Honestly, that’s all they’re good for: creating paranoia/terror/nervousness in the subject. Go read the ‘how to beat a polygraph’ book. Knowledge is calming.

Also? It’s not anything to do with symptoms showing stronger on baseline questions. The only big giveaway is breathing. I work in the medical field. Blood pressure, heart rate, bla bla bla… they all vary with frequencies and magnitudes that don’t allow them to be filtered from responses that do signify anything. The only vital sign that has a low enough rate for changes to really be detected is how often you take a breath. If you control that, the game is over. A really observant tester watching a testee attempting (poorly) to mask breathing rate may notice something is off, but it’s still a judgement call whether it’s due to nervousness and the attempt to calm down, or actual deception.

The best way to ‘pass’ a polygraph is to be just nice/cute enough to get the tester to like you somewhat, and then control your breathing. The proper test has them talking to you for at least a half hour beforehand so they can ‘get an idea’ about you, so you have plenty of time to be friendly. Take advantage of that. There is some nice research out there about self-disclosures and their effect on being liked. If they see a pattern that could be you being nervous, could be you trying to deceive, being liked will tip them towards the kinder perception.