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PubMedDate not supplied

A comparative analysis of the upper thermal tolerance limits of eastern Pacific porcelain crabs, genus Petrolisthes: influences of latitude, vertical zonation, acclimation, and phylogeny.

Marine intertidal organisms are subjected to a variety of abiotic stresses, including aerial exposure and wide ranges of temperature. Intertidal species generally have higher thermal tolerance limits than do subtidal species, and tropical species have higher thermal tolerance limits than do temperate species. The adaptive significance of upper thermal tolerance limits of intertidal organisms, however, has not been examined within a comparative context. Here, we present a comparative analysis of the adaptive significance of upper thermal tolerance limits in 20 congeneric species of porcelain crabs, genus Petrolisthes, from intertidal and subtidal habitats throughout the eastern Pacific. Upper thermal tolerance limits are positively correlated with surface water temperatures and with maximal microhabitat temperatures. Analysis of phylogenetically independent contrasts (from a phylogenetic tree on the basis of the 16s rDNA gene sequence) suggests that upper thermal tolerance limits have evolved in response to maximal microhabitat temperatures. Upper thermal tolerance limits increased during thermal acclimation at elevated temperatures, the amount of increase being greater for subtidal than for intertidal species. This result suggests that the upper thermal tolerance limits of some intertidal species may be near current habitat temperature maxima, and global warming thus may affect the distribution limits of intertidal species to a greater extent than for subtidal species.

Acclimatization↗

PubMed1988

The relationship of intralaboratory bias and imprecision on laboratories' ability to meet medical usefulness limits.

The previously described computer modeling technic empirically develops quantitative relationships between intralaboratory performance, as characterized by individual laboratories' coefficients of variation (CVs) and biases, and clinical "medical usefulness limits." These limits determine the magnitude of total analytic error, the combined effects of CV and bias that can be tolerated by the clinician. The computer model delineates all combinations of CV and bias compatible with specified medical usefulness limits. Both CV and bias are critical in determining a laboratory's ability to meet medical usefulness limits. For example, a laboratory with a 6% CV and zero bias will meet the +/- 10% or less total analytic error (medical usefulness limit) 90% of the time. If the medical usefulness limit is expanded to +/- 15%, a laboratory with a 6% CV can tolerate coexisting relative biases of up to 4% and still meet this limit 95% of the time. Plots of the limiting values for combinations of intralaboratory CV and bias are given that allow the laboratory's results to fall within medical usefulness limits of 2, 5, 10, 15, and 20%.

Clinical Laboratory Techniques↗

PubMed1995

Cognitive functioning and the incidence of limitations in activities of daily living in an elderly community sample.

Although it is well-known that cognitive impairment in the elderly is usually accompanied by limitations in activities of daily living (ADL), it is not known whether cognitive impairment predicts the onset of new ADL limitations. The purpose of this analysis was to determine whether poor scores on a brief measure of cognitive functioning at baseline (1982) would predict the onset of persistent limitations in ADL during the subsequent 3 years, in a probability sample of community-dwelling elderly persons living in New Haven, Connecticut, who were initially free of ADL limitations (n = 1,856). Cognitive functioning was assessed with Pfeiffer's Short Portable Mental Status Questionnaire. Persistent incident ADL limitations were defined as the onset of one or more ADL limitations after 1982, with no subsequent reports of zero ADL limitations. Compared with persons who scored zero to one errors on the Short Portable Mental Status Questionnaire at baseline, persistent, incident ADL limitations occurred more frequently in persons who scored four or more errors (odds ratio for males = 2.72, 95% confidence interval 1.36-5.43; odds ratio for females = 2.60, 95% confidence interval 1.52-4.44) after adjustment for the confounding effects of housing type, age, race, history of chronic health conditions, and incident health conditions. These results suggest that knowledge of scores on brief cognitive function tests can be used to forecast service needs and to develop intervention programs to prepare for the possible onset of ADL limitations.

Activities of Daily Living↗

PubMed1988

On the relationship between radiation standards for the general public and limitation of lifetime risk.

