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Varying elastance concept may explain coronary systolic flow impediment
R Krams1, P Sipkema, N Westerhof
1Laboratory for Physiology, Free University, Amsterdam, The Netherlands.
Insights
Left ventricular systolic pressure has a minimal impact on coronary blood flow amplitude. This suggests that pressure alone does not solely determine coronary flow, supporting the time-varying elastance model.
Area of Science:
- Cardiovascular Physiology
- Hemodynamics
Background:
- Coronary blood flow is crucial for myocardial function.
- Understanding the determinants of coronary inflow is essential for diagnosing and treating cardiac conditions.
Purpose of the Study:
- To investigate the relationship between left ventricular systolic pressure and phasic arterial coronary inflow.
- To test the hypothesis that left ventricular pressure is the sole determinant of coronary flow.
Main Methods:
- Measurements of phasic arterial coronary inflow in a blood-perfused isolated cat heart.
- Varying systolic left ventricular pressure under controlled conditions (constant perfusion pressure, vasomotor tone, and heart rate).
- Analysis of normalized flow amplitude (A) in relation to systolic pressure (Ps).
Main Results:
- A weak correlation was found between left ventricular systolic pressure and normalized coronary flow amplitude (A = 0.70 +/- 0.15 + 0.005 +/- 0.005 Ps).
- The hypothesis that left ventricular pressure solely impedes coronary flow was not supported.
- The observed data align with the time-varying elastance concept.
Conclusions:
- Left ventricular systolic pressure is not the sole determinant of coronary flow.
- The time-varying elastance model provides a suitable framework for explaining coronary flow dynamics.
- Both intravascular and luminal compartments are subject to time-varying elastance, influencing coronary flow similarly across different beat types.
Abstract:
We measured phasic arterial coronary inflow in the blood-perfused isolated cat heart (n = 5) with a balloon in the left ventricle under well-defined conditions, i.e., constant perfusion pressure, constant vasomotor tone (maximal vasodilation), and heart rate. The normalized amplitude (A) between systolic flow (Fs) and diastolic flow (Fd) [A = (Fd - Fs)/Fd] was related to systolic left ventricular pressure (Ps, range 1.6-17 kPa, 1 kPa = 7.5 mmHg) for different isovolumic beats obtained by changes in balloon volume and for low load isobarically ejecting beats (pressure 0.2 kPa). The data were fitted to A = a + bPs with a = 0.70 +/- 0.15 (SD) and b = 0.005 +/- 0.005 kPa-1. This relation indicates a very weak effect of left ventricular systolic pressure on normalized flow amplitude. Thus the hypothesis that left ventricular pressure is the sole determinant impeding coronary flow could not be confirmed. However, our data could be explained on basis of the time-varying elastance concept (H. Suga, K. Sagawa, and A. A. Shoukas. Circ. Res. 32: 314-322, 1973). The intravascular and luminal (cavity) compartments both are assumed to be subject to a time-varying elastance. The time-varying luminal elastance is similar for isovolumic and isobaric beats. We assume that the elastance of the vascular compartment also behaves the same for these beats, and therefore coronary flow is affected similarly.(ABSTRACT TRUNCATED AT 250 WORDS)