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PubMed1988

Lectin-enhanced accumulation of manganese-limited Rhizobium leguminosarum cells on pea root hair tips.

The ability of Rhizobium leguminosarum 248 to attach to developing Pisum sativum root hairs was investigated during various phases of bacterial growth in yeast extract-mannitol medium. Direct cell counting revealed that growth of the rhizobia transiently stopped three successive times during batch culture in yeast extract-mannitol medium. These interruptions of growth, as well as the simultaneous autoagglutination of the bacteria, appeared to be caused by manganese limitation. Rhizobia harvested during the transient phases of growth inhibition appeared to have a better attachment ability than did exponentially growing rhizobia. The attachment characteristics of these manganese-limited rhizobia were compared with those of carbon-limited rhizobia (G. Smit, J. W. Kijne, and B. J. J. Lugtenberg, J. Bacteriol. 168:821-827, 1986, and J. Bacteriol. 169:4294-4301, 1987). In contrast to the attachment of carbon-limited cells, accumulation of manganese-limited rhizobia (cap formation) was already in full progress after 10 min of incubation; significantly delayed by 3-O-methyl-D-glucose, a pea lectin haptenic monosaccharide; partially resistant to sodium chloride; and partially resistant to pretreatment of the bacteria with cellulase. Binding of single bacteria to the root hair tips was not inhibited by 3-O-methyl-D-glucose. Whereas attachment of single R. leguminosarum cells to the surface of pea root hair tips seemed to be similar for both carbon- and manganese-limited cells, the subsequent accumulation of manganese-limited rhizobia at the root hair tips is apparently accelerated by pea lectin molecules. Moreover, spot inoculation tests with rhizobia grown under various culture conditions indicated that differences in attachment between manganese- and carbon-limited R. leguminosarum cells are correlated with a significant difference in infectivity in that manganese-limited rhizobia, in contrast to carbon-limited rhizobia, are infective. This growth-medium-dependent behavior offers and explanation for the seemingly conflicting data on the involvement of host plant lectins in attachment of rhizobia to root hairs of leguminous plants. Sym plasmid-borne genes do not play a role in manganese-limitation-induced attachment of R. leguminosarum.

Carbon↗
PubMed1998

Regulation of porin-mediated outer membrane permeability by nutrient limitation in Escherichia coli.

OmpF and OmpC porins were differentially regulated by nutrient limitation and growth rate in glucose- or nitrogen-limited chemostat cultures of Escherichia coli. Transcriptional and translational ompF fusions showed a sharp peak of expression under glucose limitation at D = 0.3 h-1, with lower amounts at lower and higher growth rates. The peak of OmpR-dependent transcriptional stimulation of ompF under glucose limitation in minimal salts media was about 20-fold above nutrient excess levels and 3-fold higher than that achieved with low osmolarity. Analysis of outer membrane protein levels and results of growth competition experiments with porin mutants were consistent with the enhanced role of OmpF under glucose limitation, but not N limitation. In contrast, OmpC was the major porin under N limitation but was increasingly expressed under glucose limitation at very low growth rates approaching starvation, when OmpF was downregulated. In summary, outer membrane permeability under N-limited, sugar-rich conditions is largely based on OmpC, whereas porin activity is a complex, highly sensitive function of OmpF, OmpC, and LamB glycoporin expression under different levels of glucose limitation. Indeed, the OmpF level was more responsive to nutrient limitation than to medium osmolarity and suggested a significant additional layer of control over the porin-regulatory network.

Bacterial Proteins↗
PubMed1995

Interpreting self reported limiting long term illness.

