For years, physicians have assessed asthma by measuring how much air a patient can exhale. Now, some doctors are beginning to measure what’s in that breathed-out air – specifically, nitric oxide (NO). Scientists have discovered that the amount of nitric oxide in a patient’s breath indicates the degree of inflammation in the airways.
This is important because airway inflammation sets the stage for noisy asthma symptoms such as coughing and wheezing (bronchospasm). Physicians have found that treating the underlying inflammation with anti-inflammatory medications like inhaled corticosteroids reduces the symptoms and prevents the exacerbations associated with asthma.
Asthma treatment guidelines call for use of the lowest possible dose of inhaled corticosteroids to achieve disease control. By measuring NO, physicians will know if there is inflammation present inside the airways and can better tailor anti-inflammatory medications to treat asthma.
Research studies in patients with asthma show:
- Exhaled nitric oxide (eNO) levels may help predict asthma exacerbations before they occur
- eNO levels can help predict which patients will and will not benefit from inhaled corticosteroids
- eNO levels can help physicians determine whether allergen exposure is causing inflammation inside the lungs
- eNO levels can help physicians know if patients are actually taking their anti-inflammatory medications as prescribed
Nitric oxide tests do not replace spirometry and other lung function measurements. However, combined with lung function tests and medical history, nitric oxide measurements can help physicians determine the severity of asthma more accurately, especially among those patients whose asthma symptoms are subtle or inconsistent.
The tests are noninvasive and simple enough for people of all ages, including children, to carry out accurately. In the NIOX MINO® monitoring system, approved by the U.S. Food and Drug Administration, patients first exhale thoroughly to clear their lungs as much as possible, then inhale filtered air through the MINO machine and exhale (breathe out) into the monitor. The resulting exhaled breath is thus clean of nitric oxide that might have been in the environment. Patients control the strength of their exhalation by watching images on a screen and listening for sounds that direct them to blow more or less forcefully. The MINO measures eNO according to guidelines set by the American Thoracic Society.
Some medical researchers look forward to eNO measuring devices that will be so inexpensive that they become available for home use – like a peak flow meter. Then patients and physicians can work together to monitor and manage asthma symptoms with greater precision.
First published: Allergy & Asthma Today, Spring 2006
Reviewed: March 2009, Laurie Ross