Protein washdown as a defense mechanism against myocardial edema

Myocardial edema occurs in many pathological conditions. We hypothesized th at protein washdown at the myocardial microvascular exchange barrier would change the distribution of interstitial proteins from large to small molecu les and diminish the effect of washdown on the colloid osmotic pressure (CO P) of interstitial fluid and lymph. Dogs were instrumented with coronary si nus balloon-tipped catheters and myocardial lymphatic cannulas to manipulat e myocardial lymph flow and to collect lymph. Myocardial venous pressure wa s elevated by balloon inflation to increase transmicrovascular fluid flux a nd myocardial lymph flow. COP of lymph was measured directly and was also c alculated from protein concentration. Decreases occurred in both protein co ncentration and COP of lymph. The proportion of lymph protein accounted for by albumin increased significantly, whereas that accounted for by beta-lip oprotein decreased significantly. The change in the calculated plasma-to-ly mph COP gradient was significantly greater than the change in the measured COP gradient. We conclude that the change in the distribution of interstiti al fluid protein species decreases the effect of protein washdown on inters titial fluid COP and limits its effectiveness as a defense mechanism agains t myocardial edema formation.