If I register 0.022% BAC on a breathalyzer, can I register 0.000% BAC 45 minutes later. My doctor told me it was physically impossible.

It is impossible. First of all BAC means Blood Alcohol Content, so you cannot register a BAC on a breathalizer because it measures the amount of alcohol on your breath, not in your blood.

Alcohol leaves your breath more quick than it leaves your blood. That is why it is impossible.