Purpose: 

The present investigative study to find the relation between the blood pressure (BP) and postural sway is based on a model for adaptive compensatory cardio-postural interactions which has been proposed as a part of an integrated orthostatic reflex control system. (Blaber AP et al. Respir. Physiol. Neurobiol., 2009: in press).

Methods: 

To further validate this model, we investigated the simultaneous changes of medio-lateral center of pressure coordinates (M/L COP), filtered electromyographic activity (EMG) of muscles essential to postural stance along with continuous non-invasive BP data. Five young males between the ages of 19 to 26 volunteered to participate. Participants were seated for 20 minutes and then asked to stand with eyes closed (blindfolded) in a quiet stance for 5 minutes. All data were acquired at a sampling rate of 1000 Hz and resampled at 15 Hz. Discrete Wavelet Transform (DWT) was applied using the Daubechies 5 (db5) wavelet to decompose the signals at the 8^th scale and extract the approximation signal in the low frequency range (~ 0.11 Hz).

Results: 

The approximation signals of individual leg EMG activity and BP showed regions of significant correlation (r>0.5, p<0.0001) during last 4 minutes of quiet stance. Analysis of the correlation plots in the time domain revealed regions with opposing correlation patterns between left and right legs indicating alternating contraction of each leg in accordance to the ML posture sway. Regions of high correlation in the same direction were also observed indicating the co-contraction of both legs to regain the postural stability.

Conclusion: 

The presence of cardio-postural interactions in healthy individuals guides our way to applications for rehabilitation of returning astronauts and reducing fall proneness in the elderly.

Keywords: 

Electromyography; orthostatic reflex; Center of Pressure; Postural Sway