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PubMed1995

A simple method to detect expiratory flow limitation during spontaneous breathing.

Patients with severe chronic obstructive pulmonary disease (COPD) often exhale along the same flow-volume curve during quiet breathing as during a forced expiratory vital capacity manoeuvre, and this has been taken as indicating flow limitation at rest. To obtain such curves, a body plethysmograph and the patient's co-operation are required. We propose a simple technique which does not entail these requirements. It consists in applying negative pressure at the mouth during a tidal expiration (NEP). Patients in whom NEP elicits an increase in flow throughout the expiration are not flow-limited. In contrast, patients in whom application of NEP does not elicit an increase in flow during most or part of the tidal expiration are considered as flow-limited. Using this technique, 26 stable COPD patients were studied sitting and supine. Eleven patients were flow-limited both seated and supine, eight were flow-limited only when supine, and seven were not flow-limited either seated or supine. Only 5 of 19 patients who were flow-limited seated and/or supine had severe ventilatory impairment (forced expiratory volume in one second (FEV1) < 40% predicted). We conclude that the NEP technique provides a simple, rapid, and reliable method for detection of expiratory flow limitation in spontaneously breathing subjects, which does not require the patient's co-operation, and can be applied in different body positions both at rest and during muscular exercise. Our results also indicate a high prevalence of flow limitation in COPD patients at rest, particularly when supine.

Aged↗
PubMed1995

Detection of flow limitation during tidal breathing by the interruptor technique.

In patients with airflow obstruction, flow limitation can be established in various ways. Using body plethysmography, flow limitation is assumed when expiratory flow decreases whilst alveolar pressure increases at the same time. During forced expiration, flow limitation can be established by means of the flow interruptor technique; flow limitation is assumed when, after release of an occlusion, a spike flow superimposed on the ongoing alveolar flow (delta peak flow) is detected. In this study, the flow interruptor technique was applied to detect flow limitation during tidal breathing. The results were compared to those obtained with the body plethysmograph. The expiratory flow pattern, post-interruption, was analysed in 33 subjects; 11 patients with airflow obstruction and flow limitation established with the body plethysmograph (AO+); 11 patients with airflow obstruction without flow limitation (AO-); and 11 healthy volunteers. Mean spike areas were 27.6 +/- 18.3, 4.6 +/- 2.3 and 3.4 +/- 2.0 mL for the AO+, AO- and control group, respectively, showing a highly significant difference between the AO+ patients and the other groups. Also, significantly higher delta peak flows were found in the AO+ patients compared to the other groups. No differences in delta peak flows or spike areas could be established between patients without flow limitation and controls. We conclude that the interruptor technique may be a useful means of assessing flow limitation during tidal breathing.

Adolescent↗
PubMed1996

Expiratory flow limitation during sleep in heavy snorers and obstructive sleep apnoea patients.

Inspiratory flow limitation (FL) during sleep has previously been reported both in obstructive sleep apnoea (OSA) patients and heavy snorers (HS). Recent results from this laboratory have shown the occurrence both of inspiratory and expiratory flow limitation during muscular relaxation in awake healthy subjects and OSA patients. In this study, we have investigated whether expiratory flow limitation occurs during sleep in heavy snorers and in patients with OSA. We studied four nonapnoeic, heavy snorers and five OSA patients. Airflow was measured with a pneumotachograph attached to a tight-fitting mask, and supraglottic pressure with a catheter placed at the supraglottic level. Scoring for flow limitation was achieved by visual inspection of 200 breaths recorded during sleep. About 20% of the respiratory cycles presented isolated inspiratory flow limitation. Approximately the same percentage was observed in heavy snorers and OSA patients. Isolated expiratory flow limitation was less frequently recorded. Coupled inspiratory and expiratory flow limitations were more numerous, especially in heavy snorers. We conclude that both in heavy snorers and obstructive sleep apnoea patients, inspiratory flow limitation is associated with expiratory flow limitation. This suggests that upper airway obstruction during sleep is both an inspiratory and expiratory event.

