CPR LIFELINE

What it does

The CPR LIFELINE is a hands-free mechatronic device that performs CPR automatically by providing the required 120 compressions per minute and 2 inch (~5 cm) compression depths on the chest of any size patient, safely and accurately.

Your inspiration

There are more than 350,000 annual cases for out-of-hospital cardiac arrests in the US alone and over 270,000 annual cases in the European Union. Around 90% of all cases are fatal. The root cause of this is lack of sufficient CPR, either from bystanders or medical professionals who arrive with a delay. To minimize human effort and error, an automatic, safe, hands-free CPR solution was imagined. This would fit any size patient and provide the required rate and depth, while ensuring any injury caused during CPR is minimized on the patient. Such a design would have to be cost-effective and portable to be the best solution.

How it works

The CPR LIFELINE contains a 150 W DC motor driving a gear train to produce 120 RPM with the necessary torque. This output drives an internal scotch yoke mechanism, generating a 480 N force (~50 kg) and achieving 120 compressions per minute with a 2 inch linear reciprocation. This setup is based on studies showing that a ~50 kg mass causes a 2 inch chest compression. The ends of the reciprocating rods have an 8 cm diameter and 1.5 cm thick microfiber pad, which distributes pressure similarly to a palm, reducing skin lesions and rib fractures. In practice, a paramedic straps the CPR LIFELINE around the patient's chest, centering it at the sternum. The strap should be snug without extra tension, ensuring the microfiber pad sits flush with the chest. Once activated, the device delivers 120 compressions per minute with sufficient force for a 2 inch compression depth. The design allows space for defibrillation pads to be placed diagonally for AED use during CPR.

Design process

Firstly, the design form was found by studying a range of patient sizes. Various methods for quickly positioning the device on the patient’s chest were explored, leading to a compact padded strapping mechanism that fits normal and large patients. Secondly, after evaluating different methods for converting rotational motion to linear reciprocation, the scotch yoke mechanism was selected for its smooth operation, minimal mechanical parts, and uniform torque, essential for achieving the required force and the 2 inch chest compression. A 150 W motor was chosen based on the system's power requirements. Thirdly, tests on users' chests with materials like polyurethane foam, silicone rubber, and microfiber pads determined that microfiber pads provided the most comfort and minimal deformation while reducing pressure impact. To prove the design's functionality, a test rig was developed with a 150 W motor running at 3000 RPM, connected to a 25:1 double stage gear reducer, achieving an output of 120 RPM and 12 Nm torque. The scotch yoke mechanism, with a sliding pin at a 2.5 cm radius, enabled a 5 cm (2 inch) linear reciprocation, transmitting 480 N (~50 kg) of force at 120 compressions per minute. Compression depth was measured with a vertical scale and rate was observed with a timer.

How it is different

The current state of the art, the LUCAS CPR, has 4 major problems: it cannot fit large-sized patients who are at the highest risk of cardiac arrest, it often causes skin lesions and rib fractures more than manual CPR, it is bulky and not truly portable, and it costs a hefty $20,000, making it expensive for all parties involved. The final design addresses these crucial challenges. Firstly, the strapping mechanism accommodates large-sized patients, unlike the LUCAS CPR, which has a fixed size and restrictive backplate and attachment system. Secondly, our design connects the linear reciprocating rod to a microfiber pad with sufficient cross-sectional area, reducing pressure exerted on the skin. In contrast, the LUCAS CPR uses a suction cup with only the outer edges in contact, increasing pressure and causing skin lesions. Thirdly, our design is more compact and lightweight, enhancing portability. Finally, it has a BOM of only $200, making it cost-effective.

Future plans

Currently, all parts have been 3D printed except for the bearings, motor, and power supply. Moving forward, the design will be made with specific medical grade components as well as metal parts to increase durability of the design. Additionally, the microfiber pads used at the ends of the linear reciprocating rod will need to be optimized in terms of diameter and thickness to be able to distribute pressure more evenly on the chest. The power supply will be replaced with an optimized rechargeable lithium ion polymer battery to ensure it lasts about 30 minutes when performing operation, which is above the average CPR time of 20-25 minutes.

Awards

This is the first time this project has been presented for an award. The team members have won the following awards for similar projects in the past: University of Toronto Designathon Competition Champion 2021 and University of Toronto Mechanical Engineering Design Champion 2019.