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Cardiorespiratory mechanisms underlying the impaired oxygen uptake kinetics at exercise onset after stroke
Kazuaki Oyake1, Yasuto Baba2, Yuki Suda2
1Department of Physical Therapy, School of Health Sciences, Shinshu University, Nagano, Japan; Department of Rehabilitation Medicine, Tokyo Bay Rehabilitation Hospital, Chiba, Japan.
Background:
Oxygen uptake (V˙O2) kinetics at the onset of exercise is slower in patients with stroke than in healthy adults. However, little is known about the cardiorespiratory mechanisms underlying the impaired V˙O2 kinetics.
Objectives:
This study aimed to investigate the relative effect of impaired oxygen delivery and utilisation on V˙O2 kinetics at the onset of submaximal exercise in patients with stroke by comparing the time constants of cardiac output (τCO) and V˙O2 (τV˙O2). In addition, we aimed to examine the association between the kinetics of cardiorespiratory variables and functional outcomes.
Methods:
We included 21 patients with stroke (15 males, mean [SD] age 58.7 [9.5] years, mean days post-stroke 67.9 [30.9]). A submaximal constant-load exercise test was performed to measure τV˙O2, τCO, and the time constant of arterialvenous oxygen difference (τAVO2diff). The ratio of τCO to τV˙O2 was calculated to assess the matching of oxygen delivery and consumption. Fugl-Meyer lower-extremity motor scores, comfortable gait speeds, and Functional Independence Measure motor scores were used as functional variables.
Results:
Mean (SD) τAVO2diff was markedly shorter than τV˙O2 and τCO (26.1 [7.1] vs. 38.7 [10.2] and 46.6 [23.2 s], P<0.05), with no significant difference between τV˙O2 and τCO (P=0.444). The greater ratio of τCO to τV˙O2 was related to poorer motor function (rho=-0.484, P=0.026) and slower comfortable gait speed (r=-0.482, P=0.027).
Conclusions:
An increase in CO was slower than that in AVO2diff in patients with stroke. Therefore, V˙O2 kinetics in patients with stroke appears to be affected by a delayed increase in CO rather than AVO2diff. Furthermore, these patients with motor and gait impairments may have a poor matching of oxygen delivery and consumption during exercise onset.
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