Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Limitations”

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

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

At least 397 records · Page 22Linked to original sources
PubMed2001

Positive end expiratory pressure and expiratory flow limitation: a model study.

Patients suffering from chronic obstructive pulmonary diseases, frequently exhibit expiratory airflow limitation. We propose a mathematical model describing the mechanical behavior of the ventilated respiratory system. This model has to simulate applied positive end-expiratory pressure (PEEP) effects during expiration, a process used by clinicians to improve airflow. The proposed model consists of a nonlinear two-compartment system. One of the compartments represents the collapsible airways and mimics its dynamic compression, the other represents the lung and chest wall compartment. For all clinical conditions tested (n=16), the mathematical model simulates the removal of expiratory airflow limitation at PEEP lower than 70-80% of intrinsic end-expiratory pressure (PEEPi), i.e. the end-expiratory alveolar pressure (PAet) without PEEP. It also shows the presence of an optimal PEEP. The optimal PEEP contributes to decrease PAet from 7.4+/-0.9 (SD) to 5.4+/-0.9 hPa (p < 0.0001; mild flow limitation) and from 11.8+/-1.1 to 7.8+/-0.7 hPa (p < 0.0001; severe flow limitation). Resistance of the collapsible compartment is decreased from 53+/-7 to 8.2+/-5.9 hPa.L(-1).s (p < 0.0001; mild flow limitation) and from 80+/-11 to 6.9+/-5.4 hPa.L(-1).s (p < 0.0001; severe flow limitation). This simplistic mathematical model gives a plausible explanation of the expiratory airflow limitation removal with PEEP and a rationale to the practice of PEEP application to airflow limited patients.

Airway Resistance↗
PubMed2002

The activation state of Rubisco directly limits photosynthesis at low CO(2) and low O(2) partial pressures.

Using gas exchange, enzyme assays, and theoretical modeling of photosynthetic responses to light and CO(2), we investigated whether decarbamylation of the active site of Rubisco at low CO(2) and low light leads to a condition where the activation state of Rubisco directly limits the rate of net CO(2) assimilation. Photosynthetic limitation by a reduction in the activation state of Rubisco would be indicated as a decline in the initial slope of the photosynthetic CO(2) response relative to what is predicted using theoretical models. In bean (Phaseolus vulgaris) and oat (Avena sativa), we saw no discrepancy between predicted and observed initial slope values at 200 and 400 mbar O(2), indicating no limitation by the carbamylation state of Rubisco. At 30 mbar O(2) and light saturation, we also saw no discrepancy between predicted and observed initial slope values; however, at subsaturating light intensity, our observed initial slope values were less than the modeled initial slope values that corresponded to an RuBP regeneration limitation. Moreover, significant reduction of the Rubisco activation state occurred in both species at 30 mbar O(2) and 30 mubar CO(2). When the model was reprogrammed to account for observed levels of Rubisco deactivation, the predicted and measured initial slope values at low O(2) and low PPFD were similar, indicating the reduction in carbamylation state accounted for the discrepancy. We interpret this as evidence for a direct limitation of the carbamylation state of Rubisco, probably because of a CO(2) limitation for carbamate formation. This limitation was only observed at intercellular CO(2) levels below what is encountered in vivo. At physiologically relevant CO(2) levels in situ, the leaves maintained sufficient Rubisco activity to avoid cabamylation state limitations in the steady state.

Journal Article↗
PubMed2002

Principles of the light-limited chemostat: theory and ecological applications.

Light is the energy source that drives nearly all ecosystems on planet Earth. Yet, light limitation is still poorly understood. In this paper, we present an overview of the principles of the light-limited chemostat. The theory for light-limited chemostats differs considerably from the standard theory for substrate-limited chemostats. In particular, photons cannot be mixed by vigorous stirring, so that phototrophic organisms experience the light-limited chemostat as a heterogeneous environment. Similar to substrate-limited chemostats, however, light-limited chemostats do reach a steady state. This allows the study of phototrophic microorganisms under well-controlled light conditions, at a constant specific growth rate, for a prolonged time. The theory of the light-limited chemostat is illustrated with several examples from laboratory experiments, and a variety of ecological applications are discussed.

Bacteria↗
PubMed1995

Accuracy of breath-by-breath analysis of flow-volume loop in identifying sleep-induced flow-limited breathing cycles in sleep apnoea-hypopnoea syndrome.

