bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for an Incipient Decline in Numbers of Missing Girls in China and India
Authors: Gupta Monica Das , Chung Woojin , Shuzhuo Li
Published: June 2009

The apparently inexorable rise in the proportion of “missing girls” in much of East and South Asia has attracted much attention among researchers and policymakers. An encouraging trend was suggested by the case of South Korea, where child sex ratios (males to females under age 5) were the highest in Asia but peaked in the mid‐1990s and normalized thereafter. Using census data, we examine whether similar trends have begun to manifest themselves in the two most populous countries of this region, China and India. The data indicate that child sex ratios are peaking in these countries, and in many subnational regions are beginning to trend toward lower, more normal values. This suggests that, with continuing economic and social development and vigorous public policy efforts to reduce son preference, the “missing girls” phenomenon could eventually disappear in Asia.
The impact of maternal negative affectivity on dietary patterns of 18‐month‐old children in the Norwegian Mother and Child Cohort Study
Authors: Ystrom Eivind , Niegel Susan , Vollrath Margarete E.
Published: June 2009

Early dietary habits are formative for dietary habits later in life. Maternal personality might be an important factor in unhealthy feeding of children. The current study aims to assess the degree to which the personality trait of negative affectivity in mothers predicts their child's diet at age 18 months. This study is a part of the Norwegian Mother and Child Cohort Study conducted at the Norwegian Institute of Public Health. A total of 27 763 mothers completed 3 repeated assessments of negative affectivity before and after childbirth and of the child's diet when the child was 18 months old. Exploratory factor analysis was used to identify the dietary patterns, and structural equation modeling was used to investigate the relationship with negative affectivity adjusted for socio‐demographical variables. Exploratory factor analysis of a foods frequency questionnaire revealed two dietary patterns in the child, labeled unhealthy diet and wholesome diet. The unhealthy diet comprised foods rich in sugar and fat; the wholesome diet comprised foods rich in fibre, vitamins and minerals. Mothers high in negative affectivity were more inclined to feed their child an unhealthy diet. The results were adjusted for maternal age, years of education, relative income, marital status, number of children, having the child in daycare, maternal smoking, maternal body mass index, and child gender. This study shows that a maternal personality trait, negative affectivity, is related to feeding the child an unhealthy diet after controlling for key socio‐demographic variables.
Dietary behaviour, food and nutrient intake of pregnant women in a rural community in Burkina Faso
Authors: Huybregts Lieven Fernand , Roberfroid Dominique Albert , Kolsteren Patrick Wilfried , Van Camp John Hendrik
Published: June 2009

The aim of this study was to assess potential changes in dietary habits during pregnancy in a rural community in Houndé district, Burkina Faso. In‐depth interviews were performed on a random sample of 37 pregnant women in order to analyse specific perceptions and attitudes regarding food consumption during pregnancy. In addition to this, an interactive 24‐h recall survey was used to compare the food intake of 218 pregnant and 176 non‐pregnant women. The majority of interviewees reported dietary restrictions during pregnancy but no consistent pattern of avoided food types was found. Most of the mentioned ‘forbidden’ foods were in related to physical discomfort during gestation. Interviewees also admitted to ignoring culturally determined food prohibitions/prescriptions. No differences were observed in food intake, food choice and nutrient intake between the group of pregnant and non‐pregnant women. During the third trimester of gestation women did not show any major differences in food and nutrient intake compared with women from the first/second trimester. The mean nutrient intakes were found to be insufficient compared with the recommended daily allowances, especially for pregnant women. In conclusion, pregnant women in this rural area of Burkina Faso do not seem to restrict their diet significantly during pregnancy. The additional nutritional requirements of pregnancy are not accounted for in their dietary practises.
Evaluation of emergency medicine trainees' ability to use transport equipment
Authors: Samuel Manoj , Stella Julian
Published: June 2009

Objective:  To assess the skills of advanced emergency medicine trainees in the use of commonly used transport equipment and to determine what teaching has been undertaken and what level of confidence trainees have in their ability to use the equipment tested.

Methods:  This is a prospective multicentre observational study examining equipment use. Three pieces of equipment were examined: the infusion pump, defibrillator‐monitor and transport ventilator. A questionnaire and a series of practical tasks were used. Advanced trainees from Victorian ED were enrolled as participants. Outcomes included proportion of participants able to perform all tasks successfully, subjective registrar confidence with use of equipment and departmental training practices. Eleven ED were represented, covering metropolitan tertiary, metropolitan peripheral and regional hospitals.

Results:  There were 47 participants enrolled in the study. The range of advanced training years of participants was 1–5+. Of the 47 participants, 39 (83%; 95% CI 72.2–93.7%) had been involved as medical escorts. Eighteen participants (38.3%; 95% CI 24.4–52.2%) described some form of teaching for equipment use. The median level of confidence of participants (on a 5‐point scale) was 4 (25–75% interquartile range 3–4), which correlates with a moderate degree of confidence. Of 47 participants, 7 (14.9%; 95% CI 4.7–25.1%) rated themselves as not confident or somewhat under‐confident (i.e. 1 or 2 on the scale). Of 47, 12 passed overall (25.5%; 95% CI 13.1–38%) and 8 completely failed (17.0%; 95% CI 6.3–27.8%) the skill testing.

