluated by the following three ways: 1) assessment of geometric mean and geometric standard deviation, 2) assessment of arithmetic mean, and 3) assessment of upper limits of daily exposure distribution. In our previous report, an evaluation method on 95% upper limit or arithmetic mean of exposures was proposed. The method is useful, particularly, in case where only one or two days are being monitored, but may provide an approximate estimate because of statistical assumption. A sampling and decision scheme using one-sided tolerance limits (OTL) proposed by Tuggle (1982) can precisely evaluate the upper limits of exposures. However, many cases would be evaluated as "no decision," unless the sample size is extremely large in number. We developed a revised method based on OTL for assessment of occupational exposures. The characteristic features of this method can be summarized as follows: 1. Upper limits of lognormally distributed 8-h exposure concentrations can be evaluated in comparison with an established standard. 2. A third OTL factor was introduced into Tuggle's scheme in which two OTL factors were used. A comparison between the upper limits of exposures and the standard can be made at 50% confidence level with the factor. The factor was calculated using non-central t-distribution. 3. The usefulness of the third OTL factor in the assessment of occupational exposures was confirmed by examining the performance characteristics of the method.(ABSTRACT TRUNCATED AT 250 WORDS)

Data Interpretation, Statistical↗

Limited sampling strategy for predicting area under the concentration-time curve of mycophenolic acid in adult lung transplant recipients.

STUDY OBJECTIVE: To develop limited sampling strategies for estimation of mycophenolic acid exposure (by determining area under the concentration-time curve [AUC]) in lung transplant recipients by using sampling times within 2 hours after drug administration and a maximum of three plasma samples. DESIGN: Prospective, open-label clinical study. SETTING: Lung transplant clinic in Vancouver, British Columbia, Canada. PATIENTS: Nineteen adult (mean age 48.3 yrs) lung transplant recipients who were receiving mycophenolate mofetil therapy along with cyclosporine (9 patients) or tacrolimus (10 patients). INTERVENTION: Eleven blood samples were collected from each of the 19 patients over 12 hours: immediately before (0 hr) and 0.3, 0.6, 1, 1.5, 2, 4, 6, 8, 10, and 12 hours after administration of mycophenolate mofetil. MEASUREMENTS AND MAIN RESULTS: Mycophenolic acid levels in plasma were determined by a high-performance liquid chromatography-ultraviolet detection method. The 19 patients were randomly divided into index (10 patients) and validation (9 patients) groups. Limited sampling strategies were developed with multiple regression analysis by using data from the index group. Data from the validation group were used to test each strategy. Bias and precision of each limited sampling strategy were determined by calculating the mean prediction error and the root mean square error, respectively. The correlation between AUC and single concentrations was generally poor (r2= 0.18-0.73). Two single-concentration strategies, eight two-concentration strategies, and eight three-concentration strategies matched our criteria. However, the best overall limited sampling strategies (and their predictive performance) were the following: log AUC = 0.241 log C0 + 0.406 log C2 + 1.140 (bias -5.82%, precision 5.97%, r2= 0.828) and log AUC = 0.202 log C0 + 0.411 log C1.5 + 1.09 (bias -5.71%, precision 6.94%, r2= 0.791), where Cx is mycophenolic acid concentration at time x hours. CONCLUSION: Two-concentration limited sampling strategies provided minimally biased and highly precise estimation of mycophenolic acid AUC in lung transplant recipients. These optimal and most clinically feasible limited sampling strategies are based collectively on the number of blood samples required, r2 value, bias, and precision.

Adult↗

Genotypic and environmental variation in barley limit dextrinase activity and its relation to malt quality.

Variation in the limit dextrinase activity of barley malt, and the relationships between limit dextrinase activity and malt quality parameters were investigated using eight cultivars grown at seven diverse locations in China for two successive years. Limit dextrinase activity varied with genotype and location, with the levels ranging from 0.245 U/g to 0.980 U/g. The results showed that the variation in limit dextrinase activity was more attributable to the environment (location and year) than to the genotype. The response of limit dextrinase activity to the environment differed markedly among cultivars, and was reflected by large difference in coefficient of variation of cultivars across diverse locations. Regression analysis showed that limit dextrinase activity was negatively correlated with malt viscosity (r=-0.52, P<0.01), positively correlated with Kolbach index (r=0.38, P<0.01) and malt extract (r=0.30, P<0.05), but had no significant correlation with malt protein content and diastatic power.

