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PubMed2006

Does restructuring hospitals result in greater efficiency?--An empirical test using diachronic data.

Hospitals are being restructured more frequently. Increased cost efficiency is the usual justification given for such changes. All 20 major teaching hospitals in Australia's two most populous states were investigated by classifying each over a 5-6 year period in terms of their cost efficiency (average cost per case weighted by Australian diagnosis-related group [AN-DRG] data and adjusted for inflation) and structure, categorized as traditional-professional (TP), clinical-divisional (CD), or clinical-institute (CI). In all, 12 hospitals changed structure during the study period. There was slight evidence that CD structures were more efficient than TP structures but this was not supported by other evidence. There were no significant differences in efficiency in the first or second years following changes from either TP to CD or TP to CI structures. All four hospitals changing from CD to CI structure became significantly less efficient. This may be due to frequency rather than type of change as they were the only hospitals that implemented two structural changes. Hospitals that changed or did not change structure were similar in efficiency at the beginning and at the end of the study period, in overall efficiency during the period, and in trends toward efficiency over time. The findings challenge those who advocate restructuring hospitals on the grounds of improving cost efficiency.

Efficiency, Organizational↗

PubMed2002

Measuring efficiency of physician practices using data envelopment analysis.

PURPOSE: Medical-group practices are becoming increasingly common-place, with more than a third of licensed physicians in the United States currently working in this mode. While previous studies have focused on physician practices, little attention has been focused specifically on the contribution of internal organizational factors to overall physician practice efficiency. This paper develops a model to help determine best practices of efficient physician offices while allowing for choices between inputs. Measuring how efficient practices provide services yields useful information to help improve performance of less efficient practices. DESIGN: Data for this study were obtained from the 1999 Medical Group Management Association (MGMA) Cost Report. In this study, 115 primary care physician practices are analyzed. Outputs are defined as gross charges; inputs include square footage and medical, technical, and administrative support personnel. METHODOLOGY: Data envelopment analysis (DEA) is used in this study to develop a model of practice outputs and inputs to help identify the most efficient medical groups. DEA is a linear programming technique that converts multiple input and output measures to a single comprehensive measure of efficiency. These practices are used as a reference set for comparisons with less efficient ones. CONCLUSION: The overall results indicate that size of physician practice does not increase efficiency. There does not appear to be extensive substitution among inputs. Compared to other practices, efficient practices seem to manage each input well.

Benchmarking↗

PubMed2002

Measuring the efficiency of dental departments in medical centers: a nonparametric analysis approach.

Data envelopment analysis (DEA), a cross-sectional study design based on secondary data analysis, was used to evaluate the relative operational efficiency of 16 dental departments in medical centers in Taiwan in 1999. The results indicated that 68.7% of all dental departments in medical centers had poor performance in terms of overall efficiency and scale efficiency. All relatively efficient dental departments were in private medical centers. Half of these dental departments were unable to fully utilize available medical resources. 75.0% of public medical centers did not take full advantage of medical resources at their disposal. In the returns to scale, 56.3% of dental departments in medical centers exhibited increasing returns to scale, due to the insufficient scale influencing overall hospital operational efficiency. Public medical centers accounted for 77.8% of the institutions affected. The scale of dental departments in private medical centers was more appropriate than those in public medical centers. In the sensitivity analysis, the numbers of residents, interns, and published papers were used to assess teaching and research. Greater emphasis on teaching and research in medical centers has a large effect on the relative inefficiency of hospital operation. Dental departments in private medical centers had a higher mean overall efficiency score than those in public medical centers, and the overall efficiency of dental departments in non-university hospitals was greater than those in university hospitals. There was no information to evaluate the long-term efficiency of each dental department in all hospitals. A different combination of input and output variables, using common multipliers for efficiency value measurements in DEA, may help establish different pioneering dental departments in hospitals.

Cross-Sectional Studies↗

PubMed2001

Detection power, estimation efficiency, and predictability in event-related fMRI.

