Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ELASTICITY”

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

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

At least 541 records · Page 30Linked to original sources
PubMed1996

Analysis of forces and moments in arch guided molar protraction using Class I and Class II elastics. An in-vitro study.

The use of class I and II elastics in arch guided tooth movement of the lower molars belongs to the proven clinical methods to achieve space closure even though risks are present. The vertical force component of class II elastics tends to interact with the sagittal force and thus the vertical force may change the desired sagittal force and movement direction. The objective of the study presented here was to investigate friction behavior and the movement dynamics of the arch guided protraction of the lower first molar being acted on by differing class I and class II elastic band geometries. The influence of class I and class II elastics at different force levels (1 N and 2 N) were studied. The pattern of the force line varied in the area of angulation from 0 degree to 40 degrees relative to the arch plane. The orthodontic measurement and simulation system (OMSS) was employed to determine force loss due to friction and to analyze side effects. In the arch guided mesialization of the lower first molar, the vertical component of class II elastics induces a minor force loss in comparison with class I elastics. This holds, however, only for the lower 1 N force level. When employing class II bands at a greater force level and with increased angulation, relatively greater force loss and increased side effects, such as extrusion and mesial tipping of the first molar, occur.

Biomechanical Phenomena↗
PubMed1993

The effect of repeated stretching on the force decay and compliance of vulcanized cis-polyisoprene orthodontic elastics.

Compliance measurements, used in the past to measure the viscoelastic properties of dental impression materials, were used to assess these properties in vulcanized cis-polyisoprene orthodontic elastics, and the results were compared with traditional force decay measurements. Both methods were also used to evaluate the effect of repeated stretching on these elastics. Compliance measurements successfully characterized the viscoelastic behavior of the elastics, and the results agreed with force decay measurements. Repeated stretching significantly reduced the force and the compliance of the elastics. There was no statistical difference in the force or compliance measurements after the elastics were stretched more than 200 times. Stretching for 1000 cycles of 400% extension reduced elastic force by approximately 12%.

Analysis of Variance↗
PubMed1993

Bolus intravenous nitroglycerin predominantly reduces afterload in patients with excessive arterial elastance.

OBJECTIVES: We hypothesized that bolus intravenous nitroglycerin would be an afterload-reducing agent in patients with excessive initial afterload for their level of left ventricular systolic function. Conversely, bolus intravenous nitroglycerin should be a preload-reducing agent in patients without excessive initial afterload. BACKGROUND: Although nitroglycerin has both preload- and afterload-reducing actions, methods to predict its predominant site of action in an individual patient have not been previously described. METHODS: Left ventricular pressure-volume relations were recorded with micromanometer and conductance catheters during bolus injection of intravenous nitroglycerin in 27 patients with both normal left ventricular systolic function and varying degrees of congestive heart failure. Preload was determined by end-diastolic volume, afterload by effective arterial elastance, left ventricular systolic function by end-systolic elastance and coupling of afterload and ventricular function by the ratio of effective arterial elastance to end-systolic elastance (Ea/Ees ratio). An Ea/Ees ratio > 1 was defined as excessive afterload for the level of ventricular function. RESULTS: Patients with an initial Ea/Ees ratio < 1 (Group 1) constituted a group of normotensive patients with intact ventricular function who exhibited a predominant reduction in preload in response to intravenous nitroglycerin. Those with an initial Ea/Ees ratio > 1 and normal or mildly depressed ventricular function (Group 2a) constituted a group of patients, most of whom were hypertensive, who exhibited a predominant afterload reduction. Finally, those with an initial Ea/Ees ratio > 1 and abnormal ventricular function (Group 2b) constituted a group of patients with clinical congestive heart failure who exhibited both preload and afterload reduction but a predominant afterload reduction because stroke volume increased. CONCLUSIONS: Patients with normal arterial elastance and ventricular function respond to nitroglycerin with a predominant preload reduction, whereas patients with either excessive arterial elastance or abnormal ventricular function respond with a predominant afterload reduction.

