Spatio-temporal attributes of left ventricular pressure decay rate during isovolumic relaxation.
Am J Physiol Heart Circ Physiol
; 302(5): H1094-101, 2012 Mar 01.
Article
em En
| MEDLINE
| ID: mdl-22210748
ABSTRACT
Global left ventricular (LV) isovolumic relaxation rate has been characterized 1) via the time constant of isovolumic relaxation τ or 2) via the logistic time constant τ(L). An alternate kinematic method, characterizes isovolumic relaxation (IVR) in accordance with Newton's Second Law. The model's parameters, stiffness E(k), and damping/relaxation µ result from best fit of model-predicted pressure to in vivo data. All three models (exponential, logistic, and kinematic) characterize global relaxation in terms of pressure decay rates. However, IVR is inhomogeneous and anisotropic. Apical and basal LV wall segments untwist at different times and rates, and transmural strain and strain rates differ due to the helically variable pitch of myocytes and sheets. Accordingly, we hypothesized that the exponential model (τ) or kinematic model (µ and E(k)) parameters will elucidate the spatiotemporal variation of IVR rate. Left ventricular pressures in 20 subjects were recorded using a high-fidelity, multipressure transducer (3 cm apart) catheter. Simultaneous, dual-channel pressure data was plotted in the pressure phase-plane (dP/dt vs. P) and τ, µ, and E(k) were computed in 1631 beats (average 82 beats per subject). Tau differed significantly between the two channels (P < 0.05) in 16 of 20 subjects, whereas µ and E(k) differed significantly (P < 0.05) in all 20 subjects. These results show that quantifying the relaxation rate from data recorded at a single location has limitations. Moreover, kinematic model based analysis allows characterization of restoring (recoil) forces and resistive (crossbridge uncoupling) forces during IVR and their spatio-temporal dependence, thereby elucidating the relative roles of stiffness vs. relaxation as IVR rate determinants.
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Função Ventricular Esquerda
/
Pressão Ventricular
Tipo de estudo:
Prognostic_studies
Limite:
Adult
/
Aged
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Female
/
Humans
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Male
/
Middle aged
Idioma:
En
Ano de publicação:
2012
Tipo de documento:
Article