A COMPARISON OF 2 METHODS FOR DETERMINING NASAL IRRITANT SENSITIVITY

Nasal irritation and irritant-induced reflexes (rhinorrhea and congest ion) are prominent symptoms associated with indoor and ambient air pol lution, and marked heterogeneity in individual sensitivity has been su ggested. Nevertheless, there is currently no generally accepted functi onal index of nasal irritant sensitivity available for clinical use. T o address this issue, we compared two objective measures of nasal irri tant sensitivity: a CO2 detection task, and CO2-induced transient disr uption of respiratory pattern (pulsed CO2 acting as an odorless irrita nt). Using a respiratory flow thermocouple to produce a continuous rec ording of respiratory pattern, we challenged 20 normal adult volunteer s (13 males and 7 females, average age 39.4 years) with brief (approxi mately 3 second) pulses of the odorless irritant carbon dioxide. Incre asing levels of CO2 (10-70%, vol/vol), paired with filtered air in ran dom order, were presented unilaterally by nasal cannula of fixed geome try, synchronized with the inspiratory phase of the respiratory cycle. All subjects yielded CO2 detection thresholds, whereas within the con straints of the testing method (subjective irritation rating less than or equal to ''very strong''), only 13 of 20 subjects (65%) exhibited transient disruption of their breathing pattern. Further, although dec reased respiratory volume (indirectly measured) appeared to be a commo n feature, several distinct patterns of respiratory alteration were ob served rendering objective scoring more difficult. Finally, some subje cts showed CO2-induced respiratory disruption intermittently from tria l to trial, implying that rapid adaptation occurs. Determination of th e CO2 detection threshold therefore appears to be the more objective a nd consistently applicable endpoint for determining individual nasal i rritant sensitivity.