Conclusion:  When tested in isolation, there appears to be deficits in the equipment skills of advanced ED trainees who are expected to be proficient in transport medicine.
Education initiative improves the evidence‐based use of metoclopramide following morphine administration in the emergency department
Authors: Yeoh Bernard SK , McD Taylor David , Taylor Simone E
Published: June 2009

Objective:  We aimed to evaluate a multifaceted education initiative designed to reduce the prophylactic use of metoclopramide.

Methods:  This was a pre‐ and post‐intervention trial undertaken in a single ED. All ED doctors and nurses were targeted. The intervention comprised a specifically designed, 19‐slide ‘e‐learning module’, accessible via the ED intranet, supplemented by in‐service training and a range of reminder techniques (posters, emails and drug room flyers). The primary end‐point was the proportion of patients administered metoclopramide prophylactically with their initial morphine dose. Data were collected on random samples of patients who received morphine, using explicit medical chart review.

Results:  Both pre‐ and post‐intervention periods were of 3 month duration. The charts of 146 cases were reviewed in each period. In the post‐intervention period:

• The proportion of patients administered metoclopramide prophylactically decreased from 22.6% to 4.1% (difference 18.5% [95% CI 10.3–26.7], P < 0.001)

• The proportion of patients administered metoclopramide appropriately (for known morphine sensitivity, established nausea and rescue anti‐emesis) rose marginally from 28.8% to 32.9% (difference 4.1% [95% CI −7.2–15.4], P = 0.53)

• There was a 12.7% decrease in the number of ampoules of metoclopramide issued to the ED without a concurrent rise in the issue of other anti‐emetic drugs

Conclusion:  The education initiative resulted in a significant improvement in the evidence‐based use of metoclopramide.
Frequent attenders with mental disorders at a general hospital emergency department
Authors: Wooden Michael DG , Air Tracy M , Schrader Geoffrey D , Wieland Barbara , Goldney Robert D
Published: June 2009

Objectives:  To define the clinical and demographic characteristics of frequent attenders with mental disorders at a general hospital ED; to determine whether those persons had additional attendances at other ED in the same city; and to assess the documented care of those frequent attenders.

Method:  A retrospective descriptive study of those who attended the Queen Elizabeth Hospital, Woodville South, Australia ED on average at least once per month between 1 July 2006 and 15 March 2007.

Results:  Of 11594 attenders, 54 (0.47%) at the ED were frequent attenders with mental disorders. Their 735 attendances represented 4.5% of the total of 16 345 attendances. Of those frequent attenders, 34 (63%) also visited other Adelaide hospital ED on an additional 410 occasions. Presentations peaked on the weekends and between 18.00 h and midnight. Although 43% of frequent attenders had specific mental health‐care plans, only two‐thirds of those had been assigned to a mental health team.

Conclusions:  The documented management of frequent attenders with mental disorders at a general hospital ED appeared to be less than optimal. Furthermore, the majority of those frequent attenders also attended other general hospital ED in the same city, and this did not appear to be recognized.
Structured team approach to the agitated patient in the emergency department
Authors: Downes Michael A , Healy Paul , Page Colin B , Bryant Jennifer L , Isbister Geoffrey K
Published: June 2009

Objective:  Behavioural disturbance and aggression in the ED is an increasing problem. The present study describes the characteristics of patients with acute behavioural disturbance and their emergent treatment in an ED with a structured team approach.

Methods:  This was a retrospective review of acute behavioural emergencies that required response from the Code Black (CB) Team (duress response team) in the ED during 2006. The hospital security log and hospital incident‐reporting system identified all documented CB, and the patients' medical records were reviewed. Information extracted included patient demographics and presenting complaint, details of the CB, the use of pharmacological sedation, physical restraint and patient disposition. Injuries to hospital staff were also extracted.

Results:  There were 122 patients, median age 32 years (interquartile range: 24–43 years, range: 14–81 with 71 male patients (58%) who accounted for 143 CB activations. The primary problems were deliberate self‐poisoning or self‐harm (38%), alcohol and illicit drug intoxication (33%) and psychiatric, organic illness and drug withdrawal (29%). One hundred and eight (89%) patients had a past history of alcohol/illicit drug abuse or psychiatric illness. Indications for CB activation were threatening harm to others or behaving violently in 67% of cases. Combined pharmacological sedation and physical restraint were required on 66 (46%) occasions, pharmacological sedation alone on 20 (14%), physical restraint alone on 14 (10%) and neither on 43 (30%) occasions. Benzodiazepines were most commonly used for initial sedation, including i.m. (29%), i.v. midazolam (20%), diazepam (42%) and antipsychotics (9%), most commonly droperidol. More diazepam and droperidol were used for subsequent pharmacological sedation. A staff member was injured on only one occasion (0.7%).

