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PubMed2002

Effect of airway inflation pressure on forced expiratory maneuvers from raised lung volume in infants.

The raised lung volume technique is increasingly used to measure forced expiratory maneuvers in infants. However, there is no consensus regarding the optimal airway inflation pressure (P(inf)) required for such maneuvers, or the influence of small changes in P(inf) within and between infants. The aim of this study was to assess the effect of small differences (0.2-0.3 kPa) in P(inf) on forced vital capacity (FVC), forced expired volume in 0.5 sec (FEV(0.5)), and forced expired flow at 75% of vital capacity (FEF(75)), all derived from the raised volume rapid thoraco-abdominal compression (RVRTC) technique. Randomized paired forced expiratory maneuvers were obtained in 32 healthy infants ( 3.9-39.3 weeks old, 3.8-9.9 kg) with the safety pressure relief valve for P(inf) set to 2.7 kPa or 3.0 kPa (27 or 30 cm H(2)0). When mean (SD) P(inf) was increased by 8.4 (2.8)%, there was a significant (P < 0.01) increase in mean (SD) FVC, FEV(0.5), and FEF(75) by 5.8 (5.7)%, 6.1 (6)%, and 8.3 (16.2)%, respectively. In conclusion, relatively small differences in P(inf) will result in significant differences in FVC, FEV(0.5), and FEF(75) by RVRTC technique. Precision in setting and reporting the applied P(inf) is therefore essential, particularly if data are to be compared between centers.

Female↗

PubMed2004

Delayed and non-union of the humeral diaphysis--compression plate or internal plate fixator?

In a retrospective study, two groups of patients with delayed or non-union of the humeral diaphysis were compared. In group A, a 4.5-mm low-contact dynamic compression plate (LCDCP) was used for internal fixation and in group B, an internal plate fixator with locked screws was used. In all patients autologous bone grafting was performed. Group A consisted of 14 patients (mean age 38.9 years) and group B consisted of 19 patients (mean age 54.3 years). The mean duration of the delayed or non-union was 9.3 months (range 3-26 months) in group A and 24.8 months (range 3-216 months) in group B. In group A an average of 1.1 (range 0-2) previous operations had been performed, and in group B an average of 1.6 (range 0-4). One primary nerve palsy was diagnosed in group A and six in group B. Although the patients of group B were older, had longer-lasting non-unions, more previous operations and more severe initial injuries, only in group A was there a hardware failure due to osteoporosis which required re-osteosynthesis. All other patients showed bony consolidation without further operations. The LCDCP and the internal plate fixator both showed high consolidation rates, but we feel that the internal plate fixator may be the more reliable implant, especially in patients with poor bone stock.

Adolescent↗

PubMed2003

Management of neuropathy and foot problems in diabetic patients.

Diabetic neuropathy (DN) is a complex set of clinical syndromes that affect distinct regions of the nervous system, either singly or combined. DN is the most common form of neuropathy in the developed countries of the world and is responsible for 50% to 75% of nontraumatic amputations. It is also the most life damaging--once autonomic neuropathy sets in, the mortality rate approximates 25% to 50% within 5 to 10 years. Distal symmetric polyneuropathy, the most common form of DN, usually involves both small and large nerve fiber damage. Small nerve fiber neuropathies occur early and are often present without objective signs or electrophysiologic evidence of nerve damage. The greatest risk is foot ulceration and subsequent gangrene. Large nerve fiber neuropathies, which involve the sensory and motor nerves, are generally neuropathies of signs rather than symptoms. Clinical presentation usually includes a "glove and stocking" distribution of sensory loss and the greatest risk is Charcot's neuroarthropathy. Diagnosis of DN relies heavily on a careful patient history and physical examination. Most critical is that both the patient and the patient's shoes should be examined and corrective measures taken. Several studies have shown that good diabetes control can significantly reduce neuropathy. As new drugs and ways to enhance nerve blood flow and block pain pathways at different levels are being explored, the effective treatment of DN and the reduction of its impact on quality of life as well as mortality will become a reality. Patient education and preventive strategies, however, are still the best ways to treat the complications of neuropathy and reduce the amputation rate.

