Reduced Rate of Alveolar-Capillary Recruitment and Fall of Pulmonary Diffusing Capacity During Exercise in Patients With Heart Failure

Background: Patients with chronic heart failure (CHF) have reduced pulmonary diffusing capacity for carbon monoxide (DLco). Acute pulmonary congestion also causes reduction of DLco, which is reversible. We hypothesized for patients with CHF that the rate of rise of exercise DLco is reduced compared to healthy controls and falls near end-exercise consistent with progressive interstitial edema. Methods and Results: DLco and pulmonary blood flow ( over(Q, ̇)_C) were measured by a rebreathe technique in CHF subjects (n = 11) and controls (n = 8) at rest, during constant workload exercise, and after exercise. DLco of CHF subjects was less than controls at rest (16.5 ± 1 vs. 21.9 ± 2 mL/min/mm Hg, P < .01). CHF subjects exercised 11 ± 2 minutes to 90% peak over(V, ̇) O₂, whereas controls exercised 17 ± 2 minutes, reaching 88% peak over(V, ̇) O₂. In CHF subjects, DLco increased to 19 ± 2 mL/min/mm Hg and for controls to 38 ± 3 mL/min/mm Hg. During the final 3 minutes of exercise, DLco increased 5% in controls while decreasing 5% in CHF subjects (DLco/ over(Q, ̇)_C) was lower in CHF subjects at rest and progressively lower throughout exercise (P < .01). Conclusion: In patients with CHF, DLco has reduced rate of rise with exercise and falls near end-exercise consistent with limitation of alveolar-capillary recruitment and progressive interstitial edema.