Using Electrical Impedance Tomography in an Experimental Model of Weighted Restraint.

One restraint technique used by police and paramedical personnel is to apply weight to a prone subject. There is concern that the weight and posture cause breathing difficulties and that restraint asphyxia could contribute to rare, inexplicable arrest-related deaths. Previous studies on restraint asphyxia have used global measures of breathing, which are less sensitive to ventilation changes than other methods. We present a methodology for monitoring individual adaptations to the conditions present in weighted restraint using electrical impedance tomography, which can image the changing distribution of ventilation over time. Results from a pilot study of seven subjects indicated that loss of lung reserve volume was a common consequence of weighted restraint. Our results imply that in more extreme scenarios in which the full weight of one or more officers is applied to a subject during recovery from strenuous activity, weighted restraint may augment risk to the subject. Finally, subjects in the restraint posture of hands behind their heads on average had larger tidal volumes during recovery than subjects with hands behind their backs or at their sides, suggesting this posture permitted deeper breathing and may be preferred in practice, though further study in a larger population is needed.