The effect of duration of breath-holding on expired air carbon monoxide concentration in cigarette smokers.

Exhaled alveolar air contains carbon monoxide that has passed from the blood during a period of breath holding and so provides an accurate guide to carboxyhaemoglobin concentration, itself affected by inhaling tobacco smoke. It has been claimed that breath hold duration makes no appreciable difference to the expired air carbon monoxide (ECO) concentration obtained. A study was conducted to determine the relationship between duration of breath holding prior to exhalation and ECO value. It was found that ECO concentration increased systematically up to 25 seconds of breath holding, with the curve beginning to flatten off after 15 seconds. It is concluded that where possible a breath hold duration of at least 20 seconds should be used and that shorter durations do not provide ECO concentrations comparable with the 20-second value.