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Role of arterial hypoxemia and pulmonary mechanics in exercise limitation in adults with cystic fibrosis

Department of Respiratory Medicine and National Referral Center for Adult Cystic Fibrosis, St. Vincent's University Hospital, Dublin, Ireland

Submitted 4 May 2004 ; accepted in final form 11 April 2005

We tested the hypothesis that maximal exercise performance in adults with cystic fibrosis is limited by arterial hypoxemia. In study 1, patients completed two maximal exercise tests, a control and a test with 400 ml of added dead space. Maximal O₂ consumption was significantly lower in the added dead space study vs. control (1.04 ± 0.15 vs. 1.20 ± 0.11 l/min; P < 0.05), with no difference in peak ventilation. There was significant O₂ desaturation during exercise that was equal in both control and added dead space studies. The decrease in maximal O₂ consumption with added dead space suggests that maximal exercise in cystic fibrosis is limited by respiratory factors. We subsequently examined whether pulmonary mechanics or arterial hypoxemia limits maximal exercise performance. In study 2, patients completed two maximal exercise tests, a control and a test with 400 ml of added dead space while also breathing 38% O₂. Added dead space was used to overcome the suppressive effects of hyperoxia on minute ventilation. Maximal O₂ consumption was significantly higher with added dead space and 38% O₂ vs. control (1.62 ± 0.16 vs. 1.43 ± 0.14 l/min; P < 0.05). Peak ventilation and O₂ saturation were significantly greater in the added dead space and 38% O₂ test vs. control. The increase in maximal O₂ consumption and peak ventilation with added dead space and 38% O₂ suggests that maximal exercise in cystic fibrosis is limited by arterial hypoxemia.

oxygen; treatment; pulmonary mechanics; gas exchange

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