This paper discusses the relationship between standards for limiting radiation exposures of individuals in the general public and limitation of lifetime risk. Most current radiation standards for the public in the United States specify limits on dose for each year of exposure. Particularly for internal exposures, we show that such standards may correspond poorly with a limit on lifetime risk when the age dependence of radionuclide intakes and dose is taken into account. We then show that standards which specify limits on annual dose averaged over a lifetime, with a subsidiary limit on dose in any year, correspond more closely with a limit on lifetime risk. Finally, we discuss standards for public exposures that are expressed directly as limits on lifetime risk. The development of risk standards would require consideration of age-dependent radiogenic risks and competing risks from all other causes as well as age-dependent dosimetry. We present sample calculations of lifetime risks from acute and chronic intakes that would support such a standard. We suggest that implementation of a standard for lifetime risk would require modification or abandonment of several radiation protection practices embodied in standards which specify limits on dose.

Adolescent↗

PubMed2005

Effective dose as a limiting quantity for the evaluation of primary barriers for diagnostic x-ray facilities.

The National Council on Radiation Protection in Report 147 of NCRP has recommended that shielding design limit for diagnostic x-ray facilities must be consistent with the guidance specified in Report 116 of NCRP. In the latter report, it is specified that the limit of exposure must be in terms of effective dose received annually. New mathematical models that are different from those in Report 49 of NCRP are reported in the recently published Report 147 of NCRP, and the design limit is specified as kerma value. In this work, to provide a means of compliance with the recommendation in Report 116 of NCRP, the effective dose that is classified as the limiting quantity in Report 57 of ICRU has been incorporated into shielding algorithms for diagnostic x-ray facilities. Also, shielding models are presented using exposure, kerma-in-air, kerma-in-tissue and ambient dose equivalent as limiting quantities. A computer program, XSHIELD, was written in FORTRAN language to execute these models. With design limits set at 1 mSv y and 0.25 mSv y (as specified in Report 116 of NCRP) and using sample distribution of workload, age of patient, field sizes at image receptor, and types of projection, computations of shielding requirements were carried out for rooms designated adult and pediatric chest rooms. For same values of respective workload and design limit, the use of exposure, kerma-in-air, kerma-in-tissue, and ambient dose equivalent as limiting quantity produces thicker barriers than the use of effective dose. By the use of effective dose as limiting quantity, the shielding requirement for the same workload is independent of size of the individual to be shielded. However, irradiating the individual who is to be shielded in posterior-anterior projection requires a thicker barrier than when irradiation is in lateral projection.

Adolescent↗

PubMed2004

Limitation of life support: frequency and practice in a Hong Kong intensive care unit.

OBJECTIVE: To examine the frequency and the decision-making processes involved in limiting (withdrawing and withholding) life support therapy in critically ill Chinese patients in the intensive care unit. DESIGN: Prospective survey of patients who had life support limited between April 1997 and March 1999. SETTING: Medical and surgical intensive care unit of a teaching hospital. PATIENTS: All patients admitted to the intensive care unit of the Prince of Wales Hospital who subsequently died and/or had life support limited. Brain-dead patients were excluded from analysis. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Of 490 patients who died in the intensive care unit, limitation of life support occurred in 288 (58.8%). Relatives or patients requested limitation of life support in 32 cases (11%). The family and/or patient concurred with limitation of life support in 273 occasions (95%). Therapy was withheld in 30.8% and withdrawn in 28.0% of deaths. Therapy limited included inotropes, additional oxygen, and renal replacement therapy. CONCLUSIONS: Limitation of therapy in dying Chinese patients occurs frequently in intensive care patients, and both patients and relatives concur with medical decisions to limit therapy in these patients. Withholding therapy rather than withdrawing therapy occurs more frequently than in Western populations.

Female↗

PubMed2005

Life-history variation of a neotropical thrush challenges food limitation theory.