OBJECTIVE: To examine the association between self reported limiting long term illness and other dimensions of self reported health. DESIGN: Stratified random sample of general population. SETTING: Lothian region, Scotland, in 1993. SUBJECTS: 6212 men and women aged 16 and over. MAIN OUTCOME MEASURES: Limiting long term illness was assessed by the same question as used in the 1991 United Kingdom census. The short form 36 health survey was used to assess other dimensions of health. RESULTS: Rates of limiting long term illness were much higher than reported in the census. Scores on general and physical health scales had strong associations with limiting long term illness, but after adjustment for these associations psychosocial health measures had little influence on limiting long term illness. Being at the lower rather than the upper quartile on the physical functioning scale more than doubled the odds of having limiting long term illness. Reported prevalence of many common illnesses was between two and three times higher among those with limiting long term illness. CONCLUSIONS: A positive response to the question used by the census to define limiting long term illness was strongly associated with physical limitations on activity and less strongly influenced by scores on scales of mental and social wellbeing. Socioeconomic effects on limiting long term illness seem largely mediated through measures of general health and physical limitations on health.

Activities of Daily Living↗
PubMed2005

Non-fatal injuries among adults with activity limitations and participation restrictions.

OBJECTIVE: To investigate non-fatal unintentional injuries among adults with activity/participation limitations. DESIGN: Injuries in the previous 12 months were reported by a stratified probability sample of non-institutionalized adults. Based on self reported activity/participation limitations, 2602 respondents were classified into three groups (no limitations, moderate limitations, and severe limitations) and injury characteristics were compared. RESULTS: A total of 19.2% of respondents reported activity/participation limitations. Twenty four percent (95% confidence intervals (CI) 14.5% to 33.6%) with severe and 17.8% (95% CI 13.2% to 22.4%) with moderate limitations were injured, compared with 12.6% (95% CI 10.6% to 14.7%) of respondents without limitations. The odds ratio of injury was 3.72 (95% CI 1.94 to 7.14) for respondents with severe and 1.87 (95% CI 1.25 to 2.77) for respondents with moderate limitations. The leading cause of injuries among respondents with activity/participation limitations was falls. CONCLUSIONS: Individuals with activity/participation limitations are at an increased risk for injuries.

Accidents↗
PubMed2006

[Comparative analysis of macular hole surgery followed by internal limiting membrane removal with and without indocyanine green staining].

PURPOSE: To describe comparatively the outcomes of macular hole surgery followed by internal limiting membrane removal with and without indocyanine green staining. METHODS: We evaluated 142 consecutive macular hole surgeries with internal limiting membrane removal performed in the period from January 2001 to March 2004. These were divided into two groups, based on the use or not of indocyanine green staining. RESULTS: Both studied groups were similar concerning the patients' profile and preoperative stage of the macular holes. Mean preoperative visual acuity was 0.12+/-0.15 in the group with indocyanine green staining and 0.18+/-0.18 in the group without internal limiting membrane staining (p=0.02). Mean postoperative visual acuity was 0.27+/-0.27 in the group with internal limiting membrane staining and 0.43+/-0.25 in the group without internal limiting membrane staining (p=0.0002). We observed improvement of visual acuity in 63% of cases in the group in which internal limiting membrane staining was performed and in 80.3% of cases in the group without internal limiting membrane staining. Macular hole closure rates were 76.5% in the group treated with internal limiting membrane staining and 95.1% in the group treated without internal limiting membrane staining. CONCLUSIONS: Macular hole surgeries followed by internal limiting membrane removal without use of staining have better visual and anatomic results when compared to macular hole surgeries followed by internal limiting membrane removal guided by indocyanine green staining. We recommend caution in using indocyanine green staining in macular hole surgeries due to its possible toxic effect.

Adult↗
PubMedDate not supplied

Feasibility and costs of phosphorus application limits on 39 U.S. swine operations.

