Does carbon dioxide retention during exercise predict a more rapid decline in FEV1 in cystic fibrosis?
- Correspondence to:
Dr H C Selvadurai
Department of Respiratory Medicine, The Hospital for Sick Children, Toronto, Ontario M5G1X8, Canada;
- Accepted 5 April 2005
Background: Carbon dioxide (CO2) retention during exercise is uncommon in mild to moderate lung disease in cystic fibrosis (CF). The ability to deal with increased CO2 is dependent on the degree of airflow limitation and inherent CO2 sensitivity. CO2 retention (CO2R) can be defined as a rise in PETCO2 tension of ⩾5 mm Hg with exercise together with a failure to reduce PETCO2 tension after peak work by at least 3 mm Hg by the termination of exercise.
Aim: To ascertain if carbon dioxide retention during exercise is associated with more rapid decline in lung function.
Methods: Annual spirometric and exercise data from 58 children aged 11–15 years, with moderate CF lung disease between 1996 and 2002 were analysed.
Results: The mean FEV1 at baseline for the two groups was similar; the CO2R group (n = 15) was 62% and the non-CO2 retention group (CO2NR) was 64% (n = 43). The decline in FEV1 after 12 months was −3.2% (SD 1.1) in the CO2R group and −2.3% (SD 0.9) in the CO2NR group. The decline after 24 months was −6.3% (SD 1.3) and −1.8% (SD 1.1) respectively. After 36 months, the decline in FEV1 was −5.3% (SD 1.2) and −2.6% (SD 1.1) respectively. The overall decline in lung function was 14.8% (SD 2.1) in the CO2R group and 6.7% (SD 1.8) in the CO2NR group. Using the primary outcome measure as a decline in FEV1 of >9%, final multivariate analysis showed that the relative risks for this model were (95% CIs in parentheses): ΔPETCO2 11.61 (3.41 to 24.12), peak V˙O2 1.23 (1.10 to 1.43), and initial FEV1 1.14 (1.02 to 1.28).
Conclusion: Results show that the inability to defend carbon dioxide during exercise is associated with a more rapid decline in lung function.
- CO2, carbon dioxide
- CO2R, CO2 retention
- CO2NR, CO2 non-retention
- FVC, forced vital capacity
- FEV1, forced expiratory volume in one second
- MVV, maximal voluntary ventilation
- PaCO2, arterial partial pressure CO2
- PETCO2, end-tidal CO2 partial pressure
- SD, standard deviation
- V˙E, minute ventilation, V˙CO2, CO2 production
- V˙O2, oxygen consumption
Competing interests: none declared