Estimation of myocardial blood flow heterogeneity by transorgan helium transport functions

Following single breath inhalations of helium 49 simultaneous inlet-outlet pairs of helium dilution curves were recorded in seven dog experiments from the aortic and coronary sinus blood by use of mass spectrometric technique. After numeric deconvolution of the dilution curves the weighting function of tracer transit times was used for calculation of the mean myocardial blood flow per unit of tissue, which closely correlated with directly measured flow. Secondly, the degree of blood flow heterogeneity was estimated from the first moments of the weighting function of transit times and by compartmental analysis based on an inverse Laplace transform. In the intact heart the results suggest a rather constant dispersion of flows relative to the mean flow F in the order of sigma/F = 0.3. The apparent dispersion of flows is increased by alpha-adrenergic stimulation with pressure and volume load, particularly in a state of beta-blockade, a finding, which may be attributed to variations of intercapillary distances and to a heterogeneity of blood flow per unit of tissue.