Insensitivity of tensile failure properties of human bridging veins to strain rate: implications in biomechanics of subdural hematoma

The effects of strain rate on tensile failure properties of human parasagittal bridging veins were studied in eight unembalmed cadavers. While bathed in physiological saline at 37 degrees C, the intact vessel was stretched axially by a servo-controlled hydraulic testing machine at either a low strain rate of 0.1-2.5 s-1 or a high rate of 100-250 s-1. The mean ultimate stretch ratios for low and high strain rates, respectively, were 1.51 +/- 0.24 (S.D. n = 29) and 1.55 +/- 0.15 (n = 34), and the ultimate stresses were 3.24 +/- 1.65 (n = 17) and 3.42 +/- 1.38 MPa (n = 20). Neither difference between strain rates was significant (p greater than 0.45). Thus, our results do not support the hypothesis that sensitivity of the ultimate strain of bridging veins to strain rate explains the acceleration tolerance data for subdural hematoma in primates [Gennarelli, R. A. and Thibault, L. E. (1982) Biomechanics of acute subdural hematoma. J. Trauma 22, 680-686].     

cis-2,3-dihydro-2,3-dihydroxybiphenyl dehydrogenase and cis-1, 2-dihydro-1,2-dihydroxynaphathalene dehydrogenase catalyze dehydrogenation of the same range of substrates.

Pseudomonas putida strain G7 cis-1,2-dihydro-1, 2-dihydroxynaphthalene dehydrogenase (NahB) and Comamonas testosteroni strain B-356 cis-2,3-dihydro-2,3-dihydroxybiphenyl dehydrogenase (BphB) were found to be catalytically active towards cis-2,3-dihydro-2,3-dihydroxybiphenyl (specificity factors of 501 and 5850 s-1 mM-1 respectively), cis-1,2-dihydro-1, 2-dihydroxynaphthalene (specificity factors of 204 and 193 s-1 mM-1 respectively) and 3,4-dihydro-3,4-dihydroxy-2,2',5, 5'-tetrachlorobiphenyl (specificity factors of 1.6 and 4.9 s-1 mM-1 respectively). A key finding in this work is the capacity of strain B-356 BphB as well as Burkholderia cepacia strain LB400 BphB to catalyze dehydrogenation of 3,4-dihydro-3,4-dihydroxy-2,2',5, 5'-tetrachlorobiphenyl which is the metabolite resulting from the catalytic meta-para hydroxylation of 2,2',5,5'-tetrachlorobiphenyl by LB400 biphenyl dioxygenase.     

Use of bilirubin oxidase for probing chromophore topography in tetrapyrrole proteins

Bilirubin oxidase has been used to probe the surface topography of phycocyanins (C-phycocyanin and phycocyanin-645), peridinin-chlorophyll a-protein and phytochrome. The enzyme catalyzes oxidation of the tetrapyrrolic chromophores in these proteins. Relative rates of oxidation were 78.0 X 10(-6) s-1 (monitored at 617 nm) and 58.0 X 10(-6) s-1 (592 nm) for C-phycocyanin, 43.0 X 10(-6) s-1 for phycocyanin-645, 0.3 X 10(-6) s-1 (at 671 nm) and 1.3 X 10(-6) s-1 (at 480 nm) for peridinin-chlorophyll a-protein. The relative rate of free chlorophyllin a was 2.8 X 10(4) s-1 whereas upon binding to human serum albumin its rate of oxidation was reduced to 3.3 X 10(-3) s-1. Relative rates for the oxidation of Pr and Pfr forms of phytochrome were 2.9 and 19.5 s-1, respectively, which are consistent with earlier finding [( 1984) Plant Physiol. 74, 755-758] that indicated a preferential exposure of tetrapyrrolic chromophore in the Pfr form. In general, kcat/Km values derived from the Lineweaver-Burk plots followed the same trend as the relative rates of oxidation. For example, the kcat/Km for the free chlorophyllin a was 2.8 X 10(6) M-1 s-1 but it was only 1.1 M-1s-1 for the chlorophyll a in peridinin-chlorophyll a-protein where the chlorophyll is shielded by protein. These results reflect varying degrees of protection of the tetrapyrrolic chromophores from the enzymatic oxidation and prove that bilirubin oxidase can be generally used as a probe for deducing the topography of tetrapyrrolic chromophores.     

