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The effects of carbon dioxide on exercise‐induced asthma: an unlikely explanation for the effects of Buteyko breathing training
Author(s) -
AlDelaimy Wael K,
Crane Julian,
Hay Scott M,
Gain Kevin R,
Jones David T
Publication year - 2001
Publication title -
medical journal of australia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.904
H-Index - 131
eISSN - 1326-5377
pISSN - 0025-729X
DOI - 10.5694/j.1326-5377.2001.tb143157.x
Subject(s) - medicine , crossover study , ventilation (architecture) , asthma , respiratory minute volume , exercise induced asthma , breathing , anesthesia , physical therapy , respiratory system , mechanical engineering , alternative medicine , pathology , engineering , placebo
Objectives To examine the effect of breathing 3% CO 2 on exercise‐induced asthma (EIA), as a raised airway CO 2 level is suggested to mediate the effects of Buteyko breathing training (BBT). Design Double‐blind crossover study, using a standard laboratory‐based exercise challenge, with EIA defined as a fall of 15% or greater in the forced expiratory volume in one second (FEV 1 ) within 30 minutes of completing a standard exercise protocol. Subjects 10 adults with confirmed EIA. Intervention Air enriched with 3% CO 2 during and for 10 minutes after exercise. Outcome measures Maximum percentage fall in FEV 1 after exercise. Area under curve (AUC) of the decrease in FEV 1 with time. Results Mean maximum fall in FEV 1 was similar: 19.9% with air, and 26.9% with 3% CO 2 ( P = 0.12), The mean AUC for the total 30‐minute post‐exercise period was 355 for air and 520 for 3% CO 2 ( P = 0.07), After discontinuing the 3% CO 2 at 10 minutes after exercise, there was a further and sustained fall in FEV 1 . Mean AUC for the period 10–30 minutes post‐exercise was significantly greater for CO 2 than air (275 and 137, respectively ( P =0.02]). Mean minute ventilation was increased when subjects exercised breathing 3% CQ 2 : 77.5 L/min for 3% CO 2 , compared with 68.7 L/min for air ( P = 0.02). Conclusion Breathing 3% CO 2 during exercise does not prevent EIA. The shape of the FEV 1 response curve after 3% CO 2 suggests that a greater degree of EIA (because of increased minute ventilation during exercise) was opposed by a direct relaxant effect of CO 2 on the airway. Increased airway CO 2 alone is an unlikely mechanism for the reported benefits of BBT; nevertheless, further study of the effects of voluntary hypoventilation in asthma is warranted.