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Alcohol dilates peripheral blood vessels, but has been known to actually. constrict some blood vessels in the brain, lowering the oxygen content. Alcohol dilates peripheral blood vessels, but has been known to actually  constrict some blood vessels in the brain, lowering the oxygen content.
Alcohol supposedly stimulates the nerve endings, making nystagmus more pronounced in intoxicated persons. As a personâs blood alcohol concentration increases, the eyes will âjerkâ sooner as they move to the side. The HGN test claims to gauge intoxication by measuring the involuntary oscillation of the eyes.