Variability of the blood:breath alcohol ratio in vivo.

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Abstract
Blood:breath alcohol ratios were measured in 21 healthy men (mean age, 42 yr; mean body wt, 84 kg) 30, 60, 90, 120, 300 and 360 min after ingestion of 0.72 g of alcohol/kg of body wt as whiskey. Drinking time was 20 min. Breath samples were analyzed using an Mk II Gas Chromatograph Intoximeter. Although all subjects reached the postabsorptive phase within 2 h from the start of drinking, the times of the peak blood alcohol concentrations (BAC) varied between subjects, peaks being recorded at 30, 60, 90 and 120 min from the start of drinking in 9, 6, 4, and 2 subjects, respectively. The mean alcohol ratio between 120-360 min after the start of drinking (postabsorptive phase, BAC > 0.1 mg/ml) was 2180 .+-. 189, and inherent variability in subjects was 6.4% of the mean. Between-subject variation was 5.84% of the mean ratio. A 2-way analysis of variance showed that the alcohol ratio varied significantly between subjects (P < 0.001) and between sampling times (P < 0.001). The observed mean blood:breath ratios were below the commonly accepted mean (i.e., < 2100) during active absorption of alcohol (30, 60, 90 min), with a significant difference at 30 min (-10.95% difference; P < 0.001), and were significantly above the accepted mean at 240, 300 and 360 min (+4.81, +3.86 and +8.76%; P < 0.05 or 0.1). During the elimination phase, the ratios increased with sampling time from the start of drinking, increasing with a decrease in BAC. The regression of the ratio through time during the elimination phase was significant (P < 0.01). The findings lend support to a medicolegal definition of alcohol impairment in terms of breath alcohol concentration instead of a conversion to BAC.