Effect of Exercise on OH
Following exercise, individuals with SCI may experience improvements in the autonomic regulation of their cardiovascular system (Lopes et al. 1984). Exercise, or even passive movement of the legs, could potentially attenuate reduced central blood volume in individuals with SCI during an orthostatic challenge. For example, Dela et al. (2003), found a pronounced increase in BP in individuals with tetraplegia when their legs were passively moved on a cycle ergometer. There is also evidence that exercise training may enhance sympathetic outflow in individuals with SCI, as shown by an increase in catecholamine response to maximal arm ergometry exercise (Bloomfield et al. 1994).
Discussion
Only three exercise studies have attempted to assess the effect of exercise on orthostatic tolerance in subjects with SCI and protocol differed in each. Lopes et al. (1984) found no effects on orthostatic tolerance with the addition of upper extremity exercises during a progressive head-up tilt (HUT) protocol. Such findings are not surprising given the small muscle mass involved in the upper limbs and the fact that venous pooling occurs primarily in the lower limbs. Ditor et al. (2005) demonstrated that individuals with incomplete tetraplegia retain the ability to make positive changes in cardiovascular autonomic regulation with BWSTT. However, six months of BWSTT did not adversely affect the orthostatic tolerance in subjects with SCI. The authors found this encouraging as it suggests that orthostatic tolerance is retained after exercise training, even though this intervention probably reduced peripheral vascular resistance. Otsuka et al. (2008) found that individuals with complete tetraplegia who were involved in regular physical activity training (2 hrs/day, 2 days/wk, ≥2 yrs) demonstrated greater orthostatic tolerance than inactive individuals with SCI (<30 mins/wk).
Conclusion
There is level 2 evidence (from 1 RCT: Lopes et al. 1984) that simultaneous upper extremity exercises does not improve orthostatic tolerance during a progressive tilt exercise.
There is level 4 evidence (from 1 pre-post study: Ditor et al. 2005) that 6 months of BWSTT does not significantly improve orthostatic tolerance during a tilt test.
There is level 4 evidence (from 1 post-test study: Otsuka et al. 2008) that regular physical activity (2hrs/day, 2x/wk, ≥ 2yrs) may improve orthostatic tolerance during a tilt test.