1. Inspiratory flow limitation is involved in the pathophysiology of sleep-related breathing disorders. Since the definition of flow-limited cycle is based on a dissociation between flow and respiratory efforts, identification of inspiratory flow limitation requires upper airway or intrathoracic pressure measurements. We examined the accuracy of the analysis of the flow-volume loop of a tidal breath in identifying inspiratory flow limitation during sleep in ten patients with a sleep apnoea-hypopnoea syndrome. 2. Measurements were taken during continuous positive airway pressure trials. After data acquisition, the presence of inspiratory flow limitation was identified by the presence of an inspiratory plateau or decrease in inspiratory flow independently of the increase in inspiratory efforts. The flow-volume loop was reconstructed for each breathing cycle by plotting the instantaneous flow and the tidal volume. The instantaneous inspiratory and expiratory flows were measured at 50% of the respective portion of the tidal volume, and a breath-by-breath analysis of the mid-tidal volume-flow ratio (inspiratory/expiratory ratio) was obtained. The analysis of the flow-volume loop was compared with standard inspiratory flow limitation criteria using different values of the inspiratory/expiratory ratio threshold, below which breathing cycles were classified as flow-limited. With a lower limit of the normal inspiratory/expiratory ratio threshold of 0.97, the sensitivity and specificity of the method were both 76%. In each subject, the proportion of breathing cycles identified as flow-progressively decreased with an increasing positive pressure level.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1999

Effect of nutrient limitation on adhesion characteristics of Pseudomonas aeruginosa.

Pseudomonas aeruginosa causes a variety of diseases in humans including lung and ocular infections. Infections of the cornea are usually associated with wearing contact lenses and can result in loss of vision. This study aimed to determine the effect of carbon or nitrogen limitation on the adhesion to contact lenses of a strain of Ps. aeruginosa isolated from contact lens-related corneal inflammation. Cells were grown in a continuous culture apparatus in varying levels of glucose or ammonia to effect nutrient limitation. Adhesion to contact lenses was measured as total counts and viable counts. The cell surface hydrophobicity and charge were measured using adhesion to surface-modified Sepharose. Changes in lipopolysaccharide were determined using 1D SDS-PAGE and changes in cell-surface proteins were measured using 2D gel electrophoresis. The more the cultures were nitrogen limited, the greater the increase in adhesion to unworn hydrogel contact lenses 0.3 x 10(3) - 2.2 x 10(3) cells/mm2 on Etafilon A lenses. Cells that were carbon limited showed a greater increase in adhesion to contact lenses when the lenses had been coated in artificial tears. It appeared that lipopolysaccharide may have been involved in the constitutive adhesion to unworn lenses that occurred during C-limitation, whereas changes in the outer membrane proteins contributed to the increased adhesion under nitrogen limitation, or the change in adhesion that occurred to carbon-limited cells using contact lenses coated in artificial tears. Nine cell-surface proteins appeared during nitrogen limitation with kDa/pI of 75/4.8, 4.9, 5.0; 62/5.6; 89/6.5; 38/6.4; 28/1.5; 18/6.4; 12/4.5. Any or all of these may have been involved in the increased adhesion and further experiments are underway to examine this possibility.

Bacterial Adhesion↗
PubMed1999

Cost-effectiveness of a limited-donor blood program for neonatal red cell transfusions.

BACKGROUND: Very-low-birthweight infants have typically been given fresh red cells (RBCs), a practice in which aliquots of RBCs for several infants were issued each day from a single unit. Recently, to limit donor exposures, large volumes of RBCs are reserved for the long-term transfusion support of individual infants. STUDY DESIGN AND METHODS: Medical records were examined retrospectively to assess the costs of a limited-donor program for providing RBC transfusions to very-low-birthweight infants. Costs of multiple- and limited-donor programs were compared by using two samples of 30 consecutive infants treated at The University of Iowa Hospitals and Clinics in 1993 and 1997. Effectiveness was evaluated with respect to the number of donor exposures per infant. RESULTS: The cost, in 1997 dollars, of preparing each small-volume transfusion in the multiple-donor program was $27.86 per transfusion, while that in the limited-donor program was $34.83. This difference was largely attributable to use of white cell reduction in association with the limited-donor program in 1997. Eliminating the costs associated with white cell reduction rendered the costs of the limited- and multiple-donor transfusions comparable. The limited-donor program had donor exposures of 2.0 per infant, while the multiple-donor program had 3.6 exposures per infant (p<0.002). CONCLUSION: The limited-donor blood program reduces donor exposure without adversely affecting costs.