Conclusions:  Acute behavioural disturbance was common in the present study, and underlying causes were predominantly organic in nature. A team approach appears to be valuable in managing these incidents.
Nebulized fentanyl versus intravenous morphine in children with suspected limb fractures in the emergency department: A randomized controlled trial
Authors: Furyk Jeremy S , Grabowski Walter J , Black Lisa H
Published: June 2009

Objective:  To compare the efficacy of nebulized fentanyl (NF) with i.v. morphine (IVM) in paediatric patients presenting to the ED with clinically suspected limb fractures.

Methods:  A convenience sample of patients aged 4–13 years, presenting with clinically suspected limb fractures, were randomized to receive either NF at 4 µg/kg or IVM at 0.1 mg/kg. Pain scores were assessed at 0, 15 and 30 min using the Wong and Baker faces pain scale (0–10). Vital signs and adverse effects were also recorded.

Results:  Of the 77 patients enrolled in the study, data were available for analysis on 73 patients. Of those, 36 received NF and 37 received IVM. The two groups were similar in terms of demographics and initial pain scores. Mean pain score at 15 min was decreased by 3.06 (NF) and by 1.97 (IVM) (difference 1.09; 95% CI 2.32 to −0.32). At 30 min the decreases were 3.6 (NF) and 3.0 (IVM), respectively (difference 0.6; 95% CI 1.89 to −0.65). Decreases in pain scores for both NF and IVM were statistically significant (P < 0.0001), but the difference in the effect of NF and IVM did not reach statistical significance. There was no significant change in any vital signs or serious adverse events in either group.

Conclusion:  NF in a dose of 4 µg/kg given via a standard nebulizer provided clinically significant improvements in pain scores, comparable to IVM. NF should be considered as a treatment option for use in children presenting in acute pain.
Pain management practices in paediatric emergency departments in Australia and New Zealand: A clinical and organizational audit by National Health and Medical Research Council's National Institute of Clinical Studies and Paediatric Research in Emergency Departments International Collaborative
Authors: Herd David W , Babl Franz E , Gilhotra Yuri , Huckson Sue ,   PREDICT group
Published: June 2009

Objective:  To audit pain management practices and organization in paediatric ED across Australia and New Zealand.

Methods:  Retrospective audit of pain management practices in Paediatric Research in Emergency Departments International Collaborative ED in 20 cases each of migraine, abdominal pain and femoral shaft fracture. Review of organizational status of pain management at Paediatric Research in Emergency Departments International Collaborative sites.

Results:  Of 14 ED, 10 participated in the clinical audit. A total of 196 migraine, 197 abdominal pain and 177 femur fracture cases were reviewed. Less than half had degree of pain measured or had pain score documented on triage. Migraine received analgesia in 62% of cases (opioids in 11%). Abdominal pain received analgesia in 62% of cases (opioids in 14%). Fractured femurs received analgesia in 78% of cases (opioids 49%, femoral nerve blocks 40%). Median minutes to enteral medication were 100, 85 and 75, and for parenteral medication (mainly opiates) 103, 137 and 26, for migraine, abdominal pain and femur fracture, respectively. Thirteen hospitals participated in the organizational audit. Of all ED, 92% had pain management policies or guidelines, 92% taught pain management topics in education programmes and 62% used mandatory pain competencies. Only 15% had quality improvement programmes for pain reduction.

Conclusion:  We found a notable lack of pain assessment documentation and delays to analgesia. There is a need to improve pain assessment and management, although a majority of paediatric ED surveyed had important organizational and educational structures in place. Issues to explore include use of opioids in migraine and the underuse of femoral nerve blocks.
White‐eyed blowout fracture: Another look
Authors: Mehanna Patrick , Mehanna Daniel , Cronin Andrew
Published: June 2009

Orbital floor fractures have the potential to cause significant morbidity both in the short and long terms and commonly present to the ED for initial assessment. Although treatment of the majority of these injuries involves clinic review and possible later surgery, there is a specific subset that present to emergency clinically suggestive of a head injury. This subset, ‘white‐eyed blowout’, usually occurring under 18 years of age, with a history of trauma and little sign of soft tissue injury, describes a trap door orbital floor fracture with herniation and acute entrapment of orbital muscle and is regarded as a maxillofacial emergency. The injury presents with marked nausea, vomiting, headache and irritability suggestive of a head injury that commonly distracts from the true aetiology. It requires prompt diagnosis and treatment to avoid permanent morbidity. We present three cases and discuss their management.
Successful retrograde tracheal intubation using a central venous catheterization set: two cases
Authors: Oh Je Hyeok , Kim Sung Eun , Lee Sang Jin
Published: June 2009

Retrograde tracheal intubation (RTI) is an airway management technique requiring relatively simple skills that can be learned easily and retained. However, proper RTI equipment is not generally available in many ED. RTI requires through‐the‐needle catheters and flexible‐tip guidewires, which are included in the more generally available central venous catheterization set. We performed RTI using the central venous catheterization set in two patients with obstructed airways where specific RTI equipment was unavailable and demonstrated successful intubation in both cases. Our method might be a useful alternative for RTI in situations where the purpose‐specific equipment is unavailable.
The GermanGemeinwirtschaftslehre: Implications for modern nonprofit economics
Authors: Valentinov Vladislav
Published: June 2009

