The effects of ischemia on myocardial vascular flow and permeability

The effects of brief periods of ischemia on vascular space size, vascular permeability to albumin, tissue water and extracellular space size, and vascular resistance were studied in the perfused isolated rabbit interventricular septum. Vascular space size increased 264% over control after 30 min ischemia and 52% after 60 min ischemia, but vascular resistance increased. Total tissue water did not change after ischemia and extracellular space size did not increase after 30 min ischemia and decreased slightly after 60 min ischemia. These results demonstrate that the initial increase in vascular resistance after ischemia is not initiated by interstitial edema or cellular edema. These events appear to be later phenomena. The initiating cause of the increased vascular resistance appears to be a combination of increased vascular tone and conversion of a portion of vascular flow from low resistance large vessel flow to higher resistance small vessel flow (capillary recruitment).