Vacuum-Assisted Closure. The VAC machine, which resembles a suction machine, applies controlled localized negative pressure to a wound site. This increases the growth of granulation tissue and decreases healing time. This system is particularly useful in the treatment of stage III and stage IV pressure ulcers and other types of deep wounds. The system uses a special dressing that is applied within a wound or over a graft. The VAC is then turned on. The vacuum helps to draw the edges of the wound toward the center. The direct pressure applied to the wound also assists in removal of fluids, which reduces swelling, stimulates growth of healthy cells, and increases blood flow, thus aiding in healing.