Concerns about manure P and water quality have prompted new regulations imposing P limits on land application of manure. Previous research established that P limits increase land needs for animal feeding operations. We evaluated the effect of N, annual P, and rotation P limits on the feasibility of manure management. A mechanistic model characterized manure management practices on 39 swine operations (20 unagitated lagoon and 19 slurry operations) in five states (Iowa, Missouri, North Carolina, Oklahoma, and Pennsylvania). Extensive information collected from each operation was used to determine effects of manure storage type, ownership structure, and application limits on attributes of manure management. Phosphorus limits had substantially greater effect on slurry operations, increasing land needs 250% (0.3 hectares per animal unit [AU]) and time for manure application 24% (2.5 min AU(-1)) for rotation P limits and 41% (4.4 min AU(-1)) for annual P limits. Annual P limits were infeasible for current land application equipment on two operations and had the greatest effect on time and costs because they required all but three slurry operations to reduce discharge rate. We recommend implementing rotation P limits (not to exceed crop N need) to minimize time effects, allow most farmers to use their current manure application methods, and allow manure to fulfill crop N and P needs in the year of application. Phosphorus limits increased potential manure value but would require slurry operations to recover at least 61% of manure value through manure sales. Phosphorus limits are likely to shape the U.S. swine industry through differential effects on the various sectors of the swine industry.

Agriculture↗
PubMed2001

Comparison of seat belt force-limiting methods using the MADYMO multi-body/finite element program.

Belt force can be limited by a device in the belt retractor hardware or with force-limiting as an integral part of the webbing force/strain properties. In this research, MADYMO multi-body/finite element models of a 50th percentile Hybrid-3 male passenger in an airbag-equipped 4-door mid-size sedan were set up to compare occupant injury response under loading 1) from a baseline standard (non-force-limiting) belt system, 2) from a retractor-based force-limiting system, and 3) from a webbing-based force-limiting system. Chest acceleration was similar for the two force-limiting designs but the peak was approximately 10% greater for the standard belt. The magnitude of the head acceleration was similar for all three belts while the duration of these accelerations was much narrower for the force-limiting belts. Chest compression was similar for both force-limiting methods, and was about 60% less than the standard belt case. Compared to the baseline system and the retractor-based system, webbing-based force-limiting allowed greater pelvic excursion and a corresponding increase in femur force. It is concluded that webbing-based force limiting has some potential for reducing head and chest responses but these reductions must be evaluated with respect to other considerations such as submarining potential, non-frontal impact response, and future concepts like programmable force limiting.

Equipment Design↗
PubMed2004

Effects of disease activity, pain, and distress on activity limitations in patients with systemic lupus erythematosus.

OBJECTIVE: To evaluate the extent to which disease activity, pain, and psychological distress predict activity limitations in persons with systemic lupus erythematosus (SLE). METHODS: A sample of 93 persons with SLE completed medical and psychosocial evaluations at one study visit. Sets of measures were chosen to represent constructs of Disease Activity, Pain, Distress, and Activity Limitations. Confirmatory factor analysis was conducted to determine if the measures fit the intended constructs, and structural equation modeling was used to evaluate the direct effects of Disease Activity, Pain, and Distress on Activity Limitations, as well as indirect effects of Disease Activity as mediated by Pain and Distress, and indirect effects of Pain as mediated by Distress. RESULTS: The confirmatory factor analysis indicated a good fit of the measures to their intended constructs. The overall model predicting Activity Limitations based on Disease Activity, Pain, and Distress accounted for 68% (p < 0.001) of the variance in perceived Activity Limitations. Severity of Pain was the only construct that was directly associated with Activity Limitations (r = 0.70, p < 0.001). The effects of Disease Activity on Activity Limitations were primarily indirect via its influence on Pain. Distress was not significantly associated with Activity Limitations. When Distress was trimmed from the model, the remaining constructs accounted for 66% of the variance in Activity Limitations (p < 0.001). CONCLUSION: Disease Activity and Pain accounted for a substantial proportion of the variance in Activity Limitations. Pain Severity was the strongest predictor of Activity Limitations. This study highlights the importance of adequate pain management for maintaining quality of life in persons with SLE.

Activities of Daily Living↗
PubMed2002

Modelling of the enzymatic kinetically controlled synthesis of cephalexin: influence of diffusion limitation.

