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1 Physics, Washington University in St. Louis, St. Louis, Missouri, United States; Internal Medicine, Washington University in St. Louis, Saint Louis, Missouri, United States
2 Internal Medicine, Washington University in St. Louis, St. Louis, Missouri, United States; Physics, Washington University in St. Louis, United States; Biomedical Engineering, Washington University in St. Louis, United States
* To whom correspondence should be addressed. E-mail: sjk{at}wuphys.wustl.edu.
Average left ventricular (LV) chamber stiffness, 
PAVG/VAVG , is an important diastolic function (DF) determinant. An E-wave based determination of PAVG/VAVG by Little et al (1995) predicted that deceleration time (DT) determines stiffness according to PAVG/VAVG =(A)(
/DT) 2 . This implies that if the DTs of two LVs are indistinguishable, so is their stiffness. We observed that LVs having indistinguishable DTs may have markedly different values for PAVG/VAVG determined by simultaneous echocardiography-catheterization.
To elucidate the mechanism by which LVs having indistinguishable DTs manifest distinguishable chamber stiffness, we use a validated, kinematic E-wave model (1987), possessing stiffness (k ) and relaxation/viscoelasticity (c ) parameters. Because the predicted linear relationship between chamber stiffness k and PAVG/VAVG has been previously validated, we re-express Little et al's DT vs. stiffness (PAVG/VAVG ) relationship as:
DTk 
/(2 
k)
Using the kinematic model, we derive the general DT vs. chamber stiffness and viscoelasticity relationship as:
DTk =/(2 k)+c/(2k)
where c and k are determined directly from the E-wave, and which reduces to DTk when c<<k.
Validation involved analysis of 400 E-waves by determination of 5-beat average k and c from 80 subjects undergoing simultaneous echocardiography-catheterization. Clinical E-wave DTs were compared to model-predicted DTk and DTk,c. Clinical DT was better predicted by stiffness and relaxation/viscoelasticity jointly (r2=0.84, DT vs. DTk,c)), rather than by stiffness alone (r2=0.60, DT vs. DTk).
We conclude LVs can have indistinguishable DTs, while having significantly different PAVG/VAVG if chamber relaxation/viscoelasticity differs. We conclude that DT is a function of both chamber stiffness (k) and chamber relaxation/viscoelasticity (c). Quantitative DF assessment warrants consideration of simultaneous stiffness and relaxation/viscoelasticity effects.
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