Analysis of Variance↗
PubMed2006

The characteristics of elastic fiber assembled with recombinant tropoelastin isoform.

OBJECTIVE: It is known that elastin mRNA is transcribed from a single gene. The variety of tropoelastin isoforms results from multiple alternative splicing of the primary transcript. The purpose of this study was to investigate the characteristics of elastic fiber assembled with tropoelastin isoform, which is full-length human tropoelastin (HTE), exon 26A missing tropoelastin (Delta26A), and exon 32 missing tropoelastin (Delta32). DESIGN AND METHODS: We demonstrated the process of elastic fiber assembly and the existence of elastic fiber resistant to pancreatic elastase with HTE, Delta26A, or Delta32 fiber using an in vitro model of elastic fiber assembly. These elastic fibers were evaluated by immunofluorescent staining, the quantitative analysis of cross-linked amino acids, and semi-quantitative analysis of matrix-associated tropoelastin. RESULTS: There were no big differences getting into the matrix among these tropoelastins in immunofluorescence microscopy and semi-quantitative analysis. In the comparison with the HTE, the Delta26A and the Delta32 significantly increased and decreased, respectively, the formation of cross-linking amino acids and the binding to scaffold proteins. Furthermore, it was found that it is difficult to degrade the Delta26A assembly with pancreatic elastase as compared with HTE or Delta32 assembly. CONCLUSION: The elastic fiber assembled with the tropoelastin isoforms was characterized using an in vitro model. The present study provides important information regarding the pathology of human diseases including emphysema and atherosclerosis.

Alternative Splicing↗
PubMed1998

Muscle-tendon stresses and elastic energy storage during locomotion in the horse.

The stresses acting in muscle-tendon units and ligaments of the forelimb and hindlimb of horses were determined over a range of speed and gait based on recordings of ground reaction forces and limb kinematics. Maximum stresses of 40-50 MPa were calculated to act in several of the principal forelimb (superficial digital flexor (SDF), deep digital flexor (DDF), ulnaris lateralis (UL) and flexor carpi ulnaris/radialis (FCU/R)) and hindlimb tendons (plantaris, DDF) at the fastest galloping speeds recorded (up to 7.4 m s-1). Smaller stresses were found for the gastrocnemius (GAST) tendon (30 MPa) and suspensory ligaments (S-Ligs) (18-25 MPa). Average peak muscle stresses reached 200-240 kPa during galloping. Tendon and muscle stresses increased more steeply with changes of gait and during galloping, than during trotting. Calculations of elastic strain energy storage based on tendon stress showed similar patterns of increase with change of speed and gait, with the greatest contribution to elastic savings by the DDF tendons of the forelimb and hindlimb. In general, the hindlimb contributed two-thirds and the forelimb one-third to overall energy storage. Comparison of tendon elastic energy savings with mechanical work showed a maximum 40% recovery of mechanical work by elastic savings when the horses changed gait from a walk to a slow trot. Percentage of recovery then decreased with increased trotting speed, but increased again with a change of gait to a gallop, reaching 36% recovery at the fastest measured galloping speed (7.4 m s-1). The long length of horse tendons in relation to extremely short pennate muscle fibers suggests a highly specialized design for economical muscle force generation and enhanced elastic energy savings. However, elastic energy savings in terms of percentage of recovery of mechanical work and metabolic energy is less than that observed in wallabies and kangaroos during hopping, but similar to that in humans during running, and greater than that for dogs during trotting and galloping.

Animals↗
PubMed1999

UVB irradiation stimulates deposition of new elastic fibers by modified epithelial cells surrounding the hair follicles and sebaceous glands in mice.