This article examines the way modern nonprofit economics can be informed by theGemeinwirtschaftslehre, a strand of public and nonprofit economics that was popular in German‐speaking countries until the 1980s. Despite its present decline, theGemeinwirtschaftslehreyields a valuable implication that nonprofit firms address market failure by supplanting the pecuniary entrepreneurial motivation with a nonpecuniary one. In this article, this implication is used to reconsider two central and controversial issues in modern nonprofit economics: the rationale behind the nondistribution constraint in nonprofit firms, and the integration between the market failure and supply‐side theories of the nonprofit sector. The article concludes by discussing the emerging prospects for empirical research.
The devaluation of life
Authors: Viscusi W. Kip
Published: June 2009

The US Environmental Protection Agency (EPA) has been the target of two recent controversies involving the devaluation of life: the 2003 use of a senior discount for the value of statistical life for people over age 65, and the 2008 downward reassessment of the value of statistical life by the EPA Air Office. Even though these new values of statistical life were still among the highest used in the Federal government, there was a strong negative public reaction to each. The public outcry over the EPA policies appears to have stemmed from an irrational response to decreases in the value of statistical life. Proposed Congressional legislation that purportedly seeks to reform the valuations would politicize benefit assessments. A sounder approach is to establish a peer‐reviewed scientific advisory panel to advise agencies on the value of statistical life.
Confronting the next influenza pandemic with anti‐inflammatory and immunomodulatory agents: why they are needed and how they might work
Authors: Fedson David S.
Published: June 2009

Abstract  Despite the best efforts of influenza scientists, companies and health officials to prepare for the next pandemic, most of the world’s people will not have access to affordable supplies of vaccines and antiviral agents. They will have to rely on 19th century public health ‘technologies’ to see them through. In the 21st century, science ought to be able to provide something better. Influenza scientists study the molecular characteristics of influenza viruses and their signaling effects in cell culture and animal models of infection. While these studies have been enormously informative, they have been unable to explain the system‐wide effects of influenza on the host, the increased mortality of younger adults in the 1918 influenza pandemic and the much lower mortality rates in children who were more commonly infected with the 1918 virus. Experiments by non‐influenza scientists have defined common cell signaling pathways for acute lung injury caused by different agents, including inactivated H5N1 influenza virus. These pathways include several molecular targets that are up‐regulated in acute lung injury and down‐regulated by anti‐inflammatory and immunomodulatory agents, including statins, fibrates, and glitazones. These agents also help reverse the mitochondrial dysfunction that accompanies multi‐organ failure, something often seen in fatal Influenza. Observational studies suggest that statins are beneficial in treating patients with pneumonia (there are no such studies for fibrates and glitazones). Other studies suggest that these agents might be able to ‘roll back’ the self‐damaging host response of young adults to the less damaging response of children and thus save lives. Research is urgently needed to determine whether these and other agents that modify the host response might be useful in managing H5N1 influenza and the next pandemic.
Viscoelastic properties of Staphylococcus aureus and Staphylococcus epidermidis mono‐microbial biofilms
Authors: Di Stefano Antonio , D'Aurizio Eleonora , Trubiani Oriana , Grande Rossella , Di Campli Emanuela , Di Giulio Mara , Di Bartolomeo Soraya , Sozio Piera , Iannitelli Antonio , Nostro Antonia , Cellini Luigina
Published: June 2009

The viscoelastic properties of mono‐microbial biofilms produced by ocular and reference staphylococcal strains were investigated. The microorganisms were characterized for their haemolytic activity and agr typing and the biofilms, grown on stainless steel surface under static conditions, were analysed by Confocal Laser Scanning Microscopy. Static and dynamic rheometric tests were carried out to determine the steady‐flow viscosity and the elastic and viscous moduli. The analysed biofilms showed the typical time‐dependent behaviour of viscoelastic materials with considerable elasticity and mechanical stability except for Staphylococcus aureus ATCC 29213 biofilm which showed a very fragile structure. In particular, S. aureus 6ME biofilm was more compact than other staphylococcal biofilms studied with a yield stress ranging between 2 and 3 Pa. The data obtained in this work could represent a starting point for developing new therapeutic strategies against biofilm‐associated infections, such as improving the drug effect by associating an antimicrobial agent with a biofilm viscoelasticity modifier.
The roles of outer membrane cytochromes of Shewanella and Geobacter in extracellular electron transfer
Authors: Shi Liang , Richardson David J. , Wang Zheming , Kerisit Sebastien N. , Rosso Kevin M. , Zachara John M. , Fredrickson James K.
Published: June 2009

