Abstract

There is only little evidence on the acute effect of ventilatory pressure support (PS) during cycling exercise in hypercanic COPD patients. We evaluated whether PS could reduce arterial PCO2 during exercise.

Methods: We studied 33 moderate to severe COPD patients (age: 62±xyears old, FEV1=37± 17% predicted). Thirteen presented with resting hypercapnia (HCO2 group) and 20 with normocapnia (NCO2 group).They performed two constant workrate tests (CWT) on a cycloergometer at 70% of maximal workrate in ambient air and with PS (stopped at isotime). PS was set during a habituation test in order to decrease dyspnea and increase exercise tolerance (mean PS 13±2 cmH2O). Transcutaneous PCO2 (tcPCO2) was monitored continuously during both tests and its change with exercise was calculated from the end of the warm-up period to the end of the test.

Results: Resting tcPCO2 was 37.6±4.8 in NCO2 group and 48.4±2.3 mmHg (p<0.0001) in HCO2 group. In NCO2 group, PS did not influence the tcPCO2 change during exercise (+0.6 and +0.4mmHg, without and with PS respectively). In the HCO2 group, tcPCO2 decreased significantly during exercise with PS  (-2.5mmHg, p = 0.01) while it was not changed without PS (-1mmHg, NS). The variation of tcPCO2 change with PS tended to be significant (p=0.06).

Conclusion: the influence of PS applied during exercise on tcPCO2 was modest and observed only in hypercapnic patients.