Amputation, Surgical↗

PubMed1988

Life-sustaining treatment. A prospective study of patients with DNR orders in a teaching hospital.

We conducted a prospective survey of attending, resident, and intern physicians who had written a "do not resuscitate" (DNR) order for 93 patients in their care. After writing a DNR order, 11% of respondents would still use chest compression if their patient experienced a cardiopulmonary arrest. Many physicians did not plan to withdraw therapy except intensive care, but most physicians planned to withhold a spectrum of life-sustaining therapies, from hemodialysis (86%) to intravenous fluids (21%). Attending and house-staff physicians generally agreed on whether to withdraw a given therapy or not but frequently disagreed on whether to withhold a therapy or not. After patient discharge or death, 88 charts were reviewed. None of the 88 patients was coded. Physicians initiated 68 life sustaining therapies in 43 patients and discontinued 64 therapies in 34 patients; there was no change in management in 31 patients. We conclude that individual physicians interpret the DNR order differently. These orders often are associated with the discontinuation or noninitiation of life-sustaining therapies other than emergency CPR.

Adult↗

PubMed2002

Exploring the relationship between forced maximal flow at functional residual capacity and parameters of forced expiration from raised lung volume in healthy infants.

The raised volume rapid thoraco-abdominal compression technique (RVRTC) is being increasingly used to assess airway function in infants, but as yet no consensus exists regarding the equipment, methods, or analysis of recorded data. The aim of this study was to explore the relationship between maximal flow at functional residual capacity (V'(maxFRC)) and parameters derived from raised lung volumes, and to address analytical aspects of the latter technique in an attempt to assist with future standardization initiatives. Forced vital capacity (FVC) from lung volume raised to 3 kPa, timed forced expiratory volumes (FEV(t)), and forced expiratory flow parameters at different percentages of expired FVC (FEF(%)) were measured in 98 healthy infants (1-69 weeks of age). V'(maxFRC) using the tidal rapid thoraco-abdominal compression (RTC) technique was also measured. The within-subject relationships and within-subject variability of the various parameters were assessed. Duration of forced expiration was < 0.5 sec in 5 infants, meaning that FEV(0.3) and FEV(0.4) were the only timed volume parameters that could be calculated in all infants during the first months of life, and even when it could be calculated, FEV(0.5) approached FVC in many of these infants. It is recommended that FEV(0.4) be routinely reported in infants less than 3 months of age. Contrary to previous reports, within subject variability of V'(maxFRC) was less than that of FEF(75) (mean CV = 6.3% and 8.9%, respectively).A more standardized protocol when analyzing data from the RVRTC would facilitate comparisons of results between centers in the future.

Crown-Rump Length↗

PubMed1994

An in vitro study of proximal femoral allograft strains in revision hip arthroplasty.

Bone allografts are used frequently to replace bone stock subsequent to total hip arthroplasty. Revision of the failed hip replacement results in a complex structure of allograft bone, host bone and a metal femoral component. To evaluate the mechanics of the allograft-implant-host bone structure at the time of surgery, a strain gauge study was undertaken with six fresh/frozen human femora. Under defined loading conditions, cortical strain distributions were measured for five different cases: (1) normal bone, (2) bone with a femoral implant, (3) bone with the femoral component and an osteotomy at the mid-stem level of the implant (i.e. to stimulate the proximal allograft-host junction around the femoral stem), (4) bone with an osteotomy and an implant cemented into the 'allograft' (i.e. the proximal end of the femur), and (5) bone with an osteotomy and the implant cemented into both the proximal 'allograft' and the distal host bone. The results showed that, prior to making the osteotomy, proximal femoral strains were decreased with the insertion of a femoral stem. These strains were further decreased when an osteotomy had been made. This strain distribution did not change when the stem was cemented into the proximal 'allograft' bone, or cemented into the proximal 'allograft' and distal host bone. The decreases in strain for these test cases implied that the discontinuity between the bony segments caused an extended reduction in the tensile or compressive stresses transmitted through the cortices.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Transplantation↗

PubMed1998

In vitro simulation of contact fatigue damage found in ultra-high molecular weight polyethylene components of knee prostheses.

