Microsphere and dilution measurements of flow and interstitial space in dog heart.

The effects of coronary flow on cardiac capillary permeability-surface area products and interstitial spaces were examined at rest and after hemodilution in the canine heart. Multiple-indicator-dilution experiments and left atrial injections of microspheres were carried out in closed-chest anesthetized animals at rest and after plasma expansion with dextran. Plasma expansion was utilized to produce a large increase in coronary perfusion compared with control conditions. Values for plasma flow per unit interstitial space, derived from analysis of the indicator-dilution data, were found to correlate closely with average vascular plasma flow per gram, calculated from the cardiac microsphere data; the one reflects the other. With an increase in flow, cardiac capillary permeability-surface area product values were found to increase substantially, whereas the average sucrose extravascular or cardiac interstitial spaces remained stable. Consequently the dilution parameter, flow per unit interstitial space, which is independent of tracer loss, provided a good reflection of flow per weight of tissue in the heart, without the additional requirement for a flow probe.