Beer↗

Recruitment limitation constrains local species richness and productivity in dry grassland.

Species coexistence and local-scale species richness are limited by the availability of seeds and microsites for germination and establishment. We conducted a seed addition experiment in seminatural grassland at three sites in southern Switzerland and repeated the experiment in two successive years to evaluate various circumstances under which seed limitation and establishment success affect community functioning. A collection of 144,000 seeds of 22 meadow species including grasses and forbs of local provenance was gathered, and seeds were individually sown in a density that resembled natural seed rain. The three communities were seed limited. Three years after sowing, single species varied in emergence (0-50%), survival (0-69%), and establishment rates (0-27%). One annual and 13 perennial species reached reproductive stage. Low establishment at one site and reduced growth at another site indicated stronger microsite limitation compared to the third site. Recruitment was influenced by differences in abiotic environmental conditions between sites (water availability, soil minerals) and by within-site differences in biotic interaction (competition). At the least water-limited site, sowing resulted in an increase in phytomass due to establishment of short-lived perennials in the second and third years after sowing. This increase persisted over the following two years due to establishment of longer-lived perennials. After sowing in a wetter year with higher phytomass, however, productivity did not increase, because higher intensity of competition in an early phase of establishment resulted in less vigorous plants later on. Due to the generally favorable weather conditions during this study, sowing year had a small effect on numbers of established individuals over all species. Recruitment limitation can thus constrain local-scale species richness and productivity, either by a lack of seeds or by reduced seedling growth, likely due to competition from the established vegetation.

Climate↗

Functional limitations and disability among elders in the Framingham Study.

BACKGROUND: The measurement of physical disability as an indication of the impact of disease is commonly seen in research. However, these measures often do not clearly differentiate between functional limitations and daily performance of an activity. METHODS: We measured the differences between self-reported disability and observed functional limitations in six activities of daily living tasks among community-dwelling elders. The value of functional limitations vs disability measures in determining risk factors for disablement was ascertained. RESULTS: Systematic differences were found among the 1453 participants. At least 89% of the time when a difference was identified, the subjects ranked disability greater than the functional limitations observed. For those who were cognitively impaired, discrepancies occurred up to 11% of the time. In determining risk factors for disablement, we found that neurological impairments were associated with both functional limitations and disability, while sociocultural factors were associated with disability only. CONCLUSIONS: Our findings suggest that physical functional limitations and disability in the elderly are two distinct concepts and that the measure of choice should be determined by research objectives and the type of population being studied.

Activities of Daily Living↗

State-imposed limits on Medicaid reimbursement for nursing facility care.

OBJECTIVES: Nursing cost-center limits were examined, along with their effects on Medicaid. METHODS: A national survey of Medicaid nursing facility reimbursement provided data on cost centers for nursing, administration, and capital, whether in specific, larger, or multiple cost centers. RESULTS: Most states impose nursing and administration limits. Far fewer states impose capital limits, but only capital limits may be related to constraint of reimbursement rates. CONCLUSIONS: Shifting toward limiting capital costs, or simply eliminating cost-center limits, might accommodate cost control while removing negative constraints on direct resident care.

Cost Allocation↗

Detection of weak magnetic fields induced by electrical currents with MRI: theoretical and practical limits of sensitivity.

Detection of weak magnetic fields induced by neuronal electrical activities with magnetic resonance imaging (MRI) is a potentially effective method for functional imaging of the brain. In this study, we compared the theoretical and practical limits of sensitivity for detecting weak magnetic fields with a columnar phantom. The theoretical limit of sensitivity was estimated from signal and noise intensities in magnetic resonance images. The theoretical limit of sensitivity was approximately 10(-8)T. The practical limit was 10 times the theoretical limit. The dependence of the theoretical limit of sensitivity on acquisition parameters, such as the repetition time (TR), echo time (TE), number of pixels, and spectral width, was quantitatively evaluated. The results indicated the existence of an optimal value in T(E)/T2*.

Brain Mapping↗

Comparative studies of color fields, visual acuity fields, and movement perception limits among varsity athletes and non-varsity groups.

