Invacare Alternating Pressure Relief System aids in the treatment and prevention of stage I and II pressure sores. Features Invacare's patented air compressor chamber with ultra-quiet operation, external air filter intake, and securing straps on the mattress. Air pump cycles varying pressures from 50 - 105 mmHg over a period of 8 or 9 minutes through cells of vinyl mattress for relief of pressure points.