Analysis of the effect of using two different strain rates on the acoustic emission in bone

To study the effect of strain rate on the acoustic emission amplitude signature of bone, bovine cortical bone was milled into standard tensile specimens which were tested at two different strain rates while being monitored with acoustic emission equipment. It was demonstrated that the amplitude distribution of the acoustic events in bone is dependent on strain rate. Greater numbers of events occurred with the slower strain rate (0.0001 s-1), but these events were of lower amplitude than those emitted during the more rapid strain rate (0.01 s-1). The plot of the cumulative event amplitude distribution followed the power-law model, and the slope of this output, the b-value, represented a signature of the amplitude distribution. The mechanical test results were consistent with the behavior of a viscoelastic multi-phase composite material.     

Influence of rapidly successive head impacts on brain strain in the vicinity of bridging veins

Acute subdural hematoma due to a bridging vein rupture is a devastating but rare injury. There has to date been no satisfactory biomechanical explanation for this infrequent but costly injury. We surmise that it may be associated with multiple head impacts. Though numerical models have been used to estimate vein strains in single impact events, none to date have examined the influence on localized brain strain of rapidly consecutive impacts. Using the Simulated Injury Monitor, we investigated the hypothesis that such double impacts can increase strain beyond that created by any single impact. Input to our parametric study comprised hypothetical biphasic rotational head accelerations producing a maximum angular velocity of 40 rad./s. In each of 19 simulations, two identical angular inputs are applied at right angles to each other but with time separations varying from 0 to 40 ms. For these double impacts, it has been generally found that strain in the region of the bridging veins is different, than what would be associated with any corresponding single impact. In some cases, the effect is to actually reduce the tissue strain. In others, the strain in the region of the bridging veins is increased markedly. The mechanistic explanation for the strain increase is that the tissue strain from the first impact has not diminished fully when strain from the second impact is initiated. Rapidly consecutive impacts could be a potential mechanism leading to vein rupture that warrants further investigation.     

Interaction of super-repressible and dominant constitutive mutations for the synthesis of galactose pathway enzymes in Saccharomyces cerevisiae.

Two dominant uninducible mutant alleles in the gal80 locus were identified. The GAL80s-1 and GAL80s-2 mutants showed novel phenotypes in response to the newly isolated GAL81-1 mutant allele, a dominant constitutive mutation linked to the gal4 locus; the GAL80s-1 GAL81-1 strain was inducible and the GAL80s-2 GAL81-1 strain was uninducible. Many galactose positive revertants from the GAL80s-2 GAL81-1 strain were isolated. It was proved that each revertant was due to a secondary mutation either in the gal80 or GAL81 locus, whereas revertants due to mutation at the supposed controlling site for the structural gene cluster of the galactose-pathway enzymes have not been isolated.     

Anisotropic yield behavior of bone under combined axial force and torque

In this study the yield behavior of cortical bone was determined under combined loading conditions involving tension, compression and torsion. The axis of each test sample coincided with the long bone axis. To minimize viscoelastic behavior, tests were conducted using an effective strain rate in the range of 0.01-0.06 s-1. Experimental yield loci for bovine and human cortical bone were determined using a strain offset technique to determine the 'common yield point' for combined loading. Several failure criteria which have been used for composite materials were examined for applicability to the experimental results. Data were obtained for bovine and human tibial and femoral bone. The Tsai-Wu criterion was in best agreement to the test data, although Hill's criterion could describe the individual compression-torsion or tension-torsion regimes with good accuracy.     

Fusion of Sendai virus with human HL-60 and CEM cells: different kinetics of fusion for two isolates.

