The Effect of Postural Perturbations on Cardiovascular and Skeletal Muscle Function in Healthy Adults
Abstract
Maintenance of standing balance is vital to daily living. Traditionally, perspectives on maintaining balance are achieved through the study of visual, vestibular and somatosensory inputs on motor outputs. While evidence suggests cardiovascular regulation also functions to assist postural control during orthostatic stress, how the cardiovascular system responds to postural perturbations is not well established. This dissertation includes four studies that investigated the effects of postural perturbations on the cardiovascular system and skeletal muscle responses in healthy adults. All of the studies involved exposing standing participants to surface-translation perturbations at different velocities, with known or unknown timing, and occurred while spontaneously breathing and breathing at six breaths per minute in young and older adults. Beat-to-beat heart rate and systolic blood pressure were measured continuously, while cardiac baroreflex sensitivity was calculated using the sequence method analysis. The results of Study One illustrated that heart rate and systolic blood pressure response were modulated following a perturbation and the initial cardiac response scaled with perturbation intensity. Additionally, cardiac baroreflex engagement was found to be involved in heart rate recovery. The sensitivity of the cardiac baroreflex was increased post-perturbation but was not intensity dependent. In Study Two, anticipatory cardiovascular responses to perturbations were not observed when the timing of the perturbation was controlled by the participant and perceived state anxiety was correlated with the initial heart rate response post-perturbation. In Studies Three and Four, when breathing at six breaths per minute, the latency of muscle burst onset decreased in young and older adults and muscle burst amplitude decreased in the lower limb musculature in young adults. Slow breathing decreased systolic blood pressure but had no effect on heart rate or cardiac baroreflex sensitivity post-perturbation in older adults. Together, the findings provide evidence that cardiovascular modulation occurs when standing balance is perturbed and support the notion that the cardiovascular, respiratory and motor control systems interact in a complex manner during postural perturbations.