Nasal obstruction can be monitored objectively by measurement of nasal airflow, as evaluated by nasal peak flow, or as airways resistance/conductance as evaluated by rhinomanometry. Peak flow can be measured during inspiration or expiration. Of these measurements, nasal inspiratory peak flow is the best validated technique for home monitoring in clinical trials. The equipment is portable, relatively inexpensive, and simple to use. One disadvantage, however, is that nasal inspiratory peak flow is influenced by lower airway as well as upper airway function. Rhinomanometry is a more sensitive technique that is specific for nasal measurements. The equipment, however, requires an operator, is more expensive, and is not portable. Thus, it is applicable only for clinic visit measures in clinical trials. Measurements require patient cooperation and coordination, and not all can achieve repeatable results. Thus, this objective measure is best suited to laboratory challenge studies involving smaller numbers of selected volunteers.

A nonphysiological measure of nasal patency is acoustic rhinometry. This sonic echo technique measures internal nasal luminal volume and the minimum cross-sectional area. The derivation of these measures from the reflected sound waves requires complex mathematical transformation and makes several theoretical assumptions. Despite this, however, such measures correlate well with the nasal physiological measures, and the nasal volume measures have been shown to relate well to results obtained by imaging techniques such as computed tomography scanning or magnetic resonance imaging. Like rhinomanometry, acoustic rhinometry is not suitable for home monitoring and can be applied only to clinic visit measures or for laboratory nasal challenge monitoring. It has advantages in being easy to use, in requiring little patient cooperation, and in providing repeatable results.

In addition to nasal obstruction, allergic rhinitis is recognized to be associated with impaired mucociliary clearance and altered nasal responsiveness. Measures exist for the monitoring of these aspects of nasal dysfunction. Although measures of mucociliary clearance are simple to perform, they have a poor record of reproducibility. Their incorporation into clinical trials is thus questionable, although positive outcomes from therapeutic intervention have been reported. Measures of nasal responsiveness are at present largely confined to research studies investigating disease mechanisms in allergic and nonallergic rhinitis. The techniques are insufficiently standardized to be applied to multicenter clinical trials but could be used in limited-center studies to gain insight into the regulatory effects of different therapeutic modalities.