Final answer:
When cold water is flushed into a patient's ear, the normal response is a fast phase of nystagmus toward the opposite side, indicative of a properly functioning vestibular system. A fast phase toward the same side or an absence of nystagmus could indicate a pathologic condition.
Step-by-step explanation:
When cold water is flushed into a patient's ear, the resulting reflex is called caloric testing, which is part of an ENG (electronystagmography) or VNG (videonystagmography) test. This test evaluates the function of the vestibular portion of the inner ear, which helps with balance. Normally, when cold water is introduced into the ear, vestibular nystagmus occurs where the fast phase of the nystagmus is opposite to the side of the cold water stimulus (the fast phase is toward the unaffected or opposite ear). So, if cold water is introduced into the right ear, the fast phase should be toward the left side. This response is considered normal and indicates that the vestibular system is functioning correctly. If the fast phase is toward the same side of the cold water stimulus, or if there is no nystagmus, it could be indicative of a pathologic condition.