Limits...
Subfailure overstretch induces persistent changes in the passive mechanical response of cerebral arteries.

Bell ED, Sullivan JW, Monson KL - Front Bioeng Biotechnol (2015)

Bottom Line: This subfailure deformation could result in altered mechanical behavior.The observed softening also generally resulted in increased non-linearity of the stress-stretch curve, with toe region slope decreasing and large deformation slope increasing.These changes may have significant implications in repeated TBI events and in increased susceptibility to stroke post-TBI.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering, University of Utah , Salt Lake City, UT , USA ; Laboratory of Head Injury and Vessel Biomechanics, Department of Mechanical Engineering, University of Utah , Salt Lake City, UT , USA.

ABSTRACT
Cerebral blood vessels are critical in maintaining the health of the brain, but their function can be disrupted by traumatic brain injury (TBI). Even in cases without hemorrhage, vessels are deformed with the surrounding brain tissue. This subfailure deformation could result in altered mechanical behavior. This study investigates the effect of overstretch on the passive behavior of isolated middle cerebral arteries (MCAs), with the hypothesis that axial stretch beyond the in vivo length alters this response. Twenty nine MCA sections from 11 ewes were tested. Vessels were subjected to a baseline test consisting of an axial stretch from a buckled state to 1.05* in vivo stretch (λIV) while pressurized at 13.3 kPa. Specimens were then subjected to a target level of axial overstretch between 1.05*λIV (λz = 1.15) and 1.52*λIV (λz = 1.63). Following overstretch, baseline tests were repeated immediately and then every 10 min, for 60 min, to investigate viscoelastic recovery. Injury was defined as an unrecoverable change in the passive mechanical response following overstretch. Finally, pressurized MCAs were pulled axially to failure. Post-overstretch response exhibited softening such that stress values at a given level of stretch were lower after injury. The observed softening also generally resulted in increased non-linearity of the stress-stretch curve, with toe region slope decreasing and large deformation slope increasing. There was no detectable change in reference configuration or failure values. As hypothesized, the magnitude of these alterations increased with overstretch severity, but only once overstretch exceeded 1.2*λIV (p < 0.001). These changes were persistent over 60 min. These changes may have significant implications in repeated TBI events and in increased susceptibility to stroke post-TBI.

No MeSH data available.


Related in: MedlinePlus

(A) Data from a representative sample showing the axial stress-stretch curve for the pre-overstretch baseline test, as well as four of the seven post-overstretch baseline tests which were repeated every 10 min for 60 min after overstretch. (B) Means and SD for the various test groups and how these values evolved over time. Note, there was no significant recovery of strain energy following overstretch at any of the tested overstretch levels. [Symbols: (● Control Group, n = 5), (♦ 1.1*λIV Group, n = 5) (x 1.2*λIV Group, n = 5), (▼1.3*λIV Group, n = 6), (▲ 1.4*λIV Group, n = 4), (■ 1.5*λIV Group, n = 4)].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4309201&req=5

Figure 8: (A) Data from a representative sample showing the axial stress-stretch curve for the pre-overstretch baseline test, as well as four of the seven post-overstretch baseline tests which were repeated every 10 min for 60 min after overstretch. (B) Means and SD for the various test groups and how these values evolved over time. Note, there was no significant recovery of strain energy following overstretch at any of the tested overstretch levels. [Symbols: (● Control Group, n = 5), (♦ 1.1*λIV Group, n = 5) (x 1.2*λIV Group, n = 5), (▼1.3*λIV Group, n = 6), (▲ 1.4*λIV Group, n = 4), (■ 1.5*λIV Group, n = 4)].

Mentions: The observed changes appear to be enduring, rather than passively recoverable due to viscoelasticity (Figure 8A). In order to measure any time dependence in the observed changes, the strain energy from the repeated baseline tests was calculated and compared to that of the pre-overstretch baseline test (Figure 8B). While the magnitude of the %ΔU following overstretch increased as the imposed overstretch increased, it did not change significantly over the 60 min it was measured. Preliminary tests extended this time frame up to 6 h without a change in the result.