This paper examined effects of sports practice on patterns of color fields, limits of peripheral movement perception, and visual acuity field by comparing varsity ball players and non-varsity control groups. The first study measured extent of color fields and limits of horizontal and vertical meridians for peripheral movement perception of 139 college students. The second study tested visual acuity fields of female and male basketball players and female and male controls. The first study indicated that athletes had wider limits for horizontal movement perception, while the non-athletes had better vertical movement perception limits. Basketball players demonstrated color fields and limits for peripheral movement perception superior to those of soccer players. In the second study, athletes did not have any wider visual acuity fields than non-athletes, but their movement-perception limits were significantly wider than those of non-athletes.

Color Perception↗

The contribution of acute toxicity in animals to occupational exposure limits of chemical substances.

The correlations of lethal doses of various industrial chemicals for rats and mice with occupational exposure limit values were investigated. 50% lethal dose (LD50) values obtained by oral (p.o.) and intraperitoneal (i.p.) injection and 50% lethal concentration (LC50) values obtained by inhalation exposure were collected from Registry of Toxic Effects of Chemical Substances (RTECS). Threshold Limit Value (Time-Weighted Average) (TLVs-TWA) and Threshold Limit Value (Short Term Exposure Limit) (TLVs-STEL) recommended by American Conference of Governmental Industrial Hygienists (ACGIH) were used as exposure limits. TLVs-TWA or TLVs-STEL and LD50 or LC50 values obtained for the rats were plotted on logarithmic scales on the ordinate and abscissa, respectively. High correlations were obtained between these parameters. The order of correlations was: TLVs-STEL vs. LC50s > TLVs-TWA vs. LC50s > TLVs-TWA vs. LD50s i.p. > TLVs vs. LD50s p.o. The same calculations for the relationship between TLVs and lethal doses in mice were also performed. The order of the three types of correlations was same as that of the rats; however, correlation coefficients for TLVs-STEL vs. LC50s and for TLVs-TWA vs. LC50s obtained in mice were smaller than those in rats. TLVs-TWA are, therefore, well correlated with LC50 values rather than LD50 values, particularly with those in rats. High correlations between TLVs-STEL vs. LC50s were also obtained, as had been expected before calculation. The equation: TLV-TWA = 10b x (LC50)a can be obtained from these plottings, where the values a and b are taken from each linear regression line. TLV-TWA for each chemical can be calculated by using LC50 and the equation. The upper and lower 95% confidence limits for calculated TLV-TWA were TLV-TWA (calculated from LC50) x 22.9 and TLV-TWA (calculated)/22.9, respectively, where LC50 for rats expressed in ppm x hr was used.

Animals↗

Measures of functional limitation as predictors of disablement in athletes with acute ankle sprains.

STUDY DESIGN: Prospective multivariate design. OBJECTIVES: To determine the usefulness of activity scores, self-reported athletic ability, and selected measures of physical impairment as predictors of disability duration in athletes with ankle inversion sprains. BACKGROUND: Although several measures of physical impairment and functional limitation are used to assess the consequences of injury following ankle sprain, researchers have yet to establish which measures provide the most accurate predictions of disability duration. METHODS AND MEASURES: Physical impairment, activity limitation, and disability duration were measured in 21 athletes (13 men and 8 women; mean age = 20.3 +/- 1.7 years) with acute ankle sprains. Sagittal plane ankle range of motion and volumetric displacement were used as impairment indicators. Weight-bearing activity scores (task completion count) and self-reported athletic ability (visual analog scale) were used to represent functional limitation. Elapsed time from injury to return to full athletic participation was used as the criterion measure of disability duration. RESULTS: The impairment measures accounted for approximately one-third of the variance in disability duration (R2 = 0.342). Adding the activity limitation measures to the regression model improved predictions of disability duration (R2 = 0.670; stepwise R2 change = 0.328). The measures of activity limitation alone, however, accounted for approximately 67% (R2 = 0.665) of the total variance in the number of days lost due to injury. CONCLUSION: Measures of activity limitation were the strongest predictors of elapsed time from injury to return to full athletic participation.

Absenteeism↗

Evaluation of the order of limitation of lysine, threonine, and valine, as determined by plasma urea nitrogen, in corn-soybean meal diets of lactating sows with high body weight loss.

