Cardiovascular responses during arm exercise and orthostatic challenge in individuals with paraplegia

In this study the cardiorespiratory responses during arm crank ergometry (A CE) performed at two submaximal intensities (30% and 50% of heart rate rese rve) and moderate orthostatic challenge were investigated in individuals wi th paraplegia (PARA). The effect of concurrent electrical stimulation (ES)- induced leg muscle contractions on the responses to ACE during orthostatic challenge was also investigated. Eight PARA (T5-T12) and eight able-bodied (AB) individuals participated in this study, however only seven subjects fr om each group completed all tests and were used in subsequent data analyses . Oxygen uptake ((V)over dotO(2)), heart rate (f(c)), stroke volume (SV) an d cardiac Output ((Q)over dot(c)) were assessed during (1) ACE alone, (2) A CE and lower body negative pressure (ACE+LBNP), and, in PARA only, (3) ACELBNP with ES (ACE+LBNP+ES). In both PARA and AB, ACE+LBNP decreased SV (by 13-18% and 20-23%, respectively) and increased fc (by 13-15% and 16%, respe ctively) compared to ACE alone. The decrease in SV was greater in AB than i n PARA (significant group x trial interaction; both ACE intensities pooled) , but there was no difference in the magnitude of increase in f(c) between groups. ES-induced leg muscle contractions increased SV (up to 16%) but did not change (V)over dotO(2) or (Q)over dot(c). The smaller reduction in SV from ACE to ACE+LBNP in PARA may indicate a mechanism by which adequate cen tral blood volume can be maintained in the face of orthostatic challenge, d espite the absence of supraspinal control below the spinal cord lesion. Wit h ES-induced leg muscle contractions, the decrease in SV, which occurred du ring ACE+LBNP, was reversed via reactivation of the lower limb muscle pump and augmented venous return.