Adult↗
PubMed2003

Functional disability and school activity limitations in 41,300 school-age children: relationship to medical impairments.

OBJECTIVE: Our purpose was to examine the contribution of medical impairments to functional disability and school activity limitations in 41,300 school-age children participating in the 1994-1995 National Health Interview Survey. METHODS: The 1994 and 1995 National Health Interview Survey and Disability Interview Supplement samples provide International Classification of Diseases, Ninth Revision medical impairment codes for children with functional limitations or school activity limitations in a nationally representative US sample. Functional limitations were distributed as follows: mobility 12.4/1000 (95% confidence interval [CI]: 11.1-13.6), self-care 8.8/1000 (95% CI: 7.7-9.8), communication 52.9/1000 (95% CI: 50.2-55.5), and learning 104.6/1000 (95% CI: 100.7-108.4). Functional disability status was classified as 4.1% mild, 5.9% major, and 1.9% multiple. School activity limitations included 4.1% needing or receiving special education, 0.7% unable to attend, and 0.9% limited attendance. We categorized International Classification of Diseases, Ninth Revision impairment codes reported in conjunction with medical usage as physical disorders (n = 1251; eg, leukemia, diabetes), asthma (n = 916), neurodevelopmental disorders (n = 802; eg, cerebral palsy, epilepsy, mental retardation, autism, blindness, deafness), and learning-behavior disorders (n = 806; eg, attention-deficit/hyperactivity disorder, learning disability, anxiety) for children with functional or school activity limitations. Of children with multiple functional disabilities, 29.9% had neurodevelopmental disorders, 27.1% had learning-behavior disorders, 18.1% had physical disorders, 4.2% had asthma, and 20.8% did not have an identified medical impairment because they had not received medical services in the past year. Among children requiring special education, physical disorders accounted for 9.4%, neurodevelopmental disorders for 16.7%, learning and behavior disorders for 17%, asthma for 3.4%, and 53.4% did not have an identified medical impairment because they had not received medical services in the past year. CONCLUSIONS: Chronic health impairments, neurodevelopmental disorders, learning-behavior disorders, and functional limitations in essential activities are required to understand the complexity of disability in school-age children. A large number of children with functional disability or school activity limitations have not received ongoing medical services.

Activities of Daily Living↗
PubMed2006

Pediatric residency duty hours before and after limitations.

OBJECTIVES: The goals were to examine pediatric resident and program director experiences implementing the Accreditation Council for Graduate Medical Education work hour limits and to compare duty hours, moonlighting, and fatigue before and after the limits became effective. METHODS: National random samples of 500 pediatric residents who graduated in 2002 and in 2004 were surveyed to compare resident duty hours and fatigue before and after the Accreditation Council for Graduate Medical Education limits were implemented. In addition, all US pediatric residency program directors were surveyed at the end of the 2003/2004 academic year, to provide a complementary retrospective examination of limit implementation. RESULTS: Totals of 65%, 61%, and 83% of 2002 residents, 2004 residents, and program directors, respectively, responded. The proportion of residents who reported working >80 hours per week declined from 49% for NICU/PICU rotations before the limits to 18% after limit implementation. Resident well-being was the factor identified most often by both residents and program directors as being improved since the limitations. Multivariate modeling also showed reductions in the proportions of residents who reported falling asleep while driving from work or making errors in patient care because of fatigue. Overall, 89% of pediatric residents and program directors reported that the current system is effective in ensuring appropriate working hours. CONCLUSIONS: Since the Accreditation Council for Graduate Medical Education duty hour limits went into effect, pediatric residents report working fewer hours and making fewer patient care errors because of fatigue. Although room for additional improvement remains, the experiences of residents and program directors suggest that implementation of the Accreditation Council for Graduate Medical Education limits in pediatric residency programs is improving resident well-being.

Adult↗
PubMed2003

Excess physical limitations among adults with diabetes in the U.S. population, 1997-1999.