The kinetics of fusion of Sendai virus (Z strain) with the human promyelocytic leukemia cell line HL-60, and the human T lymphocytic leukemia cell line CEM was investigated. Fusion was monitored by fluorescence dequenching of octadecylrhodamine (R-18) incorporated in the viral membrane. For one virus isolate (Z/G), the overall rate of fusion (at 37 degrees C) increased as the pH was lowered, reaching a maximum at about pH 5, the lowest pH tested. For another isolate (Z/SF) the rate and extent of fusion were lower at pH 5 than at neutral pH. Lowering the pH from neutral to 5 after several minutes of incubation of either isolate with HL-60 cells resulted in an enhanced rate of fluorescence dequenching. Nevertheless, experiments utilizing NH4Cl indicated that fusion of the virus with cells was not enhanced by the mildly acidic pH of the endosome lumen. Analysis of the kinetics of fusion by means of a mass action model resulted in good simulation and predictions for the time-course of fusion. For the isolate which showed maximal fusogenic activity at pH 5, the rate constant of fusion (approx. 0.1 s-1) at neutral pH was in the range found previously for virus-liposome fusion, whereas the rate constant of adhesion was close to the upper limit for diffusion-controlled processes (1.4.10(10) M-1 s-1). However, for the other isolate (Z/SF) the rate constant of fusion at neutral pH was very small (less than 0.01 s-1), whereas the rate constant of adhesion was larger (greater than or equal to 2.10(10) M-1 s-1). Lowering the temperature decreased the fusion rate. Experiments involving competition with excess unlabeled virions indicated that not all binding sites for Sendai virus on HL-60 cells are fusion sites. The virus fusion activity towards HL-60 cells at neutral pH was not altered significantly by pre-incubation of the virus at pH 5 or 9, in contrast to earlier observations with liposomes and erythrocyte ghosts, or results based on erythrocyte hemolysis or cell-cell fusion.     

Mechanical properties of trabecular bone. Dependency on strain rate.

The effect of strain rate (epsilon) and apparent density (rho) on stiffness (E), strength (sigma u), and ultimate strain (epsilon u) was studied in 60 human trabecular bone specimens from the proximal tibia. Testing was performed by uniaxial compression to 5% specimen strain. Six different strain rates were used: 0.0001, 0.001, 0.01, 0.1, 1, and 10 s-1. Apparent density ranged between 0.23 and 0.59 g cm-3. Linear and non-linear regression analyses using strength, stiffness and ultimate strain as dependent variables (Y) and strain rate and apparent density as independent variables were performed using the following models: Y = a rho b epsilon c, Y = rho b(a + c epsilon; Y = (a + b rho)epsilon c, Y = a rho 2 epsilon c, E = a rho 3 epsilon c. The variations of strength and stiffness were explained equally well by the linear and the power function relationship to strain rate. The exponent was 0.07 in the power function relationship between strength and strain rate and 0.05 between stiffness and strain rate. The variation of ultimate strain was explained best using a power function relationship to strain rate (exponent = 0.03). The variation of strength and stiffness was explained equally well by the linear, power function and quadratic relationship to apparent density. The cubic relationship between stiffness and apparent density showed a less good fit. Ultimate strain varied independently of apparent density.     

The sensitivity to inter-subject variability of the bridging vein entry angles for prediction of acute subdural hematoma

Acute subdural hematoma (ASDH) is one of the most frequent traumatic brain injuries (TBIs) with high mortality rate. Bridging vein (BV) ruptures is a major cause of ASDH. The KTH finite element head model includes bridging veins to predict acute subdural hematoma due to BV rupture. In this model, BVs were positioned according to Oka et al. (1985). The aim of the current study is to investigate whether the location and entry angles of these BVs could be modelled using data from a greater statistical sample, and what the impact of this improvement would be on the model’s predictive capability of BV rupture.From the CT angiogram data of 78 patients, the relative position of the bridging veins and their entry angles along the superior sagittal sinus was determined. The bridging veins were repositioned in the model accordingly. The performance of the model, w.r.t. BV rupture prediction potential was tested on simulations of full body cadaver head impact experiments. The experiments were simulated on the original version of the model and on three other versions which had updated BV positions according to mean, maximum and minimum entry angles.Even though the successful prediction rate between the models stayed the same, the location of the rupture site significantly improved for the model with the mean entry angles. Moreover, the models with maximum and minimum entry angles give an insight of how BV biovariability can influence ASDH.In order to further improve the successful prediction rate, more biofidelic data are needed both with respect to bridging vein material properties and geometry. Furthermore, more experimental data are needed in order to investigate the behaviour of FE head models in depth.     

