THREE CYCLE PRESSURE SORE ALLEVIATION DEVICE

Adam Hagerty, Mechanical Engineering, Rochester Institute of Technology

Elizabeth Hampton, Electrical Engineering, Rochester Institute of Technology

Scott Keppel, Mechanical Engineering, Rochester Institute of Technology

Brian Phillips, Mechanical Engineering, Rochester Institute of Technology

05/12/2006

Abstract

Prevention of pressures sores is a large area of interest, especially when dealing with physically disabled individuals, due to the fact that they are unable to adjust themselves during sleep. This paper will explain the development and construction of a device that alternates contact points on a person’s body to alleviate pressure concentration points. The idea of the system is to allow the user to have cyclical relief of pressure without having to be physically adjusted during the sleep period. Most devices available only have two cycles for alleviation, but the device presented in this paper contains three such cycles and uses air cells, a pump, and a controlled valve system using pressure sensors to accomplish pressure relief. This device will help the patient in the prevention of pressure sores and also allow a more steady sleep cycle to be established. The intent of this paper is to show that three cycles for pressure alleviation is a valid method and that it allows for more flexibility in terms of cycles and possible settings for control since there are more options to choose from compared with the standard two cycle system.

Nomenclature

User Box – device with which the user will be interfacing containing the controller and 4 switches

Pump Box – device that encases the pump, pressure sensors and the valve system

System Containment – outside support for the mattress that is made from medical foam to create a full size bed


Air Cells – vinyl tubes that support the user and contain air while the device is functioning

Introduction/Research

In order to understand the needs that were determined by the customer site visit, more knowledge of pressure sores was necessary. According to www.webMD.com [12], pressure sores are areas of damaged tissue and skin that are usually

caused by lying in one position for an extended period of time which causes blood circulation to slow down and allows sores to develop under the surface of the skin. Since these sores are under the skin, they are difficult to detect until they become more severe and visible over time. These sores are classified into 4 different stages of severity seen in Figure 1. Stage 1 starts as a red blemish on the surface of the skin, which if left untreated, follows the progression to stage 4 where the pressure sore is very severe and can cause death in some cases. If a pressure sore is not properly treated it will become infected and affects the body just like an open wound.

The main points on the body that are typically affected by pressure sores are shown in Figure 2. The back of the head, shoulders, lower back, buttocks, and heels are normally the places that are in most contact with a surface during the sleep period. This constant contact in the case of a physically handicapped person can not be adjusted without outside assistance, and if no assistance is available the person is very likely to develop sores where the pressure is located.

Specifications / Target
1 / Sales Price / $1500
2 / Supportable Weight (max) / 300 lbs
3 / Number of times patient needs assistance during sleep period due to an issue with the device / <1
4 / # of Cycle Patterns / 3-5
5 / Duration of Each Cycle Pattern / 30-60 min
6 / # Of Buttons on User Interface / 5 max
7 / Life of Product / 7 yrs
8 / Selectable Duration for Each Cycle Pattern / 1-3
9 / Size of Mattress (in2) / 54”x75”
10 / # of Main Components / 10 max
11 / Distance to User Interface / 25 ft
12 / Distance to Outlet / 10 ft

Usually pressure sores have three simultaneous methods for treatment: the pressure on the sore needs to be eliminated, the sore needs to be treated, and the nutrition of the patient needs to be monitored to allow for fast healing. This project will focus on the elimination of pressure that creates the sore in the first place. Prevention is ideal when dealing with pressure sores because they are very difficult to detect in the early stages of development.

Many devices are available for the relief of pressure sores, but are usually at a higher cost than the concept this team has developed. Most of the devices found use air to alleviate sores, especially when alternating contact points are needed. Memory foam and other stationary foams and setups were briefly researched, but were not in the scope of this project. Akton polymer pads [1] are used to alleviate pressure, but mainly are just for added support of the body and give minimal relief to certain areas. Two mattresses, the Careguard [5] and the Roho [11], were found to adjust pressure with user movement and were broken up into smaller sections for more overall pressure relief. These, along with the Thera-Max-HFS memory foam [5], were found to be inadequate for this project because of the lack of alternating pressure points. Some other methods found were deemed not suitable, such as the Neuro Care 1000 [8], which used electrical stimulation to help the blood circulate more consistently to eliminate pressure areas by forcing blood flow. All of these devices were not suitable for the needs of the Arc of Monroe.

The main devices researched were ideas that involved alternating points of contact on the user’s body and were found to be much closer to what was necessary for this project. Many types of alternating pressure beds were researched from the following websites: www.medicalproductsdirect.com [6], www.sunrisemedical.com [7], and www.sentech.com [10]. These beds, although many were alternating, only contained two different cycles for alleviation. The needs of this project require that the bed has a minimum of three cycles for alleviation, limiting the usefulness of the research collected. No affordable system is available on the market that allows for three different cycles for alleviation of pressure areas. Therefore, adding a third cycle led to the need for a new concept to be developed in order to meet the customer requirements of this project.

Design Process

The customer requirements for this device helped to clarify the exact specifications needed to complete this project. The two main specifications for the mattress were that it was safe for the patient and that the team stayed within the budget of the project. Figure 3 shows the main specifications that the project had meet in order for successful implementation of the device.

