Tuesday, August 25, 2009

California DUI Lawyers use Instruction to explain accuracy of breath test result depends on one's partition ratio which varies from statutory ratio

California DUI attorneys attacking breath test results (.08 to .14) want the jury to be properly instructed in a drunk driving jury trial. Here's what should be used.

PEOPLE v. MCNEAL __ (2007) Cal. App. 4th __ Case no. E041226 filed 9 21 07

Alcohol contained only in the breath does not cause impairment. It is the impact of alcohol on the central nervous system, particularly on the brain, that causes the physical and psychological changes associated with impairment. Alcohol reaches the central nervous system through the blood. When used to establish blood alcohol levels, breath testing devices use a mathematical constant to approximate the percentage of alcohol in the blood based on the amount of alcohol present in a breath sample.

Because intoxication occurs when alcohol in sufficient amounts is carried to the central nervous system through the bloodstream, evidence of alcohol in a person’s bloodstream is relevant to proving that a defendant was under the influence of alcohol. When the evidence of blood alcohol is based on a breath test, the accuracy of the breath alcohol measurement as an indicator of the amount of alcohol in the defendant’s bloodstream is important. Such accuracy depends in part on the extent to which the defendant’s actual partition ratio varies from the statutory partition ratio. Evidence of a defendant’s personal partition ratio may show that the breath test overstates or understates the amount of alcohol in his bloodstream, thereby reducing or increasing the likelihood that he was impaired.