As key components of the electron transfer (ET) pathways used for dissimilatory reduction of solid iron [Fe(III)] (hydr)oxides, outer membrane multihaem c‐type cytochromes MtrC and OmcA of Shewanella oneidensis MR‐1 and OmcE and OmcS of Geobacter sulfurreducens mediate ET reactions extracellularly. Both MtrC and OmcA are at least partially exposed to the extracellular side of the outer membrane and their translocation across the outer membrane is mediated by bacterial type II secretion system. Purified MtrC and OmcA can bind Fe(III) oxides, such as haematite (α‐Fe2O3), and directly transfer electrons to the haematite surface. Bindings of MtrC and OmcA to haematite are probably facilitated by their putative haematite‐binding motifs whose conserved sequence is Thr–Pro–Ser/Thr. Purified MtrC and OmcA also exhibit broad operating potential ranges that make it thermodynamically feasible to transfer electrons directly not only to Fe(III) oxides but also to other extracellular substrates with different redox potentials. OmcE and OmcS are proposed to be located on the Geobacter cell surface where they are believed to function as intermediates to relay electrons to type IV pili, which are hypothesized to transfer electrons directly to the metal oxides. Cell surface‐localized cytochromes thus are key components mediating extracellular ET reactions in both Shewanella and Geobacter for extracellular reduction of Fe(III) oxides.
Mechanical Responses of Tendons to Repeated Extensions and Wait Periods
Authors: Hubbard Robert P. , Chun Keyoung J.
Published: June 2009

Tendon specimens were repeatedly extended to peak strains of either 2, 3, 4, or 6 percent. During the three 1800 s (30 min.) periods of cyclic extension, the peak loads relaxed with decreases in hysteresis and increases in slack strain. During the two 1800 s wait periods of no extension, the specimens recovered with increases in peak load and hysteresis and decreases in slack strain. However, the recovery during the wait periods was eradicated in the first few subsequent extensions and the relaxation continued as if there were no 1800 s wait periods. Stress-strain responses were well fit with power relations.
Passive Deformation Analysis of Human Leukocytes
Authors: Dong Cheng , Skalak R. , Sung Kuo-Li Paul , Schmid-Scho¨nbein G. W. , Chien Shu
Published: June 2009

The following analysis presents an experimental and theoretical study of the passive viscoelastic behavior of human leukocytes. Individual neutrophils in EDTA were observed both during their partial aspiration into a small micropipette and after expulsion from a large micropipette where the cell had been totally aspirated and deformed into a sausage shape. To analyze the data, a passive model of leukocyte rheology has been developed consisting of a cortical shell containing a Maxwell fluid which describes the average properties of the cell cytoplasm. The cortical shell represents a crosslinked actin layer near the surface of the cell and is assumed to be under pre-stressed tension. This model can reproduce the results of experiments using micropipette for both short-time small deformation and slow recovery data after large deformation. In addition, a finite element scheme has been established for the same model which shows close agreement with the analytical solution.
Smoothing Noisy Data Using Dynamic Programming and Generalized Cross-Validation
Authors: Dohrmann C. R. , Busby H. R. , Trujillo D. M.
Published: June 2009

Smoothing and differentiation of noisy data using spline functions requires the selection of an unknown smoothing parameter. The method of generalized cross-validation provides an excellent estimate of the smoothing parameter from the data itself even when the amount of noise associated with the data is unknown. In the present model only a single smoothing parameter must be obtained, but in a more general context the number may be larger. In an earlier work, smoothing of the data was accomplished by solving a minimization problem using the technique of dynamic programming. This paper shows how the computations required by generalized cross-validation can be performed as a simple extension of the dynamic programming formulas. The results of numerical experiments are also included.
A Stress Compatible Finite Element for Implant/Cement Interface Analyses
Authors: Angelides M. , Shirazi-Adl A. , Shrivastava S. C. , Ahmed A. M.
Published: June 2009

A new finite element has been developed to enforce normal and shear stress continuity at bimaterial interface points in order to alleviate the problem of high stress discontinuity predictions by the conventional displacement finite element method. The proposed element is based on a five node isoparametric quadrilateral element where the fifth node is located at the interface boundary of the element. A series of validation tests have been carried out to assess the correctness of the stress distribution obtained by the new element at interfaces of highly dissimilar materials. The results of the tests are compared to analytical solutions and to results from convergence studies performed by the conventional finite element method (SAP-IV). Overall, the proposed element has been demonstrated to have a very satisfactory degree of reliability, especially in view of the observed inability of the conventional method to yield interpretable interface stress values for most cases analyzed. Finally, the new interface element has been applied to the analysis of an axisymmetric model of the knee tibial implant. The superiority of the proposed element over the conventional one has been demonstrated in this case by a convergence study.
Nonlinear Incompressible Finite Element for Simulating Loading of Cardiac Tissue—Part I: Two Dimensional Formulation for Thin Myocardial Strips
Authors: Horowitz A. , Sheinman I. , Lanir Y. , Perl M. , Sideman S.
Published: June 2009

