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Increased steady‐state and larger O 2 deficit with CO 2 inhalation during exercise
Author(s) -
Østergaard L.,
Kjær K.,
Jensen K.,
Gladden L. B.,
Martinussen T.,
Pedersen P. K.
Publication year - 2012
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/j.1748-1716.2011.02342.x
Subject(s) - hypercapnia , inhalation , chemistry , respiratory acidosis , respiratory system , zoology , respiratory exchange ratio , ventilation (architecture) , steady state (chemistry) , acidosis , medicine , anesthesia , heart rate , blood pressure , biology , mechanical engineering , engineering
Aim: To examine whether inhalation of CO 2 ‐enriched gas would increase steady‐state during exercise and enlarge O 2 deficit.Methods: Ten physically active men ( 53.7 ± 3.6 mL min −1 kg −1 ; ± SD) performed transitions from low‐load cycling (baseline; 40 W) to work rates representing light (≈ 45%; 122 ± 15 W) and heavy (≈ 80%; 253 ± 29 W) exercise while inhaling normal air (air) or a CO 2 mixture (4.2% CO 2 , 21% O 2 , balance N 2 ). Gas exchange was measured with Douglas bag technique at baseline and at min 0–2, 2–3 and 5–6.Results: Inhalation of CO 2 ‐enriched air consistently induced respiratory acidosis with increases in PCO 2 and decreases in capillary blood pH ( P < 0.01). Hypercapnic steady‐state was on average about 6% greater ( P < 0.01) than with air in both light and heavy exercise, presumably because of increased cost of breathing (ΔVE 40–50 L min −1 ; P < 0.01), and a substrate shift towards increased lipid oxidation (decline in R 0.12; P < 0.01). during the first 2 min of exercise were not significantly different whereas the increase in from min 2–3 to min 5–6 in heavy exercise was larger with CO 2 than with air suggesting a greater slow component. As a result, O 2 deficit was greater with hypercapnia in heavy exercise (2.24 ± 0.51 L vs. 1.91 ± 0.45 L; P < 0.05) but not in light (0.64 ± 0.21 L vs. 0.54 ± 0.20 L; ns).Conclusion: Inhalation of CO 2 ‐enriched air and the ensuing respiratory acidosis increase steady‐state in both light and heavy exercise and enlarges O 2 deficit in heavy exercise.