Experimental designs for event-related functional magnetic resonance imaging can be characterized by both their detection power, a measure of the ability to detect an activation, and their estimation efficiency, a measure of the ability to estimate the shape of the hemodynamic response. Randomized designs offer maximum estimation efficiency but poor detection power, while block designs offer good detection power at the cost of minimum estimation efficiency. Periodic single-trial designs are poor by both criteria. We present here a theoretical model of the relation between estimation efficiency and detection power and show that the observed trade-off between efficiency and power is fundamental. Using the model, we explore the properties of semirandom designs that offer intermediate trade-offs between efficiency and power. These designs can simultaneously achieve the estimation efficiency of randomized designs and the detection power of block designs at the cost of increasing the length of an experiment by less than a factor of 2. Experimental designs can also be characterized by their predictability, a measure of the ability to circumvent confounds such as habituation and anticipation. We examine the relation between detection power, estimation efficiency, and predictability and show that small increases in predictability can offer significant gains in detection power with only a minor decrease in estimation efficiency.

Artifacts↗

PubMed2002

Efficient design of event-related fMRI experiments using M-sequences.

Rapid event-related fMRI (erfMRI) allows estimation of the shape of hemodynamic responses (HDR) associated with transient brain activation evoked by various sensory, motor, and cognitive events. Choosing a sequence of events that maximizes efficiency of estimating the HDR is essential for conducting event-related brain imaging experiments, since increasing efficiency is essentially equivalent to reducing scanning time or increasing the strength of the principal magnetic field. The efficiency of an erfMRI design depends critically on the temporal arrangement of the sequence of events and the noise in the fMRI signal. We introduce to erfMRI a simple method for generating efficient event sequences based on maximum-length shift register sequences, or m-sequences. We show that under the assumption of white uncorrelated MRI noise, efficiency of erfMRI experimental designs that employ m-sequences exceeds efficiency of the best randomly generated sequences. This is true for single and multiple event type experiments, which allow either parallel events (overlapping events design) or designs in which only one event occurs at a time (nonoverlapping events design). HDR estimation efficiency afforded by m-sequences grows with the number of event types, and is greatest when event sequences are relatively short, albeit within commonly used scan times (i.e., 63-255 total events per scan). The improvement in efficiency, however, comes at a cost of constraints imposed by m-sequence generation rules, such as predetermined sequence lengths; for nonoverlapping events design m-sequence-based designs are not available for all possible numbers of event types. Nevertheless, designs that are available with m-sequences cover a large subset of commonly used erfMRI experimental designs. Under conditions of characteristic time-correlated fMRI noise, randomly generated sequences may yield efficiencies that exceed those afforded by m-sequences for single event-type designs, since in this case one can generate random sequences that partially decorrelate MRI noise by chance. Our simulations suggest that for designs of realistic sequence lengths that use more than one event type, m-sequence based designs tend to outperform random designs, thus making the knowledge of noise inessential. Finally, within an r-th order m-sequence (generated by a shift register of length r) all possible combinations of subsequences of length r occur, and thus these subsequences are exactly counterbalanced. This property is essential for minimizing effects of psychological and neuronal adaptation and expectation.

Brain↗

PubMed2001

The efficiency of simian foamy virus vector type-1 (SFV-1) in nondividing cells and in human PBLs.

