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The use of glass-bonded strain gauge technology from Measurement Specialties helped bring the Zona Plus to market.

Described as the first of its kind, an electronic device is designed to reduce blood pressure by means of an isometric hand-exercise protocol. Approved by US FDA, Zona Plus from Zona Health (Boise, ID, USA) has been on the market since 1 March 2006. While the therapeutic value of isometrics has been known for decades, applying this technique to an electronic device was a challenge. One key economic hurdle was overcome when Zona Health learned about a strain gauge technology developed by Measurement Specialties (MEAS; Hampton, VA, USA). The company’s microfused manufacturing process, combined with automated assembly, resulted in a 10:1 cost reduction for the part, according to MEAS product manager Jim Pierson.

The correlation between controlled isometric exercises and reduced blood pressure was largely an accidental discovery. Cardiopulmonary physiologist Ronald Wiley was commissioned by the US Air Force in the late 1960s to find ways to increase pilot tolerance to G forces. Many of them experienced G-force blackout while piloting the new F-16 fighter jet. The study used extreme isometric exercises to rapidly elevate pilots’ blood pressure prior to subjecting them to high G loads. The technique not only increased their tolerance of G forces, but it also led to a lowering of blood pressure over time. Test subjects who had slightly elevated blood pressure at the start of the study experienced a decline in resting blood pressure, researchers noted. Over the next two decades, Wiley evaluated various isometric exercise protocols that could be incorporated into an electronic device. The optimized protocol forms the foundation of Zona Plus technology.

Resembling a joystick with an integrated screen, the Zona device instructs the user, via text commands, to alternately grip and release the handle. The entire regimen takes 12 minutes a day. According to the manufacturer, the device has an almost 100% efficacy rate in lowering systolic and diastolic blood pressure levels.

The Microfused strain gauge adapted by MEAS for the device consummates the marriage of MEMS technology to mechanical spring members, says Pierson, yielding a new class of high-reliability, low-cost load cells.

The Zona Plus device reduces blood pressure levels by means of an isometric hand-exercise protocol.

The process involves fusing micromachined silicon piezoresistive strain gauges with high-temperature glass to a stainless-steel substrate. The fusing occurs at approximately 550°C, resulting in bonds that are less prone to aging or breakdown and creep than epoxy-joined systems, claims Pierson. Operating at very low strains, the products achieve gauge factors greater than 100 and provide a practically unlimited cycle-life expectancy, high resolution, and elevated overrange margins without the need for stops. Output can be either in millivolts or an amplified 3- to 4-V ratiometric span. Similarly cost-effective Microfused pressure transducers are also currently available; accelerometers, tonometry arrays, and rotary encoders are in development, adds Pierson.

By automating bonding and assembly, the sensors can be produced for a fraction of the price of conventional systems. “In quantities of 1 million or more, we can bring the cost down to US$2 per uncompensated sensor with a millivolt output,” says Pierson. “This puts it, practically speaking, at the disposable level.”

Glass-bonded strain gauge force-sensing technology achieved a commercial breakthrough in the mid-1980s, when consumer bathroom scales with digital displays were introduced. Zona Plus is the first medical device to use this technology, says Pierson, but it won’t be the last. He cites infusion pumps as a possible application. “The sensor can detect and measure an occlusion. If the tubing is blocked, for example, the pressure builds up on a force transducer and an alarm sounds.” Because of the load cell’s force pressure capabilities, Pierson sees applications for stapling devices used in anastomosis procedures, and for tissue-clamping instruments. Other potential uses include drug-delivery products, irrigation systems, pressure-measurement devices, IV force-sensing systems, and rehabilitation equipment.

For more information, contact Measurement Specialties, 1000 Lucas Way, Hampton, VA 23666, USA; phone: +1 757 7661500; fax: +1 757 7664297; Internet: www.meas-spec.com. Pierson can be reached by phone at +1 973 4534396, by fax at +1 973 7840034, or via e-mail at jim.pierson@meas-spec.com.