Exhaled carbon monoxide: variations due to collection method and physiology.

Area of Science:

• Pulmonary Physiology
• Biomedical Measurement
• Environmental Health

Background:

• Exhaled carbon monoxide (eCO) measurement is vital for understanding physiological and disease states.
• Current limitations include sampling protocols, measurement feasibility, and understanding normal variation.
• Accurate eCO measurement requires validated methods and understanding daily/weekly fluctuations.

Purpose of the Study:

• To compare three exhaled carbon monoxide (eCO) collection methods: continuous breathing (ConB), breath-holding (BrH), and short rebreathing (SrB).
• To investigate patterns of normal variation in eCO through repeated daily and weekly measurements.
• To assess the reliability of eCO measurements for clinical and physiological research.

Main Methods:

• Phase I: Compared ConB and BrH in 10 healthy non-smokers, with repeated measurements over 21 days.
• Phase II: Compared BrH and SrB in 30 healthy non-smokers, collecting weekly prebreakfast samples for four weeks.
• Utilized a Carbolyzer mBA-2000 instrument with an electrochemical method, correcting for ambient CO.

Main Results:

• ConB yielded lower eCO than BrH, with frequent inadequate alveolar sampling indicated by low eCO2.
• eCO measured by ConB and BrH increased during the day and showed week-to-week variability.
• The short rebreathing (SrB) method was easier, produced higher eCO and eCO2 levels compared to BrH.
• Approximately 37% of participants showed week-to-week eCO changes of ≥1.0 ppm, complicating interpretation.

Conclusions:

• The short rebreathing (SrB) method offers advantages in ease of use and higher eCO/eCO2 readings over breath-holding (BrH).
• Significant week-to-week variability in exhaled carbon monoxide (eCO) exists in healthy individuals.
• This variability poses challenges for interpreting eCO in relation to physiological or disease states, necessitating careful consideration of sampling protocols.