Ventilatory determinants of self-selected walking speed in chronic heart failure

In healthy subjects, the self-selected walking speed (SSWS) corresponds to the lowest cost of transport (CT). This study tested the hypothesis that SSWS could be determined by the work of breathing instead of the CT in patients with chronic heart failure (CHF).

Seventeen patients with CHF due to left ventricular systolic dysfunction and 17 healthy controls were compared. Both groups were submitted to a walking cost protocol on the treadmill at the SSWS, at two speeds below (-0.5 and -1.0 km·h), and two speeds above (+0.5 and +1.0 km·h). The CT and ventilatory efficiency, as determined by the ventilatory equivalent for carbon dioxide (V˙E/V˙CO2), were compared.

CHF patients had a lower SSWS than healthy controls (0.75 ± 0.14 vs 0.98 ± 0.30 m·s, P < 0.01). Among the five speeds, the controls' SSWS was the most economical. For CHF patients, the SSWS was less economical than the higher speeds. However, V˙E/V˙CO2 at the SSWS was lower when compared with other speeds in both groups.

In contrast to what happens with healthy subjects, where the SSWS has the lowest CT, CHF patients choose an SSWS with higher CT, but with lower ventilatory cost. These findings are compatible with the concept that interventions that enhance ventilatory efficiency may increase SSWS in CHF.