OBJECTIVE: To estimate the prevalence of physical limitations associated with diabetes among U.S. adults > or =18 years of age. RESEARCH DESIGN AND METHODS: We conducted a cross-sectional analysis of the association between diabetes status and physical limitations using the 1997-1999 National Health Interview Survey (NHIS). Physical limitation was defined from self-reported degree of difficulty with nine tasks. RESULTS: People with diabetes had a higher proportion of any physical limitation than did people without diabetes overall (66 vs. 29%, P < 0.001), for both men (59 vs. 24%, P < 0.001) and women (72 vs. 34%, P < 0.001). Compared with those without diabetes, a higher proportion of people with diabetes had some physical limitation among all age groups, and the difference declined (all P < 0.001) with increasing age (46 vs. 18% for 18-44 years, 63 vs. 35% for 45-64 years, 74 vs. 53% for 65-74 years, and 85 vs. 70% for those 75 years and older). After controlling for demographic characteristics and several other confounders, the odds ratio of physical limitation among adults with diabetes versus those without diabetes was 1.9 (95% CI: 1.8-2.1). CONCLUSIONS: People with diabetes are much more likely to have a physical limitation than those without diabetes. Interventions are needed in this population to reduce progression from impairment to physical limitation and from physical limitation to disability, especially because the prevalence of diabetes is projected to increase dramatically in the next several decades.

Activities of Daily Living↗
PubMed2003

Stockpiled forage or limit-fed corn as alternatives to hay for gestating and lactating beef cows.

In Exp. 1, 31, 24, and 17 mature, pregnant Simmental x Angus cows (initial BW = 662.0 +/- 10.4 kg) in each of 3 yr were used to determine the efficacy of stockpiled orchardgrass, limit-fed corn, or ad libitum hay for maintaining cows in mid- to late gestation, respectively. In Exp. 2, 24 mature, pregnant crossbred cows (initial BW = 677.7 +/- 9.4 kg) per treatment in each of 3 yr were used to determine the efficacy of stockpiled orchardgrass, limit-fed corn, or ad libitum hay for maintaining cows in late gestation and early lactation, respectively. Each year, cows were assigned to treatment by BW. From November to February or from January to April, respectively, nutritional needs for mid- to late gestation (Exp. 1) or late gestation and early lactation (Exp. 2) were met either by 1) rotating cows on approximately 15.2 or 21.7 ha of predominantly orchardgrass pasture, set aside and fertilized in late August, 2) limit-feeding approximately 5.8 kg of whole shelled corn, 1.1 kg of a pelleted supplement, and 1.2 kg of hay daily, or 3) ad libitum feeding of round-baled hay. During extreme weather conditions, cows grazing stockpiled orchardgrass were limit-fed a grain-based diet. Postcalving weight (P < 0.10) was greatest for limit-fed cows in Exp. 1 and lowest for cows grazed on stockpiled orchardgrass; cows given ad libitum access to hay were intermediate in weight and did not differ from cows limit-fed or cows grazed on stockpiled orchardgrass (641.8, 657.4, and 634.0 kg, respectively). Calving date, calf birth and weaning weight, and conception rate did not differ among treatments (P > 0.15) in Exp. 1. In Exp. 2, weight at weaning did not differ among treatments (P > 0.17); however, postcalving weight (P < 0.01) was greatest for cows given ad libitum access to hay, intermediate for limit-fed cows, and lowest for cows grazed on stockpiled orchardgrass (674.8, 652.4, and 624.5 kg). Body condition score at any time point did not differ among treatments (P > 0.38), nor did calving date, calf birth and weaning weights, and conception rate (P > 0.12). Because of the few differences in cow performance, selection of energy sources for beef cows can be made based on economics. The cost to feed a cow hay in early to mid-gestation was nearly double that of limit-feeding the corn-based diet or grazing stockpiled orchardgrass. Because of lower quality pastures, the cost to graze cows on stockpiled orchardgrass during late gestation and early lactation was not as cost effective as limit feeding a corn-based diet.

