Physiological determinants of the increase in oxygen consumption during exercise in individuals with stroke

Background Understanding the physiological limitations of the increase in oxygen consumption (V̇O 2 ) during exercise is essential to improve cardiorespiratory fitness in individuals with stroke. However, the physiological determinants of the increase in V̇O 2 during exercise have not been examined using multivariate analysis in individuals with stroke. This study aimed to identify the physiological determinants of the increase in V̇O 2 during a graded exercise in terms of the respiratory function, cardiac function, and ability of skeletal muscles to extract oxygen. Methods Eighteen individuals with stroke (60.1 ± 9.4 years of age, 67.1 ± 30.8 days poststroke) underwent a graded exercise test for the assessment of cardiorespiratory response to exercise. The increase in V̇O 2 from rest to ventilatory threshold and that from rest to peak exercise were measured as a dependent variable. The increases in respiratory rate, tidal volume, heart rate, stroke volume, and arterial-venous oxygen difference from rest to ventilatory threshold and those from rest to peak exercise were measured as independent variables. Results From rest to ventilatory threshold, the increases in heart rate (β = 0.546) and arterial-venous oxygen difference (β = 0.398) were significant determinants of the increase in V̇O 2 (adjusted R 2 = 0.703, p < 0.001). From rest to peak exercise, the increases in tidal volume (β = 0.611) and heart rate (β = 0.353) were significant determinants of the increase in V̇O 2 (adjusted R 2 = 0.702, p < 0.001). Conclusion V̇O 2 is well-known to increase nearly linearly with increasing heart rate; however, our results suggest that arterial-venous oxygen difference and tidal volume are also significant physiological determinants of the increase in V̇O 2 from rest to ventilatory threshold and that from rest to peak exercise, respectively. Our findings could potentially contribute to the development of appropriate therapies to improve cardiorespiratory fitness in individuals with stroke.