References: McKone et al, 2005
J Appl Physiol. 2005 Sep;99(3):1012-8. Epub 2005 Apr 28.
Role of arterial hypoxemia and pulmonary mechanics in exercise limitation in
adults with cystic fibrosis.
McKone EF, Barry SC, Fitzgerald MX, Gallagher CG.
Dept. of Respiratory Medicine, St. Vincent's Univ. Hospital, Elm Park,
Dublin 4, Republic of Ireland.
Abstract
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.