• Airway resistance [ Time Frame: cross sectional ] [ Designated as safety issue: No ]
  

• inflammation [ Time Frame: cross sectional ] [ Designated as safety issue: No ]
  

Background

Spirometry is a useful clinical tool for the assessment and monitoring of obstructive lung disease but provides no information on the underlying mechanisms causing obstruction. The role of an increase in airflow resistance can be assessed by body plethysmography, but this technique requires elaborate equipment, a skilled operator and considerable subject co-operation. A much simpler technique, impulse oscillometry (IOS) provides a more extensive assessment of pulmonary mechanics. With IOS small volume oscillations are applied at the mouth during ordinary tidal breathing; the instantaneous pressure/flow signal produced by the imposed oscillations (impedance ,Zrs) is analyzed into its in-phase (resistance, Rrs) and out-of-phase (reactance, Xrs) components. Because Rrs is measured over a range of frequencies, IOS has the potential to distinguish between large and small airway resistance. Changes in Xrs have been less studied, but there are suggestions that these also may distinguish between different types of airflow obstruction.

Objectives

The main objective of this study is to investigate the ability of IOS to measure small airway disease by providing different impedance profiles for patients with asthma and COPD. Even though patients with asthma may show some reduction of the calibre of the small airways these changes are more a feature of patients with COPD. We hypothesize that the frequency dependent changes of IOS resistances will enable us to identify patients with COPD where we expect low frequency impedance to be higher compared to patients with asthma. Furthermore, in view of the increased lung compliance which characterizes COPD patients we expect reactance, an IOS measurement which reflects lung elastance, to be elevated compared to asthmatic subjects.

Another objective of this study is to investigate the relationship between small airway resistance and inflammation. The measurement of exhaled nitric oxide (FENO), a marker of inflammation, at multiple exhalation flow rates allows the partitioning of NO produced in the central airways from that generated in the more peripheral lung. We will investigate the relationship between the levels of peripheral airway NO and small airway resistance as assessed by IOS and plethysmography. Furthermore, we would like to measure bronchial blood flow (Qaw) which also is a marker of inflammation and may play a role in the narrowing of the small airways