Effect of plantar micromechanical stimulation on cardiovascular responses to immobility

OBJECTIVE: We investigated the cardiovascular responses of adult women to the influence of extended quiet sitting and the extent to which these responses may be reversed by micromechanical stimulation of the plantar surface. DESIGN: The cardiovascular responses of 20 healthy adult women (mean age, 55.9 +/- 4.45 yrs) were observed during quiet sitting with and without exposure to a plantar-based micromechanical stimulation. Beat-to-beat heart rate via electrocardiogram was acquired along with preexposure and postexposure blood pressures, from which heart rate variability and mean arterial pressure were determined. Seven stimulus frequencies (0, 15, 22, 44, 60, 90, and 120 Hz, all at 0.2 x g, peak to peak) were tested on each subject. RESULTS: Over one-half of the women tested (11/20) exhibited a significant resting tachycardia (mean, 8.3 +/- 0.5 beats/min) with a corresponding decline in their systolic blood pressure (9.45 +/- 1.8 mm Hg) after 20 mins of quiet sitting. Plantar stimulation at 44 Hz (25 mum, peak to peak) was able to completely reverse the effect of immobility in this group, resulting in a heart rate decline of 2.5 beats/min (P < 0.0001) and a decrease of only 1 mm Hg in systolic pressure (P = 0.006). CONCLUSION: We interpret these results to suggest that the immobility of quiet sitting has a profound effect on the cardiovascular systems in a large fraction of otherwise healthy women, perhaps due to inadequate muscle tone leading to venous insufficiency. Simple external stimulation of the plantar surface seems to be capable of preventing these cardiovascular stress-based responses.