A two-dimensional incompressible plane-stress finite element is formulated for the simulation of the passive-state mechanics of thin myocardial strips. The formulation employs a total Lagrangian and materially nonlinear approach, being based on a recently proposed structural material law, which is derived from the histological composition of the tissue. The ensuing finite element allows to demonstrate the mechanical properties of a single myocardial layer containing uniformly directed fibers by simulating various loading cases such as tension, compression and shear. The results of these cases show that the fiber direction is considerably stiffer than the cross-fiber direction, that there is significant coupling between these two directions, and that the shear stiffness of the tissue is lower than its tensile and compressive stiffness.
Nonlinear Incompressible Finite Element for Simulating Loading of Cardiac Tissue—Part II: Three Dimensional Formulation for Thick Ventricular Wall Segments
Authors: Horowitz A. , Sheinman I. , Lanir Y.
Published: June 2009

A three dimensional incompressible and geometrically as well as materially nonlinear finite element is formulated for future implementation in models of cardiac mechanics. The stress-strain relations in the finite element are derived from a recently proposed constitutive law which is based on the histological composition of the myocardium. The finite element is formulated for large deformations and considers incompressibility by introducing the hydrostatic pressure as an additional variable. The results of passive loading cases simulated by this element allow to analyze the mechanical properties of ventricular wall segments, the main of which are that the circumferential direction is stiffer than the longitudinal one, that its shear stiffness is considerably lower than its tensile and compressive stiffness, and that, due to its mechanically prominent role, the collagenous matrix may affect the myocardial perfusion.
Zero-Stress States of Arteries
Authors: Liu S. Q. , Fung Y. C.
Published: June 2009

The no-load configuration of a living organ is, in general, not the zero-stress state. The difference can be revealed by cutting up an unloaded organ to such an extent that the stress becomes zero in the tissue everywhere. For the aorta, it is shown that the configuration of the zero-stress state differs considerably from being a cylindrical tube. It is, in fact, an open sector with opening angles varying along the arterial tree. This article presents data on the zero-stress state in the arteries of the rat in normal condition.
A New Method of Measuring the Cross-Sectional Area of Connective Tissue Structures
Authors: Shrive N. G. , Lam T. C. , Damson E. , Frank C. B.
Published: June 2009

There appears to be no generally accepted method of measuring in-situ the cross-sectional area of connective tissues, particularly small ones, before mechanical testing. An instrument has therefore been devised to measure the cross-sectional area of one such tissue, the rabbit medial collateral ligament, directly and nondestructively. However, the methodology is general and could be applied to other tissues with appropriate changes in detail. The concept employed in the instrument is to measure the thickness of the tissue as a function of position along the width of the tissue. The plot obtained of thickness versus width position is integrated to provide the cross-sectional area. This area is accurate to within 5 percent, depending mainly on alignment of the instrument and pre-load of the ligament. Results on the mid-substance of the rabbit medial collateral ligaments are repeatable and reproducible. Values of maximum width and thickness are less variable than those obtained with a vernier caliper. The measured area is considerably less than that estimated assuming rectangular cross-section and slightly less than that estimated on the assumption of elliptical cross-section.
A New Method for Determining Cross-Sectional Shape and Area of Soft Tissues
Authors: Lee Thay Q. , Woo Savio L-Y.
Published: June 2009

Assessment of the mechanical properties of soft tissues requires accurate measurement of the cross-sectional area. To date, techniques for determining cross-sectional areas of ligaments and tendons have been less than ideal due to the tissues’ complex geometries and the fact that they deform easily under an applied external load. A new procedure has been developed for determining the cross-sectional area by means of an image reconstruction technique based on measurements from collimated laser beams. Using this procedure, the actual shape of the specimen cross-section can also be determined. The results are demonstrated to be highly accurate, and this methodology does not require mechanical contact with the specimen.
An In-Vivo Measurement and Analysis of Viscoelastic Properties of the Spinal Cord of Cats
Authors: Chang Guan-Liang , Hung Tin-Kan , Feng William W.
Published: June 2009

An in-vivo experimental technique was employed to determine the linear and nonlinear characteristics of viscoelastic properties of the spinal cord of anesthetized cats. The stress relaxation and recovery curves were reproducible in a group of cat experiments. The data of linear viscoelastic properties were used to develop a power law model with Boltzmann’s convolution integral. The model was capable of predicting a prolonged stress relaxation and recovery curve. For larger deformation, the results were quantified using a nonlinear analysis of viscoelastic response of the spinal cord under the uniaxial experiment.
Influence of Cardiac Flow Rate on Turbulent Shear Stress from a Prosthetic Heart Valve
Authors: Schwarz A. C. , Tiederman W. G. , Phillips W. M.
Published: June 2009

Elevated turbulent shear stresses associated with sufficient exposure times are potentially damaging to blood constituents. Since these conditions can be induced by mechanical heart valves, the objectives of this study were to locate the maximum turbulent shear stress in both space and time and to determine how the maximum turbulent shear stress depends on the cardiac flow rate in a pulsatile flow downstream of a tilting disk valve. Two-component, simultaneous, correlated laser velocimeter measurements were recorded at four different axial locations and three different flow rates in a straight tube model of the aorta. All velocity data were ensemble averaged within a 15 ms time window located at approximately peak systolic flow over more than 300 cycles. Shear stresses as high as 992 dynes/cm2 were found 0.92 tube diameters downstream of the monostrut, disk valve. The maximum turbulent shear stress was found to scale with flow rate to the 0.72 power. A repeatable starting vortex was shed from the disk at the beginning of each cycle.
LDA Measurements and Numerical Prediction of Pulsatile Laminar Flow in a Plane 90-Degree Bifurcation
Authors: Khodadadi J. M. , Vlachos N. S. , Liepsch D. , Moravec S.
Published: June 2009