Blood Donors↗
PubMed1998

Evaluation of a ventilation strategy to prevent barotrauma in patients at high risk for acute respiratory distress syndrome. Pressure- and Volume-Limited Ventilation Strategy Group.

BACKGROUND: A strategy of mechanical ventilation that limits airway pressure and tidal volume while permitting hypercapnia has been recommended for patients with the acute respiratory distress syndrome. The goal is to reduce lung injury due to overdistention. However, the efficacy of this approach has not been established. METHODS: Within 24 hours of intubation, patients at high risk for the acute respiratory distress syndrome were randomly assigned to either pressure- and volume-limited ventilation (limited-ventilation group), with the peak inspiratory pressure maintained at 30 cm of water or less and the tidal volume at 8 ml per kilogram of body weight or less, or to conventional ventilation (control group), with the peak inspiratory pressure allowed to rise as high as 50 cm of water and the tidal volume at 10 to 15 ml per kilogram. All other ventilatory variables were similar in the two groups. RESULTS: A total of 120 patients with similar clinical features underwent randomization (60 in each group). The patients in the limited-ventilation and control groups were exposed to different mean (+/-SD) tidal volumes (7.2+/-0.8 vs. 10.8+/-1.0 ml per kilogram, respectively; P<0.001) and peak inspiratory pressures (23.6+/-5.8 vs. 34.0+/-11.0 cm of water, P<0.001). Mortality was 50 percent in the limited-ventilation group and 47 percent in the control group (relative risk, 1.07; 95 percent confidence interval, 0.72 to 1.57; P=0.72). In the limited-ventilation group, permissive hypercapnia (arterial carbon dioxide tension, >50 mm Hg) was more common (52 percent vs. 28 percent, P=0.009), more marked (54.4+/-18.8 vs. 45.7+/-9.8 mm Hg, P=0.002), and more prolonged (146+/-265 vs. 25+/-22 hours, P=0.017) than in the control group. The incidence of barotrauma, the highest multiple-organ-dysfunction score, and the number of episodes of organ failure were similar in the two groups; however, the numbers of patients who required paralytic agents (23 vs. 13, P=0.05) and dialysis for renal failure (13 vs. 5, P= 0.04) were greater in the limited-ventilation group than in the control group. CONCLUSIONS: In patients at high risk for the acute respiratory distress syndrome, a strategy of mechanical ventilation that limits peak inspiratory pressure and tidal volume does not appear to reduce mortality and may increase morbidity.

Barotrauma↗
PubMed2003

Intentional limited pulmonary resection for peripheral T1 N0 M0 small-sized lung cancer.

OBJECTIVE: The present study was undertaken to demonstrate that limited pulmonary resection for peripheral small-sized lung cancer yields outcomes not inferior to those of lobectomy. METHODS: During the 9-year period from 1992 to 2000, patients with cT1 N0 M0 peripheral non-small cell lung cancer whose maximum tumor diameter was 2 cm or less on diagnostic imaging and in whom lobectomy was determined to be feasible were treated with limited resection if the patient consented to the procedure and with lobectomy if consent to limited resection was not obtained. The survival and clinical outcome of the patients whose tumors were postoperatively staged as pT1 N0 M0 were compared between the limited resection group (n = 74) and the lobectomy group (n = 159). RESULTS: The limited resection group consisted of 60 patients treated with segmentectomy and 14 patients treated with wedge resection. Among patients followed up for a mean period of 52 months after the operation, neither the 3-year nor 5-year survivals differed significantly between the limited resection group (3-year survival, 94.0%; 5-year survival, 89.1%) and the lobectomy group (3-year survival, 97.0%; 5-year survival, 90.1%). Postoperative tumor recurrence was noted in 5 patients after limited resection and in 9 patients after lobectomy, and the difference in the incidence of postoperative recurrence between the 2 groups was not significant. CONCLUSIONS: The results of this study indicate that in patients with peripheral T1 N0 M0 non-small cell lung cancer whose maximum tumor diameter was 2 cm or less, the outcome of limited pulmonary resection is comparable with that of pulmonary lobectomy.

Aged↗
PubMed2004

The SphS-SphR two component system is the exclusive sensor for the induction of gene expression in response to phosphate limitation in synechocystis.

