I've heard a few interesting proposals of placing nano-scale capsules of various medicines and chemical compounds directly in a persons blood stream. The capsules would have various sensors that could detect low oxygen levels, body temperature, chemical compounds, pH, etc.
The capsules would float around the bloodstream not impeding the human in any way except when there is an injury or infection. The capsules would disperse their medicine/chemical compounds directly where needed to combat infections, heal wounds faster, prevent clots, repair brain and heart tissue after strokes or heart attacks, and maintain all sorts of hormones and compounds, like glucose in diabetics.
This is what nanotechnology is capable of in medicine. Direct medicinal help to the body exactly when it is needed or wanted.