Clinical usefulness of oxygen uptake during usual gait in patients with cardiovascular disease

Abstract

Background: Although oxygen uptake (VO₂) during exercise stress is a surrogate marker for prognosis in patients with cardiovascular disease (CVD), the stress test is sometimes difficult to perform owing to patient conditions, such as ageing or comorbidities. We investigated the relationships between VO₂ during usual gait with physical function and prognosis in patients with CVD.

Methods: This single-centre observational study enrolled consecutive patients who were hospitalized for CVD treatment. Isometric quadriceps strength (QS) and 6-min walk distance (6MWD) as physical functions, and VO₂ during usual gait speed were measured at hospital discharge. We assessed the changes in VO₂ per body weight between at rest and during gait divided by gait speed (VO₂/kg/gait) and analysed the relationships of VO₂/kg/gait with physical functions and composite incidences of all-cause death or unplanned readmission after discharge.

Results: In 367 patients (age, 65 ± 13 years; females, 34%), 112 clinical events occurred. VO₂/kg/gait showed significant negative correlations to QS (β = -0.114, p = 0.024) and 6MWD (β = -0.163, p < 0.001) after adjusting for confounding factors. High VO₂/kg/gait was significantly associated with a high rate of clinical events (hazard ratio for 1 standard deviation of VO₂/kg/gait, 1.36; 95% confidence interval, 1.11-1.66). This association was also observed in subgroups of older age and frailty.

Conclusions: High VO₂ during usual gait was a relevant factor for low physical function and poor prognosis in patients with CVD and even in older age and frailty, meaning that VO₂ during usual gait might be a novel and useful marker in clinical practice.

Keywords: Cardiovascular disease; Energetic cost; Oxygen uptake; Physical function; Prognosis; Usual gait speed.