Related Experiment Videos
Left ventricular function depends on previous beat ejection but not previous beat pressure load
B K Slinker1, S G Shroff, R D Kirkpatrick
1Department of Medicine, University of Vermont, Burlington 05405.
Insights
Previous beat ejection, not pressure, significantly impacts left ventricular performance. This finding clarifies the mechanisms of beat-to-beat regulation in the cardiovascular system.
Area of Science:
- Cardiovascular Physiology
- Cardiac Mechanics
- Ventricular Function
Background:
- Previous beat contraction history influences current left ventricular (LV) performance.
- The specific mechanical factors (ejection vs. pressure) driving this influence are unclear.
- The magnitude of this beat-to-beat effect on LV performance is not well-defined.
Purpose of the Study:
- To determine if previous beat ejection or pressure load is the primary driver of LV performance changes.
- To quantify the effect of previous beat contraction history on LV function.
Main Methods:
- Experiments conducted on isolated rabbit left ventricle preparations.
- Precise control of LV pressure and volume using a servo-controlled linear motor system.
- Varying pressure clamp levels during test beats to assess subsequent isovolumic beats.
Main Results:
- LV developed pressure and peak positive dP/dt increased significantly as previous beat ejection pressure decreased.
- Increased LV function was directly correlated with previous beat ejection.
- LV function was not significantly related to previous beat pressure load or relaxation.
Conclusions:
- Previous beat ejection, rather than pressure load, is the critical mechanical factor influencing beat-to-beat LV performance.
- This study quantifies the impact of prior ejection on subsequent cardiac cycles.
- Findings elucidate mechanisms of beat-to-beat regulation in the cardiovascular system.
Abstract:
Previous beat contraction history, in which the performance of the left ventricle on any one beat is influenced by the mechanical events of the previous beat, may be important in the beat-to-beat regulation of left ventricular performance in the intact cardiovascular system. Prior studies of this phenomenon have established that mechanical events of the previous beat influence the function of the current beat, but it is not known whether the important mechanical influence is exerted by previous beat ejection or previous beat pressure. In addition, the magnitude of the effect of previous beat contraction history on left ventricular performance is unknown. To make these determinations, we performed experiments in six isolated rabbit left ventricle preparations buffer perfused at 30 degrees C. Left ventricular pressure and volume were controlled precisely with a servo-controlled linear motor system. After steady-state ejecting conditions were established by clamping left ventricular ejection pressure at 60% of peak isovolumic pressure, single test beats, which were pressure clamped at 40%, 60%, 80%, and 100% of peak isovolumic pressure, were introduced and followed by an isovolumic reference beat. As the level of pressure clamp decreased from 100% to 40%, developed pressure on the isovolumic beat following the single test beats increased from 139 +/- 15 (mean +/- SD) to 151 +/- 13 mm Hg. Similarly, peak positive left ventricular dP/dt increased from 1,718 +/- 209 to 1,864 +/- 181 mm Hg.sec-1 (both p less than 0.01). Multiple regression analysis showed that this increase in left ventricular function was related to previous beat ejection but not to previous beat pressure load or relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)