High blood pressure, also called hypertension, is deadly: it can lead to heart failure, stroke, and kidney failure. One-third of Americans have it, and in the developing world it’s the leading killer of pregnant women due to lack of screening.
Existing blood pressure tests are painless but the equipment is flawed: it’s delicate and impractical in many settings, and it contains mercury, which is toxic when released into the environment. It’s also prone to human error, because it depends on a doctor listening to the patient’s pulse through a stethoscope.
So we came up with a DIY blood pressure monitor that’s better. It’s portable and battery-powered, making it great for areas with unreliable electricity. It’s solid-state, so it’s tough and reliable and doesn’t contain mercury. And it detects high blood pressure automatically, drastically reducing error.
Here’s how you can build one for less than $50 and test your blood pressure anytime.
Our Self-powered, Environmental, Affordable Blood Pressure Monitor (SEA-BPM, or sea-bump) is easy to use. An inflatable arm cuff contains an electronic pressure sensor that measures the air pressure inside the cuff. When the cuff is inflated sufficiently it completely occludes the artery. As the cuff is deflated blood starts to flow through the artery, and pressure on the arterial walls rises and falls with every heartbeat.
This causes oscillations of the cuff’s pressure that are detected by the sensor, and can be used to calculate both the systolic (maximum) and diastolic (minimum) blood pressures. This is known as the oscillometric blood pressure method (for details, see makezine.com/go/obpm). Our algorithm to calculate both pressures is implemented in C for programming onto a PIC microchip.
For energy efficiency in areas of the world without reliable electricity, our device uses NiCad batteries that are recharged using a hand crank generator. Fully charged, they power the device for about 50 hours. We also removed the delicate mechanical pressure meter from the device to reduce the size and weight and make it more robust. Since it’s automated, readings are more precise and not prone to human error. A reading takes less than 30 seconds.
Blood pressure, one of your vital signs, is the pressure exerted by circulating blood on the walls of your blood vessels as your heart pumps. During each heartbeat, it varies between the minimum (diastolic) and maximum (systolic) pressure. In the U.S. classification, you’d ideally have systolic pressure at 90–119 and diastolic at 60–79 millimeters of mercury (mmHg). If either of them is raised, you have high blood pressure, aka hypertension.
Blood pressure rises with age. It’s also affected by exercise, stress, diet, and sleep. If it stays high over time, it can damage the body in many ways, including heart failure and stroke. Hypertension disorder occurs in 5%–14% of all pregnancies and is the leading source of maternal mortality.