Exercise endurance before and after long-term noninvasive ventilation in patients with chronic respiratory failure

Noninvasive mechanical ventilation (NIV) is known to reduce hypoventilation and improves respiratory and peripheral muscle endurance in patients with chronic respiratory failure (CRF) due to thoracic restriction.

To compare the effect of short-term NIV on endurance in patients with CRF due to thoracorestriction and chronic obstructive pulmonary disease (COPD) and to evaluate differences in spiroergometric data during exercise testing.

Thirty-five patients with CRF due to COPD and 24 patients with CRF due to thoracorestriction entered the trial. Constant work rate exercise testing at 75% of the maximal workload, pulmonary function and arterial blood gas testing were performed before and after 3 months of NIV. Measurements were compared between and within groups.

The non-COPD group increased their exercise time significantly from 4.7 +/- 1.81 to 6.59 +/- 3.15 min (p = 0.0032). There was no change in the COPD group (4.57 +/- 2.19 min before and 5.39 +/- 3.09 min after NIV, p = 0.09). CO(2) levels at rest fell in both groups (COPD 52.30 +/- 7.77 to 46.06 +/- 4.61 mm Hg and non-COPD 47.82 +/- 5.19 to 43.79 +/- 4.15 mm Hg). While COPD patients increased their minute ventilation (13.47 +/- 2.73 to 14.88 +/- 2.67 l/min), non-COPD patients decreased their oxygen uptake from 6.27 +/- 1.61 to 5.54 +/- 1.35 ml/kg.

NIV improved endurance only in the non-COPD group. This and the reduction in CO(2) are achieved by lowering energetic requirements. COPD patients though decreased their resting CO(2) by increased minute ventilation.