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Diastolic ventricular-vascular stiffness and relaxation relation: elucidation of coupling via pressure phase plane-derived indexes

¹Department of Physics and ³Department of Electrical and Systems Engineering, Washington University, and ²Cardiovascular Biophysics Laboratory, Cardiovascular Division, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri

Submitted 13 March 2006 ; accepted in final form 25 May 2006

Because systole and diastole are coupled and systolic ventricular-vascular coupling has been characterized, we hypothesize that diastolic ventricular-vascular coupling (DVVC) exists and can be characterized in terms of relaxation and stiffness. To characterize and elucidate DVVC mechanisms, we introduce time derivative of pressure (dP/dt) vs. time-varying pressure [P(t)] (pressure phase plane, PPP)-derived analogs of ventricular and vascular "stiffness" and relaxation parameters. Although volume change (dV) = 0 during isovolumic periods, and time-varying left ventricular (LV) stiffness, typically expressed as change in pressure per unit change in volume (dP/dV), is undefined, our formulation allows determination of a PPP-derived stiffness analog during isovolumic contraction and relaxation. Similarly, an aortic stiffness analog is also derivable from the PPP. LV relaxation was characterized via , the time constant of isovolumic relaxation, and vascular (aortic pressure decay) relaxation was characterized in terms of its equivalent (windkessel) exponential decay time constant . The results show that PPP-derived systolic and diastolic ventricular and vascular stiffness are strongly coupled . In support of the DVVC hypothesis, a strong linear correlation between relaxation (rate of pressure decay) indexes and ( = 9.89 – 90.3, r = 0.81) was also observed. The correlations observed underscore the role of long-term, steady-state DVVC as a diastolic function determinant. Awareness of the PPP-derived DVVC parameters provides insight into mechanisms and facilitates quantification of arterial stiffening and associated increase in diastolic chamber stiffness. The PPP method provides a tool for quantitative assessment and determination of the functional coupling of the vasculature to diastolic function.

ventricular-vascular coupling

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