Since David Lack first proposed that birds rear as many young as they can nourish, food limitation has been accepted as the primary explanation for variation in clutch size and other life-history traits in birds. The importance of food limitation in life-history variation, however, was recently questioned on theoretical grounds. Here, we show that clutch size differences between two populations of a neotropical thrush were contrary to expectations under Lack's food limitation hypothesis. Larger clutch sizes were found in a population with higher nestling starvation rate (i.e. greater food limitation). We experimentally equalized clutches between populations to verify this difference in food limitation. Our experiment confirmed greater food limitation in the population with larger mean clutch size. In addition, incubation bout length and nestling growth rate were also contrary to predictions of food limitation theory. Our results demonstrate the inability of food limitation to explain differences in several life-history traits: clutch size, incubation behaviour, parental feeding rate and nestling growth rate. These life-history traits were better explained by inter-population differences in nest predation rates. Food limitation may be less important to life history evolution in birds than suggested by traditional theory.

Adaptation, Physiological↗

PubMed1995

Derivation and application of upper limits for prostate specific antigen in men aged 50-74 years with no clinical evidence of prostatic carcinoma.

OBJECTIVE: To derive age-specific upper limits for prostate specific antigen (PSA) level in men 50-74 years of age with no clinical evidence of prostatic carcinoma, and to test the sensitivity and specificity for cancer detection of these upper limits. SUBJECTS AND METHODS: A total of 6166 men were recruited for a multicentre study of prostate cancer detection and underwent a serum PSA determination and digital rectal examination (DRE). Men considered to be clinically free of prostatic carcinoma were those with a normal DRE and a PSA level < or = 4.0 ng/mL, and men with an abnormality in either parameter who underwent ultrasonography-guided prostate biopsy that revealed no evidence of carcinoma. By these criteria, 5469 men had no evidence of prostatic carcinoma. Dividing the population into 5-year age increments, three statistical methods were assessed to derive upper limits for serum PSA level by age; the mean +2 SD, the 99th percentile, and a 97.5% prediction interval based on linear regression. RESULTS: Newly-derived upper limits calculated by each method in the 50-54 and the 70-74 age group were 3.9 ng/mL and 7.6 ng/mL (mean +2 SD), 5.2 ng/mL and 14.0 ng/mL (99th percentile), and 4.7 ng/mL and 8.2 ng/mL (97.5% prediction interval). The sensitivity of the newly-derived upper limits was tested using receiver operating characteristic curves derived from men with no suspicious findings on DRE and a serum PSA concentration > 4.0 ng/mL. Although the specificity of the test increased with increasing PSA upper limits, no upper limits derived from these three methods yielded adequate sensitivity to detect cancer; sensitivities by age range were from 53 to 94%, using mean +2 SD, from 25 to 50% with the 99th percentile, and from 47 to 64% with the 97.5% prediction interval. CONCLUSION: We do not recommend age-referenced adjustments in upper limits for serum PSA concentration, but recommend that an upper limit of 4.0 ng/mL be used in all men 50-74 years of age.

Aged↗

PubMed2006

Limited literacy and mortality in the elderly: the health, aging, and body composition study.

BACKGROUND: While limited literacy is common and its prevalence increases with age, no prospective study has assessed whether limited literacy is associated with mortality in older adults. OBJECTIVE: To assess the association of limited literacy with mortality. DESIGN AND SETTING: Five-year prospective study from 1999 to 2004 of community-dwelling elders from Memphis, TN, and Pittsburgh, PA, who were from the Health, Aging, and Body Composition study. Subjects' literacy was assessed with the Rapid Estimate of Adult Literacy in Medicine. Scores were categorized into limited (0 to 8th grade reading level) or adequate literacy (> or = 9th grade reading level). PARTICIPANTS: Two thousand five hundred and twelve black and white elders without baseline functional difficulties or dementia. MEASUREMENTS: Time to death. RESULTS: Participants' mean age was 75.6 years, 48% were male, 38% were black, and 24% had limited literacy; the median follow-up time was 4.2 years. Compared with those with adequate literacy, those with limited literacy had a higher risk of death (19.7% vs 10.6%) with a hazard ratio (HR) of 2.03 (95% confidence intervals [CI], 1.62 to 2.55). After adjusting for demographics and socioeconomic status, co-morbid conditions, self-rated health status, health-related behaviors, health care access measures, and psychosocial status, limited literacy remained independently associated with mortality (HR 1.75; 95% CI, 1.27 to 2.41). CONCLUSIONS: Limited literacy is independently associated with a nearly 2-fold increase in mortality in the elderly. Given the growth of the aging population and the prevalence of chronic diseases, the mechanisms by which limited literacy is associated with mortality in the elderly warrant further investigation.