Current retroviral vectors based on murine leukemia virus (MuLV) are unable to efficiently transduce nondividing cells. Lentiviruses, such as the human immunodeficiency virus 1 (HIV-1) are efficient at transducing nondividing, growth-arrested, and post-mitotic cells, but due to complex safety considerations, they may have limited potential for human clinical gene transfer. For this reason, alternatives to MuLV and HIV-1 vectors need to be explored. In this paper, we have found that simian foamy virus vector (SFV-1) containing a CMV-LacZ expression cassette is able to efficiently transduce multiple cell types of various species that include epithelial, lymphoid, and hematopoietic-derived human cell lines and fibroblast cell lines of several species. Previously it was reported that foamy virus replication is cell cycle dependent (P. D. Bieniasz, R. A. Weiss, and M. O. McClure, 1995. J. Virol. 69, 7295-7299). However, others studies demonstrated nuclear import of viral DNA in arrested cells (A. Saibi, F. Puvion-Dutilleul, M. Schmid, J. Peries, and H. d. The 1997. J. Virol. 71, 1155-1161). Here, we show efficient LacZ transduction by SFV-1 vectors in several chemically arrested cell lines and terminally differentiated human neurons. SFV-1 vector can transduce cell lines arrested in G1/S phase of the cell cycle by aphidicolin treatment with similar efficiencies to that of dividing cells. The terminally differentiated human neural cell line, NT2N, was transduced with 30-50% efficiency, corroborating our data obtained with the arrested cell lines. To further examine whether the SFV-1 vector can efficiently deliver a gene into clinically important cells for gene therapy, we transduced primary human peripheral blood cells (PBLs) in the presence and absence of phytohemagglutanin (PHA) stimulation. We observed 81% transduction efficiency in non-stimulated PBLs and 87% in PHA-stimulated PBLs with vector infection carried out twice in 8 hours intervals at a multiplicity of infection of 1. Together, these data indicate that SFV-1 based retroviral vectors may provide a safe, efficient alternative to current onco- and lentiviral vectors for gene transfer in cells from a broad spectrum of lineages across species boundaries.

Animals↗

PubMed2004

Effects of low-efficiency pollinators on plant fitness and floral trait evolution in Campanula americana (Campanulaceae).

Floral visitors vary in their pollination efficiency and their preferences for floral traits. If low-efficiency pollinators decrease the amount of pollen available to higher efficiency visitors, then low-efficiency visitors may actually have negative fitness consequences for the plants that they visit. We used experimental arrays in two populations to determine the floral preferences and the fitness effects of low-efficiency (or "ugly") pollinators on Campanula americana. These ugly pollinators (halictid bees) preferentially visited flowers with pollen over flowers that had had their pollen removed. C. americana pollen color varies quantitatively from light tan to dark purple, and we found that natural variation in pollen color influenced the magnitude of halictid preferences for flowers with pollen. In general, preferences for flowers with pollen were stronger when the ugly pollinators foraged in arrays of flowers with tan-colored pollen than in arrays with purple-colored pollen. When plants received few visits by efficient Bombus pollinators, visits by ugly pollinators significantly decreased siring success relative to plants where visits by ugly pollinators were prevented. In contrast, ugly pollinators did not influence siring success when higher efficiency pollinators were more abundant. Thus, the relationship between low-efficiency pollinators and the plants that they visit varies from commensalistic to antagonistic depending on the presence of other pollinators in the community. Our findings suggest that the negative fitness effects and floral preferences of low-efficiency or "ugly" pollinators may contribute to the maintenance of a pollen color polymorphism in C. americana.

Analysis of Variance↗

PubMed2004

The optimal mechanical efficiency of laparoscopic forceps.

BACKGROUND: Laparoscopic forceps have a large amount of friction in the mechanism, leading to a limited mechanical efficiency, which impairs the pinch force feedback. The advantage of a small amount of friction is that it is easier to maintain a constant pinch force on the tissue. Therefore, to obtain the optimal mechanical efficiency of the forceps, the influence of mechanical efficiency on the performance of several static and dynamic operative tasks, such as grasping tissue and estimating pressure, is quantified. METHODS: A grasper with adjustable mechanical efficiency and a load cell to measure the pinch force on the tissue was developed. Using this grasper, subjects performed several tasks on pig bowel tissue and simulation tissue: grasping tissue, reproducing a requested constant or variable pinch forces, and estimating the pressure in a tube. RESULTS: With increasing mechanical efficiency, a variable pinch force could be reproduced more accurately (deviation from the requested pinch force decreased from 34.4 to 24.9%, p = 0.016). The performance on the grasping tissue, reproducing a constant pinch force, and estimating pressure tasks did not improve with increased mechanical efficiency. CONCLUSIONS: The optimal mechanical efficiency of laparoscopic forceps is dependent on the task that is performed. For tasks requiring little movement of the forceps, such as grasping and holding tissue, a low mechanical efficiency is sufficient, whereas for tasks requiring repeated movement of the forceps to feel tissue, a high mechanical efficiency is required.

