Heather Dewey-Hagborg and Vaishali Khandare O.T.
A collaboration of the Interactive
Telecommunications Program and the Department of Occupational Therapy,
Occupational Therapists currently use pressure garments to apply deep pressure input to the bodies of children with sensory modulation or processing disorders. There are two main problems with the pressure vests currently available, consistency and repetitive manual application. The Smart Hug inflatable pressure vest aims to solve these problems by automating the process of applying and removing the vest making the amount of pressure a child receives consistent and repeatable day to day. An additional goal of the technology is to begin collecting data about how much pressure children need, and to analyze the benefits of pressure garments in therapeutic use.
Occupational Therapists currently use neoprene pressure vests to apply deep pressure input to the bodies of children with sensory modulation or processing disorders. Pressure vests in particular are often used in school settings to help the child to improve concentration and attention span, eye contact, and to decrease self stimulatory behavior through the regular use of circumferential pressure to the torso. The vest aids the proprioceptive sense, allowing the child to better understand the relationship between his body and the environment. The vest also helps in the regulation of the arousal level of the child, which is important for optimal performance in the classroom. The pressure vests currently on the market are made of neoprene and are manually strapped tightly on the body of the child. Vests are commonly used in 20 – 40 minute intervals, depending on the child’s need. They are used repeatedly throughout the day. The idea behind the Smart Hug is to automate that process, saving therapists the hassle of repeatedly strapping on and removing the vest and allowing easier carryover for use in the classroom throughout the day.
There are two main problems with the pressure vests currently available, consistency and repetitive manual application. Because these vests do not incorporate a sensing mechanism to inform the therapist of how much pressure they are applying, application relies on the therapist’s intuition and subjective measure, such as placing a finger between the vest and the child’s body to “feel” the pressure. This means that the actual amount of pressure applied to the body is unknown and is likely to be inconsistent between sessions. Additionally, because tools are not readily available for measuring this pressure against the body, little quantitative research has been done into the amount of pressure children require and the benefits thereof.
The second problem is the manual nature of applying and removing the vest. Because vests are used in 20-40 minute intervals throughout the day, the therapist or teacher is put in the position of timing the child’s use. This requires not only remembering to change the vest but also stopping the flow of classroom activity to apply or remove it.
The Smart Hug project aims to solve these problems through electronic automation, regulation and sensing. The first goal is to automate the process of applying and removing the pressure vest. The second is to make the amount of pressure a child needs and receives consistent and repeatable day to day. The final goal is to begin collecting data about how much pressure children need and currently receive, and to analyze the benefits of pressure garments in therapy in a quantitative fashion.
DESIGN AND IMPLEMENTATION
The major physical components of the vest are the inflatable bladder, the casing for the bladder, the pocket to hold the electronics, and the adjustable shoulder straps. Our first prototype of the vest was patterned after an actual vest. It contained a handmade natural rubber bladder and a big pocket in back to hold the electronics. The vest casing was made from a soft cotton inner and outer casing, over a stiff nylon layer which served the necessary purpose of pushing the rubber bladder toward the body and preventing outward inflation like a balloon. The problem with this prototype was that it was far too heavy and large, and due to its size the bladder was slow to fill with air. There were no provisions for size adjustment and therefore could not fit a range of people properly. The pocket containing the electronics was located at the back of the vest, which we subsequently learned was a poor placement choice. Additionally the vest was not very aesthetically pleasing. Our second prototype attempted to resolve these issues. We worked with an inflatable bladder manufacturing company, Custom Service Labs Of NJ, Inc. to design a lightweight, industrial strength bladder made of 200 Denier urethane coated nylon fabric. We wanted the vest be more versatile in terms of size so we shaped it as a large adjustable cuff that wraps around the torso, fitting children and adults with torsos measuring 11” to 38” in circumference. We added stretchy neoprene shoulder straps that can attach anywhere along the top edge of the cuff to fit a wider range of shoulder widths. We moved the electronics pocket to the front of the vest for more ergonomic placement, and made every layer independent and removable for washing purposes. We chose blue denim for the outer shell which served the dual purpose of creating an aesthetically pleasing style and providing the stiffness necessary to push the inner bladder towards the body.
The circuit we designed consists of four interacting modules, sensory input, inflation control, timing and user interface, all processed by a PIC16F877A microcontroller.
An Interlink Force sensitive resistor sensor was chosen for measuring pressure against the body. As part of a voltage division circuit this sensor sends out a voltage proportional to the amount of pressure applied to it. We determined that this pressure was more pertinent to measure than air pressure within the bladder because it is more directly related to how the user feels inside the vest. This information will also be more valuable for future research in determining the amount of pressure is actually needed for therapeutic purposes.
The noise, and weight and efficiency of the pump used to control inflation were prime concerns. Because the vest is designed for children, it needs to be as light and inconspicuous as possible. Because it is used in a classroom setting it also needs to be portable and battery powered. We decided to use two Parker Hannifin T2-03e compact diaphragm pumps, one for inflating the bladder and the other for deflating it. Each pump was connected to an independent valve on the bladder. These pumps weigh only 33 grams, are quiet, and run on 6 volts. We used Parker Hannifin X-Valves to control air flow in and out of the vest. Running at 5 volts with a weight of only 4.5 grams, these were by far the smallest and most efficient valves we found on the market. Control of both the pumps and the valves is digital using 4 TIP120 transistors.
For the user interface, we wanted to create a design that was as simple and intuitive as possible. We decided on two rotary switches to choose the amount of time the vest would be inflated and and the amount of time it would be deflated ranging in 5 minute increments from 15 minutes to 50 minutes. We used DPDT switches for both power and programming. We used three LEDS; red, green and amber to show power on, programming, and inflating states.
The microcontroller was programmed in C with a timing control loop. First the pressure level is programmed, then the rotary switches are read to determine time on and off. When the user presses the start button the program runs through a loop turning on the inflation pump and closing the air valve, inflating until the desired pressure is reached, staying at that state until the desired time has elapsed, then deflating, remaining deflated for the desired time and repeating until stopped.
How it works:
Working with the vest is fairly simple. First the therapist straps the cuff section of the vest comfortably on the user’s torso. Next the shoulder straps are affixed to provide upper pressure. The therapist then determines the amount of pressure to be applied by depressing the program button to begin inflation. When the desired amount of pressure is achieved the therapist presses the program button once more and that amount is recorded for future iterations. To run the vest after programming the therapist simply chooses the number of minutes they want the pressure on and off on two separate dials. They turn on the power, press the start button, and automation takes care of the rest.
EVALUATION AND DISCUSSION
A questionnaire was developed to assess how therapists feel about the automated vest. Preliminary feedback suggests there is a definite need for quantifying and standardizing the amount of pressure applied to the child’s body. There has also been conversation suggesting that the vest could be useful outside of its intended scope, for example being used for contracture management on different joints of the body and on adults. Due to the legal difficulties associated with testing a physical device which straps on a child’s body, finding an environment in which to test our prototype has been challenging. We have recently started working with a private institution for children with autism. A single subject research methodology has been devised and we plan on pursuing further testing this summer.
We would like to thank our teachers, Michael Schneider, Anita Perr, and Marianne Petit for their boundless encouragement.
We also would like to thank our classmates for all the helpful feedback and
suggestions, and Thomas Dexter for the cute name, “Smart Hug”. Thanks to Panagiotis Rekoutis at the
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