UVB irradiation stimulates the synthesis of elastin in the skin of humans and experimental animals. In this study we localized the site and the cells that are responsible for the synthesis of murine dermal elastic fibers. SKH-1 hairless mice were irradiated with UVB and the skin removed for light microscopy, electron microscopy, in situ hybridization, immunohistochemistry, and biochemical studies. In response to chronic low doses of UVB there was an initial moderate increase in tropoelastin mRNA in the papillary dermis. By contrast, there was a continuous marked elevation of collagen alpha1(I) message localizing to sites of inflammatory cell influx throughout the upper and lower dermis. After 25 wk of UV irradiation there was a 2-fold increase in skin elastin, yet total collagen remained unchanged. Serial desmosine analysis from en face sections indicated the increase in elastin content was due to dermal elastic fibers, an increase in the size and number of the dermal cysts, and an increase in subpanniculus elastic fibers. Elastin stains of en face sections suggested that the elastic fibers in the upper dermis were exclusively derived from cells lining the epithelial root sheath and sebaceous glands. In response to UV irradiation, the elastic fibers increased in number and size, wrapping around these structures and aligning in both directions as long fibers parallel to the body axis. Electron micrographs indicated that modified epithelial cells in close proximity to the flattened epithelial cells that encircled the root sheath and sebaceous glands were the source of the elastic fibers.

Animals↗
PubMed1999

Inelastic leg compression is more effective to reduce deep venous refluxes than elastic bandages.

BACKGROUND: Deep venous refluxes play an important triggering role for the development of venous leg ulcers. Compression therapy is able to reduce these refluxes depending on pressure and the kind of material being used. OBJECTIVE: To compare the efficacy of compression bandages of varying pressure and material (elastic, long-stretch versus inelastic, short-stretch bandages, four-layer bandages). METHODS: Venous volume (VV) and venous filling index (VFI) as a quantitative parameter of venous reflux were measured using an airplethysmograph (APG) in a total of 21 patients presenting with venous leg ulcers and deep venous refluxes. Bandage pressure was measured in every experiment. The influence of elastic and inelastic bandages with increasing pressure and the changes in these parameters using different bandages with the same pressure were investigated. RESULTS: The initial median value of VFI without compression was 8.45 ml/sec. VV and VFI were significantly reduced by increasing external pressure, more strongly with inelastic than with elastic material. With a pressure of 25 mmHg inelastic bandages diminished VFI to a median of 3.25 ml/sec while the elastic material did not even approach this value with a pressure of 40 mmHg (4.25 ml/sec). Applying bandages of different material with the same pressure of 30 mmHg, the most intense reduction of VV and VFI was obtained by inelastic and by four-layer bandages. The effect on venous reflux was statistically significantly superior with inelastic compared to elastic material. CONCLUSION: Using the same bandage pressure, inelastic material is more effective at reducing deep venous refluxes than elastic bandages in patients with venous ulcers. Four-layer bandages show similar efficacy to inelastic bandages.

Adult↗
PubMed2000

The effect of medical elastic compression stockings with different slope values on edema. Measurements underneath three different types of stockings.

BACKGROUND: Medical elastic compression stockings are widely used in venous diseases. Their effects on the venous system have been shown in the past. Up to now, little is known about the slope or stiffness factor of stockings. OBJECTIVE: To evaluate the effect of different slope and stiffness factors of medical elastic compression stockings on the venous system. METHODS: Examinations were carried out in 29 legs of 25 different patients (12 men, 13 women) with a mean age of 66.0 years. All patients were known with chronic venous insufficiency. On all these patients three different elastic medical compression stockings were tested; one with a low slope, one with a high slope, and one with a low slope but a higher pressure at the ankle. The tests were carried out by determining capillary filtration rate (CFR) with air-plethysmography (APG) while wearing the stockings. RESULTS: The mean value of the CFR without wearing a stocking was 4.65 ml/min (SD = 1.68), with Compriform (low slope, 30 mmHg) the mean CFR was 3.54 ml/min (SD = 1.22), with Bellavar (high slope, 30 mmHg) a mean CFR of 3.15 ml/min (SD = 1.17) was found, and the mean CFR related to Fast-fit (low slope, 34.5 mmHg) was 3.02 ml/min (SD = 1.12). There is a highly statistically significant difference in CFR between no stockings and wearing a stocking (paired Student's t-test; P < 0.01). Regarding the individual stocking, there is a highly statistically significant difference in CFR between the Compriform and the other two stockings (paired Student's t-test; P < 0.01). Between Bellavar and the Fast-fit the difference was not statistically significant. CONCLUSIONS: There is a statistically significant difference in CFR, and consequently in the development of edema, between not wearing an elastic compression stocking and wearing an elastic compression stocking. There is also a statistically significant difference in CFR between elastic compression stockings with the same compression, but a low slope profile and a high slope profile. Stockings with a low slope, but a higher compression may perform as well as stockings with a higher slope but a lower compression in reducing the CFR. In patients with a strong tendency to develop edema it may be advisable to prescribe stockings with a high slope profile.

