Abstract: The apparatus comprises a pad and a sequential pressure device that includes a pneumatic system and a control system. The pad comprises a plurality of adjacent chambers extending transverse to the pad's longitudinal centerline and has a lower section with at least two chambers and an upper section with at least three chambers. Two adjacent chambers of the lower section have approximately the same transverse cross-sectional area for about their lengths. Each chamber of the upper section includes a right portion, a left portion and an intermediate portion which has a narrowed center portion of reduced cross-sectional area connecting with the right and left portions. Inflation of an upper section chamber causes expansion of the right, left and intermediate portions thereof with a void created about the narrowed intermediate portion.