Animal Feed↗
PubMed2001

Limits of 80%-125% for AUC and 70%-143% for Cmax. What is the impact on bioequivalence studies?

OBJECTIVE: The US Food and Drug Administration (FDA) currently uses bioequivalence (BE) limits for fasting BE studies that are based on the 90% confidence interval for the ratio of difference of the test and reference products Cmax and AUC falling within 80% to 125%. The FDA has also proposed that BE limits be used similarly for AUC and Cmax measurements from fed BE studies. In some cases, regulatory agencies have considered a wider BE limit for Cmax, because of the typically higher variability of Cmax compared to AUC. We investigated the consequences of changing from an 80%/ 125% limit for both pharmacokinetic measures to one that uses a limit of 80%/125% for AUC and 70%/143% for Cmax. METHODS: We computed the sample sizes required for BE studies using 80%/125% for AUC and 70%/143% for Cmax as BE limits. We also determined the range of the ratios of Cmax and AUC values in a study that could meet the 70%/143% and 80%/125% BE limits. RESULTS: The sample size for the study, in order to have adequate power with 80%/125% for AUC and 70%/143% for Cmax, will be determined primarily by the intrasubject variability of AUC, though with a substantial proportion of studies (about one third) still determined by the variability of Cmax. The ratio of mean Cmax values that can pass a wider 70%/143% BE limit could easily be as high as 128%. CONCLUSION: Without further scientific or clinical rationale, we find it difficult to justify widening the bioequivalence limit for Cmax to 70%/143% for either fasting or fed BE studies.

Area Under Curve↗
PubMed1989

[A study of the risk factors in calcium oxalate stone formation--simple method for measuring metastable limits by the microplate method].

The stone forming urinary environment may be conducive to spontaneous nucleation of calcium oxalate, since it is generally characterized by a reduced metastable limit. This study indicates that the microplate method offers simple and reliable measures for estimating calcium oxalate's propensity for spontaneous nucleation. In measuring the metastable limit by the microplate method, 200 microliters aliquots of each urine sample were treated with sodium oxalate to give final concentrations of 0-1.5 mmol. The urine samples were then incubated at 37 degrees C for 20 min and the minimum amount of oxalate necessary to induce nucleation detectable by inverted microscopy was taken to be the measured metastable limit of each urine. The metastable limit by microplate method positively was correlated (p less than 0.001) with the metastable limit found by the Coulter counter method and inversely correlated (p less than 0.001) with the concentration product ratio. The metastable limits were significantly lower (p less than 0.001) in recurrent stone formers than in the control subjects. The metastable limit rose significantly (p less than 0.01) during treatment with thiazides. Moreover, the metastable limit was inversely correlated (p less than 0.01) with the stone episode rate. It is concluded that the metastable limits by the microplate method are useful in stone forming potential identification in urine as well as in the assessment of the response to the therapy.

Adult↗
PubMedDate not supplied

Economic analysis of the use of limited coronal computed tomography scans in the management of sinusitis.

BACKGROUND: As medical costs increase, less expensive alternatives to standard diagnostic tests are sought to reduce the economic burden placed on society. One alternative is using limited, non-consecutive cut computed tomography (CT) scans for the evaluation of sinonasal disease. This study evaluates the cost-effectiveness of using limited CT scans instead of full sequence CT scans in the diagnosis and management of rhinosinusitis. METHODS: A Medline search was performed to obtain data for the sensitivity and specificity of limited CT scans, the prevalence of abnormal CT scans, and recommendations on using limited CT scans for operative management. A standard cost-effectiveness analysis, including a sensitivity analysis, was performed using a hypothetical population of patients with sinus complaints who failed prior appropriate medical therapy. RESULTS: At baseline, the limited CT scan was found to be less cost-effective than the full CT scan, costing $217.13 more per correct diagnosis. The sensitivity analysis demonstrated that changes in the prevalence of abnormal CT scans and the percentage of surgeons who would operate using a limited scan had the greatest impact on cost, whereas changes in the price of the full CT or limited CT scan had the least effect. CONCLUSIONS: This study finds the use of limited CT scans to be economically unsound as a method to reduce costs in the defined population. Published literature recommends obtaining a full CT scan before operative management. Basing intervention on limited CT scans increases the possibility of erroneous diagnoses leading to either excessive or inadequate treatment of patients.