An in vitro simulation of fatigue loading of ultra-high molecular weight polyethylene (UHMWPE) knee components was carried out on a knee simulator and on a rolling and sliding wear tester. Tibial components for the knee simulator were gamma-sterilized, implantable components taken from manufacturing inventory. The rolling/sliding UHMWPE discs were machined from bar stock and either gamma sterilized in air and accelerated aged, or left as non-sterilized (controls). Cracking and delamination of samples that had been gamma sterilized in air and aged were observed in both types of tests. Contact fatigue damage was visible in as few as 150,000 cycles using the knee simulator at loads of 122 N (275 1b). The rolling/sliding samples showed signs of damage in as few as 130,000 cycles with an estimated stress of 15 MPa and 25 per cent sliding. However, cracking and delamination were not generated in the never-sterilized or recently sterilized controls. UHMWPE that has been gamma sterilized in air and aged is shown to be susceptible to contact fatigue damage. These results are important to the interpretation of in vitro total knee replacement simulations used to assess the performance of tibial bearings.

Compressive Strength↗

PubMed2006

[Fence grafting for acetabular reconstruction with a cementless cup].

Acetabular reconstruction is difficult after loss of bone stock and socket remodeling. Several techniques have been proposed ranging from a metal backing to allografting. We propose fence grafting. After explantation, the acetabulum is carefully cleaned of all interface tissue and precisely measured. If the vertical diameter is clearly greater than the anteroposterior diameter, a tricortical graft is harvested from the iliac crest and modeled to perfectly fit between the anterioinferior iliac spine and the residual posterior wall as well as the fundus medially. One or two oblique screws are inserted for stabilization. Any superior bone loss is filled by bone substitute (without mechanical value). The acetabulum is then reamed from the obturator foramen sparing the anterior and posterior columns. Residual bony defects are filled with cancellous bone. A hemispheric cup is then press fit and maintained with two or three screws. We performed this procedure in eight patients with SO.F.C.O.T. stage III acetabular loosening with segmentary bone loss and an oval acetabular cavity. Clinical follow-up was more than four years. The Postel-Merle-d'Aubigné score improved from 9.8 to 15.7 on average. Radiographically, there were no implant mobilization or migration and no circumferential lucent lines were observed. A nearly anatomic position was achieved in all cases except two (technical imperfection). At more than one-year follow-up, the grafts could not be distinguished from adjacent bone. For us, high-positioned or jumbo cups do not offer a satisfactory reconstruction option. There is a risk of compression with allografts from a head bank. We have not used the cemented metal-backed solution nor impacted grafts. The major drawback with fence grafting is the iliac harvesting (possible residual limping because of the extensive disinsertion of the gluteus medius. The reliable acetabular reconstruction is the major advantage. This technique is not simply an acetabular block widened laterally but it decreases the vertical dimension. This is a reliable but minute technique which allows true long-lasting reconstruction of the acetabulum.

Adult↗

PubMed2005

The use of pressure change on standing as a surrogate measure of the stiffness of a compression bandage.

