Lung function testing and assessment of distal airways in asthma

Introduction Small airways are defined (in humans) as those <2mm in diameter. Background They were originally described as the "quiet zone" of the lungs contributing less than 10% of the total resistance to airflow. Pulmonary function tests remain the most used method to assess distal airway flow limitation. Viewpoints However, these tests are limited in adults and also in children because MEF25-75% and FEF50% are highly variable spirometric indices and they depend on vital capacity, which increases with expiratory time in obstructed subjects. There is a need for promising non invasive new tools like the forced oscillation technique to measure resistance. The increased availability of the exhaled fraction of nitric oxide (FeNO) measurement means that this method is accessible and attractive. Conclusion The production of nitric oxide (NO) can be assessed by measuring the fraction of NO during a prolonged expiration (FENO) or by estimating other parameters of NO exchange including the alveolar NO concentration (CalvNO) and may provide information about small airway inflammation and assist the optimal control of the disease.