Cost-Benefit Analysis↗
PubMed1990

[A concept of limiting genetic factors of expression, organization, and evolution].

Elicitation and analysis of limiting genetic factors represent convenient method for approximate description of complex molecular-genetic systems. In sequential metabolic ways, the limiting is based on the minimum of catalytic activity, in parallel ones--on the maximum activity. In polygenic systems, the expressing polygenes affect always the limiting oligogenes. Limiting genes are only available to selection on the population level, the non-limiting genes being neutrally evolving. This result eliminates the acuteness of the Haldane's dilemma. The complex genetic systems could be quickly evolving by relay-race principle with sequentional change of limiting genes and without violation of Haldane's dilemma. The limiting factors of organization which restrict the possibilities of some special evolutionary directions have the key role in evolution. These limits were historically overcome by acceptance of evolutionary acquirements of wide usage. The sequence of such limits and acquirements was assumed as a basis of "scenario" of Prebiological and Biological Molecular Evolution. The concept is illustrated by some examples and results of theoretical analysis.

Animals↗
PubMed1987

Multiband compression limiting for hearing-impaired listeners.

Four multiband compression limiters and two linear amplification systems were compared in terms of the intelligibility of consonant-vowel-consonant (CVC) nonsense syllables for two hearing-impaired listeners over a 30 dB range of input levels. Each system incorporated one of two frequency-gain characteristics and one of three limiting characteristics (no limiting, moderate limiting, or severe limiting). The subjects were instructed to choose overall listening levels that would permit speech spanning the range of input levels to be as intelligible as possible and comfortable for long-term listening. Relative to linear amplification, the overall gain selected by the subjects increased by roughly 5 and 11 dB for the moderate and severe limiter, respectively. With linear amplification, the maximum score, 82 percent correct, was obtained at the highest input level and scores fell roughly 34 percentage points as input level was reduced. With compression limiting, although the maximum scores, 81 percent and 79 percent correct, were obtained at lower input levels, performance was comparable to that with linear amplification. Also, scores spanned a range of only 22 and 9 percentage points across the range of input levels with the moderate and severe limiter, respectively. This benefit was due to the improved scores provided by compression limiting at the low input levels. However, this advantage was offset somewhat by the disadvantage provided by compression at high input levels relative to linear amplification. Error analysis indicated that the spectral degradations introduced by independent compression of 16 frequency bands may have caused the reduced intelligibility at higher input levels.

Adult↗
PubMed1985

[Limited operation for lung cancer].

The availability of a limited operation for the treatment of primary lung cancer was discussed on 67 cases who underwent either wedge resection or segmentectomy. The reasons for the application of limited operation were mainly cardiopulmonary failures such as hypertension, abnormal finding on the ECG and obstructive ventilatory failure including the elderly over 70 years of age. Favorable prognosis of a limited operation was obtained in T1N0 and T2N0 cancer when compared to those who underwent lobectomy. Improved prognosis following a limited operation was more attributable to N-factor rather than T. Furthermore, early postoperative course and performance status after a limited operation were more favorable rather than lobectomy. In particular, on the first day of a limited operation, hemodynamic changes in an increased afterload of the right ventricle and reduced left ventricular work tend to minimize in patients with a limited operation. An experimental study also elucidated the advantage of this operative procedure in terms of cardiac function after one or bilobectomy on coronary diseased dogs whose descending coronary artery was made to be a 50% stenosis. In conclusion, it was emphasized that a limited operation should be indicated for patients with T1N0 and T2N0 cancers of primary lung cancer and limited cardiopulmonary function.