Three experiments were conducted to evaluate the order of limitation for Lys, Thr, and Val in corn-soybean meal diets of lactating sows experiencing high BW loss during lactation. Plasma urea N (PUN) was used as the response criterion. Experimental diets used in all 3 experiments were derived from the basal diet (BSL) formulated to 0.51% Lys using corn and soybean meal as the only sources of AA. The BSL diet was formulated by diluting a reference corn-soybean meal diet (17.2% CP, 0.90% Lys, 0.65% Thr, 0.82% Val, and 0.28% Met) with cornstarch, sucrose, and soybean oil to maintain the same ratio of corn to soybean meal. Experiment 1 was conducted to determine whether PUN is sensitive to dietary Thr and Val levels and whether a 4-d feeding period was adequate to observe a PUN response. The results demonstrated that PUN could be used as the response criterion and that a 4-d feeding period was adequate. Experiment 2 was conducted to determine whether Thr or Val was most limiting in the BSL diet. Dietary treatments used in Exp. 2 consisted of 1) BSL supplemented with 0.09% L-Lys and 0.02% DL-Met, which served as the negative control (NC2); 2) NC2 plus 0.14% L-Thr (NC2 + T); 3) NC2 plus 0.17% L-Val (NC2 + V); and 4) NC2 plus 0.14% L-Thr and 0.17% L-Val (NC2 + T + V). The value for PUN was lower for the NC2 + T and NC + T + V treatments compared with the NC2 and NC2 + V treatments (5.18 and 5.33 vs. 6.43 and 6.62; P < 0.01), indicating that Thr was most limiting in the NC2 diet. Experiment 3 was conducted to determine whether Thr or Lys was most limiting in the BSL diet. Dietary treatments used in Exp. 3 consisted of 1) the BSL diet supplemented with 0.02% DL-Met only, which served as the negative control diet (NC3); 2) the NC3 diet supplemented with 0.20% L-Lys (NC3 + L); 3) the NC3 diet supplemented with 0.14% L-Thr (NC3 + T); and 4) the NC3 diet supplemented with 0.20% L-Lys and 0.14% L-Thr (NC3 + L + T). The value for PUN was lower for NC3 + L compared with NC3 and NC3 + T (7.45 vs. 9.11 and 8.45 mg/dL; P < 0.01), and PUN for NC3 + L + T was lower than the PUN measured for NC3 + L (5.94 vs. 7.45; P < 0.01). The results of Exp. 2 and 3 indicate that Lys was first-limiting and Thr second-limiting in the BSL diet.

Animal Feed↗

Effect of initially limited resuscitation in a combined model of fluid-percussion brain injury and severe uncontrolled hemorrhagic shock.

OBJECT: Studies of isolated uncontrolled hemorrhage have indicated that initial limited resuscitation improves survival. Limited resuscitation has not been studied in combined traumatic brain injury and uncontrolled hemorrhage. In this study the authors evaluated the effects of limited resuscitation on outcome in combined fluid-percussion injury (FPI) and uncontrolled hemorrhage. METHODS: Twenty-four swine weighing 17 to 24 kg each underwent FPI (3 atm) and hemorrhage to a mean arterial pressure (MAP) of 30 mm Hg in the presence of a 4-mm aortic tear. Group I (nine animals) was initially resuscitated to a goal MAP of 60 mm Hg; Group II (nine animals) was resuscitated to a goal MAP of 80 mm Hg; and Group III (control; six animals) was not resuscitated. After 60 minutes, the aortic hemorrhage was controlled and the animals were resuscitated to baseline physiological parameters and observed for 150 minutes. Mortality rates were 11%, 50%, and 100% for Groups I, II, and III, respectively (Fisher's exact test; p = 0.002). The total hemorrhage volume was greater in Group II (69+/-32 ml/kg), as compared with Group I (41+/-18 ml/kg) and Group III (37+/-3 ml/kg) according to analysis of variance (p < 0.05). In surviving animals, cerebral perfusion pressure, cerebral blood flow (CBF), cerebral venous O2 saturation (ScvO2), and cerebral metabolic rate of O2 did not differ among groups. Although CBF was approximately 50% of baseline during the period of limited resuscitation in Group I, ScvO2 remained greater than 60%, and arteriovenous O2 differences remained within normal limits. CONCLUSIONS: In this model of FPI and uncontrolled hemorrhage, early aggressive resuscitation, which is currently recommended, resulted in increased hemorrhage and failure to optimize cerebrovascular parameters. In addition, a 60-minute period of moderate hypotension (MAP = 60 mm Hg) was well tolerated and did not compromise cerebrovascular hemodynamics, as evidenced by physiological parameters that remained within the limits of cerebral autoregulation.

