Effect of short-term smoking halt on carboxyhemoglobin levels and P50 values.

Fifteen informed volunteers who smoked one to two packs of cigarettes per day were studied to measure changes in carboxyhemoglobin levels and P50 after smoking was stopped for 12 hr. Before smoking was stopped, carboxyhemoglobin levels (6.55 +/- 0.40%) were above normal, and the P50 (22.92 +/- 0.25 mm Hg) was significantly shifted to the left. After smoking was stopped for 12 hr there was a significant decrease in carboxyhemoglobin levels to 1.06 +/- 0.16% (P less than 0.001), and P50 shifted towards normal to 26.41 +/- 0.14 mm Hg (P less than 0.001). The authors conclude that within even as little as 12 hr after cessation of smoking, carboxyhemoglobin and P50 levels change towards normal values.