Ventilatory and gas exchange abnormalities on exercise in chronic heart failure

The mechanism of breathlessness on exertion in patients with chronic heart failure are still not fully understood. We therefore investigated the effects of ventilatory and gas exchange abnormalities on exercise capacity in chronic heart failure. Exercise testing was performed in 30 patients with exertional breathlessness due to chronic heart failure and in 30 controls, using continuous transcutaneous blood gas monitoring. Maximal symptom-limited oxygen consumption as (V'O₂) as a percentage predicted was reduced in patients (45 ± 10%; mean ± SD) compared to controls (87 ± 7). The ventilatory response (minute ventilation/carbon dioxide production (V'E/V'CO₂)) was significantly increased in patients compared to controls (39.9 ± 7.7 and 25.9 ± 3.6, respectively). The dead space to tidal volume ratio (VD/VT) was raised in patients compared to controls at rest (0.45 ± 0.04 vs 0.35 ± 0.02, respectively) and this persisted on exertion (0.40 ± 0.05 in patients and 0.20 ± 0.05 in controls). At maximal symptom-limited exercise, V'E/V'CO₂ was inversely related to the % prodicted V'O₂ in patients, but not in controls (r = -0.62 and r = -0.24, respectively). In patients, V'E/V'CO₂ was significantly correlated with VD/VT at maximum exercise (r = 0.82). Patients with chronic heart failure have a significant degree of 'wasted ventilation' on exertion, which is associated with increased ventilatory response. The increased ventilatory response on exertion appears to contribute to exercise limitation in these patients.