Adult↗
PubMed2005

[Centromere elasticity].

In addition to the role in the spindle apparatus and associated motors, the chromosome themselves play an important role in facilitating chromosome segregation. Sister chromatids are joined at the centromere through a protein complex called cohesin. Chromatids separation requires the degradation by separase of specific proteins acting as a glue to form the cohesin complex. This evolutionally complex is required for the establishment and maintenance of sister chromatids in a ring like structure. It is therefore a key question whether cohesin is indeed a main component of active centromere. Cohesin is insufficient to resist the splitting force exerted by microtubules until anaphase and must be renforced by cohesion provided by flanking DNA. The ring model suggests that cohesine might possess a considerable mobility when associated with chromatin. Observations demonstrate that the interior region of the centromere behaves as an elastic element. Chromosomes display remarkable elasticity, returning to their initial shape after being extended by up to 10 times. For larger deformations the thick filament is converted in thin filament which can be stretched six times before breaking. This article suggests an additional and novel role for the protein titin on chromosome structure and dynamic. Titine was identified as a chromosomal component and it was hypothesised that titin may provide elasticity to chromosome and resistance to chromosome breakages during mitosis. The elastic properties of purified titin correspond well to the elastic properties of chromosome in living cells. The deformability and bending rigidity are consistent with a model developed for titin elasticity. The association of the presence of cohesine ring and the activity of titin could be necessary for segregation.

Cell Cycle Proteins↗
PubMed2003

Effect of elastic compression stockings on venous hemodynamics during walking.

PURPOSE: Venous hemodynamics evaluated during walking better reflect changes that occur under active physiologic conditions than do conventional static modes of exercise such as tip-toe exercise, knee bending, or dorsiflexion. We prospectively studied the efficacy of air-plethysmography (APG) in monitoring venous hemodynamics during ambulation, and with this method we determined the hemodynamic effects of graduated elastic compression stockings on the lower limb during walking at various speeds. METHODS: The residual volume fraction (RVF%) during treadmill walking was monitored with APG in 10 limbs with primary chronic venous insufficiency (CVI)(CEAP(2-4)) at four speeds (1.0, 1.5, 2.0 and 2.5 km/h consecutively), with and without elastic compression (21 mm Hg at the ankle). The method was validated in comparison with standard APG, which is based on tip-toe exercise. RVF obtained during treadmill walking at 1.5 km/h was correlated with RVF measured with standard APG in 30 subjects: 12 healthy volunteers, 11 patients with primary CVI, and 7 postthrombotic limbs. Data were analyzed with nonparametric statistics. RESULTS: RVF measurements during walking were reproduced with an intra-day coefficient of variation of 5.1% to 16.5%. RVF during walking correlated well with RVF during standard APG (tip-toe) (r = 0.5, P =.004). At each of the investigated walking speeds, stockings improved venous hemodynamics by decreasing RVF, from a median of 50.5% without stockings to 40.5% with stockings at 1.0 km/h (19.8% decrease), from 49% to 39.5% at 1.5 km/h (19.4% decrease), from 50.5% to 41% at 2.0 km/h (18.8% decrease), and from 53% to 45.5% at 2.5 km/h (14.2% decrease) (all speeds, P <.02). Efficacy of the stockings in decreasing RVF (percent change in RVF) was similar across the spectrum of examined speeds (P =.47). During walking with elastic stockings, nominal RVF values were also similar across the spectrum of walking speeds, except at 2.5 km/h (P =.012). During walking without stockings, RVF did not change with treadmill speed, nor did it differ from that obtained with conventional APG (tip-toe) (P =.46). The percentage decrease in RVF generated with elastic stockings correlated with the venous filling index (r = 0.73, P =.017) at 1.0 km/h. CONCLUSIONS: APG is a reproducible and valid method for monitoring venous hemodynamics during walking. Graduated elastic compression stockings significantly improved venous hemodynamics by reducing RVF in limbs with primary CVI at all examined walking speeds (1.0 to 2.5 km/h). The effect was linearly correlated with the amount of reflux (1.0 km/h). The modified application of APG during walking offers a new noninvasive method for assessment of venous hemodynamics in limbs with CVI, enabling quantification of the actual effect of elastic compression therapy during ambulation.

