Cardiovascular Systemic Regulation by Plantar Surface Stimulation

Abstract

The decreased blood pressure and flow rates associated with orthostasis have been implicated in the etiology of numerous clinical conditions, including deep vein thrombosis, chronic fatigue syndrome, and more recently osteoporosis. Here, we investigate the potential of low-magnitude vibration, applied at the plantar surface, to inhibit the cardiovascular responses of adult women to the orthostatic stress associated with quiet sitting. Thirty healthy women, aged 22-82 years, were exposed to a plantar-based vibration immediately after taking a seated position. Seven stimulus frequencies (0, 15, 22, 44, 60, 90, and 120 Hz, all at 0.2g) were tested on each subject, and cardiovascular responses were followed for 20 minutes. Each subject experienced only a single test frequency on any day. Pre- and poststimulus blood pressures and continuous electrocardiogram results were obtained, from which mean arterial pressure (MAP) and heart rate variability (HRV) were calculated. In the per-protocol study population (n = 25), 20 minutes of quiet sitting was associated with an average depression of 8.95 mm Hg in systolic pressure and of 1.9 mm Hg in diastolic blood pressure, corresponding to an average decrease in MAP of 5.15 mm Hg. These orthostasis-based changes in blood pressure were significantly reduced by exposure to plantar vibration, in a frequency-dependent manner, with essentially complete suppression of the drop in MAP achieved with plantar stimulation at 44 Hz (P < or = . 01). In the orthostatically hypotensive subpopulation (n = 15), both the 9.3-mm Hg depression in MAP and the decline in HRV were eliminated by exposure to plantar vibrations in the 40- to 60-Hz range (P = .01 and P = .03, respectively). These results are consistent with the hypothesis that the plantar vibration may be stimulating type IIA muscle fiber activity in the leg, which is critical for effective skeletal muscle pumping in the absence of locomotion. Our findings lead us to suggest that noninvasive, low-level, plantar-based vibration in the regime of 30-60 Hz can significantly inhibit the effects of the orthostatic stress of quiet sitting on the cardiovascular system.