Day-to-Day Changes in Coronary Hemodynamics Secondary to Constriction of Circumflex Branch of Left Coronary Artery in Conscious Dogs

The studies were carried out in four dogs. The effects of applying ameroid constrictors to the circumflex branch were observed on the circumflex blood flow, circumflex and peripheral circumflex pressures, circumflex reactive hyperemia and aortic-circumflex pressure difference. Recordings were successfully made for periods of 16 to 64 days. During this time the circumflex branch became completely occluded in three of the dogs. The circumflex blood flow remained in the normal range until reactive hyperemia (following a 10- to 12-second occlusion of the circumflex branch) almost disappeared; the flow then decreased to zero in 5 to 10 days. Although there was some rise in mean peripheral circumflex pressure and aortic-circumflex pressure difference before circumflex blood flow decreased, the major rise in these variables occurred only when flow and reactive hyperemia became markedly decreased. The maximum rate of rise of mean peripheral circumflex pressure varied from 6 to 15 mm Hg/24 hours. The experiments indicate that a severe degree of coronary insufficiency precedes a rise in mean peripheral circumflex pressure to 60 to 70 mm Hg. We interpret such increments in mean peripheral circumflex pressure to mean that large collaterals must be open; the studies with injection of Schlesinger mass confirmed this interpretation.