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1 Department of Sports Medicine, Graduate School of Health Sciences, Hiroshima University, Hiroshima, Hiroshima, Japan
2 Department of Physiology, Graduate School of Health Sciences, Hiroshima University, Hiroshima, Hiroshima, Japan
3 Department of Health and Sport Sciences, Fukuyama Heisei University, Fukuyama, Hiroshima, Japan
* To whom correspondence should be addressed. E-mail: matsuk{at}hiroshima-u.ac.jp.
The purpose of the present study was 1) to investigate whether an increase in heart rate (HR) at the onset of voluntary static arm exercise in tetraplegic subjects was as similar as normal subjects and 2) to identify how the cardiovascular adaptation during static exercise was disturbed by sympathetic decentralization. Mean arterial blood pressure (MAP) and HR were non-invasively recorded during static arm exercise at 35% of maximal voluntary contraction in six tetraplegic subjects, who had complete cervical spinal cord injury (C6-C7). Stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR) were estimated using a Modelflow method simulating aortic input impedance from arterial blood pressure waveform. In tetraplegic subjects, the increase in HR at the onset of static exercise was blunted as compared to age-matched control subjects, whereas the peak increase in HR at the end of exercise was similar between the two groups. CO increased during exercise with no or slight decrease in SV. MAP increased approximately one third of the control pressor response but TPR did not rise at all throughout static exercise, indicating that the slight pressor response is determined by the increase in CO. We conclude that the cardiovascular adaptation during voluntary static arm exercise in tetraplegic subjects is mainly accomplished by increasing cardiac pump output according to the tachycardia, which is controlled by cardiac vagal outflow, and that sympathetic decentralization causes both absent peripheral vasoconstriction and a decreased capacity to increase HR, especially at the onset of exercise.
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