OBJECTIVES: To measure interface pressure and stiffness of short-stretch and long-stretch bandages applied with variable strength. These parameters have a deciding influence on the efficacy of compression therapy in chronic venous disease. DESIGN: Prospective experimental study. MATERIALS AND METHODS: Compression bandages constructed of different materials were applied with light, moderate and high pressure. Interface pressure was measured over the medial aspect of leg in 12 healthy individuals. Long-stretch bandages were compared to short-stretch bandages. The difference between standing and supine pressure was used to characterise stiffness. RESULTS: In the low pressure range the median pressure of the final bandage in the supine position was between 18 and 30 mmHg for the long-stretch and 25-33.5 mmHg for the short-stretch bandages (p<0.01, Mann-Whitney U-test). The median differences between standing and supine pressure were between 2.0 and 8.5 for the long-stretch and 6.0-10.5 mmHg for the short-stretch material. In the group of moderate pressure the median values in the supine position were in a range 33.0-58.0 mmHg, for long-stretch and 39.0-49.5 mmHg for short-stretch bandages, with an increase after standing of 6.0-7.0 mmHg with long-stretch, and 14.0-21.0 mmHg with short-stretch bandages (p<0.01, Mann-Whitney U-test). The median supine pressure values in the high pressure group were between 52.0 and 67.0 mmHg for long-stretch and 59.5-67.0 mmHg for short-stretch material. The median increase during standing ranged between 8.5 and 14.5 mmHg in the elastic group and 23.0-33.0 in the inelastic group (p<0.01, Mann-Whitney U-test). CONCLUSION: A bandage applied with light pressure corresponds to the moderate pressure category of stockings. The difference between the sub-bandage pressure from supine to standing can be used to characterise the stiffness of a bandage.

Adult↗

PubMed2006

Augmentation of osteoporotic bone: effect of pulsed jet-lavage on injection forces, cement distribution, and push-out strength of implants.

Demographic change in the population leads to higher incidence of fragility fractures. Fracture fixation with standard implants may lead to implant cut-out due to reduced purchase. Augmentation of the bone stock with bone cements might overcome this problem. However, cancellous bone infiltration with the viscous cement dough reveals problems of fat embolism or high pressures during application of the cement. This study investigates the improved quality of bovine cancellous bone augmentation when pulsed jet-lavage is used for fat and marrow removal. Parameters such as injection forces, cement dough distribution through cannulated implants and mechanical strength of the fixation were applied for quantification. Injection of 5 mL of acrylic bone cement required significantly lower forces in the lavaged as compared to the untreated bone (50 N vs. > 300 N). Cement distribution was much more homogeneous and push-out forces significantly higher in the pretreated bone group (8.33 +/- 1.41 kN vs. 1.66 +/- 0.63 kN). The application of pulsed jet-lavage for fat removal prior to acrylic cement augmentation led to much more controlled outcomes of the augmentation. This seems to be a relevant step towards safe and efficient injection of bone cements into cancellous bone structures.

Bone Cements↗

PubMed2001

Influence of jacket placement on respiratory compliance during raised lung volume measurements in infants.

SUMMARY. Recent introduction of the raised lung volume rapid thoraco-abdominal compression (RVRTC) technique for measuring forced expiratory maneuvers in infants provides the potential opportunity to assess respiratory mechanics simultaneously by using multiple linear regression (MLR) of the relaxed breaths preceding jacket inflation to force expiration. This study was undertaken to investigate whether data obtained from raised lung volume are influenced by placement of the rapid thoraco-abdominal compression (RTC) squeeze jacket. Paired measurements of tidal volume (V(T)) and respiratory rate (RR) during tidal breathing, and of inflation volume (V(inf)), respiratory system compliance (C(rs)), and resistance (R(rs)) during passive lung inflations were made in 60 (30 male) healthy term infants with and without a fastened, but uninflated RTC jacket in place. Jacket placement was associated with a significant reduction (P < 0.0001) in weight-corrected V(inf) [-1.86 (95% confidence interval, -2.46, -1.27) mL.kg(-1)] and C(rs) [-0.77 (-1.04, -0.49) mL.kPa(-1).kg(-1)]. This represented a reduction in weight-corrected C(rs) from 9.00 to 8.24 mL.kPa(-1).kg(-1), with the fall being >10% in 42% of infants studied. There was no significant change in R(rs) or weight-corrected V(T). If passive respiratory mechanics are to be measured during raised lung volume maneuvers, they should be performed prior to the jacket being fastened, unless considerable care is taken with each infant to ensure that the jacket does not restrict chest wall movement during maximum inflation.

Airway Resistance↗

PubMed2007

The biomechanics of human femurs in axial and torsional loading: comparison of finite element analysis, human cadaveric femurs, and synthetic femurs.