In this study the influence of diffusion limitation on enzymatic kinetically controlled cephalexin synthesis from phenylglycine amide and 7-aminodeacetoxycephalosporinic acid (7-ADCA) was investigated systematically. It was found that if diffusion limitation occurred, both the synthesis/hydrolysis ratio (S/H ratio) and the yield decreased, resulting in lower product and higher by-product concentrations. The effect of pH, enzyme loading, and temperature was investigated, their influence on the course of the reaction was evaluated, and eventually diffusion limitation was minimised. It was found that at pH >or=7 the effect of diffusion limitation was eminent; the difference in S/H ratio and yield between free and immobilised enzyme was considerable. At lower pH, the influence of diffusion limitation was minimal. At low temperature, high yields and S/H ratios were found for all enzymes tested because the hydrolysis reactions were suppressed and the synthesis reaction was hardly influenced by temperature. The enzyme loading influenced the S/H ratio and yield, as expected for diffusion-limited particles. For Assemblase 3750 (the number refers to the degree of enzyme loading), it was proven that both cephalexin synthesis and hydrolysis were diffusion limited. For Assemblase 7500, which carries double the enzyme load of Assemblase 3750, these reactions were also proven to be diffusion limited, together with the binding-step of the substrate phenylglycine amide to the enzyme. For an actual process, the effects of diffusion limitation should preferably be minimised. This can be achieved at low temperature, low pH, and high substrate concentrations. An optimum in S/H ratio and yield was found at pH 7.5 and low temperature, where a relatively low reaction pH can be combined with a relatively high solubility of 7-ADCA. When comparing the different enzymes at these conditions, the free enzyme gave slightly better results than both immobilised biocatalysts, but the effect of diffusion limitation was minimal.

Catalysis↗
PubMed2006

Monitoring population disability: evaluation of a new Global Activity Limitation Indicator (GALI).

OBJECTIVE: To evaluate a single item instrument, the Global Activity Limitation Indicator (GALI), to measure long-standing health related activity limitations, against several health indicators: a composite morbidity indicator, instruments measuring mental health (SCL-90R, GHQ-12), physical co-morbidity and physical limitations (ADLs, SF-36). METHODS: Cross-sectional data (n = 9168) of the 2001-National Health Interview Survey in Belgium was used to compare the GALI with other health indicators across gender, age, educational attainment and language. RESULTS: Responses to the GALI were similar to responses to other indicators of physical limitations (Limitations in Activities of Daily Living (by severity or by number of limitations), the SF-36 physical domain), to an indicator of chronic physical comorbidity and to indicators of mental health. The probability of reporting absence of long-standing activity limitation with the GALI was high in subjects without physical limitations or physical or mental conditions. This probability decreased as the severity or number of limitations, the number of physical or mental conditions increased. CONCLUSIONS: The GALI performs appropriately against other health indicators and appears to reflect long-standing activity limitation associated with both mental and physical conditions.

Activities of Daily Living↗
PubMed2003

Interaction of nutrient limitation and protozoan grazing determines the phenotypic structure of a bacterial community.

We examined the impact of nutrient conditions (carbon and phosphorus limitation) and grazing by protozoans on the phenotypic community structure of freshwater bacteria in continuous culture systems. Lakewater bacteria were grown on mineral medium, which was supplemented with glucose and amino acids and adjusted by different phosphorus concentrations to achieve either carbon or phosphorus limitation. Each nutrient treatment was inoculated with the same bacterial community and consisted of a nongrazing and a grazing treatment, to which the heterotrophic nanoflagellates Spumella sp. and Ochromonas sp. were added. We found that nutrient conditions alone resulted in differences in the phenotypic structure of the bacterial community: small and motile bacteria dominated under C limitation while large, elongated, and capsulated bacteria were characteristic for P limitation. The genotypic community composition as measured by T-RFLP (terminal restriction fragment length polymorphism) was not severely influenced by the two nutrient treatments. In the presence of flagellate predators, grazing-resistant bacteria developed under both nutrient conditions, but with different survival mechanisms: highly motile bacteria prevailed under C limitation, whereas the P-limited grazing treatment was dominated by filamentous forms. T-RFLP analysis revealed only moderate changes in bacterial community composition due to grazing, which were most pronounced under P limitation. Analysis by video microscopy revealed that high swimming speed is an efficient nonmorphological survival mechanism for bacteria to reduce the capture success of the flagellate predator. The rejection of optimal-sized, nonmotile bacteria under P limitation suggests the importance of other nonmorphological, surface-located cell properties. Our results illustrate that the realized mechanisms of grazing resistance are linked to the actual limitation conditions, and that the combined effects of nutrient limitation and grazing are major determinants of bacterial community structure.