Subfailure overstretch induces persistent changes in the passive mechanical response of cerebral arteries.

Bell ED, Sullivan JW, Monson KL - Front Bioeng Biotechnol (2015)

(A) Data from a representative sample showing the axial stress-stretch curve for the pre-overstretch baseline test, as well as four of the seven post-overstretch baseline tests which were repeated every 10 min for 60 min after overstretch. (B) Means and SD for the various test groups and how these values evolved over time. Note, there was no significant recovery of strain energy following overstretch at any of the tested overstretch levels. [Symbols: (● Control Group, n = 5), (♦ 1.1*λIV Group, n = 5) (x 1.2*λIV Group, n = 5), (▼1.3*λIV Group, n = 6), (▲ 1.4*λIV Group, n = 4), (■ 1.5*λIV Group, n = 4)].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4309201&req=5

Figure 8: (A) Data from a representative sample showing the axial stress-stretch curve for the pre-overstretch baseline test, as well as four of the seven post-overstretch baseline tests which were repeated every 10 min for 60 min after overstretch. (B) Means and SD for the various test groups and how these values evolved over time. Note, there was no significant recovery of strain energy following overstretch at any of the tested overstretch levels. [Symbols: (● Control Group, n = 5), (♦ 1.1*λIV Group, n = 5) (x 1.2*λIV Group, n = 5), (▼1.3*λIV Group, n = 6), (▲ 1.4*λIV Group, n = 4), (■ 1.5*λIV Group, n = 4)].
Mentions: The observed changes appear to be enduring, rather than passively recoverable due to viscoelasticity (Figure 8A). In order to measure any time dependence in the observed changes, the strain energy from the repeated baseline tests was calculated and compared to that of the pre-overstretch baseline test (Figure 8B). While the magnitude of the %ΔU following overstretch increased as the imposed overstretch increased, it did not change significantly over the 60 min it was measured. Preliminary tests extended this time frame up to 6 h without a change in the result.

Bottom Line: This subfailure deformation could result in altered mechanical behavior.The observed softening also generally resulted in increased non-linearity of the stress-stretch curve, with toe region slope decreasing and large deformation slope increasing.These changes may have significant implications in repeated TBI events and in increased susceptibility to stroke post-TBI.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering, University of Utah , Salt Lake City, UT , USA ; Laboratory of Head Injury and Vessel Biomechanics, Department of Mechanical Engineering, University of Utah , Salt Lake City, UT , USA.

ABSTRACT
Cerebral blood vessels are critical in maintaining the health of the brain, but their function can be disrupted by traumatic brain injury (TBI). Even in cases without hemorrhage, vessels are deformed with the surrounding brain tissue. This subfailure deformation could result in altered mechanical behavior. This study investigates the effect of overstretch on the passive behavior of isolated middle cerebral arteries (MCAs), with the hypothesis that axial stretch beyond the in vivo length alters this response. Twenty nine MCA sections from 11 ewes were tested. Vessels were subjected to a baseline test consisting of an axial stretch from a buckled state to 1.05* in vivo stretch (λIV) while pressurized at 13.3 kPa. Specimens were then subjected to a target level of axial overstretch between 1.05*λIV (λz = 1.15) and 1.52*λIV (λz = 1.63). Following overstretch, baseline tests were repeated immediately and then every 10 min, for 60 min, to investigate viscoelastic recovery. Injury was defined as an unrecoverable change in the passive mechanical response following overstretch. Finally, pressurized MCAs were pulled axially to failure. Post-overstretch response exhibited softening such that stress values at a given level of stretch were lower after injury. The observed softening also generally resulted in increased non-linearity of the stress-stretch curve, with toe region slope decreasing and large deformation slope increasing. There was no detectable change in reference configuration or failure values. As hypothesized, the magnitude of these alterations increased with overstretch severity, but only once overstretch exceeded 1.2*λIV (p < 0.001). These changes were persistent over 60 min. These changes may have significant implications in repeated TBI events and in increased susceptibility to stroke post-TBI.

No MeSH data available.


Related in: MedlinePlus