Omron home blood pressure monitor taps semiconductor scaling

Allan Yogasingam

October 11, 2010

Allan Yogasingam

There has always been a natural convergence between the worlds of technology and medicine. As long ago as 1612, Italian physicist Sanctorius’ development of the first medical thermometer hinted at how science and engineering would increasingly be relied upon to advance the practice of medicine. Over time, other scientific discoveries and developments, such as the harnessing of X-rays by German physicist Wilhelm Conrad Roentgen in 1895 and the invention of the electrocardiograph by Dutch physiologist Willem Einthoven in 1906, further advanced the state of the medical arts.

A milestone for the melding of technology and medicine was the invention of the silicon transistor in 1954; from there the integration of electronics into medical applications took off, leading to such developments as the first successful implantation of an artificial cardiac pacemaker in 1958; the use of ultrasound imaging for diagnostics by 1960; the invention of computed tomography scanning in 1972; and the arrival of commercial MRI scanners in 1980.

As semiconductor technology improved and met increasingly stringent requirements for performance, reliability, power consumption and compact size, its utility for medical apps became more apparent to designers and engineers. The characteristics and form factor of ASICs and FPGAs have made them a natural fit for use in small patient monitors such as blood glucose meters and blood pressure monitors. For example, ultralow-power ASICs have been designed into hearing aids to improve utility without comprising the units’ small size.

Systems-on-chip are increasingly being designed into portable and implantable medical equipment. And RFICs and other wireless sensors are being pursued for their ability to transmit data from inside the body via small, implantable units to external devices that monitor a patient’s organ activity.



Inside a BP monitor

Some of semiconductor scaling’s contributions to medical technology can now be found at the corner drug store. At my local pharmacy, for example, I was able to purchase the Omron HEM-790ITCAN arm cuff blood pressure monitor.

Until very recently, if you wanted an accurate determination of your blood pressure, you would visit your doctor’s office, where the doctor or an assistant would take your reading using a medical laboratory-grade sphygmomanometer. If you had a chronic ailment that required continual monitoring of your blood pressure, you would have to make repeated office visits—unless you had your own lab-grade sphygmomanometer and the medical training to operate it properly and then accurately interpret the results.

Blood pressure monitors like the Omron model now let you measure your pressure easily at home, using electric inflation, sensors and algorithms to return readings that can be stored in the devices’ software management system and reviewed by your doctor.

How have advancements in technology made such home medical devices a reality? A look inside the Omron unit revealed a simple design that effectively uses semiconductor technology to replicate a classic medical instrument.

The pressure sensor itself is notable. Within the sensor part of the unit, the active sensor is a pressure transducer. As the arm cuff is inflated and then deflated, a membrane within the transducer flexes as the air pressure changes. The sensor measures the differential pressure and produces an output voltage that varies with the pressure measured in the cuff. Special circuitry within the pressure sensor minimizes errors caused by changes in temperature, and an amplifier circuit conditions the signal sent from the pressure transducer. With that circuit, the output voltage from the blood pressure sensor becomes linear with respect to the pressure measurement.

The main board of the blood pressure monitor features two ICs that help implement its primary functions. The Cypress Semiconductor enCoRe (enhanced component reduction) USB combination low-speed USB and PS/2 peripheral controller is the primary interface between the blood pressure unit and the user-designated computer on which the data will be stored. The Cypress device, an 8-bit RISC microcontroller, features 256 bytes of RAM and a Serial Peripheral Interface communications block.

Data received from the pressure sensor is handled by the Toshiba 8-bit CP23AUG microcontroller, which features 48 kbytes of ROM; 2 kbytes of RAM; and an eight-channel, 10-bit A/D converter.

The future of medicine is one in which technology will have penetrated every facet of health care. And with advances in technology that have seen computers scaled down to the size of a dime and wireless technology readily available through evolutions in wireless architecture, the future of medicine is now.

Health care facilities and professionals are embracing the advances in computing and wireless technology to provide more efficient, more effective care.

Click on image to enlarge.

Click on image to enlarge.

About the author
Allan Yogasingam (ayogasingam@ubmtechinsights.com) is technical marketing analyst for UBM TechInsights.