Wk. Al-delaimy et al., The effects of carbon dioxide on exercise-induced asthma: an unlikely explanation for the effects of Buteyko breathing training, MED J AUST, 174(2), 2001, pp. 72-74
Citations number
12
Categorie Soggetti
General & Internal Medicine","Medical Research General Topics
Objectives: To examine the effect of breathing 3% CO2 on exercise-induced a
sthma (EIA), as a raised airway CO2 level is suggested to mediate the effec
ts of Buteyko breathing training (BBT).
Design: Double-blind crossover study, using a standard laboratory-based exe
rcise challenge, with EIA defined as a fall of 15% or greater in the forced
expiratory volume in one second (FEV1) within 30 minutes of completing a s
tandard exercise protocol.
Subjects: 10 adults with confirmed EIA.
Intervention: Air enriched with 3% CO2 during and for 10 minutes after exer
cise.
Outcome measures: Maximum percentage fall in FEV1 after exercise. Area unde
r curve (AUC) of the decrease in FEV1 with time.
Results: Mean maximum fall in FEV1 was similar: 19.9% with air, and 26.9% w
ith 3% CO2 (P=0.12). The mean AUC for the total 30-minute post-exercise per
iod was 355 for air and 520 for 3% CO2 (P=0.07). After discontinuing the 3%
CO2 at 10 minutes after exercise, there was a further and sustained fall i
n FEV1. Mean AUC for the period 10-30 minutes post-exercise was significant
ly greater for CO2 than air (275 and 137, respectively [P= 0.02]). Mean min
ute ventilation was increased when subjects exercised breathing 3% CO2: 77.
5 L/min for 3% CO2, compared with 68.7 L/min for air (P= 0.02).
Conclusion: Breathing 3% CO2 during exercise does not prevent EIA. The shap
e of the FEV1 response curve after 3% CO2 suggests that a greater degree of
EIA (because of increased minute ventilation during exercise) was opposed
by a direct relaxant effect of CO2 on the airway. Increased airway CO2 alon
e is an unlikely mechanism for the reported benefits of BET; nevertheless,
further study of the effects of voluntary hypoventilation in asthma is warr
anted.