Adult↗
PubMed2001

Buckling and nonlocal elasticity of charged membranes.

The elastic behavior of an interacting, and, in specific, of a charged flexible membrane is considered. In the first part of this paper the effective nonlocal elastic energy of a membrane due to a pairwise and arbitrary intra-membrane interaction is derived. Nonlocal elasticity is included to all orders, this description, therefore, corresponds to an infinite resummation of the standard gradient expansion. In the second part, the pair interaction between segments of an (on average) neutral membrane consisting of mobile positive and negative charges is derived both field theoretically in the Gaussian approximation and using a simple ion-pairing approximation. This model might also apply to strongly charged membranes with strongly condensed counter ions. The resulting contribution to the elastic energy is negative and thus favors undulations of the membrane. The bending modulus is extracted from the large-scale or small-momentum behavior of the elastic kernel and found to be comparable to k(B)T for the case where ion pairing is dominant. The large-momentum elastic response exhibits a markedly different scaling than the small-momentum regime and sensitively depends on the small-distance cutoff and thus on molecular details.

Journal Article↗
PubMed2001

Singularities, structures, and scaling in deformed m-dimensional elastic manifolds.

The crumpling of a thin sheet can be understood as the condensation of elastic energy into a network of ridges that meet in vertices. Elastic energy condensation should occur in response to compressive strain in elastic objects of any dimension greater than 1. We study elastic energy condensation numerically in two-dimensional elastic sheets embedded in spatial dimensions three or four and three-dimensional elastic sheets embedded in spatial dimensions four and higher. We represent a sheet as a lattice of nodes with an appropriate energy functional to impart stretching and bending rigidity. Minimum energy configurations are found for several different sets of boundary conditions. We observe two distinct behaviors of local energy density falloff away from singular points, which we identify as cone scaling or ridge scaling. Using this analysis, we demonstrate that there are marked differences in the forms of energy condensation depending on the embedding dimension.

Journal Article↗
PubMed2004

Linear splay elasticity in surface-induced films of tilted smectic liquid crystals.

