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Noninvasive cardiac material mechanics: Application to left ventricular function in quadriplegia

  • Biomechanics
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Abstract

Left ventricular function was studied in six quadriplegic subjects by M-mode echocardiography with respect to cardiac material mechanics. Myocardial wall deformation and ventricular viscoelastic compliance were studied during systole and diastole. The left ventricle was assumed to be a sphere and to keep this shape over the cardiac cycle. The viscoelastic properties were determined with respect to the mid-wall. The haemodynamic results indicated that the ejection fraction of quadriplegics was significantly greater than in normals but that their cardiac output was significantly lower. The ratio of viscous compliance coefficient to elastic compliance coefficient was called the system time constant. The myocardial material results indicated that the inequality diastolic time constant ≤ systolic time constant was satisfied in the six quadriplegics. The ratio of end-systolic to end-diastolic wall area was significantly greater in quadriplegics than in normals. These results were consistent with the left ventricle of quadriplegics being deconditioned so that the ventricular wall is more compliant during systole and myocardial wall deformation is greater.

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Abbreviations

AR ϕ :

left ventricular longitudinal cross-sectional area ratio, dimensionless

AR ES :

AR ϕ at end-systole

AR max :

maximumAR ϕ during a cardiac cycle

M :

left ventricular internal diameter (LVID), cm

V CF :

mid-wall circumferential fibre velocity, lengths s−1

V CFD :

value of diastolicV CF at\(\hat t_D \), lengths s−1

V CFS :

value of systolicV CF at\(\hat t_S \), lengths s−1

W :

left ventricular wall thickness (LVWTh), cm

A ϕ :

longitudinal face area of a unit element at the left ventricular equator, cm2

A ϕD :

end-diastolicA ϕ, cm2

δA ϕ :

infinitesimal change inA ϕ, cm2

δθ:

small angle that subtendsA ϕ, rad

R :

radius of curvature of the endocardial wall at the left ventricular equator, cm

δθ D :

end-diastolic δθ, rad

l :

a depth (thickness) into the myocardial wall as measured from the endocardial surface, cm

dl :

infinitesimal change inl, cm

t D :

time during the cardiac diastolic interval, s

\(\hat t_D \) :

point in diastolic time at which σ1 = σ2, s

t s :

time during the cardiac systolic interval, s

\(\hat t_S \) :

point in systolic time at which σ1 = σ2, s

ε:

mid-wall circumferential fibre strain, dimensionless

εD :

ε at\(\hat t_D \), dimensionless

εS :

ε at\(\hat t_S \), dimensionless

η:

coefficient of viscous compliance, N s m−2

μ:

coefficient of elastic compliance, N m−2

σ:

total left ventricular mid-wall circumferential fibre stress, N m−2

σ1 :

component of σ attributable to the elastic element, N m−2

σ2 :

component of σ attributable to the viscous element, N m−2

τ:

mid-wall circumferential fibre system time constant, s

τD :

diastolic τ, s

τS :

systolic τ, s

τπ :

relaxation time for constant stress, s

D :

end-diastolic value

S :

end-systolic value

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Authors and Affiliations

  1. Department of Biomedical Engineering, Physiology and Biophysics, Wright State University, 45435, Dayton, OH, USA

    C. A. Phillips

  2. Cox Heart Institute, Wright State University School of Medicine, 45435, Dayton, OH, USA

    D. M. Danopulos & P. Kezdi

Authors
  1. C. A. Phillips
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  2. D. M. Danopulos
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  3. P. Kezdi
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Phillips, C.A., Danopulos, D.M. & Kezdi, P. Noninvasive cardiac material mechanics: Application to left ventricular function in quadriplegia. Med. Biol. Eng. Comput. 26, 333–341 (1988). https://doi.org/10.1007/BF02442288

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  • DOI: https://doi.org/10.1007/BF02442288

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