Aged↗

PubMed1994

Medical decision-making in the last six months of life: choices about limitation of care.

OBJECTIVE: To characterize the limitation of care in routine geriatric practice in advance of and at the time of a patient's final episode of illness. DESIGN: A descriptive study performed by retrospective chart review. SETTING: An outpatient geriatric practice affiliated with a community teaching hospital. PATIENTS: Fifty-nine recipients of primary care who were community-dwelling and older than 65, died in the years 1988-1991, and were enrolled in the practice for at least 6 months prior to death. MEASUREMENTS: We recorded the type(s) of care patients (or, in the case of incompetence, their families) and their physicians chose to limit during the last episode of illness preceding death and during previous episodes of illness by examining those instances when therapy other than that considered "standard" was given. We also examined whether the presence of dementia, functional impairment, chronic disease, terminal illness, site of routine care (home vs hospital), and location of death were associated with the limitation of care. RESULTS: A choice to limit diagnostic tests or treatment was made by the patient or surrogate in 40% of the 59 patients during the 6 months before the patient's final episode of illness. Most frequently limited were diagnostic tests, surgery, and hospitalization for purposes other than surgery. Terminal illness and location of death were associated with the limitation of care, but dementia, functional impairment, chronic illness, and location of care were not. By comparison, 89% of the patients had limitation of care during the final episode of illness, and more aggressive therapies such as cardiopulmonary resuscitation and intubation constituted the majority of therapies withheld. CONCLUSIONS: In one geriatric practice, care is frequently limited before a patient's final illness in the course of routine practice. In contrast to recent discussion focusing on limitation of end-of-life interventions or interventions in the severely impaired, these results suggest that there are multiple points in the course of a community-dwelling elderly patient's illness at which choices about level of care can be made. Given this opportunity, a significant number of elderly patients of their surrogates will choose less intensive therapy.

Activities of Daily Living↗

PubMed2004

Inflammatory markers and incident mobility limitation in the elderly.

OBJECTIVES: To examine the relationship between indicators of inflammation and the incidence of mobility limitation in older persons. DESIGN: Prospective cohort study: the Health, Aging and Body Composition Study. SETTING: Pittsburgh, Pennsylvania, and Memphis, Tennessee. PARTICIPANTS: A total of 2,979 men and women, aged 70 to 79, without mobility limitation at baseline. MEASUREMENTS: Serum levels of interleukin (IL)-6, tumor necrosis factor alpha (TNFalpha), and C-reactive protein (CRP) and soluble cytokine receptors (IL-2sR, IL-6sR, TNFsR1, TNFsR2) were measured. Mobility limitation was assessed and defined as reporting difficulty or inability to walk one-quarter of a mile or to climb 10 steps during two consecutive semiannual assessments over 30 months. RESULTS: Of the 2,979 participants, 30.1% developed incident mobility limitation. After adjustment for confounders (demographics, prevalent conditions at baseline, body composition), the relative risk (RR) of incident mobility limitation per standard deviation (SD) increase was 1.19 (95% confidence interval (CI)=1.10-1.28) for IL-6, 1.20 (95% CI=1.12-1.29) for TNFalpha, and 1.40 (95% CI=1.18-1.68) for CRP. The association between inflammation and incident mobility limitation was especially strong for the onset of more severe mobility limitation and when the levels of multiple inflammatory markers were high. When persons with baseline or incident cardiovascular disease events or persons who were hospitalized during study follow-up were excluded, findings remained similar. In a subset (n=499), high levels of the soluble receptors IL2sR and TNFsR1 (per SD increase: RR=1.23 (95% CI=1.04-1.46) and RR=1.28 (95% CI=1.04-1.57), respectively) were also associated with incident mobility limitation. CONCLUSION: Findings suggest that inflammation is prognostic for incident mobility limitation over 30 months, independent of cardiovascular disease events and incident severe illness.

