Effects of coronary flow reduction on capillary-myocardial exchange in dogs

The effects of coronary flow reduction on tracer capillary permeability surface area (PS) and distribution volumes were studied in open-chest dog preparations. A mixture of ⁵¹Cr-labeled red blood cells, ¹²⁵I-labeled albumin, [¹⁴C]sucrose, and tritiated water (³H₂O) was introduced into a shunt connecting the carotid and left anterior descending coronary arteries. Sampling from the coronary sinus produced a multiple indicator curve from which [¹⁴C]sucrose PS and ³H₂O volumes were computed. Curves were observed in control situations and after the cannula was partially clamped. In 6 dogs, cardiac lymph was collected and analyzed for total protein. Paired comparison of control and flow-restricted indicator curves showed that flow reduction decreased the absolute values of PS and tracer volumes. The ratio of sucrose volume to weight of perfused tissue increased with flow reduction. The ratio of sucrose PS to weight of perfused tissue increased with moderate flow reduction and decreased with severe flow reduction. The results suggest that flow reduction has 2 effects which competitively affect exchange: (1) flow restriction reduces surface area by capillary derecruitment, and (2) the remaining functional capillaries appear to undergo an increase in permeability to small molecules.