Breath sensor predicts an asthma attack the day before

A HANDHELD breath sensor can warn someone with asthma that an attack is imminent, buying them time to take preventive medication, perhaps as much as 24 hours.

The breath sensor, developed by Siemens, measures telltale rise in levels of nitrogen monoxide. NO is produced naturally in the body, and can signal the beginnings of inflammation in the bronchial tubes. If unchecked, the inflammation will constrict the airways and trigger an asthma attack.

"Nitrogen monoxide (in the breath) indicates that the bronchial system is inflamed," says Siemens's Maximilian Fleischer, who helped develop the sensor. "This means there is danger of an upcoming asthma attack."

The sensor can detect levels of NO in the breath as low as 1 part per billion, but the higher the level the more severe the impending attack may be.

When the user breathes into the device's mouthpiece, the air first passes over a potassium permanganate catalyst, which converts any NO present into NO2. The air then flows over a film containing phthalocyanin, a blue dye which binds to the NO2 molecules, so that they stick to the surface of the film. This generates a voltage, which is detected by an underlying transistor. The strength of the voltage depends on the amount of NO2 present, which in turn equates to the NO levels and hence inflammation.

Peter Barnes of the National Heart and Lung Institute at Imperial College London says: "I think it will work, but it will probably be of most benefit to people with unstable asthma, who have unexpected attacks quite frequently, and they may have to take measurements quite often."