An experimental and numerical study of pulsatile laminar flow in a plane 90-degree bifurcation is presented. Detailed LDA velocity measurements of the oscillatory flow field have been carried out. The numerical predictions, which are based on an iterative, finite-difference numerical procedure using primitive dependent variables, are in good agreement with the measurements. The results show that one separation zone is established near the bottom wall of the main duct and another near the upstream wall of the branch. The location and size of the separation zones vary within the cycle and are influenced by the Reynolds number, the flow rate ratio, and the Stokes number.
Respiratory Effect on the Blood Volume of Pulmonary Capillaries
Authors: Lee Jen-shih , Fallon Timothy , Hunter Margaret , Ye Qiang , Lee Lian-pin
Published: June 2009

We measured the density variations of aortic blood from rabbits ventilated by a positive end inspiratory pressure of 6 mmHg or a negative box pressure of the same magnitude. When calculated from the density variations, the fluctuations in blood volume of the pulmonary capillaries within one cycle as induced by an intermittent positive pressure ventilation were found to be similar to the ones induced by an intermittent negative pressure ventilation. Using these volumetric fluctuations as a means to assess the transpulmonary pressure and the transmural pressure across the pulmonary capillaries, we conclude that the switching of the ventilation method did not alter the cyclic fluctuations of these pressures.
The Influence of Red Cell Mechanical Properties on Flow Through Single Capillary-Sized Pores
Authors: Frank R. S. , Hochmuth R. M.
Published: June 2009

The resistive pulse technique was used to study the influence of specific mechanical properties of the red cell on its ability to enter and flow through single capillary-sized pores with diameters of 3.6, 5.0 and 6.3 μm and lengths of 11 μm. A two-fold increase in membrane shear elasticity resulted in a 40 percent increase in the cell’s transit time through a 3.6 μm pore but produced no change in transit time through a 6.3 μm pore. A two-fold increase in membrane shear viscosity produced a 40 percent increase in transit time through the 3.6 μm pore and small but significant increases in transit times through the larger pores. Osmotically dehydrated cells showed no increase in transit time through a 6.3 μm pore, but showed increases in transit times of 50 to 70 percent through 5.0 and 3.6 μm pores. Dense red cells showed increased transit times through both 5.0 μm and 6.0 μm pores. These results indicate that for cells with normal geometric properties, the membrane’s shear viscosity and elasticity only influence the cell’s transit through pores of 5 μm or less in diameter. However, alterations in the cell’s geometric properties can extend the influence of membrane shear properties to larger diameter pores.
Noninvasive Determination of Ulnar Stiffness From Mechanical Response—In Vivo Comparison of Stiffness and Bone Mineral Content in Humans
Authors: Steele C. R. , Zhou L.-J. , Guido D. , Marcus R. , Heinrichs W. L. , Cheema C.
Published: June 2009

An approach referred to as Mechanical Response Tissue Analysis (MRTA) has been developed for the noninvasive determination of mechanical properties of the constituents of the intact limb. Of specific interest in the present study is the bending stiffness of the ulna. The point mechanical impedance properties in the low frequency regime, between 60 and 1,600 Hz are used. The procedure requires a proper design of the probe for good contact of the skin at midshaft and proper support of the proximal and distal ends of the forearm to obtain an approximation to “simple support” of the ulna. A seven-parameter model for the mechanical response is then valid, which includes the first mode of anterior-posterior beam bending of the ulna, the damping and spring effect of the soft tissue between probe and bone, and the damping of musculature. A dynamic analyzer (HP3562A) provides in seconds the impedance curve and the pole-zero curve fit. The physical parameters are obtained from a closed-form solution in terms of the curve-fit parameters. The procedure is automated and is robust and analytically reliable at about the five percent level. Some 80 human subjects have been evaluated by this mechanical response system and by the Norland single photon absorptiometer, providing for the first time in vivo, a comparison of elastic bending stiffness (ulna) and bone mineral content (radius). Three functional parameters of potential clinical value are the cross-sectional bending stiffness EI, the axial load capability Pcr (Euler buckling load) and the bone “sufficiency” S, defined as the ratio of Pcr to body weight. The correlation between EI and bone mineral (r = 0.81) is only slightly less than previous in vitro results with both measurements on the same bone (r = 0.89). When sufficiency is taken into consideration, the correlation of Pcr and bone mineral content is improved (r = 0.89). An implication is that “quality” of bone is a factor which is not indicated by bone mineral content but which is indicated by stiffness. Bone mineral is necessary for proper stiffness but not sufficient. Therefore mechanical measurement should provide a new dimension to be used toward a better understanding of the factors related to bone health and disease.
The Mechanical Role of the Trunk and Lower Extremities in a Seated Weight-Moving Task in the Sagittal Plane
Authors: Son K. , Miller J. A. A. , Schultz A. B.
Published: June 2009