Animals↗

PubMed1989

Control of reovirus messenger RNA translation efficiency by the regions upstream of initiation codons.

The 10 species of reovirus messenger RNA are translated in vivo with efficiencies/frequencies that differ by as much as 100-fold. The s1 mRNA, which is translated 10 times less efficiently than the s4 mRNA but 10 times more efficiently than the/1 and m1 mRNAs, has a unique BamH1 cleavage site located immediately downstream of its initiation codon. Because the reovirus mRNAs have been cloned, this provides the opportunity for placing modified and altered sequences upstream of its coding sequence. The translation efficiencies of the variant mRNAs, transcribed via the SP6 in vitro transcription system, can then be measured in the rabbit reticulocyte lysate in vitro translation system. Using this system it was found that replacing the 5'-upstream sequence of the s1 mRNA with that of the s4 mRNA increases its in vitro translation efficiency by 4-fold; that the trinucleotide immediately upstream of the s1 initiation codon renders it very weak, and that it is only slightly superior to the weakest Kozak consensus sequence; that the nature of the nucleotides further upstream than position -3 can profoundly affect translation efficiency; that the nature of this effect is in turn markedly modified by the nature of nucleotides in positions -1 to -3; and that there is a minimum optimal 5'-upstream sequence length of about 14 nucleotides. We also investigated the effect of secondary structure involvement on the ability of 5'-upstream sequences to promote translation. Two effects were noted. First, being part of moderately stable stem loops (delta G, -18 kcal/mol) decreased translation efficiency about 3-fold; second, mRNA in which only three 5'-terminal nucleotides were unpaired were translated five times less efficiently than mRNA in which six nucleotides were unpaired. Accessibility of the 5'-cap as well as secondary structure of the 5'-upstream sequences are therefore factors that affect translation efficiency. Finally, we showed that the m1 mRNA, which is transcribed very poorly in vivo, is translated very efficiently in vitro; and that its 5'-upstream sequence is as effective in increasing protein sigma 1 formation as that of s4 mRNA. Since both m1 mRNA and protein mu 2 are stable in infected cells, the reason why m1 mRNA is translated so inefficiently in vivo therefore remains unexplained.

Codon↗

PubMed1995

Human efficiency for recognizing 3-D objects in luminance noise.

The purpose of this study was to establish how efficiently humans use visual information to recognize simple 3-D objects. The stimuli were computer-rendered images of four simple 3-D objects--wedge, cone, cylinder, and pyramid--each rendered from 8 randomly chosen viewing positions as shaded objects, line drawings, or silhouettes. The objects were presented in static, 2-D Gaussian luminance noise. The observer's task was to indicate which of the four objects had been presented. We obtained human contrast thresholds for recognition, and compared these to an ideal observer's thresholds to obtain efficiencies. In two auxiliary experiments, we measured efficiencies for object detection and letter recognition. Our results showed that human object-recognition efficiency is low (3-8%) when compared to efficiencies reported for some other visual-information processing tasks. The low efficiency means that human recognition performance is limited primarily by factors intrinsic to the observer rather than the information content of the stimuli. We found three factors that play a large role in accounting for low object-recognition efficiency: stimulus size, spatial uncertainty, and detection efficiency. Four other factors play a smaller role in limiting object-recognition efficiency: observers' internal noise, stimulus rendering condition, stimulus familiarity, and categorization across views.

Contrast Sensitivity↗

PubMed1995

Human efficiency for recognizing and detecting low-pass filtered objects.

