Heightened neural drive promoting a ventilatory response beyond that required to overcome an increased “wasted” ventilation led to hypocapnia and poor exercise ventilatory efficiency in chronic obstructive pulmonary disease–heart failure overlap. Excessive ventilation led to better arterial oxygenation but at the expense of earlier critical mechanical constraints and intolerable dyspnea. Twenty-two ex-smokers with combined chronic obstructive pulmonary disease (COPD) and heart failure with reduced left ventricular ejection fraction undertook, after careful treatment optimization, a progressive cycle exercise test with capillary (c) blood gas collection.

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