Living organisms respond to phosphate limitation by expressing various genes whose products maintain an appropriate range of phosphate concentrations within each cell. We identified previously a two component system, which consists of histidine kinase SphS and its cognate response regulator SphR, which regulates the expression of the phoA gene for alkaline phosphatase under phosphate-limiting conditions in the cyanobacterium Synechocystis sp. PCC 6803. In the present study, we used DNA microarrays to investigate the role of SphS and SphR in the regulation of the genome-wide expression of genes in response to phosphate limitation. In wild-type cells, phosphate limitation strongly induced the expression of 12 genes with induction factors greater than 7. These genes were included in three clusters of genes, namely, the pst1 and pst2 clusters that encode phosphate transporters; the phoA gene and the nucH gene for the extracellular nuclease. Phosphate limitation strongly repressed the expression of only the urtA gene with induction factors below 0.2. Inactivation of either of SphS or SphR completely eliminated the phosphate limitation-inducible expression of the 12 genes and the phosphate limitation-repressible expression of the urtA gene. These results suggest that the SphS-SphR two component system in Synechocystis sp. PCC 6803 is the dominant sensory system that controls gene expression in response to phosphate limitation.

Alkaline Phosphatase↗
PubMed2003

An investigation of stability limits while holding a load.

The objective of this study was to investigate the effects of load height and foot placement on the functional base of support (FBOS) limits and the postures that participants used when they reached their FBOS limits. Twelve young male participants were tested while holding a 12-kg load at reach (above their heads), at shoulder and knuckle height, and unladen under both wide and narrow foot placements. The FBOS limits and the centre of pressure (COP) excursion length were calculated based on data from a force platform. Postural angles when participants reached their FBOS limits were calculated from records of a 2-D motion analysis system. The results showed that the load height had greater effect on the posterior FBOS limit. As the load height decreased, the COP excursion length decreased. Participants were prone to using a hip strategy to maintain postural balance when reaching their FBOS limits. Quantitative data of FBOS limits and postural control while participants hold a load at various heights when reaching their FBOS limits is of value for designing a safe materials handling workplace.

Adolescent↗
PubMed1995

A cross-validation of the NIOSH limits for manual lifting.

The psychophysical, biomechanical, and physiological criteria used in establishing the NIOSH limits for manual lifting were cross-validated against the data published by different researchers in the subject literature. Assessment of the 1991 NIOSH lifting equation indicated that: (1) NIOSH-based limits are significantly different from the psychophysical limits in the (i) low and high frequencies of lift, and (ii) small and large horizontal distances; (2) NIOSH limits are highly correlated with the data of Snook and Ciriello (1991) in the low frequency range, with the Recommended Weight Limit (RWL) protecting about 85% of the female population and 95% of the male population; (3) the 3.4kN limit for compression on the lumbosacral joint cannot protect the majority of the worker population on the basis of damage load concept; and (4) energy expenditure limits used in development of the RWL index can be sustained by 57 to 99% of worker population when compared to the physiological limits based on previous fatigue studies. Results of the cross-validation for psychophysical criterion confirmed the validity of assumptions made in the 1991 NIOSH revised lifting equation. However, the results of cross-validation for the biomechanical and physiological criteria were not in total agreement with the 1991 NIOSH model.

Adult↗
PubMed2002

Shock-duration reduction on the basis of interresponse times: the effect of the interresponse time limit.

Rats were trained on a free-operant procedure in which the duration of randomly occurring shocks depended on the interresponse times of lever presses. Shocks of 1.6-mA intensity were delivered at random intervals with an average density of 10 shocks per min. Each shock that was delivered lasted 0.3 s as long as the interresponse times were within a preset limit. Whenever the interresponse time exceeded the limit, the shocks that were delivered lasted 1 s until the occurrence of a response that met the limit. The limit was reduced in 3-s steps from 15 s to either 6 s or 3 s, at which point 3 of the animals were exposed to an ascending series. The avoidance of long-duration shocks was highly efficient at the 15-s and 12-s limits, and it decreased at the 9-s limit. With the exception of one animal, performance was substantially worse at the 6-s limit and it deteriorated for all the animals that were exposed to the 3-s limit. The data suggest that shock-duration reduction is quite effective as negative reinforcement for avoidance but is perhaps less effective than shock-intensity reduction.

Animals↗
PubMed1997

On confidence limits associated with Chow and Shao's joint confidence region approach for assessment of bioequivalence.

