Fig. 4

Schematic illustration summarizing the relative sizes of different myocardial compartments and their change between rest and adenosine stress. The bars, representing 100% of the left ventricular (LV) mass, illustrate that myocardial blood volume (MBV) is approximately 9% at rest, and consists of plasma and red blood cells (RBC). The myocardial extracellular volume (ECV) is approximately 27% at rest, and consists of plasma and interstitium. The rest of the LV mass consists of cardiomyocytes. At stress, in terms of percentage of the LV mass, MBV increases to 12%, likely due to a balanced increase in both plasma and RBC. Myocardial ECV also increases to 31%, likely reflecting the increase in plasma. It is not known if the absolute LV mass increases during stress. Considering that compartments other than the cardiomyocytes (interstitium, blood) do increase during stress, it is likely that the absolute volume of cardiomyocytes stays the same, and the total LV mass increases slightly during stress. This can explain why, in this illustration, the cardiomyocyte compartment appears to have decreased in size, when expressed as a percentage of total LV mass. Furthermore, it is not known if the relationship between the increase in the RBC and plasma components of MBV is 1:1, since most of the increase lies within capillaries, which may have a different hematocrit compared to the blood in larger vessels