Recently, Tjan, Braje, Legge and Kersten [(1995) Vision Research, 35, 3053-3069] found that human efficiency for object recognition was less than 10%, indicating that humans fail to use much of the information available to an ideal observer. We examine two explanations for these low efficiencies: (1) humans are inefficient in using high spatial-frequency information; and (2) humans are inefficient in detecting image samples. We tested the first possibility by measuring human efficiency for recognizing low-pass filtered objects, rendered as line drawings and silhouettes, in luminance noise. Efficiency did not improve when high frequencies were removed, and the first explanation was rejected. We tested the second explanation by comparing efficiencies for object detection and recognition. Recognition efficiency was higher than detection efficiency for silhouettes but not line drawings, showing that detection efficiency does not place a ceiling on recognition efficiency. The results indicate that human vision is designed to extract image features, such as contours, that enhance recognition. A computer simulation suggests that this can occur if the observer views the world through a band-pass spatial-frequency channel.

Algorithms↗

PubMed2006

Is Achilles tendon compliance optimised for maximum muscle efficiency during locomotion?

Tendon elasticity is important for economical locomotion; however it is unknown whether tendon stiffness is appropriate to achieve an optimal efficiency in various muscles. Here we test the hypothesis that the Achilles tendon is of an appropriate stiffness to maximise medial gastrocnemius muscle efficiency during locomotion with different power requirements. To test this hypothesis we used a three element Hill muscle model to determine how muscle fascicles would be required to change length if the series elastic element stiffness is varied, whilst the limb kinematics and muscle properties are held constant. We applied a model of muscle energetics to these data to predict muscle efficiency for a range of stiffness values in both walking and running conditions. We also compared the model results to in vivo data collected using ultrasonography. The muscle model predicted that optimal series elastic element stiffness for maximising efficiency is equal or slightly higher than that of the average Achilles tendon in running and walking, respectively. Although the peak efficiency values for running (26%) and walking (27%) are similar, the range of stiffness values achieving high efficiency in running is much smaller than that during walking. These results suggest that a compliant tendon, such as the Achilles tendon, is required for efficient running. Such a finding is important, because it describes how the stiffness of a tendon may be adapted to achieve optimal efficiency for particular athletic pursuits. The influence of varying tendon stiffness on kinematic performance may, however, play an important role in determining the efficiency of the muscle.

Achilles Tendon↗

PubMed2004

Aggregate eco-efficiency indices for New Zealand--a principal components analysis.

Eco-efficiency has emerged as a management response to waste issues associated with current production processes. Despite the popularity of the term in both business and government circles, limited attention has been paid to measuring and reporting eco-efficiency to government policy makers. Aggregate measures of eco-efficiency are needed, to complement existing measures and to help highlight important patterns in eco-efficiency data. This paper aims to develop aggregate measures of eco-efficiency for use by policy makers. Specifically, this paper provides a unique analysis by applying principal components analysis (PCA) to eco-efficiency indicators in New Zealand. The study reveals that New Zealand's overall eco-efficiency improved for two out of the five aggregate measures over the period 1994/1995-1997/1998. The worsening of the other aggregate measures reflects, among other things, the relatively poor performance of the primary production and related processing sectors. These results show PCA is an effective approach for aggregating eco-efficiency indicators and assisting decision makers by reducing redundancy in an eco-efficiency indicators matrix.

Conservation of Natural Resources↗

PubMed1998

Length of stay and efficiency in pediatric intensive care units.

