Introduction: Recruitment of pulmonary blood flow has been poorly investigated in COPD patients during exercise.

It may be impaired, especially in patients with pulmonary distension.

Methods: We measured simultaneously pulmonary capillary blood flow (Qs, uptake of acetylene) and Transfer Capacity of CO (TLCO), at rest and during three stages of a submaximal exercise in 19 COPD patients (FEV1=51±18% pred) and 9 controls. Twelve patients had a Residual Volume >150%pred and formed the hyperinflated subgroup (HI).

Results: Patients had lower values of Qs and TL than controls, both at rest and at each phase of the exercise. Qs and TLCO increases were respectively 81±49% and 25±12% for the last exercise phase in HI and 191±48% and 47±12% in controls (p<0.01 and 0.05 respectively). This variation was significantly lower for Qs in the last two steps of exercise in HI compared to controls but did not differ between non-hyperinflated patients and controls. We found a linear relation between TL and Qs with a similar slope, both in patients and controls.

Conclusions: We found a reduced capability to recruit functional capillaries and so increase TL in hyperinflated COPD patients. The impact of treatments to reduce hyperinflation should now be evaluated using this methodology.