[The elimination of carboxyhemoglobin--gender-specific and circadian effects].

We investigated sex-specific and circadian variations of carboxyhemoglobin (COHb) elimination in healthy volunteers. COHb elimination follows an exponential function with a baseline found in nonsmoking women at 1.72% and in nonsmoking men at 1.79% COHb saturation. During the day, the elimination half-life time (t1/2), determined by eleven hourly samples after stopping smoking was significantly (Wilcoxon-test, p less than .01) shorter in women (3.2 +/- .4 hours, mean +/- standard deviation, n = 7) than in men (4.5 +/- 0.4, n = 6). During the night, too, t1/2 calculated from 2-point measurements after the smoking halt was significantly (Wilcoxon-test, p less than .05) shorter in women (4.3 +/- 1.1, n = 4) than in men (8.0 +/- 1.6, n = 5). In men, t1/2 during the night was significantly longer (p less than .01, Wilcoxon-test) than during the day. The day/night difference may be caused by reduced alveolar ventilation during sleep. Less muscle mass and, therefore, less myoglobin as a depot for carbon monoxide may account for the shorter half-life time of carboxyhemoglobin in women. We conclude that these variations of COHb-elimination should be taken into account when a smoking halt is advised, for instance, preoperatively.