Acute Effects of Whole Body Vibration on Central and Peripheral Hemodynamics and Oxygen Consumption in Individuals with Spinal Cord Injury

Abstract

A substantial body of evidence suggests spinal cord injury (SCI) increases cardiovascular disease and mortality risk in aging individuals with SCI. Based on retrospective assessments, excess mortality after SCI has been related to neurological level and completeness of injury. Performing routine arm exercise moderately stimulates the cardiovascular system; whereas functional electrical stimulation (FES) has been shown to elicit greater venous return and myocardial performance. FES is potentially painful and can induce adverse responses such as autonomic dysreflexia especially in quadriplegics and high paraplegics. Therefore, developing a safe and effective exercise intervention to improve cardiovascular health must be a priority for this population. Whole-body vibration (WBV) exercise is emerging as a potential treatment to improve locomotor capabilities in individuals with SCI. The use of WBV exercise to improve on cardiovascular response in the SCI population has yet to be investigated. Thus, the purposes of this study were: 1) to determine the acute effects of whole body vibration (WBV) exercise on central and peripheral hemodynamics and oxygen consumption, and 2) to compare the physiological responses to WBV between three different frequencies (30, 40, and 50 Hz) in individuals with SCI compared to age and activity matched able-bodied individuals. Eleven males with SCI (injury levels: C5-T6; ages: 50.39 ± 8.16) and ten age and gender matched able-bodied controls (ages: 48.17±6.78) completed three WBV exercise protocols at 30, 40 and 50 Hz. Heart rate, systolic blood pressure, diastolic blood pressure, stroke volume, cardiac output, oxygen consumption, and relative changes in oxyhemolobin, de-oxyhemoglobin and total hemoglobin values were obtained during pre-WBV seated steady-state, pre-WBV standing steady-state, WBV first minute, WBV steady-state, post-WBV standing steady-state, and post-WBV seated steady state. Moreover, leg skin temperatures were obtained pre-WBV, immediately post-WBV, 10 minute post, and 15 minute post-WBV. Multi-analysis of Covariance with random subject-effect was used to analyze the effect of the treatments on the dependant variables. Follow up univariate ANCOVAs and t-tests were utilized to compare the treatment and con¬trol groups on the outcome measures. 30, 40, and 50 Hz of WBV elicited slight increases in heart rate, stroke volume and cardiac output both in the SCI and able-bodied group. Systolic blood pressure was significantly increased following WBV at 30 and 40 Hz in the SCI group. Both groups demonstrated significant increases in oxygen consumption during and following WBV; yet the increase in oxygen consumption was more pronounced in the SCI group. Muscle oxygenation and lower leg skin temperature was significantly increased following WBV only in the SCI group. Moreover no specific frequency effect was revealed within or between groups. The WBV parameters used in the present study do not appear to induce significant cardiovascular benefits for the individuals with SCI as well as for able-bodied individuals. Physiological responses to 30, 40, and 50 Hz were similar.