A pulse radiolysis investigation of the reactions of myeloperoxidase with superoxide and hydrogen peroxide

Using pulse radiolysis, the rate constant for the reaction of ferric myeloperoxidase with O2- to give compound III was measured at pH 7.8, and values of 2.1.10(6) M-1.s-1 for equine ferric myeloperoxidase and 1.1.10(6) M-1.s-1 for human ferric myeloperoxidase were obtained. Under the same conditions, the rate constant for the reaction of human ferric myeloperoxidase with H2O2 to give compound I was 3.1.10(7) M-1.s-1. Our results indicate that although the reaction of ferric myeloperoxidase with O2- is an order of magnitude slower than with H2O2, the former reaction is sufficiently rapid to influence myeloperoxidase-dependent production of hypochlorous acid by stimulated neutrophils.     

The effect of Haversian remodeling on the tensile properties of human cortical bone

The purpose of this study was to determine the effect of Haversian remodeling on the tensile properties of human cortical bone by testing specimens containing, as far a possible, a single type of bone tissue. Fifty-one specimens were prepared from sixteen fresh tibias, removed at autopsy. Age range was 19-35. Regions were selected so that the specimens would consist almost exclusively of either primary bone or Haversian bone. The ultimate tensile strength, ultimate strain and Young's modulus of elasticity were determined at a loading rate of 0.05 mm s-1. The primary bone specimens were found to have a significantly higher ultimate tensile strength and modulus of elasticity than those formed of Haversian bone.     

Differential inhibitory properties of dog and human alpha 1-proteinase inhibitors

Dog alpha 1-proteinase inhibitor (alpha 1-PI) was found to be an effective inhibitor of bovine chymotrypsin and also of porcine pancreatic elastase as in the case of human inhibitor. The dog inhibitor inactivated both proteinases at a molar ratio of 1:1. However, compared to the human inhibitor, dog alpha 1-PI was a relatively poor inhibitor of bovine trypsin. The association rate constants (kass) of the interactions of dog alpha 1-PI with bovine chymotrypsin and with porcine elastase were determined to be 6.9 +/- 0.3 X 10(6) M-1 s-1 and 6.4 +/- 0.1 X 10(5) M-1 s-1, respectively. These values are 1.3- and 2.7-fold higher than the corresponding values for the human inhibitor. On the other hand, kass for the dog inhibitor with bovine trypsin (2.6 +/- 0.3 X 10(4)M-1 s-1) was found to be about 5 times smaller than that of the human inhibitor.     

Kinetics of the inhibition of free and elastin-bound human pancreatic elastase by alpha 1-proteinase inhibitor and alpha 2-macroglobulin

At pH 8.0 and 25 degrees C alpha 1-proteinase inhibitor and alpha 2-macroglobulin bind human pancreatic elastase with rate constants of 4.7.10(5) M-1.s-1 and 6.4.10(6) M-1.s-1, respectively. The corresponding delay times of elastase inhibition in plasma are 0.4 s and 0.2 s, respectively, indicating that both inhibitors may act as physiological antielastases. Elastin impairs the elastase inhibitory capacity of alpha 1-proteinase inhibitor and alpha 2-macroglobulin. In presence of human elastin, the former behaves like a slow-binding elastase inhibitor, with a rate constant of about 260 M-1.s-1. In contrast, alpha 2-macroglobulin is a fast-binding inhibitor of elastin-bound elastase, but only one of its two sites is functioning in presence of elastin.     

Photolysis intermediates of human rhodopsin.

