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Coronary arterial inflow impediment during systole is little affected by capacitive effects
P Bouma1, P Sipkema, N Westerhof
1Laboratory for Physiology, Institute for Cardiovascular Research, Free University, Amsterdam, The Netherlands.
Insights
Coronary arterial inflow impediment during heartbeats is not significantly affected by capacitive flow effects. This study suggests dynamic contractions minimally impact coronary inflow compared to static ones.
Area of Science:
- Cardiovascular Physiology
- Cardiac Mechanics
- Coronary Circulation
Background:
- Cardiac contraction impedes coronary arterial inflow and augments venous flow.
- This is attributed to reduced intramyocardial blood vessel diameter during systole.
- Capacitive flow, a consequence of volume changes, is hypothesized to contribute to inflow impediment.
Purpose of the Study:
- To quantify the contribution of capacitive flow to total coronary inflow impediment during cardiac contraction.
- To differentiate the effects of dynamic versus static contractions on coronary blood flow.
Main Methods:
- Utilized isolated, blood-perfused, vasodilated rat hearts with intraventricular balloons.
- Compared coronary inflow impediment during dynamic (isovolumic beats) and static contractions (prolonged systoles).
- Varied left ventricular pressure to assess systolic flow-pressure relationships.
Main Results:
- The ratio of coronary inflow impediment in dynamic versus static contractions was not significantly different from unity.
- This indicates capacitive effects have minimal impact on coronary inflow impediment under tested conditions.
- Systolic pressure-volume relationship and maximal elastance were used to define contractility.
Conclusions:
- Capacitive flow has a negligible effect on coronary inflow impediment during dynamic cardiac contractions.
- Coronary resistance changes during systole are primarily driven by factors other than capacitive volume shifts.
- Findings challenge the significant role of capacitive flow in explaining systolic coronary inflow reduction.
Abstract:
During cardiac contraction coronary arterial inflow is impeded, whereas venous flow is augmented. These effects are assumed to be caused by diameter reductions of intramyocardial blood vessels. The reduction in vascular diameter (and thus vascular volume) during contraction increases coronary resistance and/or decreases back pressure so that flow decreases and the rate of change of volume results in a capacitive flow. The aim of this study was to estimate the contribution of capacitive flow to total coronary inflow impediment. Isolated blood-perfused (100 mmHg and constant), maximally vasodilated, ryanodine-pretreated rat hearts (n = 8) with intraventricular balloons were used. The coronary inflow impediment during isovolumic beats at a heart rate of 2-3 Hz (dynamic contractions) and during prolonged systoles obtained by fast pacing (static contractions, no capacitive flow impediment) were compared. Changing left ventricular balloon volume enabled us to vary left ventricular pressure and to relate systolic flow to systolic left ventricular pressure. We found that for the same contractility (expressed in terms of systolic pressure-volume relationship and maximal elastance) and same left ventricular pressure, the ratio of coronary inflow impediment in dynamic and static contractions is not significantly different from unity (P < 0.005). This implies that under our experimental conditions coronary inflow impediment in dynamic contractions is little affected by capacitive effects.