To assess the performance of femoral orthopedic implants, they are often attached to cadaveric femurs, and biomechanical testing is performed. To identify areas of high stress, stress shielding, and to facilitate implant redesign, these tests are often accompanied by finite element (FE) models of the bone/implant system. However, cadaveric bone suffers from wide specimen to specimen variability both in terms of bone geometry and mechanical properties, making it virtually impossible for experimental results to be reproduced. An alternative approach is to utilize synthetic femurs of standardized geometry, having material behavior approximating that of human bone, but with very small specimen to specimen variability. This approach allows for repeatable experimental results and a standard geometry for use in accompanying FE models. While the synthetic bones appear to be of appropriate geometry to simulate bone mechanical behavior, it has not, however, been established what bone quality they most resemble, i.e., osteoporotic or osteopenic versus healthy bone. Furthermore, it is also of interest to determine whether FE models of synthetic bones, with appropriate adjustments in input material properties or geometric size, could be used to simulate the mechanical behavior of a wider range of bone quality and size. To shed light on these questions, the axial and torsional stiffness of cadaveric femurs were compared to those measured on synthetic femurs. A FE model, previously validated by the authors to represent the geometry of a synthetic femur, was then used with a range of input material properties and change in geometric size, to establish whether cadaveric results could be simulated. Axial and torsional stiffnesses and rigidities were measured for 25 human cadaveric femurs (simulating poor bone stock) and three synthetic "third generation composite" femurs (3GCF) (simulating normal healthy bone stock) in the midstance orientation. The measured results were compared, under identical loading conditions, to those predicted by a previously validated three-dimensional finite element model of the 3GCF at a variety of Young's modulus values. A smaller FE model of the 3GCF was also created to examine the effects of a simple change in bone size. The 3GCF was found to be significantly stiffer (2.3 times in torsional loading, 1.7 times in axial loading) than the presently utilized cadaveric samples. Nevertheless, the FE model was able to successfully simulate both the behavior of the 3GCF, and a wide range of cadaveric bone data scatter by an appropriate adjustment of Young's modulus or geometric size. The synthetic femur had a significantly higher stiffness than the cadaveric bone samples. The finite element model provided a good estimate of upper and lower bounds for the axial and torsional stiffness of human femurs because it was effective at reproducing the geometric properties of a femur. Cadaveric bone experiments can be used to calibrate FE models' input material properties so that bones of varying quality can be simulated.

Aged↗

PubMed2006

Lung function tests in neonates and infants with chronic lung disease: forced expiratory maneuvers.

This fourth paper in a review series on the role of lung function testing in infants and young children with acute neonatal disorders and chronic lung disease of infancy (CLDI) addresses measurements of forced expiration using rapid thoraco-abdominal compression (RTC) techniques and the forced deflation technique. Following orientation of the reader to the subject area, we focus our comments on the areas of inquiry proposed in the introductory paper to this series. The quality of the published literature is reviewed critically, and recommendations are provided to guide future investigation in this field. All studies on infants and young children with CLDI using forced expiratory or deflation maneuvers demonstrated that forced flows at low lung volume remain persistently low through the first 3 years of life. Measurement of maximal flow at functional residual capacity (V'maxFRC) is the most commonly used method for assessing airway function in infants, but is highly dependent on lung volume and airway tone. Recent studies suggested that the raised volume RTC technique, which assesses lung function over an extended volume range as in older children, may be a more sensitive means of discriminating changes in airway function in infants with respiratory disease. The forced deflation technique allows investigation of pulmonary function during the early development of CLDI in intubated subjects, but its invasive nature precludes its use in the routine setting. For all techniques, there is an urgent need to establish suitable reference data and evaluate within- and between-occasion repeatability, prior to establishing the clinical usefulness of these techniques in assessing baseline airway function and/or response to interventions in subjects with CLDI.

Airway Resistance↗

PubMed2002

Relative ability of full and partial forced expiratory maneuvers to identify diminished airway function in infants with cystic fibrosis.