Aged↗

PubMed1998

Relationship between the upper limit of vulnerability determined in normal sinus rhythm and the defibrillation threshold in patients with implantable cardioverter defibrillators.

The upper limit of vulnerability is the strength above which ventricular fibrillation is no longer inducible with a shock delivered during the vulnerable phase of the cardiac cycle. It has been demonstrated that the upper limit of vulnerability correlates with the defibrillation threshold in a paced rhythm. The purpose of this study is to evaluate the correlation of the upper limit of vulnerability determined in normal sinus rhythm with the defibrillation threshold using a simplified protocol in patients undergoing placement of an ICD. We studied 28 patients who underwent ICD implantation. CPI generators and Endotak leads were used in all patients. Device-based testing was used to determined the defibrillation threshold and the upper limit of vulnerability. The upper limit of vulnerability was tested with three shocks delivered at 0, 20, and 40 ms before the peak of the T wave during normal sinus rhythm. The defibrillation threshold was determined by a simple step up-down protocol. The upper limit of vulnerability (9.0 +/- 4.5 J) did not significantly differ from the defibrillation threshold (9.9 +/- 4.0 J), P = NS. A close correlation was present, correlation coefficient = 0.75, P < 0.0001. The upper limit of vulnerability was within 5 J of the defibrillation threshold in 27 (96%) of the 28 patients. The upper limit of vulnerability underestimated the defibrillation threshold by 10 J in one patient who had a defibrillation threshold of 15 J. The upper limit of vulnerability determined in normal sinus rhythm correlates significantly with the defibrillation threshold in patients undergoing ICD implantation. The protocol is simple and easily implemented clinically.

Anti-Arrhythmia Agents↗

PubMed1990

Physiological and Morphological Changes Induced by Nutrient Limitation of Pseudomonas fluorescens 378 in Continuous Culture.

Pseudomonas fluorescens 378 was studied in continuous culture at a dilution rate of 0.05 or 0.15 h and under a limitation of carbon/energy, nitrogen, phosphorus, iron(III), or oxygen. Cultures were examined for nutritional consumption, production of biosurfactant AP-6 and lipase, and electron microscopy morphology. Morphological features were lysis and plasmolysis of the cells, vacuoles in the cells, granules in cell nuclei, and DNA coagulation during transmission electron microscopy preparation. Biosurfactant and lipase production were lost after 8 to 15 retention times, but under iron limitation and at low dilution rate they were maintained for more than 30 retention times. Consumption of nutrients varied between different cultures. Between 2.4 and 6.0 g of succinic acid per g (dry weight) was consumed; the highest value was obtained under phosphorus limitation. The uptake of nitrogen was mostly about 0.16 g/g (dry weight), and that of phosphorus varied between 13 and 58 mg/g (dry weight). Phosphorus-limited cells reduced their phosphorus consumption by at least 50% compared with other limitations. Cell morphology varied among different cultures. Up to 25% cell lysis occurred at the higher dilution rate. The frequencies of plasmolysis varied between 0 and 85%. Granules in nuclei were found in 65 to 100% of the cells. Vacuoles appeared mostly in low numbers, but at the lower dilution rate under phosphorus or iron limitation the frequencies increased to between 25 and 85%. At high dilution rate, the DNA coagulated in 30 to 70% of the cells. Multivariate data analysis demonstrated a general difference between the two tested dilution rates; i.e., both nutritional and morphological features differed more between the two tested dilution rates than between the different limitations. Cultures at the lower dilution rate changed more with time; this was especially pronounced for phosphorus or iron limitation. The data analysis also showed a correlation between plasmolysis or vacuoles in the cells and an increased carbon uptake under phosphorus limitation.