OBJECTIVE: Assessment of pediatric intensive care unit (PICU) efficiency with a length of stay prediction model and validation of this assessment by an efficiency measure based on daily use of intensive care unit-specific therapies. DESIGN: Inception cohort study of data acquired between 1989 and 1994. SETTING: Thirty-two PICUs, 16 selected randomly and 16 volunteering. SUBJECTS: Consecutive admissions of 10,658 patients (466 deaths) who stayed at least 2 hours and up to 12 days in the PICU. MEASUREMENTS: Length of stay and its prediction from a model with admission day data (PRISM III-24, diagnostic factors, mechanical ventilation). For validation 11 PICUs recorded each patient's "efficient" days, that is, days when at least one PICU-specific therapy was given. PICU efficiency was computed as either the ratio of the observed efficient days or the days accounted for by the predictor variables to the total care days, and the agreement was assessed by Spearman's rank correlation analysis. RESULTS: The total care days provided by each PICU (n = 32) were well predicted by the length of stay model (r = 0.946). The agreement in 11 validation PICUs between therapy-based efficiency (range 0.30 to 0.67) and predictor-based efficiency (range 0.31 to 0.63) was excellent (rank correlation r = 0.936, p < 0.0001). CONCLUSION: PICU efficiency comparisons with either method are nearly equivalent. Predictor-based efficiency has the advantage that it can be computed from admission day data only.

Cohort Studies↗

PubMed2002

Metallothioneins (I+II) and thyroid-thymus axis efficiency in old mice: role of corticosterone and zinc supply.

Thymic atrophy or thymus absence causes depressed thyroid-thymus axis (TTA) efficiency in old, young propyl-thiouracil (PTU) (experimental hypothyroidism) and in young-adult thymectomised (Tx) mice, respectively. Altered zinc turnover may be also involved in depressed TTA efficiency. Zinc turnover is under the control of zinc-bound metallothioneins (Zn-MTs) synthesis. Thyroid hormones, corticosterone and nutritional zinc affect Zn-MT induction. Zn-MT releases zinc in young-adult age during transient oxidative stress for prompt immune response. In constant oxidative stress (ageing and liver regeneration after partial hepatectomy), high liver Zn-MTs, low zinc ion bioavailability and depressed TTA efficiency appear. This last finding suggested that MT might not release zinc during constant oxidative stress leading to impaired TTA efficiency. The aim of this work/study is to clarify the role of Zn-MTs (I+II) in TTA efficiency during development and ageing. The main results are (1) Old and PTU mice display high corticosterone, enhanced liver MTmRNA, low zinc and depressed TTA efficiency restored by zinc supply. Increased survival and no significant increments in basal liver Zn-MTs proteins occur in old and PTU mice after zinc supply. (2) Lot of zinc ions bound with MT in the liver from old mice than young (HPLC). (3) Young-adult Tx mice, evaluated at 15 days from thymectomy, display high MTmRNA and nutritional-endocrine-immune damage restored by zinc supply or by thymus grafts from old zinc-treated mice. (4) Young-adult Tx mice, but evaluated at 40 days from thymectomy, display natural normalisation in MTmRNA and nutritional-endocrine-immune profile with survival similar to normal mice. (5) Stressed (constant dark for 10 days) mice overexpressing MT display low zinc, depressed immunity, reduced thymic cortex, high corticosterone, altered thyroid hormones turnover showing a likeness with old mice. These findings, taken altogether, show that corticosterone is pivotal in MTs induction under stress. MTs bind preferentially zinc ions in constant oxidative stress, but with no release of zinc from MT leading to impaired TTA efficiency. Zinc supply restores the defect because zinc has no interference in affecting pre-existing Zn-MTs protein concentrations in old and PTU mice. Therefore, free zinc ions are available for TTA efficiency after zinc supply. Thymus from old zinc-treated mice induces the same restoring effect when transplanted in Tx recipients. However, Tx mice display natural normalisation in MTmRNA and in nutritional-endocrine-immune profile in the long run. Therefore, Zn-MTs (I+II) are crucial in zinc homeostasis for endocrine-immune efficiency during the entire life assuming a role of potential and novel 'biological clock of ageing'.

Aging↗

PubMed2002

Influences of preparation conditions on particle size and DNA-loading efficiency for poly(DL-lactic acid-polyethylene glycol) microspheres entrapping free DNA.

