M.Sc Student | Nahmani Shlomo |
---|---|
Subject | The Effect of Ejection Velocity of the Whole Heart Pressure Generation |
Department | Department of Biomedical Engineering | Supervisor | Professor Amir Landesberg |
Left ventricle (LV) performances are determined by the intracellular control of contraction. The muscle
power capability, at the cellular level, is derived from the force-velocity
relation and relates to the linear dependence of the cross-bridge (the
molecular motor) weakening rate (g) on the shortening velocity, .
The time independent parameter g1 determines the maximal power. The
study aims to quantify the whole heart power capability and to define a
measurable index for cardiac contractility that will relate to the basic
cardiac fiber characteristics. Methods. Swine (n=7) were anesthetized
and the heart was exposed by mid-sternotomy. Three orthogonal pairs of
sono-crystal were implanted in the LV wall to measure LV diameters. An occluder
and a flow-meter were placed around the proximal ascending aorta. A tube
connected to a syringe was inserted into the LV cavity via the apex. Programmed
step-motor determined the forced ejection velocity (VEJE) and
the time onset of ejection into the syringe. Isovolumic contractions were
imposed by inflating the occluder. Forced ejections were imposed by pulling
blood through the apical tube while the occluder was inflated. Results.
The instantaneous pressure deficit (DP)
between the isovolumic pressure (PISO) and the ejecting beat
pressure was found to be:
,
where Dt is the ejection duration and G1=
2.47 +/- 0.693 [%/cc]. The normalized DP
was
independent of the time onset of the forced ejection and hence independent of
the activation level. Conclusion. A measurable time independent index (G1)
of LV contractility was defined, that links global heart function to the basic
properties of the cross-bridges.