Electrically induced and voluntary activation of physiologic muscle pump: a comparison between spinal cord-injured and able-bodied individuals

Objective: To evaluate the central haemodynamic responses during position changes from supine to sitting and during 30 min of standing between able-bodied and spinal cord-injured subjects. Also to assess the effects of the physiologic muscle pump in both groups during 30 min of standing. Design: A repeated measure design. Both groups were tested on two different days under two conditions of 30 min of stationary standing and 30 min of dynamic standing (voluntary activation of the lower leg muscles in able-bodied and FES-induced activation of these muscles in spinal cord injured). The order of testing was random. Setting: Rehabilitation hospital. Subjects: Fifteen healthy able-bodied and 14 healthy spinal cord-injured subjects. Main outcome measured: Stroke volume, cardiac output, heart rate, systolic blood pressure, diastolic blood pressure, mean arterial pressure and total peripheral resistance during supine-pre sitting, sitting-pre standing and during 30 min of standing. Results: Significant reductions (p< 0.05) in systolic blood pressure, diastolic blood pressure and mean arterial pressure were found when spinal cord-injured subjects moved from sitting to standing during stationary standing; these values were maintained during dynamic standing. These values were maintained during both standing sessions in able-bodied subjects. During 30 min of stationary standing, there were significant reductions in stroke volume, cardiac output in both able-bodied and spinal cord-injured while their total peripheral resistance increased (p< 0.05). During 30 min of dynamic standing, both groups maintained their haemodynamics at pre-standing values with the exception of significant reduction in stroke volume at 30 min of standing. Conclusion: FES-induced activation of the physiologic muscle pump during change in position from sitting to standing prevented orthostatic hypotension in spinal cord-injured subjects. During standing it had equal or even greater effect on improving blood circulation when compared with voluntary activation in able-bodied subjects. The use of FES during standing and tilting in spinal cord-injured individuals may prevent orthostatic hypotension and circulatory hypokinesis and improve tolerance to tilting and standing.