Five and a half years ago I was in a serious automobile accident and spent three weeks in the ICU. During that time a filter was placed in my vein to catch blood clots from my legs. The filter did work and caught a lot of clots. When I was released from the ICU and went to a different hospital for therapy, the filter was left in my vein because the walls of the vein were becoming embedded with the filter, and the doctor said removing the filter would be a "messy" job.
I began to believe that the filter was restricting my blood-flow and thus my performance. I discussed this with my doctor and was referred to a blood-clot specialist for consultation about this. The specialist suggested that I have a CT scan of my legs so they could get a good view of my veins, the filter, and associated things. The CT scan gave the following findings.
There is an infrarenal IVC filter in place. Subtle material of decreased attenuation is noted throughout the course of the left and common iliac vein which is concerning for thrombus. There is contrast on both sides of this possible thrombus which suggests it is chronic in nature. There is normal opacification of the remaining visualized lower extremity veins without evidence of a filling defect to suggest a thrombus. Atherosclerotic calcification of the lower extremity arteries is noted. There is prominence of the pelvic and scrotal vasculature which is compatible with varicoceles.
A doctor who specializes in veins reviewed the CT images and concluded that (a) the filter couldn't be removed, (b) my body had been robust in creating collateral veins around the filter, and (c), I have a restriction in the blood flow in my left leg. The blood-clot specialist reviewed this with me and encouraged me to continue running or walking robustly. He also reminded me that it has been a year since I did distance running, and my performance has dropped significantly during that time, just due to my reduced running during the past year.