Regulation of left ventricular pressure fall

Abstract

Left ventricular pressure (LVP) fall is a manifestation of relaxation and is therefore regulated by non-uniformity and load, besides regulation by muscle inactivation. Non-uniformity and load are important and independent regulators of LVP fall. Non-uniformity induces a premature onset and decreased rate of LVP fall. With regard to load, the effects of preload, systolic LVP levels and systolic LVP waveform are distinct. In order to assess underlying muscle inactivation with indexes of LVP fall, it is critical to control non-uniformity and various aspects of load. This control should be inherent in experiments designed to evaluate interventions. If careful control of non-uniformity and load cannot be achieved, at least the effects of non-uniformity and load on timing and rate of LVP falls should be appreciated. Isovolumetric left ventricular pressure fall is a complex event including a rapid early and slower late phase. As a consequence, LVP fall cannot be described by a single index. Peak--dP/dt is measured at the transition between early and late LVP fall. Its value can be affected by changes of both phases. Interpretation of peak-dP/dt should therefore be cautious. LVP fall at and after mitral valve opening might be regulated differently from late LVP fall, as evaluated by the time constant tau. Loading effects of LVP fall after mitral valve opening can therefore not always be predicted from changes in tau. Load dependence is a concept based on experimental observations in isolated cardiac muscle, which describes the separation in time between shorter isotonic and longer isometric twitches. Temporal separation is illustrated by the response of cardiac muscle to late systolic load.(ABSTRACT TRUNCATED AT 250 WORDS)