A two-dimensional, sagittally-symmetric biomechanical model was developed to analyze the joint moments required to stabilize the trunk in a seated, dynamic, weight-moving task. Kinematic and reaction force data were measured while subjects moved a hand-held weight (0–4 kgf) at shoulder level to and fro at 1 Hz. These data were then used for model input and validation purposes. A second, simpler model was used to simulate how joint loads varied with weight held, trunk inclination, and movement frequency. The results for this seated task demonstrate a) significant trunk, hip, knee, and ankle joint moments (37, 13, 4, 13 percent of maximum strength values, respectively) were required, b) considerable intersubject differences in mean joint moments (more than 66 percent) were found, which primarily were due to subtle differences in body segment kinematics and lower extremities use, and c) the important role of the lower extremities in stabilizing the trunk in the seated posture.
Measurement of Wall Shear Stress Distal to a Tri-Leaflet Valve in a Rigid Model of the Aortic Arch With Branch Flows
Authors: Nandy S. , Tarbell J. M.
Published: June 2009

Flush mounted hot film anemometer probes were used to measure wall shear stress magnitudes on the inside and outside walls of a rigid model of the human aortic arch. The effects of the presence of an Ionescu-Shiley tri-leaflet bioprosthetic heart valve at the entrance of the aortic arch and the side flows through arteries located in the mid-arch region on wall shear stress magnitudes were determined. It was found that the presence of the tri-leaflet valve leads to an elevation of wall shear stress (relative to the same flow without a valve) over the entire aortic arch region by as much as 50 percent. The valve influence extended to about 180 deg from the entrance to the aorta on the inside wall and even further on the outside wall based on extrapolation of available data. Peak wall shear stress magnitudes measured on the outside wall were in the range of 1.5—4.0 N/m2 (15—40 dynes/cm2) over the length of the aortic arch and took on their highest values in the mid-arch region. Inside wall values were of comparable magnitude. It was observed that the presence of the aortic valve and side flow from the top of the aortic arch reduced wall shear stress reversal in the arch region.
A Model for the Nonlinear Elastic Response of Large Arteries
Authors: Elad D. , Foux A. , Kivity Y.
Published: June 2009

The nonlinear elastic response of large arteries subjected to finite deformations due to action of biaxial principal stresses, is described by simple constitutive equations. Generalized measures of strain and stress are introduced to account for material nonlinearity. This also ensures the existence of a strain energy density function. The orthotropic elastic response is described via quasi-linear relations between strains and stresses. One nonlinear parameter which defines the measures of strain and stress, and three elastic moduli are assumed to be constants. The lateral strain parameters (equivalent to Poisson’s ratios in infinitesimal deformations) are deformation dependent. This dependence is defined by empirical relations developed via the incompressibility condition, and by the introduction of a fifth material parameter. The resulting constitutive model compares well with biaxial experimental data of canine carotid arteries.
The Application of a Homogeneous Half-Space Model in the Analysis of Endothelial Cell Micropipette Measurements
Authors: Theret D. P. , Levesque M. J. , Sato M. , Nerem R. M. , Wheeler L. T.
Published: June 2009

Experimental studies have shown that endothelial cells which have been exposed to shear stress maintain a flattened and elongated shape after detachment. Their mechanical properties, which are studied using the micropipette experiments, are influenced by the level as well as the duration of the shear stress. In the present paper, we analyze these mechanical properties with the aid of two mathematical models suggested by the micropipette technique and by the geometry peculiar to these cells in their detached post-exposure state. The two models differ in their treatment of the contact zone between the cell and the micropipette. The main results are expressions for an effective Young’s modulus for the cells, which are used in conjunction with the micropipette data to determine an effective Young’s modulus for bovine endothelial cells, and to discuss the dependence of this modulus upon exposure to shear stress.
Structural Three-Dimensional Constitutive Law for the Passive Myocardium
Authors: Horowitz A. , Lanir Y. , Yin F. C. P. , Perl M. , Sheinman I. , Strumpf R. K.
Published: June 2009

A three-dimensional constitutive law is proposed for the myocardium. Its formulation is based on a structural approach in which the total strain energy of the tissue is the sum of the strain energies of its constituents: the muscle fibers, the collagen fibers and the fluid matrix which embeds them. The ensuing material law expresses the specific structural and mechanical properties of the tissue, namely, the spatial orientation of the comprising fibers, their waviness in the unstressed state and their stress-strain behavior when stretched. Having assumed specific functional forms for the distribution of the fibers spatial orientation and waviness, the results of biaxial mechanical tests serve for the estimation of the material constants appearing in the constitutive equations. A very good fit is obtained between the measured and the calculated stresses, indicating the suitability of the proposed model for describing the mechanical behavior of the passive myocardium. Moreover, the results provide general conclusions concerning the structural basis for the tissue overall mechanical properties, the main of which is that the collagen matrix, though comprising a relatively small fraction of the whole tissue volume, is the dominant component accounting for its stiffness.