The prefrozen films that may be observed at the surface of isotropic liquid crystal droplets, close to the isotropic-smectic phase transition, or surface-induced films, are essentially asymmetric. If moreover, the molecules are tilted inside the smectic layers, as in the smectic-C (SmC) or smectic-C(A) (SmC(A)) phases, the c director that we may define as the order parameter of the film, is a real vector. Thus, the surface-induced films of MHTAC exhibit vectorial or polar properties, though the molecules are not chiral. The film free energy therefore contains a surface-elasticity term, K(1)c(2) c, that is a linear function of the splay distortion, and that may be negative enough to promote a mechanical instability. A spontaneous c distortion, or c modulation, then invades the whole film and produces an array of parallel stripes, with a typical four-fringe periodicity when observed between crossed polarisers. Here, we present optical measurements of the distortion for different film thicknesses, and we propose a linear analysis of the data to test our model. Due to the limitations inherent to the Fourier expansion that we use, the calculations are valid only between two limits: a large q limit where splay domains collapse into disclination lines, and a small q borderline below which the distortion evolves towards a system of independent solitons. We find that the sign of the spontaneous splay elastic constant K1 alternates as a function of the number of layers, N, a property that is reminiscent of the alternate structure of the SmC(A) phase. We argue that the two-dimension elastic constant, K1, originates from the interactions between the molecules in contact to the isotropic phase, and we deduce K1 approximately -(-1)(N)x10(-11) N and the elastic anisotropy, with a ratio of the splay over bend elastic constants K(s)/K(b) approximately 4.5. Similar properties could be observed also in other types of ultrathin films, e.g., in free-standing, ferroelectric (SmC*) or antiferroelectric (SmC(*)(A)), films, in Langmuir films, and even in particular biological films. In some cases, a second, electric instability may occur and superimpose onto the elastic one.

Journal Article↗
PubMed1994

Fibrillin immunoreactivity is associated with normal or fragmented elastic microfibrils at the dermal-epidermal junction in recessive dystrophic epidermolysis bullosa.

Elastic microfibrils containing fibrillin are a part of the fibroreticular network of normal epidermal basement membrane. In dystrophic epidermolysis bullosa (DEB) at least one other fibroreticular component, anchoring fibrils, which contain type VII collagen, is known to be abnormal. We therefore questioned whether elastic microfibrils and fibrillin expression might also be abnormal in DEB. By indirect immunofluorescence, and pre-embedding immunogold electron microscopy using a monoclonal antifibrillin antibody, we found no difference from control samples in either the quantity of the labelling or in the ultrastructural appearances of the immunolabelled fibrils in intact DEB skin. In areas of dermal-epidermal separation, however, we observed a number of thin, fragmented sublamina densa wisp-like structures, which still labelled for fibrillin despite lacking the typical ultrastructural features of normal elastic microfibril bundles. As a consequence of blistering in DEB, elastic microfibril bundles are disrupted, and fragmented microfibrils may still remain attached to the blister roofs. Many of these elastic microfibrils cannot be distinguished from rudimentary or altered anchoring fibrils on morphology alone, and might therefore account for misinterpretation of ultrastructural disorders of the dermal-epidermal junction. We postulate that, in intact skin, elastic microfibrils might contribute to dermal-epidermal adherence, in the absence of normal-functioning anchoring fibrils.

Adolescent↗
PubMed1996

Effects of nitric oxide and sodium nitroprusside on the intrinsic elastic properties of pressurized rat coronary artery.

The study was designed to assess the influence of either nitric oxide (NO) or sodium nitroprusside and the absence of endothelium on the intrinsic elastic properties of coronary arteries from WKY rats. For this purpose, segments of the right interventricular coronary were mounted in an arteriograph where wall thickness and internal diameter were continuously monitored while intraluminal pressure was controlled in the absence of flow. To study the passive properties, pressure-diameter relationships were determined by measuring the corresponding internal diameter for each stepwise increase in intraluminal pressure. Thus, wall stress, strain and incremental elastic modulus (Einc) were assessed in the following experimental conditions: control, incubation with nitro-L-arginine methyl ester (L-NAME, 100 microM) or L-NAME + L-arginine (L-arg, 100 microM), incubation with sodium nitroprusside (SNP, 100 microM), endothelium removal (CHAPS). The Einc-stress relationship was not significantly different in the different experimental conditions, but values of Einc plotted as function of strain were significantly decreased after L-NAME incubation and partly reversed after L-arg addition. The same effect was observed after endothelium destruction but to a lesser extent. After SNP incubation, values of Einc were significantly decreased for small values of strain and increased for high values of this parameter. These results show that NO synthase inhibition induced, for a given strain, a decrease of elastic modulus in coronary arteries. It can be speculated that functional antagonism exerted by NO against spontaneous contractile tone was reduced. Thus, the smooth muscle cells were in a greater state of activation and probably more strongly involved in the intrinsic elastic properties of this preparation. However, an unexplained effect of NO on wall stiffness cannot be excluded. Conversely, SNP increased the initial diameter and induced an initial decrease in stiffness followed by a subsequent increase. After endothelium destruction, stiffness was significantly decreased compared to control conditions. It can be concluded that NO modulates the intrinsic elastic properties of the coronary arteries through smooth muscle cell relaxation. Furthermore, results with SNP support the hypothesis that the lower the state of activation of the smooth muscle cells, the higher the elastic modulus of the arterial wall in this coronary artery preparation.