Aged↗
PubMed2006

Mobility limitations and cognitive deficits as predictors of institutionalization among community-dwelling older people.

PURPOSE: Mobility limitations and cognitive disorders have often been observed as risks for institutionalization. However, their combined effects on risk of institutionalization among initially community-dwelling older people have been less well reported. DESIGN: A prospective cohort study with 10-year surveillance on institutionalization. SUBJECTS: Study population (n = 476) consisted of 75- and 80-year-old people who were community-dwelling, had not been diagnosed with dementia, and participated in tests on walking speed and cognitive capacity at a research centre. MEASURES: Cognitive capacity was measured with three validated psychometric tests that were from the Wechsler Adult Intelligence Scale, Wechsler Memory Scale and Schaie-Thurstone Adult Mental Abilities Test. Mobility was measured with walking speed over a 10-m distance. Exclusive distribution based study groups were formed with cut-offs at the lowest third as follows: no limitation, solely mobility limitation, solely cognitive deficits, and combined mobility limitation and cognitive deficits. Cox proportional hazards model was used to determine the relative risks of institutionalization for the study groups. RESULTS: Eleven percent of the participants were institutionalized during the 10-year surveillance. The risk for institutionalization was 4.9 times greater (95% confidence interval: 2.1-11.2) for those who had co-existing mobility limitations and cognitive deficits than for those with no limitations. CONCLUSIONS: The findings show that the accumulation of limitations in physical and cognitive performance substantially decreases the possibility for a person remaining at home. This might be due to a decreased reserve capacity and ineffective compensatory strategies. Therefore, interventions targeted to improve even one limitation, or prevent accumulation of these risk factors, could significantly reduce the risk of institutionalization.

Aged↗
PubMed2000

Functional limitations and key indicators of well-being in children with disability.

OBJECTIVES: To compare measures of well-being in children with and without different types and severity of limitations. DESIGN: Nationally representative data for American children aged 5 to 17 years were drawn from the 1994 and 1995 National Health Interview Surveys on Disability (NHIS-D) (N = 41,300) and the Year 2000 Health Supplement to the 1994 NHIS-D (N = 9530). Family resources, safety, health status, and health access were measures of environment. The presence and severity of limitations were measured in the domains of mobility, self-care, communication, and learning. RESULTS: Children with functional limitations were more likely to live in families with limited resources and have greater exposure to secondhand smoke, less access to health care, and lower health status. Children with a limitation were not less likely to have a regular source of medical care, but they more often were delayed or prevented from getting necessary health care due to cost or insurance. CONCLUSIONS: Standard measures of child well-being were appropriate for children with functional limitations and showed their unfavorable situations. Children with functional limitations more often have unfavorable family resources, less healthy home environments, poorer health status, and less health service access than other children, making them more susceptible to developmental difficulties beyond those difficulties associated with the challenges of their specific functional limitations.

Activities of Daily Living↗
PubMed1993

Risk comparisons between limit values for ionizing radiation, PAH, and benzene in Sweden.

The background of regulatory limit values for carcinogenic agents in Sweden is discussed and exemplified with the ambient and occupational air pollutants benzene and PAH (especially benzo[a]pyrene, BaP), ionizing radiation, and radon. The estimated cancer risks at different limit values are compared, as is the estimated number of cancer cases annually due to existing pollutant levels. Although the individual lifetime cancer risks are much higher at the occupational limit values for benzene and BaP than what is recommended for the general public, the estimated number of cancer cases annually is lower at existing pollutant levels. The individual cancer risk at the occupational dose limit for ionizing radiation is comparable to the occupational cancer risk with BaP, but higher than the one for benzene. At the dose limit for the general public, the radiation risk would be higher than what is recommended for individual air pollutants. However, doses from man-made radiation are usually much lower than the dose limit due to optimization. Thus, the estimated number of cancer cases annually due to radiation is low and comparable to the estimated number due to the chemical air pollutants discussed. In contrast, the lung cancer risk with radon in dwellings both at limit values and existing levels is high and comparable to occupational limits for the chemical carcinogens and for radiation. The estimated number of cancer cases annually at existing radon concentrations (1100 cases) is much higher than for the other discussed pollutants (0.03-7 cases each) and also higher than the estimated number of lung cancer cases due to total air pollution (approximately 100 cases).