Journal Article↗

PubMed1984

Enhancement of chemotaxis in Spirochaeta aurantia grown under conditions of nutrient limitation.

Spirochaeta aurantia M1 cells were grown in a chemostat under conditions of energy and carbon source limitation. The chemotactic responses of the chemostat-grown cells were compared with those of S. aurantia cells grown in batch culture in the presence of excess energy and carbon source. Chemotactic responses were measured by determining the number of cells that entered a capillary tube containing a solution of attractant. S. aurantia cells grown in the chemostat under energy and carbon source limitation exhibited enhanced chemotactic responses and detected lower concentrations of attractant, as compared with cells grown in batch culture. The chemotactic response toward an attractant was specifically enhanced when that attractant was the growth-limiting energy and carbon source. The medium used contained either D-glucose or D-xylose as the sole energy and carbon source. Cells had the greatest chemotactic response toward glucose when grown at a dilution rate (D) of 0.045 h-1 under glucose limitation and toward xylose when grown at D = 0.06 h-1 under xylose limitation. When cells were grown under glucose limitation (D = 0.045 h-1), they sensed concentrations of attractant (glucose) ca. 1,000 times lower than those sensed by batch-grown cells. A similar enhancement of sensing ability (toward xylose) was observed in cells grown under xylose limitation. The results indicated that S. aurantia cells are able to regulate their chemosensory system in response to nutrient limitation. Maximum enhancement of chemotaxis occurs in cells growing at very low concentrations of energy and carbon source. Most likely, this property provides the spirochetes with competitive advantages when the availability of nutrients becomes severely limited in their habitats.

Chemotaxis↗

PubMed1999

Prognostic value of symptom limited versus low level exercise stress test before discharge in patients with myocardial infarction treated with thrombolytics.

OBJECTIVE: To evaluate the benefits and risks of symptom limited exercise testing versus low level exercise testing soon after a thrombolytic treated acute myocardial infarction. DESIGN AND PATIENTS: 98 patients (71 men, 27 women), mean (SD) age 64 (9) years (range 45-75 years), were investigated 5-8 days after admittance to hospital. An ergometer cycle test was used, starting at 30 W with 10 W increments per minute. Each exercise test was interpreted at the symptom limited end point and a low level end point, which was defined as the point at which the patient rated exhaustion as 13 on the 6-20 point Borg scale for rating perceived exertion. SETTING: A university hospital. RESULTS: 75 of the 98 patients were able to perform a predischarge exercise test. Of the remaining 23 patients who could not perform an early exercise test (because of unstable angina, heart failure, or thrombus detected at echocardiography), five died or had a myocardial infarction and six underwent bypass surgery or percutaneous transluminal coronary angioplasty (PTCA) during a follow up period of one year. There were no complications related to the symptom limited exercise tests. The test results were positive in 15 patients at the low level end point and in 39 patients (p < 0.001) at the symptom limited end point. During a follow up period of one year, six of the 75 patients died or had a myocardial infarction. Two of these six patients had a positive low level exercise test and four had a positive symptom limited exercise test. Twenty three of the 75 patients who performed an exercise test had a cardiac event within one year (death, myocardial infarction, bypass surgery or PTCA); of these, 19 had a positive symptom limited exercise test and nine had a positive low level exercise test (p = 0.025). Four of the 36 patients with a negative symptom limited test suffered cardiac events within a year (two patients had a myocardial infarction and two had bypass surgery). CONCLUSION: Symptom limited exercise testing soon after thrombolytically treated myocardial infarction will identify more patients with exercise induced ST depression or chest pain than a low level test, and seems safe. A negative symptom limited test has a better negative predictive value (11% risk of an event within a year) than a negative low level (25% risk of an event within a year).

Adult↗

PubMed1997

Detection of expiratory flow limitation during exercise in COPD patients.

