Company: University of Texas SW Medical Center, Dallas Texas

Project: Cardiac Rehab Exercise Chair

Request: Design and build a home exercise machine to monitor recovery of patients after heart surgery.

Ideation: This is a fun part of the process for me. The requirements were the machine was to be used by patients up to 300 pounds, fit through a household doorway, be easy to transport, and easy to use/ adjust.

At this point no idea is a bad idea. The most interesting idea I sketched was a manual pump connected to a heart shaped inflatable sack that required the user to keep “filling” the sack with air. The clever part was an adjustable bypass valve that continuously let air out of the sack, so the user had to keep working to keep the sack inflated!

After my initial brainstorming presentation, a leg extension machine (like what you see in a gym) was chosen because it isolates the large quadricep muscles and was familiar to patients.

1st prototype: A chair was built using 80/20 aluminum extrusion to keep weight low, and padded upholstered seat and back. The resistance was a heavily modified Concept2 Rowing machine. To make it easy to transport rollerblade wheels were mounted on the rear which engaged with the ground when the unit tipped back. A single prototype was made.

1st Prototype testing: The chair was sturdy, adjustable, and comfortable. The Concept2 resistance unit was heavy and hung off one side, making it less than ideal for getting in and out of patients’ homes, but it did fit. The resistance was also too high for the patients even on the lowest setting. The 300-pound patients thought the chair was too small.

2nd Prototype: This unit was built wider and deeper to accommodate the larger patients. It also used a Whipr resistance unit which I discovered on IndieGoGo. The Whipr was a rowing machine designed for travelers. It has a small form factor and allows it to be mounted under the chair (with modifications) rather than on the side. The Whipr resistance was also too high, but it was easy to remove a couple of magnets in the resistance unit to lower the resistance. The rear transportation wheels were also sized up to 110mm (about 4.33 in) scooter wheels to make transportation easier. Since there was space on the sides, adjustable handles were added to the sides to provide patient stability. A special lightweight climbing carabiner with a keylock nose that would not catch on the patient’s ankle cuff, and a hook just under the seat to retain the carabiner when not in use. A single prototype was made.

2nd prototype testing: This unit was easier to transport with its lighter weight and larger wheels. The lower resistance worked well for the patients. It was easy to attach the carabiner to the ankle cuff, and switch between left and right legs. The chair was comfortable and sturdy for most patients. The only challenge was the patients were still telling us it was too small.