Photochemical studies were conducted on human rhodopsin at 20 degrees C to characterize the intermediates which precede the formation of metarhodopsin II, the trigger for the enzyme cascade mechanism of visual transduction. Human rhodopsin was prepared from eyes which had previously been used for corneal donations. Time resolved absorption spectra collected from 10(-8) to 10(-6) s after photolysis of human rhodopsin in detergent suspensions displayed biexponential decay kinetics. The apparent lifetimes obtained from the data are 65 +/- 20 and 292 +/- 25 ns, almost a factor of 2 slower than the corresponding rates in bovine rhodopsin. The spectra can be fit well using a model in which human bathorhodopsin decays toward equilibrium with a blue-shifted intermediate (BSI) which then decays to lumirhodopsin. Spectra and kinetic rate constants were determined for all these intermediates using a global analysis which showed that the spectra of the human intermediates are remarkably similar to bovine intermediates. Microscopic rate constants derived from this model are 7.4 x 10(6) s-1 for bathorhodopsin decay and 7.5 x 10(6) s-1 and 4.6 x 10(6) s-1 for the forward and reverse reactions of BSI, respectively. Decay of lumirhodopsin to later intermediates was studied from 10(-6) to 10(-1) s after photolysis of rhodopsin in human disk membrane suspensions. The human metarhodopsin I in equilibrium metarhodopsin II equilibrium appears to be more forward shifted than in comparable bovine studies.     

Significance of source and size in the mechanical response of human cerebral blood vessels

Cerebral blood vessels are frequently damaged in traumatic brain injury. Mechanical properties of fresh human cerebral vessels obtained through surgeries have been reported. Because surgical sources of human specimens are rare and produce a limited amount of material, we sought to compare the properties of more readily available cerebral arteries and veins obtained from cadavers to fresh vessel data. Additionally, because the previous study was limited to small vessels available in surgery, it was unknown how generally applicable the results were to larger cerebral arteries and veins. In the current study, large and small cerebral vessels from autopsy were stretched axially. Data from these and similar tests on fresh vessels were combined to determine the significance of source and size on mechanical properties. Structural comparisons of histological samples were additionally utilized to characterize differences. Results indicate that specimens from autopsy and surgery behave similarly except that vessels from autopsy tend to be less extensible. While tests on large vessels were limited, small arteries obtained from autopsy tended to be slightly stiffer than large arteries. In contrast, bridging veins from cadavers were typically stiffer and stretched less before structural failure than cortical veins from the same source. These effects are, however, secondary to differences identified between arteries and veins in the previous study.     

Kinetic studies on the interaction of eglin c with human leukocyte elastase and cathepsin G

We have investigated the inhibition of human leukocyte elastase and cathepsin G by recombinant Eglin c under near physiological conditions. The association rate constants k on of Eglin c for elastase and cathepsin G were 1.3 X 10(7) M-1 s-1 and 2 X 10(6) M-1 s-1, respectively. Under identical conditions, the k on for the association of human plasma alpha 1-proteinase inhibitor with the two leukocproteinases were 2.4 X 10(7) M-1 s-1 and 10(6) M-1 s-1, respectively. The consistency of these data could be verified using a set of competition experiments. The elastase-Eglin c interaction was studied in greater detail. The dissociation rate constant k off was determined by trapping of free elastase from an equilibrium mixture of elastase and Eglin c with alpha 1-proteinase inhibitor or alpha 2-macroglobulin. The rate of dissociation was very low (k off = 3.5 X 10(-5) s-1). The calculated equilibrium dissociation constant of the complex, Ki(calc) = k off/k on, was found to be 2.7 X 10(-12) M. Ki was also measured by adding elastase to mixtures of Eglin c and substrate and determining the steady-state rates of substrate hydrolysis. The Ki determined from these experiments (7.5 X 10(-11) M) was significantly higher than Ki(calc). This discrepancy might be explained by assuming that the interaction of Eglin c with elastase involves two steps: a fast binding reaction followed by a slow isomerization step. From the above kinetic constants it may be inferred that at a therapeutic concentration of 5 X 10(-7) M, Eglin c will inhibit leukocyte elastase in one second and will bind this enzyme in a "pseudo-irreversible" manner.     