The negative expiratory pressure (NEP) method was used to detect expiratory flow limitation at rest and at different exercise levels in 4 normal subjects and 14 patients with chronic obstructive pulmonary disease (COPD). This method does not require performance of forced expirations, nor does it require use of body plethysmography. It consists in applying negative pressure (-5 cmH2O) at the mouth during early expiration and comparing the flow-volume curve of the ensuing expiration with that of the preceding control breath. Subjects in whom application of NEP does not elicit an increase in flow during part or all of the tidal expiration are considered flow limited. The four normal subjects were not flow limited up to 90% of maximal exercise power output (Wmax). Five COPD patients were flow limited at rest, 9 were flow limited at one-third Wmax, and 12 were flow limited at two-thirds Wmax. Whereas in all patients who were flow limited at rest the maximal O2 uptake was below the normal limits, this was not the case in most of the other patients. In conclusion, NEP provides a rapid and reliable method to detect expiratory flow limitation at rest and during exercise.

Adult↗

PubMed2004

Detection of expiratory flow limitation in COPD using the forced oscillation technique.

Expiratory flow limitation (EFL) during tidal breathing is a major determinant of dynamic hyperinflation and exercise limitation in chronic obstructive pulmonary disease (COPD). Current methods of detecting this are either invasive or unsuited to following changes breath-by-breath. It was hypothesised that tidal flow limitation would substantially reduce the total respiratory system reactance (Xrs) during expiration, and that this reduction could be used to reliably detect if EFL was present. To test this, 5-Hz forced oscillations were applied at the mouth in seven healthy subjects and 15 COPD patients (mean +/- sD forced expiratory volume in one second was 36.8 +/- 11.5% predicted) during quiet breathing. COPD breaths were analysed (n=206) and classified as flow-limited if flow decreased as alveolar pressure increased, indeterminate if flow decreased at constant alveolar pressure, or nonflow-limited. Of these, 85 breaths were flow-limited, 80 were not and 41 were indeterminate. Among other indices, mean inspiratory minus mean expiratory Xrs (deltaXrs) and minimum expiratory Xrs (Xexp,min) identified flow-limited breaths with 100% specificity and sensitivity using a threshold between 2.53-3.12 cmH2O x s x L(-1) (deltaXrs) and -7.38- -6.76 cmH2O x s x L(-1) (Xexp,min) representing 6.0% and 3.9% of the total range of values respectively. No flow-limited breaths were seen in the normal subjects by either method. Within-breath respiratory system reactance provides an accurate, reliable and noninvasive technique to detect expiratory flow limitation in patients with chronic obstructive pulmonary disease.

Aged↗

PubMed2006

Does expiratory flow limitation predict chronic dyspnoea in adults with cystic fibrosis?

Tidal expiratory flow limitation (EFL) may promote dynamic hyperinflation and contribute to chronic dyspnoea. The purpose of this study was to assess the contribution of EFL to chronic dyspnoea in adults with cystic fibrosis (CF). The presence of EFL was determined in 102 adults with stable CF (forced expiratory volume in one second (FEV1) 17.3-91.5% predicted) and 20 age-matched control subjects using the negative expiratory pressure technique. Measurements of inspiratory capacity (IC) and spirometry were performed, and chronic dyspnoea was evaluated using the modified Medical Research Council scale. EFL was present in 34 subjects (33%), with 18 subjects flow limited in the sitting position and 16 subjects flow limited only in the supine position. Flow limitation in the sitting position was associated with older age and lower FEV1 compared with flow-limited supine position and non-flow-limited subjects. A significant reduction in IC accompanied EFL in both the sitting and supine positions. Flow limitation in the sitting position was associated with significantly higher levels of chronic dyspnoea. Ordinal regression analysis indicated that EFL was the best predictor of chronic dyspnoea in a model that included FEV1 % pred. Expiratory flow limitation in cystic fibrosis is associated with reduced forced expiratory volume in one second, older age and dynamic hyperinflation. Expiratory flow limitation significantly contributes to chronic dyspnoea in cystic fibrosis.

Adult↗