Confidence limits associated with Chow and Shao's 90% joint confidence region method (C&S CR limits) were derived to assess the bioequivalence (BE) of drug products. The C&S CR method provides three conditions that must be simultaneously satisfied to conclude BE, which is applicable only for raw scale data. The C&S CR limits method extends its applicability to both raw scale and log-transformed data. In addition, it is easy to interpret. The quantitative limits provide information, such as how much the test product deviates from the reference product in bioavailability. The data sets of peak plasma concentration (C(max)) and area under plasma concentration curve (AUC) of 13 BE studies involving 10 drugs were used to compare the performances of classic confidence interval (classic CI), C&S CR, and C&S CR limits methods. The results indicate that the same BE conclusion can be reached for C&S CR and C&S CR limits methods. The C&S CR and its limits method offered a distinctive advantage in terms of percentage passing the BE criteria by taking account of the correlation and variability of sample means. Similar BE conclusion was observed for C&S CR limits method by using raw and log-transformed data in this study.

Biological Availability↗
PubMed1998

Impact of chronic diseases on functional limitations in elderly Chinese aged 70 years and over: a cross-sectional and longitudinal survey.

OBJECTIVE: To examine the association of some common medical conditions with functional limitation in elderly Chinese aged 70 years and over, to estimate the percentage of disability attributable to individual diseases, and to attempt to identify predisposing factors by documenting the development of functional limitation over an 18-month period in those subjects with a particular disease who were independent initially. SUBJECTS AND METHODS: The cross-sectional data set consisted of 2,032 (999 M, 1,033 F) subjects aged 70 years and over recruited by random sampling (stratified by age and sex) of all recipients of old-age and disability allowance, which covers over 90% of the elderly population. Information regarding medical condition and functional assessment of ten basic activities of daily living using the Barthel Index were obtained by personal interviews and physical assessment of the respondents at their places of residence. The longitudinal data set consisted of 1,334 subjects with no functional limitation at baseline who were alive after 18 months. Functional status was reassessed. RESULTS: After adjusting for age and sex, diseases associated with severe functional limitation (Barthel Index < 15) were dementia, stroke, Parkinson's disease, and fractures. Those associated with mild to moderate functional limitation (Barthel Index 15-19) were the same, with the addition of asthma and diabetes mellitus. The attributable fraction for severe limitation was highest for stroke, dementia, and fractures. Stroke and arthritis were identified as diseases predisposing to mild to moderate functional limitation over an 18-month period among those subjects who were independent initially. CONCLUSION: Stroke, dementia, and fractures were the main chronic diseases associated with severe functional limitation in elderly Hong Kong Chinese. Attempts to reduce the disability burden in this population should target these diseases.

Age Distribution↗
PubMed1996

An intrinsic positive end-expiratory pressure lung model, with and without flow limitation.

OBJECTIVE: To design an intrinsic positive end-expiratory pressure (PEEP) lung model that has the property of air flow limitation. DESIGN: Mechanical lung model study of intrinsic PEEP. SETTING: Lung models were set up in the research laboratory. INTERVENTIONS: Intrinsic PEEP lung models were created with and without flow limitation. In the model with flow limitation, intrinsic PEEP was created by replacing a portion of the expiratory circuit with a collapsible Penrose tube and by placing this portion the circuit under water. The expiratory circuit became a part of the respiratory airway, with flow limitation occurring at the Penrose drain. In the model without flow limitation, intrinsic PEEP was generated with a fixed linear resistor, which was inserted in the expiratory circuit to produce a similar level of intrinsic PEEP. Multiple levels of external PEEP, both above and below the initial intrinsic PEEP, were applied. MEASUREMENTS AND MAIN RESULTS: At each level of external PEEP, peak airway pressure, plateau airway pressure, isovolume air flow, internal lung pressure, and intrinsic PEEP were measured. Peak airway pressure, plateau pressure, and internal lung pressure were minimally affected if the external PEEP was less than the intrinsic PEEP in the lung model with flow limitation. Intrinsic PEEP was reduced with external PEEP. However, if intrinsic PEEP was induced without dynamic airway closure or flow limitation, any level of external PEEP caused an immediate increase in peak airway pressure, plateau airway pressure, and internal lung pressure and a decrease in isovolume flow. External PEEP has little effect on the levels of intrinsic PEEP. CONCLUSIONS: We demonstrated two different models of an intrinsic PEEP lung model. The interactions between intrinsic PEEP and externally applied PEEP were different. The lung model with collapsible tube closely simulated the human respiratory system with flow limitation. This lung model may be useful for the future study of intrinsic PEEP and pulmonary mechanics.

Humans↗
PubMed2000

Dose limits for astronauts.

