Cardiovascular and respiratory responses to passive leg cycle exercise in people with spinal cord injuries

The purpose of this study was to determine the effect of passive leg cycle exercise (PLE) on cardiovascular and respiratory responses in people with spinal cord injuries (PSCI). Eight PSCI with lesions from T8 to L1 and five control subjects (CS) performed PLE at pedalling frequencies of 20 or 40 rpm for 7 min at room temperature of about 25°C. We measured, at rest and during PLE, the pulmonary ventilation (V(̇)(E)), oxygen uptake (V(̇)O₂), cardiac output (Q(̇)), stroke volume (SV), heart rate (HR) and arterial blood pressure, as well as the skin blood flow (SBF) in the lower limb after PLE. An increase in pedalling frequency promoted an increase in V(̇)(E) and V(̇)O₂ in both groups. Compared with the CS, the PSCI showed significantly smaller increases in V(̇)O₂ (P < 0.05). The Q(̇)(c) significantly elevated during PLE at 20 and 40 rpm in CS, and at 40 rpm in PSCI (P < 0.05). In CS, it resulted from increases in both SV and HR, whereas in PSCI, it was contributed to by a greater increase in SV without a rise in HR. In CS, the increase in pedalling frequency promoted the increases in SV and HR and consequently in Q(̇)(c). In PSCI, however, the values remained constant irrespective of pedalling frequency. The arterial blood pressure and SBF in the lower limbs were unchanged by PLE in both groups. These results would suggest that passive leg exercise promotes venous return from the paralyzed lower limbs in PSCI.