All Direct Subsidized and Unsubsidized Loans disbursed between July 1, 2014 and June 30, 2015 carry a fixed interest rate of 4.66% for undergraduates. Graduate or professional students receiving a Direct Unsubsidized Loan disbursed between July 1, 2014 and June 30, 2015 will have a fixed interest rate of 6.21%.
There is a problem when the valve that controls what blood is good and what blood is used, no longer is strong enough to control this flow. Heart valves get damaged or simply wear out. I think you are asking what causes blood to flow in the wrong direction. My guess is that it would be a faulty heart valve.
Along with scarring of the veins, a blood clot may injure the valves (two leaflets lying in the vein which shut to stop the backward flow of blood) causing incompetence and deep venous reflux or back flow (Figure 1) . This will allow the blood togo backward in the vein and down the leg rather than up to the heart.