Relation of concavity in the expiratory flow-volume loop to dynamic hyperinflation during exercise in COPD

• The spontaneous flow-volume curves become concave in COPD patients during exercise.
• Some show marked, others moderate concavity depending on their resting FEV1.
• The degree of concavity of the spontaneous flow-volume curves during exercise correlates with the developing dynamic hyperinflation in patients with COPD.

Active expiration during exercise can increase intrathoracic pressure yielding concavity in the expiratory flow-volume loop in COPD. We investigated the relationship between this concavity and dynamic hyperinflation (DH). 17 COPD patients (FEV1: 38 ± 10%pred, GOLD stage 3–4) and 12 healthy subjects performed cycle ergometer incremental exercise. Expiratory limb of the spontaneous flow-volume loop was analyzed breath-by-breath using a geometric approach (rectangular area ratio (RAR), Respir. Med., 104(3):389–96, 2010). RAR below 0.5 demonstrates expiratory limb concavity. DH was determined with serial inspiratory capacity maneuvers. 5 of 17 patients displayed little end-exercise concavity (RAR = 0.52 ± 0.04, group LCONC). 12 patients had concavity at rest and end-exercise RAR reached 0.40 ± 0.03 (group HCONC). Healthy subjects showed no concavity. End-exercise RAR correlated with resting FEV1%pred (R2 = 0.81, P < 0.05). Group HCONC, compared to groups LCONC and H, reached significantly lower work rate, minute ventilation, and more dyspnea. DH inversely correlated with RAR (R2 = 0.81, P < 0.05). Detection of concavity in spontaneous flow-volume loops may help assess DH and exercise limitation in COPD.