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Biomedical subjects

J M Gosline

Publications and source records attributed to J M Gosline.

35 records · Page 2Linked to original sources
PubMed1995

Arterial Windkessels in marine mammals.

In marine mammals, the aortic arch is enlarged relative to the descending aorta to varying degrees in different species. The ratio of maximal diameter of the arch to that of the thoracic aorta is about 2.3 in the harbour seal (Phoca vitulina), 3.6 in the Weddell seal (Leptonychotes weddelli) and 3.2 in the fin whale (Balaenoptera physalus), compared with only 1.4 in the dog. This anatomical specialisation probably provides increased volume capacitance in the arterial circulation as an adaptation to diving bradycardia. Data on the morphometric and mechanical properties of aortic tissues from seals and fin whale are compared. In the harbour seal, more than 80% of the volume change in the entire thoracic aorta that results from a pressure pulse occurs in the bulbous arch, and this is more than 90% in the Weddell seal and fin whale. The enhanced capacitance of the arch in the harbour seal is primarily due to its larger diameter, as the relative wall thickness and elasticity of the arch and thoracic aorta are the same. A similar situation appears to exist in the larger Weddell seal, although extrapolation of the pressure-volume curves suggests that the arch might be somewhat less stiff than the thoracic aorta. In addition to being greatly expanded, the aortic arch of the fin whale is also much more distensible than the relatively thin-walled and much stiffer descending aorta. At the estimated mean blood pressure, the elastic modulus of this vessel is 12 MPa, or 30 times that of the aortic arch. The major haemodynamic consequence of this type of arterial modification is that the aortic arch acts as a Windkessel, i.e. the capacitance of the aorta is increased significantly close to the heart, leading to a reduced characteristic impedance and probably reduced pulsatility in the descending aorta. In the extreme case of the whale, the arterial capacitance is shifted entirely to the arch, and the impedance change at the entrance to the thoracic aorta is so high that this probably represents the major reflection site in the arterial tree.

Adaptation, Physiological↗
PubMed1994

Arterial mechanics in the fin whale suggest a unique hemodynamic design.

An analysis of the dimensions of the aortic tree and the mechanical properties of arterial wall tissues in the fin whale (Balaenoptera physalus) is presented. The aortic arch is greatly expanded, having an internal radius at an estimated mean blood pressure (13 kPa) that is 2.5 times greater than that of the descending thoracic aorta. At this pressure, the elastic modulus of the arch wall (0.4 MPa) is 30 times less than that of the descending aorta (12 MPa). Consequently, even though some capacitance is provided anteriorly by the relatively compliant innominate and carotid arteries, > 90% of the arterial capacitance resides in the arch. The characteristic pressure wave velocity (C0) and impedance (Z0) were calculated from vessel dimensions and elasticity. A predicted 20-fold increase in Z0 between the arch and thoracic aorta should provide a major reflecting site, effectively uncoupling the arch from the remainder of the arterial tree. The dimensions of the arch relative to the likely pressure wavelengths within it suggest that it acts like a compliant windkessel that greatly reduces the pulsatility of the inflow to the descending aorta, which itself likely acts as a rigid, tapered manifold. It is suggested that the presence of both a highly compliant arch and a relatively rigid descending aorta is an adaptation for diving.

Animals↗
PubMed1994

The effects of heating on the mechanical properties of arterial elastin.

Autoclaving is a standard way of purifying arterial elastin for mechanical testing, but recent evidence suggests that heating native elastin might affect its mechanical behavior. We therefore examined the quasi-static tensile properties of pig arterial tissue to see if the mechanical properties of native elastin are altered by autoclaving. From an analysis of the shapes of the stress-extension ratio curves of tissues before and after 8 h of autoclaving, we determined that the mechanical characteristics of elastin dominated the behavior of unautoclaved arterial tissue at wall stresses around 25+/-5 kPa. Autoclaving did not change the tangential modulus of the tissue at this wall stress (+/-4% 95% CI), indicating that elastin can be heated during purification without affecting its mechanical behavior. Autoclaved tissue was tested daily to determine the effects of prolonged heating of autoclaved elastin. Between tests the elastin was incubated at either 80 degrees C (experimental group) or 37 degrees C (control group). After 6 days the average modulus of the control group was unchanged from the initial value, while the average modulus of the experimental group was 7%+/-2% (95% CI) lower. At shorter times the modulus of the experimental group was not significantly reduced. The slight decrease in modulus suggests a slow chemical degradation may occur with prolonged heating, but its time course and magnitude are such that it would not affect standard mechanical tests.