Animals↗
PubMed1999

Effect of nitrogen limitation on foliar antioxidants in relationship to other metabolic characteristics.

The long-term effect of limiting soil nitrogen (N) availability on foliar antioxidants, thermal energy dissipation, photosynthetic and respiratory electron transport, and carbohydrates was investigated in Spinacia oleracea L. Starch, sucrose, and glucose accumulated in leaves of N-limited spinach at predawn, consistent with a downregulation of chloroplast processes by whole-plant sink limitation in response to a limited supply of N-based macromolecules throughout the plant. On a leaf-area or dry-weight basis, levels of chlorophyll, carotenoid pools, photosynthetic electron transport capacity, as well as activities for the predominantly chloroplast-localized antioxidant enzymes ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2) were much lower in N-limited versus N-replete plants. When expressed on a chlorophyll basis, foliar levels of all of these parameters were similar in N-replete versus N-limited plants. However, on a total-protein basis, antioxidant enzyme activities were higher in N-limited plants. Nitrogen-limited spinach showed higher levels of thermal energy dissipation and of zeaxanthin and antheraxanthin at midday, as well as slightly higher ascorbate contents relative to chlorophyll. These results indicate that strong, long-term N limitation led not only to alterations in the balance between different processes but also to an overall downregulation of light collection, photosynthetic electron transport capacity, and chloroplast-based antioxidant enzymes. This is further supported by the finding that glucose-feeding of excised leaves led to strong concomitant decreases in photosynthetic electron transport capacity and ascorbate peroxidase activity. On a leaf-area basis, neither superoxide dismutase (EC 1.15.1.1) activity nor dark repiration rates showed a treatment effect. This indicates that overall mitochondrial electron transport activity does not decrease under long-term N limitation and is consistent with localization of an important fraction of foliar superoxide dismutase in mitochondria.

Journal Article↗
PubMed1993

Comparison of symptom-limited and low level exercise tolerance tests early after myocardial infarction.

OBJECTIVES: This study was conducted to determine the diagnostic yield and risks of a symptom-limited treadmill exercise test before hospital discharge. BACKGROUND: Currently, predischarge low level and 6-week symptom-limited exercise treadmill tests are recommended for risk stratification after myocardial infarction. However, few data exist on the safety and value of a predischarge symptom-limited exercise test. METHODS: We utilized a modified Bruce protocol starting at 1.7 mph and 0 grade with 3-min stages in 150 consecutive patients 6.4 +/- 3.1 days after myocardial infarction. Each exercise test was interpreted for duration, symptoms and ST segment changes at the low level (70% of predicted heart rate) and symptom-limited end point. RESULTS: There were no complications related to the symptom-limited exercise tests. The test results were positive in only 23% of the patients at the low level end point, but were positive in 40% of the patients at the later symptom-limited end point (p < 0.001). During a mean follow-up period of 15 +/- 5 months in 138 patients (92%), 50 patients (36%) had a cardiac event. Of the patients with a cardiac event, significantly more (p < 0.001) had a positive exercise test at the symptom-limited end point (31 vs. 16 patients). Five patients with a negative and 14 patients with a nondiagnostic symptom-limited exercise test had an event. CONCLUSIONS: In patients with uncomplicated myocardial infarction, we demonstrated the safety of an early symptom-limited treadmill exercise test. Symptom-limited exercise tests will identify more patients with inducible ischemia who are at risk of future cardiac events and who may benefit from early intervention.

Electrocardiography↗
PubMed2003

The concept of multiple-nutrient-limited growth of microorganisms and its application in biotechnological processes.

