NEW YORK (CNN/Money) - The way bonds keep running higher, everybody is wondering when they're going to run out of breath.

Thanks to suggestions from the Fed that it will rekindle the economy by any means necessary, the yield on the 10-year bond has swooped down to 3.18 percent -- yet another 45-year low. And other rates have come tumbling down with it: 30-year mortgages are at all-time lows and the yields on corporate bonds have dipped to their lowest levels since Moody's started tracking them.

How long could this go on? If the Fed has its way, long-term rates will remain low well after the economy picks up steam. The central bank wants to ensure that the recovery doesn't sputter and that the United States doesn't see its first deflationary episode since the Great Depression.

But the Fed may not get its way.

Already, there are murmurings in the market that the Fed has perhaps become too aggressive and that its easy-money stance, plus the generous stimulus that's coming from the tax cut, could overheat the economy. Visions of wheelbarrows and rentenmarks (the trillion-mark note that Germany issued in the 1920s) dance through some worriers' heads.

Even the suggestion of an inflationary threat is enough to keep bond portfolio managers up at night. Bonds offer a near-guaranteed return on investment, after all, but when inflation comes into play the money they return isn't worth so much.

In the past, to prevent this from happening, some bond investors -- coined the "bond market vigilantes" by Prudential strategist Ed Yardeni back in the 1980s -- come into town. Like an unruly posse that's finished with the tar and feathers long before Sheriff Greenspan has even put on his spurs, they drive interest rates higher.

How does this happen? Some bond managers -- the vigilantes -- reverse course and start shorting long-term Treasurys aggressively. The way shorting works, you borrow the bonds and then turn around and sell them, believing that you can buy them back, and return them to the lender, at a cheaper price. The selling in itself sends bonds lower and yields upward. At the same time, some big portfolio managers decide that, given the inflation risks, bonds aren't worth buying any more. They can be quite vocal about their view (think Pimco), influencing other market players. Finally, portfolio managers and financial institutions who have been "surfing the yield curve" -- borrowing money at low short term rates to buy longer-term instruments -- begin to get squeezed, and unwind their positions.

The end result is that higher long-term Treasury yields force the economy into a cooling-off period. Mortgage rates go higher, muting housing activity, as do corporate rates, making it harder for companies to raise capital. The message to the Fed is clear: Raise short-term rates, or we'll keep raising long-term ones. Eventually, the Fed acquiesces.