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Anna Bancroft, CPR Aid, 4/9/2012

Problem Statement

According to the American Heart Association, nearly 383,000 out-of-hospital sudden cardiac arrests occur annually, 88% of them in the home, and 70% of Americans may feel helpless to act. That means for a population the size of the UNM student body, more than 35 people will experience cardiac arrest this year and only 10 of them will have a bystander start CPR. Immediate CPR has been proven to be a key factor in post-cardiac arrest recovery, both as an indicator of the likelihood of returning spontaneous circulation and associated with increased neurological function after recovery. Studies have shown that real-time feedback increases rescuer confidence and a confident bystander is more likely to start CPR. The goal of this project is to design a device that will provide real-time feedback for layperson rescuers during non-medical provider cardiopulmonary resuscitation.

Goal Outline

First and foremost, this project aims to meet all the tennants of AHA 2010 layperson CPR, however there are some extra concerns. It is important for this project that the device is easily accesible to people outside of medical careers. As a result, some of the secondary goals of this project include:

  • ease of user interface
  • low cost
  • long shelf-life
  • small size

Additionally, as guidelines differ significantly for adult, child, and infant CPR, our first focus will be on a device for adult CPR.

Push Hard

The first of the three main tennants of CPR is to "push hard". This means at least 2" in an adult or 1/3 the depth of the chest in a child or infant. This could be approached from several directions, but it helps to know that the logic behind this is to create a higher intrathoracic pressure in order to "pulse" the vena cava. There are a few ways to measure the adequacy of a compression externally

Strain Gage
Spring Circuit

accurate displacement measurement

small, durable, low power consumption

easy to manufacture, least tech required


bulky, expensive, high power requirement

backing-material dependent, requires flexible mount

needs fine calibration, readings may change with heat/use

After consideration, the strain gage and spring circuit are those models most likely to fit the needs of the project. Two experimental setups are displayed below.

Stress Gage circuit diagram Spring Circuit side view

Push Fast

The 2010 AHA CPR guidelines state that a rescuer must compress the chest at least 100 times per minute to be effective at CPR. This generates a rate of 5 compressions every 3 seconds; however it is important to note that no compression will be effective unless the thoracic cavity is given a full chance to recoil before and after. This presents us with two problems to solve:

Compression Rate

We approached the compression rate problem with a simple and elegant solution. A control chip will be required to interpret the data and provide feedback. The timer on the control will be used to count off, like a metronome, and strobe an LED every time a compression is needed.

Chest Recoil

The measure of chest recoil will be based on a reading of zero pressure by the strain gage or spring circuit. The unit will be programmed to read this half-way between the peaks of counted compressions

Minimize Interruptions

The American Heart Association recommends no interruptions. To further this goal, the device will have a feedback light or sound every second compressions are not performed for 10 seconds when it will emit continuous feedback until compressions are resumed.