The "law of the minimum" (Liebig's law) states that usually one nutrient restricts the maximum quantity of biomass that can be produced within a system, whereas all other nutrients are in excess. This general rule has been applied also to the growth of microorganisms, e.g., by adjusting the relative concentrations of the individual nutrients in growth media such that one of them, in the case of heterotrophic microbes, usually the carbon source, determines the maximum cell density that can be obtained in a culture. However, experimental data demonstrated that growth of microbial cultures can be limited simultaneously by two or more nutrients. These authors reported that during growth of bacteria and yeasts at a constant dilution rate in the chemostat, three distinct growth regimes were recognised as a function of the C:N ratio in the inflowing medium: (1) a clearly carbon-limited regime with the nitrogen source in excess, (2) a transition ("double-nutrient-limited") growth regime where both the carbon and the nitrogen source were below the detection limit, and (3) a clearly nitrogen-limited growth regime with the carbon source in excess. Subsequent calculations suggested that the extension and position of this double-nutrient-limited zone should be strongly dependent on the imposed growth rate: Whereas it is very narrow at high growth rates it should become very broad during slow growth. This pattern as a function of growth rate has now been confirmed for a number of different organisms. In industrial processes, microbial growth is always in some way controlled by the limited availability of nutrients, and limitation of specific nutrients is frequently used to force microbial cultures into a productive physiological state. This article will discuss what the consequences of multiple-nutrient-limited growth are for industrial processes and how the concept might be applied. Specific examples will be given that demonstrate the advantages and the potential of multiple nutrient-limited growth conditions for industrial production processes.

Bacteria↗
PubMed1975

Effects of sulphate-limited growth in continuous culture on the electron-transport chain and energy conservation in Escherichia coli K12.

Growth of Escherichia coli K12 in a chemostat was limited by sulphate concentrations lower than 300 muM. The synthesis of extracellular polysaccharide and a change in morphology accompanied sulphate-limited growth. Growth yields with respect to the amount of glycerol or oxygen consumed were sixfold and twofold lower respectively under these conditions than when growth was limited by glycerol. Sulphate-limited cells lacked the proton-translocating oxidoreduction segment of the electron-transport chain between NADH and the cytochromes, and particles prepared from these cells lacked the energy-dependent reduction of NAD+ by succinate, DL-alpha-glycerophosphate or D-lactate, suggesting the loss of site-I phosphorylation. Glycerol-limited cells contained cytochrome b556, b562 and o, ubiquinone and low concentrations of menaquinone. Sulphate limitation resulted in the additional synthesis of cytochromes d, a1, b558 and c550; the amount of ubiquinone was decreased and menaquinone was barely detectable. Non-haem iron and acid-labile sulphide concentrations were twofold lower in electron-transport particles prepared from sulphate-limited cells. Recovery of site-I phosphorylation could not be demonstrated after incubating sulphate-limited cells with or without glycerol, in either the absence or presence of added sulphate. The loss of site-I phosphorylation in sulphate-limited cells is discussed with reference to the accompanying alterations in cytochrome composition of such cells. Schemes are proposed for the functional organization of the respiratory chains of E. coli grown under conditions of glycerol or sulphate limitation.

Cytochromes↗
PubMed2004

Chronic diseases, locomotor activity limitation and social participation in older women: cross sectional survey of British Women's Heart and Health Study.

OBJECTIVES: To examine the association of chronic degenerative diseases with locomotor activity limitation and social participation among older British women. METHODS: Cross-sectional survey of 4,286 women aged 60-79 years from 23 towns in England, Scotland and Wales. RESULTS: The prevalence of locomotor activity limitation was 37.2% and 33.5% of women had difficulty with some aspect of social participation. This prevalence of locomotor activity limitation and difficulties with social participation increased with increasing age and with increasing number of chronic diseases. All chronic diseases assessed were independently (of each other and confounding factors) associated with locomotor activity limitation. Associations were particularly strong for stroke (OR 5.44, 95% CI 3.38-8.75), arthritis (OR 3.95, 95% CI 3.25-4.81) and coronary heart disease (OR 2.26, 95% CI 1.77-2.88). The population attributable fraction for locomotor activity limitation was greatest for arthritis: 37.8% (95% CI 32.0-43.1) and coronary heart disease: 6.7% (95% CI 4.8-8.8). Locomotor activity limitation was strongly associated with social participation. Most chronic diseases of ageing were independently (of locomotor activity limitation, other chronic diseases and confounding factors) associated with reduced social participation. CONCLUSIONS: Locomotor activity limitation and difficulties in social participation are common. Arthritis and coronary heart disease contribute importantly to locomotor activity limitation and difficulties with social participation. Effective strategies to prevent or limit the disabling impact of these conditions are essential to improving the quality of life of older women.

