The rise in carboxyhemoglobin from repeated pulmonary diffusing capacity tests

The purpose of this study determined the rise in carboxyhemoglobin percentage (COHb) from repeated pulmonary diffusing capacity tests using 5 or 10 s single breath-hold maneuvers. Five male and four female non-smokers [baseline COHb = 1.2 (SD 0.5%)] performed repeated pulmonary diffusing capacity testing on two separate days. The days were randomized to either repeated 10 s (0.28% CO), or 5 s (0.28% CO, 55 ppm NO) breath-hold maneuvers. Twenty-two 5 s breath-hold maneuvers, each separated by 4 min rest, raised COHb to 11.1 (1.4)% and minimally raised the methemoglobin percentage (METHb) by 0.3 (0.2)% to a value of 0.8 (0.2)%. After the 22nd test, pulmonary diffusing capacity for carbon monoxide (DLCO) was reduced by about 4 mL/min/mmHg, equating to a 0.44% increase in COHb per 5 s breath-hold maneuver and a concomitant 0.35 mL/min/mmHg decrease in DLCO. Pulmonary diffusing capacity for nitric oxide (DLNO) was not altered after 22 tests. On another day, the 10 s single breath-hold maneuver increased COHb by 0.64% per test, and reduced DLCO by 0.44 mL/min/mmHg per test. In conclusion, 5 s breath-hold maneuvers do not appreciably raise METHb or DLNO, and DLCO is only significantly reduced when COHb is at least 6%.

► Repeated 5-s single breath-hold diffusing capacity tests were performed. ► 55 ppm NO and 0.28% CO, 19.5% O2, 9.5% He, Bal N2, was inhaled per test. ► Carboxyhemoglobin percentage increased by 0.44% per test between the second and 22nd test. ► Pulmonary diffusing capacity for CO was significantly reduced when carboxyhemoglobin percentage was 6% (the 10th test). ► Pulmonary diffusing capacity for NO was not altered after 22 tests while methemoglobin percentage only changed minimally.