Role of leg vasculature in the cardiovascular response to arm work in wheelchair-dependent populations.

To assess the effects of leg vasculature on cardiovascular dynamics during submaximal arm work, oxygen uptake (VO2), cardiac output (Q) and heart rate (HR) were measured during arm-crank ergometry (ACE) at 35 W (45% peak ACE VO2) in five able-bodied subjects, five wheelchair-dependent paraplegics, and five wheelchair-dependent bilateral amputees who represented the conditions of active, passive, and absence of leg musculature respectively. Arteriovenous oxygen difference (a-v O2) and stroke volume (SV) were calculated from VO2, Q and HR. An index of leg fluid accumulation and leg blood flow was measured in the paraplegics and able-bodied subjects during rest and ACE. VO2, Q, and a-v O2 during ACE were not statistically different among the three groups. However, paraplegics exhibited higher HR (P less than 0.05) and lower SV (P less than 0.06) during exercise compared to both amputees and able-bodied subjects. Greater (P less than 0.05) leg fluid accumulation was measured in paraplegics compared to able-bodied subjects, although no statistically significant differences in leg blood flow were observed. Although our results are limited to a small number of subjects, these data suggest that an active muscle pump contributes significantly to elevated venous return and stroke volume during ACE. The legs of the paraplegic appear to act as a reservoir for fluid accumulation which may limit cardiac filling, particularly during moderate arm work to support wheelchair function.