Jeremy Vile

The polygraph measures such things as heartbeat, blood pressure, and respiration. The polygraph is not a lie detector because changes in heartbeat, blood pressure, and respiration can be caused by many things. Nervousness, anger, sadness, embarrassment, and fear can all be causal factors in altering one's heart rate, blood pressure, or respiration rate. Having to go to the bathroom can also be causative. There are also a number of medical conditions such as colds, headaches, constipation, or neurological and muscular problems that can cause the physiological changes measured by the polygraph