Blood is mostly made up of water, as are our organs and muscles. To read specifically about edema, swelling caused by fluid retention where excess fluid is trapped in the body's tissues, see our article Edema: Causes, Symptoms and Treatments.
If you use the Amsoil Ea15K01 and the ASM oil (For 3rd gen Prius), then you can safely go 15,000 miles between oil changes. I drive 25,000 miles per year in my Prius. Amsoil backs up their products by a written warranty.
But here's the trick: I don't, and you don't have to either. Just like many cars, our Prius needs an oil change twice a year, based on how we drive. For such a shop, it is no more difficult to put on the mounted winter tires than to rotate the tires on the car.