The present invention relates to patient support systems and more particularly to a patient support system which combines attributes of a fluidized air bed and a low air loss bed. 
Two types of patient support systems preferred for long-term patient care include air fluidized beds such as those described in U.S. Pat.  Nos.  3,428,973 to Hargest et al, 3,866,606 to Hargest, 4,483,029 to Paul, 4,564,965 to Goodwin, 4,637,083 to Goodwin, 4,672,699 to Goodwin, and low air loss beds such as those described in U.S. Pat.  Nos.  4,694,520 to Paul et al.  4,745,647 to Goodwin, and 4,768,249 to Goodwin. 
Each type has advantages for particular segments of the patient population.  For example, patients with respiratory problems require elevation of the chest.  However, this tends to cause the patient to slide toward the foot of the bed.  Since a fluidized bed in the fluidized condition provides no shear forces against the patient, and some shear forces are provided by the low air loss bed, patient elevation is performed more easily in a low air loss bed.  However, to completely overcome this slippage, some sort of knee gatch is required to be fitted to the bed to provide a surface against which the buttocks of the patient may be retained when the patient's chest is elevated. 
Moreover, the same shear forces which assist in retaining the patient in the low air loss bed from slipping to the foot of the bed when the chest is elevated, become undesirable for patients with skin grafts.  The shear forces tend to tear such skin grafts from the patient, and this is not only painful but also interrupts the healing process.  The absence of shear forces in a fluidized bed permits the patient with skin grafts to move about without fear that the grafts will be torn from the patient's body.  In a fluidized bed, the patient can lie on a skin graft and be confident that when the patient moves, the sheet will move with the patient across the supporting mass of fluidized material and not displace the graft as would be the case if the patient were moved across a conventional mattress or a low air loss bed support for that matter. 
The large mass of fluidizable material required to sustain operation of a fluidized bed contributes significantly to the weight of the bed.  In addition, the large mass of fluidizable material requires a large blower to fluidize the beads, and such blowers require significant amounts of electricity for their operation. 
The sides of a fluidized bed are rigid to retain the fluidizable material and to attach the cover sheet thereto.  Ingress to and egress from the fluidized bed by patients must be performed with due regard to the rigidity of the sides of the bed. 
The fluidizable material in a fluidized bed can be soiled and must be removed for cleaning at regular intervals and when particular circumstances dictate.  Because of intermixing of the fluidizable material during fluidization, a localized soiling becomes distributed throughout the mass of material.  Removal of the entire mass of material for cleaning is a time consuming and labor intensive task.