Fractal Approaches to the Microcirculation

That there is marked heterogeneity of regional myocardial blood flows has long been recognized (Yipintsoi et al., Circ. Res. 33:573, 1973). The suspicion that much of the heterogeneity might have been an artifact of the microsphere deposition technique has been laid to rest by the studies of Baer et al. (Am. J. Physiol. 246:H418, 1984), King et al. (Circ. Res. 57:285, 1985), and by Bassingthwaighte et al. (Circ. Res. 66:1328, 1990) who showed that the technique had high reproducibility, with error much smaller than the variance in regional flows. The standard deviations of left ventricular myocardial blood flows in 100 mg pieces were 25 to 30% of the mean flow, with ranges from 1/5 of the mean to about twice the mean, while the microsphere variability is only about 8%.