Low air loss systems use a series of connected, air-filled cushions or compartments. These cushions are inflated to specific pressures to provide loading resistance based on the patient's height, weight and distribution of body weight. An air pump circulates a continuous flow of air through the device, replacing any air that is lost through the surface's pores. The inflation pressures of the cushions vary with patient weight distribution and some systems have individually adjustable sections for the head, trunk, pelvic or foot areas . One manufacturer offers the ability to individualize each of the compartments rather than just the sections . In addition to static low air loss systems, these products are now available with alternating and pulsating pressure features.