Aged↗
PubMed2004

Wood density and anatomy of water-limited eucalypts.

We hypothesized that seedlings grown under water-limited conditions would develop denser wood than seedlings grown under well-watered conditions. Three Eucalyptus species (E. grandis Hill (ex Maiden), E. sideroxylon Cunn. (ex Woolls) and E. occidentalis Endl.) were grown in a temperature-controlled greenhouse for 19 weeks with watering treatments (well-watered and water-limited) applied at six weeks. The water-limitation treatment consisted of four drought cycles. Wood density increased by between 4 and 13% in the water-limited seedlings, but this increase was mainly due to extractive compounds embedded in the cell wall matrix. Once these compounds were removed, the increase was 0-9% and was significant for E. grandis only. Water-limitation significantly reduced mean vessel lumen area; however, this was balanced by a trend toward greater vessel frequency in water-limited plants, and consequently there was no difference in the proportion of stem area allocated to vessels. Conduit efficiency value was lowest in the water-limited plants, indicating that there was a cost in terms of stem hydraulic conductivity for decreasing vessel lumen area. Wood density was negatively correlated with vessel lumen fraction in well-watered plants, but this relationship broke down in the water-limited plants, possibly because of the significantly larger proportion of the stem taken up by pith in water-limited seedlings. Diurnal variation in leaf water potential was positively correlated with wood density in well-watered plants. This relationship did not hold in the water-limited plants owing to the collapse of the pressure gradient between soil and leaf. We conclude that drought periods of greater than 1 month are required to increase wood density in these species and that increases in wood density appear to result in diminished capacity to supply water to leaves.

Dehydration↗
PubMed2004

Heart disease, comorbidity, and activity limitation in community-dwelling elderly.

PURPOSE: The purpose of this study was to describe the impact of self-report heart disease, other chronic comorbidities, and perceived health status on activity limitation among community dwelling persons older than 50 years of age. METHODS: Odds ratios for activity limitation in activities of daily living, mobility, and other activities were estimated for respondents with self-report heart disease, eight other chronic comorbid conditions, and perceived health status using data generated in two nationally representative cross-sectional surveys, the Health and Retirement Survey (HRS; respondents aged 51 to 60 years) and the Assets and Health Dynamics of the Oldest Old study (AHEAD; respondents aged 70 years and older). RESULTS: The prevalence of activity limitation increased significantly across the spectrum from activities of daily living to mobility to other activities in both surveys in respondents with and without heart disease. There was a significantly increased likelihood of mobility and other activity limitation among those with heart disease. Among the HRS respondents with heart disease, five or more of the eight comorbid conditions plus poor or fair perceived health were associated with a significantly increased limitation in each activity category. Among the AHEAD respondents with heart disease, three comorbid conditions plus perceived health were associated with a significantly increased limitation in activities of daily living whereas six comorbid conditions plus perceived health were associated with a significantly increased limitation in mobility and in other activities. CONCLUSIONS: As a prime objective of cardiac rehabilitation is to reduce activity limitation, the strong associations between comorbidity and activity limitation observed in this study among persons older than 50 years with heart disease suggest that the burden of comorbidity-associated is considerable but should not be an automatic exclusion criterion for referral to cardiac rehabilitation. The lack of rigorous scientific information on how these associations may influence clinicians who refer patients to rehabilitation and those who manage these programs strongly reinforces the need for more research to explore the real-world spectrum of comorbidity among persons with heart disease and the impact on activity limitation.

Activities of Daily Living↗