Microprocessor controller and method of initializing and controlling low air loss floatation mattress

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BACKGROUND OF THE INVENTION

This invention relates to a pressurizing system for inflating a low air loss floatation mattress (or other supporting cell system or sub-system) so as to insure that excessive bearing forces are not exerted on the tissue of the person using the mattress (or pad) over extended periods of time so as to minimize the tendency of the person using the mattress from developing ulcers (bed sores) and to enhance comfort. This invention further has application as a support cushion system or sub-system of support cells for wheelchair seats or for other chair cushions where the user spends long periods of time in the chair and where comfort is important to the functioning of the user.

Referring now to patients confined in bed or in wheelchairs for extended periods, such patients may tend to develop bed sores. This is particularly true if the portions of the patient's body bearing on the mattress or cushion have a decubitus or interface pressure exerted on them greater than about 28 mm Hg or about 15-20" of water. The heart and the circulatory system can overcome and maintain adequate circulation to such parts of the patient's body if the decubitus pressure is less than about 10" of water. If the pressure exceeds this limit over a long period of time, improper circulation may result and the patient may develop bed sores and/or other medical problems related to restricted limb or torso blood circulation.

Air floatation mattresses have been developed to minimize the tendency of the patient to develop bed sores. One type of air floatation mattress, referred to as a low air loss mattress, has a number of separate chambers or pillows extending transversely of the mattress which are inflated with air to a desired pressure so the pillows will support various parts of the body without applying excessive decubitus pressures to any one part of the patient's body. For example, one such prior art air floatation mattress system has 16 cells grouped into head, torso, and leg zones. Air is continuously pumped under pressure (up to about 10" of water) from an air pressurization source, such as a variable speed blower or air pump, into a common manifold or plenum and the air from the plenum enters the cells comprising the torso zone of the mattress. The outer cells of the torso zone are, respectively, in communication with the next adjacent cell constituting the first cell of the adjacent head or foot zones so that air from the first cells of the head and foot zones are supplied with air from the torso zone. All of the cells comprising the head and foot zones are in communication with one another. In this manner, all of the cells of the mattress are continuously supplied with air from the blower. In other low air loss mattresses, all of the cells may be supplied with air directly from the common air manifold or supply. All of the cells have a multiplicity of air discharge holes therein so that air is continuously lost from all of the cells and so that air must constantly be supplied to the cells so as to maintain the cells at their desired inflated pressures. Other types of low air loss mattresses are known where all of the cells are supplied air directly from the air manifold.

Currently, upon placing a new patient on one of these prior art low air loss floatation mattresses, a skilled nurse must set up the mattress and the blower so that none of the cells exerts excessive decubitus pressures on any area of the patient. This takes time and the nurse must have special training and equipment to carry out this task. This setup task may involve inserting a pressure measuring device between the patient and the mattress so as to determine the decubitus pressure and to then regulate the air pressure and flow of the continuously operable blower so as to not exceed a desired pressure level. Often, it is necessary for the nurse or technician to input the patient's height and weight data into the controller so as to initialize the operation of the blower to the particular patient to be supported on the mattress.

Reference may be made to the following prior art U.S. Patents which show low air loss mattresses and other types of air floatation mattresses and support cushions and air supply systems therefore: U.S. Pat. Nos. 4,631,767, 4,686,722, 4,944,060, 5,022,110, 5,168,589, 5,235,713, 5,249,319, 5,279,010, 5,323,500, 5,483,709 and 5,487,196.

SUMMARY OF THE INVENTION

Among the several objects and features of the present invention may be noted the provision of a control system for supplying air to a low air loss mattress or pad which may be automatically initialized for a particular patient in such manner that a skilled nurse or special equipment is not required to set the mattress and/or the blower for a particular patient;

The provision of such a control which operates to automatically initialize or adapt itself to a new patient by laying on the mattress and by initiating an initializing procedure of the control system such that neither trained personnel or special equipment is required to regulate the air source for the mattress so as to supply air at a particular pressure and flow rate so as to maintain all of the cells of the mattress in an inflated condition and without being fully inflated thereby to insure that the decubitus pressure on any part of the person's body does not exceeds a predetermined level;

The provision of such a control system which, once initialized, will maintain a continuous flow of pressurizing air to the cells of the low air loss mattress so that none of the cells exceeds a predetermined maximum pressure or drops below a minimum pressure level thereby to insure that a maximum decubitus pressure is not exceeded and so that all portions of the patient's body are supported by the air floatation mattress;

The provision of such a control system which may be programmed to vary the pressure of the air loss mattress in such manner as to periodically alternate the pressure within the mattress between a predetermined pressure level above and below a desired setpoint pressure so as to vary the pressure supporting the patient while not exerting a pressure on any part of the patient above a predetermined maximum decubitus pressure and while not allowing the cells of the mattress to filly collapse;

The provision of such a control system which may be utilized to directly control and monitor the pressure in each cell;

The provision of such a pressurizing system which, after the above-noted initialization procedure, maintains a sufficient flow of air into the low air loss mattress so as to support the person without exceeding a predetermined maximum decubitus pressure (e.g., 10" of water) and without allowing any of the cells of the mattress to collapse; and,

The provision of such a control system which is inexpensive to manufacture and use, which is reliable in operation, and which has a long service life.

