Bronchial asthma is a chronic respiratory disease with a high prevalence, especially in children. There are many methods applied in the diagnosis of bronchial asthma today, including the technique of measuring NO gas concentration.

Nitric oxide (NO) has been known as a gas in the environment polluted by vehicle exhaust and cigarette smoke. However, recently NO in the breath has become more known thanks to its association with the FeNO test - a highly reliable test.