Alveolar carbon monoxide: a comparison of methods of measurement and a study of the effect of change in body posture.
1. We have compared rebreathing, breath-hold and mean alveolar methods of measuring alveolar carbon monoxide (CO), at levels similar to those found in smokers, as a preliminary to using them as indirect measures of carboxyhaemoglobin levels. In the present study alveolar CO levels were raised by rebreathing a 2% CO mixture. 2. Breath-hold CO was measured after breath-hold times of 0-35 s in 5 s increments. Using generalized linear models, the maximum value for breath-hold CO was estimated to occur at 23 s. Breath-hold CO after a 20 and 25 s breath-hold were similar to and significantly greater than those of less than 20 s or greater than 25 s. 3. As expired CO increased, the difference between breath-hold and mean alveolar CO became proportionally larger. On average, breath-hold CO was 24% larger than mean alveolar CO. 4. Rebreathing, breath-hold and mean alveolar CO were compared at four different inspired oxygen concentrations. Expired CO increased significantly with increasing oxygen for all three methods. At end-tidal oxygen levels of less than 25%, breath-hold and rebreathing CO were similar, however, the overall mean difference between the three methods was significant. 5. While rebreathing CO was unaffected by changes in ventilation/perfusion of the lung, induced by change in body posture, both breath-hold and mean alveolar CO showed a significant fall with change from the supine to erect posture.(ABSTRACT TRUNCATED AT 250 WORDS)
Kirkham
A J
AJ
Cardiothoracic Institute, Midhurst, West Sussex, U.K.
Guyatt
A R
AR
Cumming
G
G
D000328:Adult; D001944:Breath Tests / Q000379:methods*; D002248:Carbon Monoxide / Q000032:analysis*; D002263:Carboxyhemoglobin / Q000032:analysis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture; D011650:Pulmonary Alveoli / Q000378:metabolism*
D002248:Carbon Monoxide; D002263:Carboxyhemoglobin