Briefly stated, a pressurization system of the present invention for a low air loss air floatation mattress or cushion is disclosed. The mattress has a plurality of separate cells with each of the cells having an air inlet and a plurality of air outlets. At least some of the air inlets for certain of the cells are in communication with a common supply of pressurized air such that air from the source enters each of the cells at a rate faster than air from within the cell is vented via the outlets such that the cells are maintained in an inflated condition so as to support the portion of a person's body in contact with the cells with a decubitus pressure less than a desired maximum decubitus pressure. The pressurization system comprises a source for continuously supplying air under pressure to the common supply. A controller is provided for controlling the source to supply air to the common source within a range of pressures and flowrates so as to inflate all of the cells and to maintain a flow of air to all of the cells over an extended period of time while maintaining all of the cells at a desired level of inflation for the air floatation support of the patient without any of the cells exerting decubitus pressures above the maximum desired decubitus pressure and so as to prevent collapse of any of the cells. A sensor is provided for sensing the pressure of the air within the common supply. The controller includes a microprocessor responsive to signals generated by the sensor for initializing the controller to a particular patient to be supported by the mattress and for the air floatation support of the patient over an extended period of time without exceeding a maximum decubitus pressure on any portion of the person's body in contact with the mattress and without permitting any of the cells to collapse. The initializing procedure comprises inflating the mattress with the person supported thereon and determining when at least one of the cells becomes fully inflated thereby determining a maximum inflation pressure not to be exceeded during the course of treatment and then deflating the mattress and determining the pressure at which at least one of the cells collapses thereby determining a lower pressure level above which pressure within the mattress is to be maintained during the course of treatment. The controller monitors the pressure of the air supplied to the common source and regulates operation of the source of pressurized air so as to be at a predetermined pressure between the minimum and the maximum pressure.

The method of the present invention involves the initialization and control of the inflation of a low air loss air floatation mattress or other pad so as to support a person's body with a decubitus pressure maintained below a desired maximum decubitus pressure level during an extended period of use and so as to insure that no portion of the mattress collapses during the extended period of use. An air supply system is utilized which continuously supplies air to the mattress. The mattress has an air inlet and a multiplicity of air discharge opening such that air must be continuously supplied to the mattress at a flowrate and pressure to maintain the mattress at a desired inflation pressure. The method comprises the steps of placing the person to be supported by the mattress on the mattress. The mattress is then inflated, and the rate of the change of the inflation pressure of the mattress is monitored. The pressure at which at least a portion of the mattress becomes fully inflated is determined. Then, the mattress is deflated and the pressure at which at least a portion of the mattress attains at least a partially collapsed condition is determined. Operation of the source of pressurized air is controlled over an extended period of time so as to maintain a pressure within the mattress intermediate the full inflation pressure and the collapse pressure whereby the person is supported by the mattress with a decubitus pressure less than a desired maximum decubitus pressure.

Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a low air loss mattress having a plurality of cells, a blower for continuously supplying air at a desired pressure and flowrate to a common manifold so as to maintain the cells in an inflated condition between a maximum and a minimum pressure level and a microprocessor controller for controlling operation of the blower;

FIG. 2 is a side elevational view of the low air loss mattress shown in FIG. 1 with all of the cells fully inflated;

FIG. 3 is a side elevational view of the low air loss mattress with a person supported thereon and illustrates a first step of the automatic initialization procedure of the control system of the present invention wherein the cells of the mattress are inflated with the person supported on the mattress until at least one of the cells is fully inflated;

FIG. 4 is a side elevational view of the low air loss mattress illustrating a second step in the initialization procedure of the present invention in which the mattress with a person supported thereon is deflated until at least one cell collapses;

FIG. 5 is a side elevational view of the mattress with a person supported thereon after the initialization procedure is complete with the mattress inflated at a minimum operational pressure at which the person is properly supported in an air floatation mode;

FIG. 6 is a view similar to FIG. 5 in which the mattress inflated at a maximum pressure at which the person is properly supported in a floatation mode;

FIG. 7A is a graph illustrating a first step of the initializing procedure of the present invention in which the pressure within the cells of the mattress is increased with full inflation of at least one of the cells of the mattress causing a substantial rise in the rate of the change of pressure;

FIG. 7B is a graph illustrating a second step of the initializing procedure of the present invention in which the mattress is deflated with the collapse of at least one of the cells of the mattress causing a substantial decrease in the rate of the change of pressure;

FIG. 8 is a graph of the operating pressure for a lo