Benzene↗
PubMed1995

An understanding of flow- and diffusion-limited vs. carrier-mediated hepatic transport: a simulation study.

Concentration-dependent changes in the hepatic extraction ratio E and tissue accumulation of drugs were examined in a simulation study, wherein plasma protein binding, flow, and mode of entry were altered. A tubular flow model that described carrier-mediated (influx: Kml = 20 microM, Vmax1 = 1000 nmol min-1; efflux, Km2 = 200 microM, Vmax2 = 250 nmol min-1), flow-limited (influx clearance CLin = efflux clearance CLef = 50 ml min-1), or diffusion-limited (CLin = CLef = 0.1 ml min-1) hepatocytic entry was employed; drug removal was solely via biliary excretion (Km3 = 100 microM, Vmax3 = 1500 nmol min-1). Other parameter space and the combination of carrier-mediated transport and passive diffusion were also explored. Increased plasma protein binding reduced the hepatic extraction of the substrate, and in some instances, constituted the rate-controlling factor, especially at lower input concentrations for which tighter binding existed. Increased flow rate also brought about a reduction in E, affecting E almost inversely when values of E were low (e.g., for the diffusion-limited case or at higher input concentration). Tissue accumulation patterns and the apparent tissue distribution equilibrium ratio, i.e., tissue to plasma unbound concentration ratio Kp, differed among the systems. The behavior of Kp may be used as an identifier for the mode of drug transport: A declining (concave-down) Kp curve or a parabolic Kp that approached unity with input concentration (Cln) is associated with carrier-mediated entry; a rising Kp curve that approaches unity with Cln suggests flow limitation; and a waning concave-up Kp curve of very low magnitude represents diffusion limitation. Since the unbound tissue concentration (Ct) differs from the logarithmic average of the unbound input and output concentrations in plasma (Cu) for carrier-mediated and diffusion-limited systems, excretion parameters may be obtained only upon fitting of the overall excretion rate vs. Ct in the Michaelis-Menten equation; whereas when data are fitted with Cu, the rate-limiting step, influx, or deviations of influx, efflux, and excretion, will be obtained. When Ct equals Cu, as in flow-limited systems, accurate excretion parameters will be provided with the fitting of data against either Ct or Cu.

Carrier Proteins↗
PubMed2000

Mobility limitations in the Swedish population from 1968 to 1992: age, gender and social class differences.

Mobility limitations are closely related to disability in old age. The study of mobility limitations in the population may improve the understanding of the development of disability, as well as gender and class patterns in disability in old age. Representative samples of the Swedish population between the ages of 18 and 75 years were interviewed in 1968, 1974, 1981, and 1991. A further sample of people aged 76+ years was interviewed in 1992. The questionnaire included the ability to walk 100 meters, to walk up and down stairs, and to run 100 meters. Mobility limitations begin to appear around age 40 years, and increase with age. In 1992 nearly none in the oldest age group (85+) could run 100 meters, and less than half could walk 100 meters, or go up and down stairs without difficulty. Between 1968 and 1991, the proportion of people with mobility limitations was reduced by one third, with the most prominent reduction among the oldest age groups. Women were more likely to report mobility limitations compared to men at all waves; however, the gender difference decreased between 1968 and 1991. Blue-collar workers had more mobility limitations than white-collar workers, and this discrepancy did not decrease over time. Mobility limitations often begin early in life, and differences between cohorts, men and women, and social classes can be seen well before the age of 50. The results suggest that gender differences in functional limitations among elderly people may decrease in the future, while social class inequalities are likely to persist.

Adolescent↗