Animals↗
PubMed1987

Functional design of horse hoof keratin: the modulation of mechanical properties through hydration effects.

Tensile moduli and J-integral fracture toughness values were determined for horse hoof-wall keratin at four hydration levels. The stiffness of hoof-wall was influenced by water content to a greater degree than is the stiffness of other mammalian hard keratins. Young's modulus increased from 410 MPa at 100% relative hydration (RH) to 14.6 GPa at 0% RH. Fracture toughness was maximal (22.8 kJ m-2) at an intermediate hydration (75% RH), which represents a two-fold increase over both fully hydrated and dehydrated material. Maximum fracture toughness occurred at a hydration level which is within the range that has been found in vivo in the hoof wall. These results lead to the hypothesis that the density of secondary bonding sites within the hoof-wall keratin matrix proteins provides the hoof organ with the means to modulate tissue properties, even though this epidermal tissue functions after the cells have died.

Animals↗
PubMed1986

Fracture toughness design in horse hoof keratin.

An engineering fracture mechanics approach was applied to the analysis of the fracture resistance of equine hoof-wall. The relationship between fracture toughness and the morphological organization of the keratin hoof tissue was investigated. Fracture toughness was evaluated using the J-integral analysis method which employs the compact tension test geometry. Tensile tests were also conducted to evaluate the effect of the morphological organization on the stress-strain behaviour. Hoof-wall has greatest fracture resistance for cracks running proximally, parallel to the tubular component of the wall keratin. For fully hydrated material tested in this direction the mean critical J-integral value at failure was 1.19 X 10(4)J m-2. This was nearly three times greater than the value determined for the weakest orientation, in which the crack ran parallel to the material between the tubules. The lower fracture toughness of the intertubular material dominates the fracture behaviour of this tissue. The tubular components of the wall appear to reinforce against fracture along the weak plane and the entire wall organization provides the mechanical capability for limiting and controlling fracture in this tissue.

Animals↗
PubMed1982

Solute effects on the mechanical properties of arterial elastin.

We have examined the effects of various solutions (SDS, DMSO, NaCl) on the swelling and mechanical properties of arterial elastin. Our results indicate that SDS-swollen elastin is stiffer, stronger, and appears to fail at smaller extensions than water-swollen elastin. In order to determine if these changes in mechanical properties are due to swelling changes or to a specific effect of SDS bound to the elastin network, we studied the effect of DMSO on the mechanical properties of elastin. DMSO swells elastin to the same extent as 0.1 M SDS, but DMSO is uncharged and probably does not interact directly with the elastin protein. The data for DMSO-swollen elastin corrected for swelling changes are virtually identical to those of water-swollen elastin but significantly different from those of SDS-swollen elastin. Thus, there is apparently a specific SDS effect, and this effect probably arises from the high negative charge density due to bound SDS. Lastly, studies of changes induced by sodium chloride concentrations in the physiological range indicate that there is no significant change in stiffness, strength, or extensibility due to increased NaCl levels.

Animals↗
PubMed1981

Elastic arteries in invertebrates: mechanics of the octopus aorta.

The aorta of the octopus, Octopus dofleini, is a highly distensible, elastic tube. The circumferential elastic modulus increases with inflation in the physiological range from abut 10(4) to 10(5) newtons per square meter. Rubber-like fibers have been isolated, apparently for the first time, from the aorta of an invertebrate. These fibers have an elastic modulus, like elastin, of about 4 x 10(5) newtons per square meter and are present in sufficient quantity to account for the elastic properties of the intact vessel under physiological conditions. Thus the circulatory system of an invertebrate animal provides an "elastic reservoir" (much like that of the vertebrate system), which increases the efficiency of the circulation.

Animals↗
PubMed1980

Optical properties of single elastin fibres indicate random protein conformation.

