Contingent reinforcement for reduced carbon monoxide levels in cigarette smokers.

Expired air carbon monoxide (CO) was evaluated simultaneously as the target for a contingent reinforcement intervention to promote smoking reduction and as a measure of within-subject changes in recent smoking rates and patterns. Eleven volunteer smokers participated in a three-week study which utilized an A-B-A design. CO levels were measured on weekday afternoons between 3:00 and 4:30 p.m. and detailed self-report records of smoking were kept by subjects throughout the study. A monetary payment of +5.00 was available during study week 2 for CO readings which were 50% or less of the average reading obtained for that subject during study week 1. Contingent payment was withdrawn during study week 3. Three measures of smoking changed in an orderly manner during the study. CO readings were reduced from initial baseline levels during study week 2 but generally did not return to original baseline levels when the contingency was withdrawn. Number of daytime cigarettes recorded decreased and minutes of cigarette abstinence prior to the afternoon study contact increased during the contingent intervention period compared to baseline study phases. The average within-subject correlation between expired air CO level and number of daytime cigarettes was 0.67 (p less than 0.01), that between CO and time since last cigarette was -0.59 (p less than 0.05). Expired air CO appears to be an appropriate target for contingent reinforcement intervention as well as an objective measure which reflects rates and patterns of recent smoking in individual subjects.