Poly-DL-lactic acid-polyethylene glycol (PELA) with different contents and different molecular weight of polyethylene glycol (PEG) was used as a DNA delivery system. DNA-loaded PELA or poly(DL-lactic acid) (PLA) microspheres were prepared by the emulsion evaporation technique, which was based on the water-in-oil-in-water solvent evaporation method. The purpose of the present work was to investigate the factors influencing particle size and DNA loading efficiency for the PELA microspheres containing free DNA. During the preparation process, different conditions were used and the resulting microspheres were characterized by particle size and DNA loading efficiency. Microspheres prepared by PELA with a PEG (molecular weight: 6000 Da) content of 6-10% obtained the highest loading efficiency and smaller particle size among other PELA copolymer and PLA homopolymer. When the solvent of the oil phase was composed of methylene chloride and ethyl acetate (1:1, v/v), the highest loading efficiency and smaller particle size were also obtained for the PELA microspheres. The presence of the surfactant in oil phase influenced both the particle size and loading efficiency. Increasing the concentration of polymer in oil phase resulted in an increase of particle size and loading efficiency for DNA-loaded PELA microspheres. The addition of a hydrophilic polymer into the internal water phase ameliorated the DNA loading efficiency and reduced the particle size. Significant influences of DNA molecular weight and structure on the particle size and loading efficiency were observed. The volume and concentration of the external water phase also influenced the particle size and loading efficiency.

DNA↗

PubMed1996

Efficiency of the flexor tendon pulley system in human cadaver hands.

The efficiency of the flexor tendon system was examined in a human cadaver model. Pulleys were randomly sectioned, and the results were evaluated on the basis of the tendon excursion, force generated at the fingertip, and the work (force multiplied by distance) involved, as compared to the intact pulley system. When a single minor pulley (A1 or A5) was cut, there was no statistical difference in work efficiency or excursion efficiency from controls. Cutting all minor pulleys (A1, A3, A5) lead to a significant loss in excursion efficiency. The intact three pulley systems of A2, A3, and A4 were near normal and statistically better than A2 and A4 together for work efficiency. Cutting one of the major pulleys (A2, A4) resulted in significant changes in efficiency, but what was unexpected was to find an 85% loss of both work and excursion efficiency for the loss of A4 but only an excursion difference of 94% for the loss of A2. Our findings demonstrated that in this model, with the influence of the skin removed, A4 absence produced the largest biomechanically measured efficiency changes and that a combination of A2, A3, and A4 was necessary to preserve both work and excursion efficiency.

Biomechanical Phenomena↗

PubMed1998

Breathing efficiency during inspiratory threshold loading in patients with chronic obstructive pulmonary disease.

Patients with chronic obstructive pulmonary disease (COPD) demonstrate an increased oxygen cost of breathing. It is as yet unclear whether this is related to a decreased breathing efficiency. The aim of the present study was to compare breathing efficiency in 16 patients with COPD (11 men, five women) and 16 healthy elderly subjects (seven men, nine women), and to investigate a possible relationship between breathing efficiency and resting energy expenditure (REE). REE was measured using a ventilated hood system. Breathing efficiency was assessed by measuring oxygen consumption (V'O2), mean inspiratory mouth pressure (MIP) and flow during breathing at rest and subsequently during breathing against an inspiratory threshold (40% of maximal inspiratory pressure). During loaded breathing there was a significant increase in V'O2, MIP, and external work of breathing compared with unloaded breathing in both groups. As intended, ventilation did not increase significantly during the breathing efficiency test in the patients with COPD. The breathing efficiency (median, range) of the patients with COPD was similar (3.7%, 1.4-8.7%) to that of the healthy elderly subjects (3.2%, 1.7-8.3%). Breathing efficiency was not correlated with REE in either group. In the present study, in which dynamic hyperinflation was probably prevented, no difference in breathing efficiency was found between healthy elderly subjects and COPD patients when breathing against an external inspiratory threshold. Furthermore, breathing efficiency was not related to REE in both groups.

Adult↗