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Blood flow heterogeneity in the heart
1Institut für Physiologie Medizinische Fakultät Carl Gustav Carus, TU Dresden, Germany.
Insights
Myocardial blood flow is uneven even in healthy tissue. This spatial heterogeneity, influenced by factors like sample size, is stable over time and linked to local aerobic metabolism.
Area of Science:
- Cardiovascular Physiology
- Biomedical Engineering
- Myocardial Perfusion Imaging
Background:
- Local microsphere deposition density in myocardium is heterogeneous under physiological conditions.
- Biological heterogeneity must be distinguished from methodological factors like injection volume, regional blood flow, and sample mass.
Purpose of the Study:
- To investigate the nature and contributing factors of spatial heterogeneity in myocardial blood flow.
- To differentiate biological heterogeneity from methodological influences on microsphere deposition.
Main Methods:
- Analysis of microsphere deposition density variability using coefficients of variation (CV) for spatial (spat), temporal (temp), and methodological (meth) factors.
- Fractal and autocorrelation analyses to assess spatial correlation of myocardial blood flow.
- Comparison of metabolic markers between low and high flow myocardial regions.
Main Results:
- Spatial flow heterogeneity is the largest contributor to observed variability in microsphere deposition density.
- This heterogeneity is independent of myocardial layer, increases with decreasing sample mass and mean flow.
- Myocardial blood flow exhibits spatial correlation and is nonrandom.
- Local blood flow correlates with metabolic and transport rates, but not with markers of tissue hypoxia.
Conclusions:
- Histologically homogeneous myocardium exhibits inherent spatial blood flow heterogeneity.
- This heterogeneity is temporally stable, resolution-dependent, largely layer-independent, nonrandom, and linked to local aerobic metabolism.
Abstract:
Local deposition density of microspheres is heterogeneous in histologically homogeneous myocardium under physiological conditions. The underlying biological heterogeneity must be distinguished from a methodological heterogeneity which depends preferentially on the number of microspheres injected, blood flow to a particular myocardial region and sample mass. As the variables space (spat), time (temp), and method (meth) are independent of each other, the observed (obs) variability may be approximated using the coefficients of variation (CV) of the individual variables: CVobs = (CV2spat+CV2temp+CV2meth)0.5. Studies in which these different variables have been quantified indicate that the largest fraction of the observed variability of microsphere deposition density is contributed by spatial flow heterogeneity which exists independent of the myocardial layer. Spatial flow heterogeneity increases with decreasing sample mass and decreasing mean flow. Fractal and autocorrelation analyses have shown that adjacent myocardial flows are spatially correlated and nonrandom. Local blood flow was shown to correlate with various metabolic and transport rates, while no differences were found between low and high flow regions with respect to several metabolic markers of tissue hypoxia. In conclusion, the evidence available to date indicates that 1) in histologically homogeneous myocardium there exists a spatial blood flow heterogeneity which 2) is temporally stable, 3) resolution dependent, 4) largely layer-independent, 5) nonrandom, and 6) related to local aerobic metabolism.