Radiation exposures to individuals in space can greatly exceed natural radiation exposure on Earth and possibly normal occupational radiation exposures as well. Consequently, procedures limiting exposures would be necessary. Limitations were proposed by the Radiobiological Advisory Panel of the National Academy of Sciences/National Research Council in 1970. This panel recommended short-term limits to avoid deterministic effects and a single career limit (of 4 Sv) based on a doubling of the cancer risk in men aged 35 to 55. Later, when risk estimates for cancer had increased and were recognized to be age and sex dependent, the NCRP, in Report No. 98 in 1989, recommended a range of career limits based on age and sex from 1 to 4 Sv. NCRP is again in the process of revising recommendations for astronaut exposure, partly because risk estimates have increased further and partly to recognize trends in limiting radiation exposure occupationally on the ground. The result of these considerations is likely to be similar short-term limits for deterministic effects but modified career limits.

Astronauts↗
PubMed2000

Expiratory flow limitation confounds ventilatory response during exercise in athletes.

INTRODUCTION: A significant number of highly trained endurance runners have been observed to display an inadequate hyperventilatory response to intense exercise. Two potential mechanisms include low ventilatory responsiveness to hypoxia and ventilatory limitation as a result of maximum expiratory flow rates being achieved. PURPOSE: To test the hypothesis that expiratory flow limitation can complicate determination of ventilatory responsiveness during exercise the following study was performed. METHODS/MATERIALS: Sixteen elite male runners were categorized based on expiratory flow limitation observed in flow volume loops collected during the final minute of progressive exercise to exhaustion. Eight flow limited (FL) (VO2max, 75.9+/-2.4 mL x kg(-1) x min(-1); expiratory flow limitation, 47.3+/-20.4%) and eight non-flow limited subjects (NFL) (VO2max, 75.6+/-4.8 mL x kg(-1) x min(-1); expiratory flow limitation, 0.3+/-0.8%) were tested for hypoxic ventilatory responsiveness (HVR). RESULTS: Independent groups ANOVA revealed no significant differences between FL and NFL for VO2max, VE max (136.2+/-16.0 vs 137.5+/-21.6 L x min(-1)), VE/VO2, (28.4+/-3.2 vs 27.6+/-2.9 L x lO2(-1)), VE/VCO2 (24.8+/-3.1 vs 24.4+/-2.0 L x lCO2(-1)), HVR (0.2+/-0.2 vs 0.3+/-0.1 L x %SaO2(-1)), or SaO2 at max (89.1+/-2.4 vs 86.6+/-4.1%). A significant relationship was observed between HVR and SaO2 (r = 0.92, P < or = 0.001) in NFL that was not present in FL. Conversely, a significant relationship between VE/VO2 and SaO2 (r = 0.79, P < or = 0.019) was observed in FL but not NFL. Regression analysis indicated that the HVR-SaO2 and SaO2-VE/VO2 relationships differed between groups. DISCUSSION: When flow limitation is controlled for, HVR plays a more significant role in determining SaO2 in highly trained athletes than has been previously suggested.

Adult↗
PubMed2006

Experimental evaluation of different methods of limiting the maximum output of hearing aids.

OBJECTIVE: A series of experiments designed to test the preferences of people with moderate to profound hearing losses for limiting the output of hearing aids by using peak clipping (PC), fast compression limiting (FCL), PC and FCL, and these three methods in combination with slow compression limiting (SCL) was conducted. DESIGN: Nineteen participants with moderate to profound sensorineural or mixed losses were recruited. In the first experiment, preferences for either PC or FCL were tested in a field trial in the participants' usual environments.A second experiment examined the acceptance of PC, FCL, and FCL + PC, using paired comparisons in a laboratory setting. The third experiment involved further paired comparisons in the laboratory to evaluate whether participants preferred PC, FCL, PC and FCL combined, or the three methods when combined with SCL. RESULTS: The participants showed no statistically significant preferences for either peak clipping or fast compression limiting in the field trial. In the laboratory trial, both FCL + PC and FCL were significantly preferred over PC alone, and the addition of FCL to PC was most advantageous to participants who required the lowest maximum limiting output. The most dramatic laboratory result was the convincing preference in paired comparison testing of combining SCL with PC and/or FCL. CONCLUSIONS: Slow compression limiting appears to be a desirable feature in hearing aids for clients with a moderate to profound hearing loss. Preferences were not as pronounced when peak clipping, fast compression limiting, and peak clipping plus fast compression limiting were compared, but participants favored the condition that had the least amount of peak clipping.

Adult↗