Abstract
Cardiac sympathetic decentralization is a phenomenon in which supraspinal sympathoadrenal control to the heart is deprived. The dysfunction of the sympathetic nervous system may contribute to blood pressure abnormalities, arrhythmias, diminished heart rate variability, restricted peak heart rate, and decreased venous return and stroke volume. Cardiac inotropic insufficiency might also be a result of sympathetic dysfunction. The potential inotropic abnormalities and altered cardiac loading conditions can eventually result in loss of left ventricular muscle mass, predisposing the heart to failure. Individuals who have complete cervical spinal cord injury (ccSCI) model this phenomenon. To date, almost all studies examining cardiac function in relation to its extrinsic regulation following cardiac sympathetic decentralization in SCI have used animal models. The few human investigations that are available have focused only on the hemodynamic response to an exercise challenge without considering the effect of cardiac sympathetic decentralization on the inotropic state. A study is needed to characterize the change in left ventricular inotropicity from rest to a severe exercise challenge in the sympathetically decentralized heart. This dissertation is a feasibility study conducted primarily to determine 1) if the bioimpedance cardiography (ZCG) technology currently available is sufficient for measuring cardiac inotropicity during an arm crank exercise in subjects with ccSCI; 2) if subjects with ccSCI could complete the protocol to be used, allowing for adequate data collection; and 3) the level of difficulty associated with recruitment of subjects with complete cervical SCI. Results of this feasibility study demonstrated that the current ZCG technology is adequate for measuring cardiac inotopicity in subjects with ccSCI, and subjects with ccSCI could perform an arm crank exercise and complete an incremental exercise test to volitional exhaustion sufficiently for ZCG data collection. This study also demonstrated that recruitment of subjects with ccSCI according to the present list of inclusion and exclusion criteria was difficult. Suggestions are offered regarding protocol refinement and increasing the recruitment yield.