Animals↗

Production performance of white Leghorn layers limited fed.

Three trials were conducted to determine if the age at start of limited feeding or the amount of time laying hens were given to consume feed could be used to reduce feed intake without affecting egg weight (EW) or egg production. The age at start of limiting feed did not affect hen-day egg production (HDEP) or EW in any trial. In Trial 2, a significant difference in HDEP due to feeding times at 26 weeks of age was observed. Laying hens fed 7 hr/day at 26 weeks of age had a significantly lower HDEP than any other feeding time. Limited feeding in Trials 1 and 2 significantly decreased feed consumption, body weight gain (WG), and EW when compared with laying hens fed ad libitum. No difference in HDEP or EW was observed due to limited feeding in Trial 3. Laying hens fed 9 or 10 hr/day gained significantly less weight than laying hens fed ad libitum (Trial 3). Limited feeding did not improve feed efficiency in any trial. No consistent improvement in mortality could be attributed to limited feeding.

Age Factors↗

The use of category and similarity information in limiting hypotheses.

Previous studies have shown that adults usually select diverse evidence for generalizing hypotheses. We investigated what kind of evidence people select in another type of inductive task: limiting hypotheses. Whereas generalizing entails extending a property to all members of a category, limiting entails restricting a property to only members of a category. For example, if you know that elephants have property X, which would you test to determine whether only mammals have property X: a hippopotamus, a fox, a crocodile, or a snake? Both category and similarity information are relevant to selecting evidence to generalize or limit a hypothesis. Although 70% of participants chose diverse evidence for generalizing a hypothesis, only 25% chose the analogous evidence for limiting one. However, the percentage of participants choosing the appropriate evidence for limiting increased to 70% when they were given a rule for category membership. These results suggest that hypothesis-limiting behavior is affected by how participants establish category boundaries.

Cognition↗

Assessment of concentration peaks in setting exposure limits for air contaminants at workplaces, with special emphasis on narcotic and irritative gases and vapors.

In various countries, concentration peaks of gaseous air contamination are assessed by a standard formula. Toxicologic data are not sufficient to warrant occupational short-term exposure limits for the majority of substances. In this article the literature on exposure to concentration peaks is reviewed, and the problem is analyzed from general toxicokinetic and physicochemical points of view. Several ways are suggested to achieve better standards. One straightforward and reasonably simple method is summarized in the following three points, which should be considered in the setting of occupational exposure limits: (i) For substances with fast or moderately fast action, only ceiling limits should be considered; (ii) when structure analogy is justified for narcotic and irritating gases, the correct way is to set the limits at the same thermodynamic activity (relative saturation) of the substances in question and not at the same concentration; (iii) for substances absorbed and eliminated slowly time-weighted exposure limits, combined with rules for excursions, or short-term exposure limits derived from such rules are appropriate, but the possible accumulation of large absolute quantities of the substances should be considered. This point is particularly important when the critical effect is narcosis or irritation, as the thermodynamic equipotency means that the effective concentration of water-soluble gases and vapors is higher than that of substances with low water solubility.

Air Pollutants, Occupational↗

Medicare and Medicaid programs; schedule of limits on home health agency costs per visit for cost reporting periods beginning on or after July 1, 1984--HCFA. Proposed rule.

This rule sets forth a proposed schedule of limits on home health agency (HHA) costs that may be reimbursed under the Medicare program and a proposed revision of the regulations governing the limits. The schedule is an update of the limits to take into account more recent data and the effects of inflation on HHA operating costs and would apply to HHA costs for entire cost reporting periods beginning on or after July 1, 1984. The schedule would also explain the basic methodology for computing the cost limits, the change in terminology involving metropolitan statistical areas and a proposed change to the method of deriving the share of labor cost contained in the limits. The proposed revision to the regulations would clarify our policy concerning exceptions from the cost limits for newly established HHAs .

Centers for Medicare and Medicaid Services, U.S.↗