The tidal and raised volume rapid thoracoabdominal compression techniques are increasingly used to detect diminished airway function in infancy. The aim of this study was to assess the relative ability of parameters measured by these techniques to identify diminished airway function in infants newly diagnosed with cystic fibrosis (CF) with and without clinical evidence of prior lower respiratory illness. A cross-sectional, prospective study design was used in which maximal flow at functional residual capacity (VmaxFRC) from the tidal technique and FVC, FEV0.5, FEF75, and FEF25-75 from the raised volume technique were measured in 47 infants with CF and 187 healthy infants of similar body size, sex distribution, ethnic group, and exposure to maternal smoking. Multiple linear regression was used to assess group differences and to calculate SD scores for each parameter for the infants with CF. Airway function was also compared with clinical assessments of respiratory status made by pediatric pulmonologists. FEV0.5 was significantly diminished in 13 infants with CF, of whom 4 had been identified by clinicians as having normal respiratory status. Only one infant with CF had a VmaxFRC below the estimated normal range. Airway function is diminished in infants with CF irrespective of prior lower respiratory illness and in those whose respiratory status is considered normal by pediatric pulmonologists. In infants with CF, the raised volume technique identified diminished airway function more frequently than the tidal technique.

Age Factors↗

PubMed2003

Cancellous and cortical morselized allograft in revision total hip replacement: A biomechanical study of implant stability.

To restore femoral intramedullary bone stock loss in revision surgery of failed total hip arthroplasties, impacted morselized cancellous allograft is recommended. This study investigated the mechanical properties of both impacted cortical (group A) and cancellous (group B) morselized bone graft for reconstruction of femoral bones. Ten matched pairs of fresh frozen human femora were prepared by over-reaming to create a smooth-walled cortical shell. Each pair had one cortical and one cancellous impacted morselized allograft and cement. Stem subsidence was evaluated by a cyclic axial load, which was applied by a servohydraulic test. The stem subsidence was measured for initial subsidence (subsidence at the first 1000 cycles), the total axial subsidence (subsidence at the end of cycles under load) and the final axial subsidence (subsidence after the unloading phase). Torque test was measured by torsional loads through the prosthetic femoral heads. Total axial subsidence was significantly higher in group B (mean: 1.32+/-0.32 mm) compared to group A (mean: 0.94+/-0.26 mm) (P<0.01). There was no significant difference between the two groups in terms of initial subsidence (P=0.09) and final axial subsidence. The mean maximum torque before failure was 39.5+/-22.2 N-m for the cortical morselized allograft and 32.5+/-18.1N-m for cancellous. We concluded that impacted morselized cortical bone graft used for reconstruction of contained femoral bone loss in revision hip arthroplasty, may reduce the stem subsidence. Further animal experimentation for mechanical and histological evaluation of in vivo application is warranted.

Arthroplasty, Replacement, Hip↗

PubMed2006

Early detection of cystic fibrosis lung disease: multiple-breath washout versus raised volume tests.

BACKGROUND: Lung clearance index (LCI), a measure of ventilation inhomogeneity derived from the multiple-breath inert gas washout (MBW) technique, has been shown to detect abnormal lung function more readily than spirometry in preschool children with cystic fibrosis, but whether this holds true during infancy is unknown. OBJECTIVES: To compare the extent to which parameters derived from the MBW and the raised lung volume rapid thoraco-abdominal compression (RVRTC) techniques identify diminished airway function in infants with cystic fibrosis when compared with healthy controls. METHODS: Measurements were performed during quiet sleep, with the tidal breathing MBW technique being performed before the forced expiratory manoeuvres. RESULTS: Measurements were obtained in 39 infants with cystic fibrosis (mean (SD) age 41.4 (22.0) weeks) and 21 controls (37.0 (15.1) weeks). Infants with cystic fibrosis had a significantly higher respiratory rate (38 (10) vs 32 (5) bpm) and LCI (8.4 (1.5) vs 7.2 (0.3)), and significantly lower values for all forced expiratory flow-volume parameters compared with controls. Girls with cystic fibrosis had significantly lower forced expiratory volume (FEV(0.5) and FEF(25-75 )) than boys (mean (95% CI girls-boys): -1.2 (-2.1 to -0.3) for FEV(0.5) Z score; FEF(25-75): -1.2 (-2.2 to -0.15)). When using both the MBW and RVRTC techniques, abnormalities were detected in 72% of the infants with cystic fibrosis, with abnormalities detected in 41% using both techniques and a further 15% by each of the two tests performed. CONCLUSIONS: These findings support the view that inflammatory and/or structural changes in the airways of children with cystic fibrosis start early in life, and have important implications regarding early detection and interventions. Monitoring of early lung disease and functional status in infants and young children with cystic fibrosis may be enhanced by using both MBW and the RVRTC.

