Simply put, no.  A polygraph is not used to determine truthfulness by means of assessing how nervous someone is.  Physiological factors do fluctuate during a polygraph due to nerves; however, a well trained, experienced, and competent polygraph examiner understands this, and can differentiate between the homeostatic level of nervousness, and the physiological arousal that occurs when someone lies.  Additionally, general nervousness is just that – generalized. It appears as something akin to “background noise” to a competent examiner. Deception on the other hand prompts physiological responses which are extremely specific to a particular question or questions if more than one lie is told.