Cardiorespiratory factors related to the increase in oxygen consumption during exercise in individuals with stroke

Abstract

Background Understanding the cardiorespiratory factors related to the increase in oxygen consumption (VO _2) during exercise is essential for improving cardiorespiratory fitness in individuals with stroke. However, cardiorespiratory factors related to the increase in VO _2 during exercise in these individuals have not been examined using multivariate analysis. This study aimed to identify cardiorespiratory factors related to the increase in VO _2 during a graded exercise in terms of respiratory function, cardiac function, and the ability of skeletal muscles to extract oxygen. Methods Eighteen individuals with stroke (aged 60.1 ± 9.4 years, 67.1 ± 30.8 days poststroke) underwent a graded exercise test for the assessment of cardiorespiratory response to exercise. The increases in VO _2 from rest to first threshold and that from rest to peak exercise were measured as a dependent variable. The increases in respiratory rate, tidal volume, minute ventilation, heart rate, stroke volume, cardiac output, and arterial-venous oxygen difference from rest to first threshold and those from rest to peak exercise were measured as the independent variables. Results From rest to first threshold, the increases in arterial-venous oxygen difference (β = 0.711) and cardiac output (β = 0.572) were significant independent variables for the increase in VO _2 (adjusted R2 = 0.877 p < 0.001). Similarly, from rest to peak exercise, the increases in arterial-venous oxygen difference (β = 0.665) and cardiac output (β = 0.636) were significant factors related to the increase in VO _2 (adjusted R2 = 0.923, p < 0.001). Conclusion Our results suggest that the ability of skeletal muscle to extract oxygen is a major cardiorespiratory factor related to the increase in VO _2 during exercise testing in individuals with stroke. For improved cardiorespiratory fitness in individuals with stroke, the amount of functional muscle mass during exercise may need to be increased.