Five concepts were developed to meet the needs of the ARC of Monroe. The first of the alternative concepts used air cylinder actuators to adjust the pressure points on the body during the sleep cycle. Although this concept was feasible for most of the specifications, cost and maintenance had a large affect on deciding against the idea. The air cylinders alone would have used most of the budget available, making this a poor choice for the project. The second alternative was a type of alternating track that would continuously adjust the pressure on the patient’s body. This again had a high cost associated with it and many safety factors due to the moving mechanical portions of the concept. The third alternative was to use a mechanical flipping mechanism to rotate the patient from side-to-side during the sleep cycle. The ARC of Monroe has a no rail policy that would not allow a device like this to be implemented in the facility. The fourth alternative was similar to the concept selected for this project except it involved water instead of air to alternate pressure on the body. The cost and pump required along with the water line or reservoir needed made this concept a poor choice.

The air cell mattress that this project explains was the concept selected for design and build. The air cells were able to be easily manipulated to adjust pressure contact points along the patient’s body. The air pump and components needed for the design fell within the $1500.00 budget, the cells chosen were rated to hold 300 lbs, and all other specifications could be met with the use a of PBASIC microcontroller.

Design and Engineering Model

The design that was decided on consists of 6 major components, each with individual needs and demands. The system is composed of an air pump that is hooked to a series of air cells that support the user. There is a user interface that feeds input into a controller and, in turn, the controller receives input from two pressure sensors that control the valves connected to the pump. The system containment also is able to enclose the air cells for safety and sanitary reasons. The last major component of the system is the housing for the user interface and the controller as well as the housing for the pump, pressure sensors and other small components.

Pump

The primary requirements of the pump were to operate quietly, supply enough pressure to inflate the cells, and be affordable. It also had to operate on 120V household electricity, require zero maintenance, supply enough airflow to inflate the system fully within a 20 minute period, and be certified for medical use.

Figure 14 was produced using information provided by Sentech [10], a company that manufactures pressure sore beds. The team slowly increased client weight and entered it into a program and the corresponding pump pressures were recorded. From Figure 14, the required pump pressure for the 115 pound client is approximately 20 mm Hg. This number will be the goal pressure for the air cells contained in the mattress.

Air pump flow rate analysis

There are 10 air cells total

L=36in. (length of each cell)

D=5.25in. (diameter of each cell)

The goal of this project for initial startup time was 20 minutes. This means that the cells have to fully inflate in that period of time.

The pump must produce an airflow rate of in order to meet required goal. The results were converted to the standard unit of measurement for airflow rate.

The air pump must produce at .23cfm to properly inflate the mattress in 20 minutes.

The pump that was selected for use in this project came as part of the Sentry 1200 system that was developed by Sentech [10] and purchased for specific use of the air cells. The pump was removed from the system and integrated into the team’s designed system. The pump and air cells from the Sentech system met all of the stated needs, and additionally, saved a significant amount of money that was used on other components necessary for the project.

Air Cells

The air cells have several different requirements in order to operate correctly in the system, and of these needs, the most important are the ability to hold pressure, be easily washed if the bed is soiled, and last the estimated lifetime of the bed. The cells needed to be waterproof even though a protective, waterproof layer will be placed over the whole system as another failsafe for the system.

Air cell safety analysis

Average Pressure, P

Client Statistics:

W=115lbs.

H=56in.

Assumption: 18in. wide patient

Maximum Pressure, Pmax

Patient Statistics:

W=300lbs.

H=56in.

Assumption: 18in. wide patient

Worst-Case Scenario

Worst-case scenario is when one cycle of air cells holds 100% of the weight (i.e. 5 cells are holding 300 lbs without rupture).

P= .278 psi (mattress with each of the 3 cycles holding equal amounts of weight)

When one of the cycles holds all of the weight it changes the area in the calculation by one third.

Therefore (Worst Case):

W=300lbs.

The maximum pressure that the air cells should ever be subjected to is .893psi which is well above the necessary pressure that the client requires for safety.

The air cells that best fit the requirements of the project are produced by the company Sentech. Figure 5 shows the air cell that will be incorporated into the project design. These cells were purchased as part of a system and were chosen because of their size, availability, and low price when bought as part of the Sentry 1200 system.

User Box

The requirements for the user box were straightforward in that it had to be large enough to encompass the microcontroller and have an area for the 4 lighted switches to be mounted and labeled. The user box was mounted to the wall outside of the room so it had to contain areas for the screws to be inserted to hold the box up. Not only did it have to be mounted in the desired location, it had to be resistant to spills or tampering.

The user box design used an electrical enclosure from www.fibox.com [3] that contained the controller, the four lighted switch buttons, and other components to ensure functionality of the buttons and controller as seen in Figure 6.

System Containment

The base and containment for the mattress system was designed out of foam certified for bedding material. The major needs were for it to be rigid enough to support the user effectively, be easily sculpted to the desired profile, and maintain durability throughout the projected lifetime of the bed. Other needs included being comfortable for the user and allowing attachment points for the inflatable air cells themselves.

The best solution to the needs defined for the mattress system came from an internet source for custom foam applications, www.efoamstore.com [2] which was chosen over www.foamorder.com [4] due to the lower cost of the foam. Each foam component pictured in Figure 7 was ordered independently based on its individual size and were then attached to each other to form the base (1”x54”x75”), the lower support layer (5”x9”x54”), the upper support layer (5”x10”x54”), the tubing for the third cycle, which was adjusted during testing for best comfort, and the side containments (5”x9”x56”) for the air cells. The attachment points for the air cells are rows of button snaps located along the inside edge of the side foam containments, attached to the base foam using glue.