Re: The issue is not that people lie
Pathological liar who lies about everything - Include obvious questions. If the person lies about those, put him aside as such and investigate further.
Sociopath - Use questions that may trigger alternate responses. Sociopaths rarely are perpetually calm; they merely react differently and can be tested for such.
Delusion - Test for delusion using contextual questions. If subject is deluded enough to believe his own lie, set aside for psychiatric evaluation.
Random/erratic pulse/breating for other reasons - Check for these before the polygraph. If they're like this before the test, you can predict inconsistency and try another way.