Proportional assist ventilation as an aid to exercise training in severe chronic obstructive pulmonary disease.
BACKGROUND
The effects of providing ventilatory assistance to patients with severe chronic obstructive pulmonary disease (COPD) during a high intensity outpatient cycle exercise programme were examined.


METHODS
Nineteen patients (17 men) with severe COPD (mean (SD) forced expiratory volume in 1 second (FEV(1)) 27 (7)% predicted) underwent a 6 week supervised outpatient cycle exercise programme. Ten patients were randomised to exercise with ventilatory assistance using proportional assist ventilation (PAV) and nine (two women) to exercise unaided. Before and after training patients performed a maximal symptom limited incremental cycle test to determine peak work rate (Wpeak) followed by a constant work rate (CWR) test at 70% of Wpeak achieved in the baseline incremental test. Minute ventilation (VE), heart rate, and arterialised venous plasma lactate concentration [La(+)] were measured before and after each test.


RESULTS
Mean training intensity (Wt/Wpeak) at 6 weeks was 15.2% (95% CI 3.2 to 27.1) higher in the group that used ventilatory assistance (p=0.016). Peak work rate after training was 18.4% (95% CI 6.4 to 30.5) higher (p=0.005) in the assisted group (p=0.09). [La(+)] at an identical workload after training was reduced by 30% (95% CI 16 to 44) in the assisted group (p=0.002 compared with baseline) and by 11% (95% CI -7 to 31) (p=0.08 compared with baseline) in the unassisted group (mean difference 18.4% (95% CI 3.3 to 40), p=0.09). A significant inverse relationship was found between reduction in plasma lactate concentration (DeltaL) at an equivalent workload after training during the CWR test and Wt/Wpeak achieved during the last week of training (r=-0.7, p=0.0006).


CONCLUSIONS
PAV enables a higher intensity of training in patients with severe COPD, leading to greater improvements in maximum exercise capacity with evidence of true physiological adaptation.