Animals↗
PubMed1991

Immunohistochemical demonstration of actinically damaged elastic fibers in keratoacanthomas: an aid in diagnosis.

The inclusion of elastic fibers within the epithelium of keratoacanthomas is a phenomenon suggested to be an aid in differentiating this lesion from squamous cell carcinoma. Antilysozyme antibodies have recently been noted to stain actinically damaged elastic fibers but not those from sunprotected skin. In this study, 54 keratoacanthomas and 46 squamous cell carcinomas were stained with a histochemical elastic tissue stain and polyclonal antibody to lysozyme using an immunoperoxidase technique. Elastic fibers were demonstrated in keratoacanthomas (37/54, 68%) significantly more often than squamous cell carcinomas (12/46, 26%) (p less than 0.001) using both techniques. This study confirms that the inclusion of elastic fibers occurs significantly more often in keratoacanthomas than squamous cell carcinomas. These elastic fibers were also actinically damaged, suggesting a role for sun damage in the evolution of keratoacanthoma.

Adult↗
PubMedDate not supplied

Errors with small volume elastic seepage meter bags.

The use of small volume elastic collection bags (condoms) has become popular in seepage meter studies in recent years, despite minimal field or laboratory validation of their use and, specifically, the impact of their elasticity on seepage measurements. A laboratory study was initiated after field results using small elastic collection bags produced seepage data that did not correlate with hydrometric data. The laboratory data demonstrate that condoms undergo significant mechanical relaxation during seepage measurement times typically observed in field settings. Unlike conventional nonelastic collection bags, which mechanically relax over several minutes, the condoms suffered from a slow mechanical relaxation or equilibration. Over nine hours, condoms gained 43 mL of water, approximately 50% of maximum workable volume (between mechanical relaxation effect and elastic limit), under stagnant flow conditions. This long-term equilibration invalidates simple subtraction of equilibration volumes from collection volumes as a correction technique. Previously published studies using flexible small-volume elastic measurement bags (condoms) have not reported a mechanical relaxation effect. Overall, because the condom's small workable volume and inherent variability, we would not recommend any small-volume elastic measurement bags for quantitative seepage measurements.

Environmental Monitoring↗
PubMedDate not supplied

Relationship between right ventricular wave speed and elastance in dogs.

Wave speed (c) must be known to separate forward- and backward-going waves during wave-intensity analysis, which measures the energy transported by the waves in the circulation. c is related to elastance; the present study was performed to measure right ventricular (RV) c during the cardiac cycle and to compare c with RV elastance. In 7 dogs, we measured right atrial, pulmonary arterial, pericardial and 2 RV pressures, and pulmonary arterial flow. A pulse generator was connected to the RV apex, and c was measured by determining the transit time between the 2 high-fidelity RV pressure transducers; the distance was measured roentgenographically. Eight sonomicrometry crystals were implanted in the RV endocardium to calculate RV volume and, thereby, elastance. RV c ranged from approximately 1 m/s during diastole to approximately 4 m/s during systole. Log-log plots of c vs. elastance were linear. These slopes represent the power relationships between c and elastance and ranged from 0.30 to 0.56; for the combined data, it was 0.31. Given knowledge of c, forward- and backward-going waves can be identified and their energy quantitated. In the canine RV, c is approximately proportional to 1/3 the power of elastance: log c = 0.31.log E - 2.05.

Animals↗