Leaf hydraulic capacity in ferns, conifers and angiosperms: impacts on photosynthetic maxima

* The hydraulic plumbing of vascular plant leaves varies considerably between major plant groups both in the spatial organization of veins, as well as their anatomical structure. * Five conifers, three ferns and 12 angiosperm trees were selected from tropical and temperate forests to investigate whether the profound differences in foliar morphology of these groups lead to correspondingly profound differences in leaf hydraulic efficiency. * We found that angiosperm leaves spanned a range of leaf hydraulic conductance from 3.9 to 36 mmol m2 s-1 MPa-1, whereas ferns (5.9-11.4 mmol m-2 s-1 MPa-1) and conifers (1.6-9.0 mmol m-2 s-1 MPa-1) were uniformly less conductive to liquid water. Leaf hydraulic conductance (Kleaf) correlated strongly with stomatal conductance indicating an internal leaf-level regulation of liquid and vapour conductances. Photosynthetic capacity also increased with Kleaf, however, it became saturated at values of Kleaf over 20 mmol m-2 s-1 MPa-1. * The data suggest that vessels in the leaves of the angiosperms studied provide them with the flexibility to produce highly conductive leaves with correspondingly high photosynthetic capacities relative to tracheid-bearing species.     

Kinetics and mechanism of bilirubin binding to human serum albumin

The kinetics of bilirubin binding to human serum albumin at pH 7.40, 4 degrees C, was studied by monitoring changes in bilirubin absorbance. The time course of the absorbance change at 380 nm was complex: at least three kinetic events were detected including the bimolecular association (k1 = 3.8 +/- 2.0 X 10(7) M-1 S-1) and two relaxation steps (52 = 40.2 +/- 9.4 s-1 and k3 = 3.8 +/- 0.5 s-1). The presence of the two slow relaxations was confirmed under pseudo-first order conditions with excess albumin. Curve-fitting procedures allowed the assignment of absorption coefficients to the intermediate species. When the bilirubin-albumin binding kinetics was observed at 420 nm, only the two relaxations were seen; apparently the second order association step was isosbestic at this wavelength. The rate of albumin-bound bilirubin dissociation was measured by mixing the pre-equilibrated human albumin-bilirubin complex with bovine albumin. The rate constant for bilirubin dissociation measured at 485 nm was k-3 = 0.01 s-1 at 4 degrees C. A minimum value of the equilibrium constant for bilirubin binding to human albumin determined from the ratio k1/k-3 is therefore approximately 4 X 10(9) M-1.     

Recombination dynamics in bacterial photosynthetic reaction centers.

The time dependence of magnetic field effects on light absorption by triplet-state and radical ions in quinone-depleted reaction centers of Rhodopseudomonas sphaeroides strain R-26 has been investigated. Measurements on the time scale of the hyperfine interaction in the radical pair [(BChl)2+. ...BPh-.)] provided kinetic data characterizing the recombination process. The results have been interpreted in terms of a recently proposed model that assumes an intermediate electron acceptor (close site) between the bacteriochlorophyll "special pair" (BChl)2 and the bacteriopheophytin BPh (distant site). Recombination is assumed to proceed through this intermediate acceptor. The experiments led to effective recombination rates for the singlet and triplet channel: k(Seff) = 3.9 . 107 s-1 and k(Teff) = 7.4 . 10(8) s-1. These correspond to recombination rates ks = 1 . 10(1) s-1 and kT = 7.1 . 10(11) s-1 in the close configuration. The upper bound of the effective spin dephasing rate k2eff approximately equal to 1 . 10(9) s-1 is identical with the rate of the electron hopping between the distant site of zero spin exchange interaction and the close site of large interaction. Interpretation of data for the case of direct recombination yields the recombination rates, spin dephasing rate, and exchange interaction in a straightforward way.