Measurement of Diffusing Capacity for Carbon Monoxide (D sub LCO)

摘要

Single breath calculations of diffusing capacity for carbon monoxide (D sub LCO) rely on the concentrations of carbon monoxide measured in the expired gas. Automated equipment generally collects data after the subject exhales a preset washout somewhat larger than the expected dead space. However, subjects with very high peak expiratory flows may exhale tha washout volume before the gas analyzer step response has stabilized. A small sample volume recorded during rapid flow at that time may yield incorrectly low carbon monoxide concentrations, leading to falsely high Dsub LCO values. This report proposes that investigators inspect gas concentration vs. time graphs and choose the sample starting time to exclude the analyzer instability. This choice will result in a variety of washout volumes that are dependent on the peak expiratory flow generated by ths subjects. Sample volumes of 1 L are recommended, to help to average out some of the experimental noise. The increased sample size adds less than 1 second to the 10-second breath-hold time.