Area Under Curve↗

PubMed2002

Influence of jacket tightness and pressure on raised lung volume forced expiratory maneuvers in infants.

While the use of the raised volume rapid thoraco-abdominal compression (RVRTC) technique has been shown to provide new insights into airway and pulmonary pathophysiology in infants, and appears to resemble the spirometric techniques used in older subjects, there is as yet no consensus regarding measurement procedures, which are known to vary considerably between laboratories (Gappa [1999] Pediatr Pulmonol 28:391-393). The aims of this study were to assess the effects of tightness of jacket fit, the efficiency with which pressure is transmitted from the jacket to the intrathoracic airways, and the effect of jacket pressure on parameters derived from the RVRTC technique. Paired forced expiratory maneuvers were performed in 20 infants with the jacket snugly or loosely wrapped around the infant's torso, and in a further 21 infants using "optimal" or a higher jacket pressure (P(j)) (1-2 kPa above "optimal" P(j)). When either a loosened jacket or a higher than "optimal" P(j) was used, forced expired flow at low lung volumes (FEF(75)) was significantly reduced by, on average, 8% and 7%, respectively. There were, however, minimal changes in forced vital capacity (FVC) or forced expired volume in 0.4 sec (FEV(0.4)). The observed changes may have been due to the increased pressure transmitted to the intrathoracic structures under these experimental conditions, and emphasize the need to assess optimal jacket pressure within each infant when using the RVRTC technique. In addition, when using a loosened jacket or a higher than "optimal" P(j), chest wall and upper airway reflexes such as glottic closure, peripheral airway closure, and negative flow dependence were more evident.

Confidence Intervals↗

PubMed2003

Straining of the intact and fractured proximal humerus under physiological-like loading.

Surgical treatment of proximal humeral fractures remains challenging in elderly patients, primarily due to insufficient implant fixation. Both bone quality and physiological-like loading conditions are commonly overlooked during pre-clinical in vitro evaluation. However, this knowledge is necessary in order to improve surgical treatment of the proximal humerus and the mechanical behavior of implants, particularly in patients with complex fractures and weak bone stock. We hypothesize that the bone quality has a high influence on the bone straining, independent of the arm position. The goal of this study was to determine the straining of the intact and fractured proximal humerus under physiological-like loading conditions. Furthermore, the impact of augmentation on tissue straining was evaluated. Two representative humeri were selected for this study, one osteoporotic and one reference quality, and scanned using both QCT and DEXA (average DEXA value=0.26 and 0.49 g/cm2 respectively). Subcaptial defects were generated, then stabilized with a plate prior to mechanical stiffness testing. From the QCT data, finite element models were generated and the in vitro stiffness tests analytically simulated. Under physiological-like loading conditions, the straining of the bone and implant were analyzed for 0 degrees, 90 degrees forward flexion, and 90 degrees abduction. Maximal strain values were found for the intact and fractured bone at 90 degrees abduction. This study demonstrates that the straining in a fractured bone of poor quality leads to considerably higher bone strains (up to +30%) than in a more healthy bone. Augmentation of a central void under physiological-like loading with commercial cement led to mechanical failure at the bone-cement interface. New concepts for the surgical treatment of complex fractures of the proximal humerus should take bone distribution into account and thereby allow effective treatment of fractures in osteoporotic patients. The ultimate salvage procedure of augmentation has mechanical limitations as long as current cement materials are used in osteoporotic patients.

Activities of Daily Living↗