In describing the properties of fibrous proteins it has been common practice to attribute the macroscopic mechanical properties to the organization at the molecular level. Hence, the high tensile stiffness of collagen and silk has been viewed as an inevitable consequence of their crystalline structure. For elastin, however, there has been considerable controversy and confusion in assigning a conformation to this rubber-like protein. The mechanical and thermodynamic properties of elastin are consistent with the kinetic theory of rubber elasticity, and this theory is based on an isotropic network of kinetically free, random-coil molecules. In contrast, numerous electron microscope studies of negatively stained elastins obtained by autoclave and alkali purification, as well as coacervates of the various soluble elastins, reveal a highly ordered (anisotropic) structure, consisting of 3- to 5-nm filaments that apparently run parallel to the long axis of elastin fibres. These filaments have been accepted as evidence for an anisotropic molecular structure in elastin that is dramatically different from the random network of the kinetic theory. We have now used polarized light microscopy to distinguish these two types of structure. We find that both purified and unpurified, water-swollen, single elastin fibres are optically isotropic, in agreement with the predictions of the kinetic theory of rubber elasticity.

Animals↗
PubMed1978

Pressure effects on water-swollen elastin. A model for hydrophobic interactions in proteins.

The effect of pressure on the swelling of elastin in pure water was investigated. Because elastin is a very non-polar protein, and because the swelling of elastin can be directly related to changes in the strength of hydrophobic interactions, we have used elastin as a model to study the effect of pressure on hydrophobic interactions in proteins. The elastin swelling model is particularly useful because it is based on a macromolecular system very similar to a globular protein and not on dilute aqueous solutions of small non-polar compounds. Increased pressure causes elastin to increase its swollen volume, and the observed swelling changes were analyzed in terms of the Flory-Rehner theory (Flory, P.J. and Rehner, Jr., J (1943) J. Chem. Phys. 11, 521--526) for the swelling of kinetically free, random polymer networks. Our calculations provide a measure of the volume change for the process of transferring 1 mol of an average non-polar amino acid side chain from a region where the side chains are surrounded by other non-polar groups and have no contact with water (i.e. a hydrophobic region) into contact with water. The results indicate that there is a small, negative volume change associated with this process, and quantitative estimates indicate that the volume change is of the order of --6 ml/mol side chain. The results support the hypothesis that the free energy required to transfer a non-polar side chain from a hydrophobic region into water becomes less positive (i.e. the hydrophobic interaction becomes weaker) as hydrostatic pressure is increased.

Elastin↗
PubMedDate not supplied

The effects of hydration on the dynamic mechanical properties of elastin.

The dynamic mechanical properties of elastin have been quantified over a temperature and hydration range appropriate for a biological polymer. Composite curves of the tensile properties at constant water contents between 28.1 and 44.6% (g water/100 g protein) were typical of an amorphous polymer going through its glass transition. Water content had no effect on the shape of the curves, but shifted them a distance aC along the frequency axis. The combined effects of hydration and temperature are given in a series of isoshift curves where elastin's properties are constant along any one curve. A 1% change in hydration has the same effect as a 1 degrees-2 degrees change in temperature, depending on the initial water content and temperature. Theoretical isoshift curves that matched the experimental data were predicted using the WLF equation and coefficients determined from the data. These data form a basis to predict the role of elastin in arterial disease based on changes in its chemical and physical environment.

Animals↗
PubMedDate not supplied

The effects of polar solutes on the viscoelastic behavior of elastin.

The viscoelastic behavior of arterial elastin in aqueous solutions of polar solutes has been studied to establish both its range of behavior and the mechanisms by which the behavior is altered by the solutes. We were particularly interested in whether a solute interacted directly with the elastin or whether it acted only indirectly to reduce the activity of water. The behavior of elastin in solutions of glucose, NaCl, ammonium sulphate, and in low concentrations of ethylene glycol was similar to that of elastin that had been directly dehydrated or indirectly dehydrated using osmotic agents such as dextran or polyethylene glycol. This similarity suggests that these solutes interact with elastin only indirectly. Thiocyanate and high concentrations of dimethyl sulfoxide and ethylene glycol appeared to interact directly with the elastin, altering both the swelling and the viscoelastic behavior of the network.

Animals↗