Cardiovascular responses to an orthostatic challenge and electrical-stimulation-induced leg muscle contractions in individuals with paraplegia

The purpose of this study was to investigate the cardiovascular and haemody namic responses that occur during moderate orthostatic challenge in people with paraplegia, and the effect of electrical stimulation (ES)-induced leg muscle contractions on their responses to orthostatic challenge. Eight male s with complete spinal lesions between the 5th and 12th thoracic vertebrae (PARA) and eight able-bodied individuals (AB) volunteered for this study. C hanges in heart rate (f(c)), stroke volume (SV), cardiac output ((Q)over do t(c)), mean arterial pressure (MAP), total peripheral resistance (TPR), lim b volumes and indices of neural modulation of JE, [parasympathetic (PNS) an d sympathetic (SNS) nervous system indicators] were assessed during: (I) su pine rest (REST), (2) REST with lower-body negative pressure at -30 torr (L BNP -30, where 1 torr = 133.32 N/m(2)), and (3) for PARA only, LBNP -30 wit h ES-induced leg muscle contractions (LBNP + ES). LBNP -30 elicited a decre ase in SV (by 23% and 22%), (Q)over dot(c) (by 15% and 18%) and the PNS ind icator, but an increase in f(c) (by 10% and 9%), TPR (by 23% and 17%) and c alf volume (by 1.51% and 4.04%) in both PARA and AB subjects, respectively. The SNS indicator was increased in the AB group only. Compared to LBNP -30 , LBNP + ES increased SV (by 20%) and (Q)over dot(c) (by 16%), and decrease d TPR (by 12%) in the PARA group. MAP was unchanged from REST during all tr ials, for both groups. The orthostatic challenge induced by LBNP -30 elicit ed similar cardiovascular adaptations in PARA and AB subjects. ES-induced m uscle contractions during LBNP -30 augmented the cardiovascular responses e xhibited by the PARA group, probably via reactivation of the skeletal muscl e pump and improved venous return.