1. Reflex bronchial changes have been demonstrated after nasal stimulation in both man and experimental animals. The existence of a pulmonary-nasal reflex is less established. We have examined whether induced narrowing of the intrathoracic airways leads to increases in nasal airflow resistance (R naw) in patients with asthma.

2. We have used a non-invasive forced oscillation method to measure total respiratory resistence (R rs) at 8 Hz during tidal breathing sequentially via the nose (R rs, na) and via the mouth (R rs, mo) and derived R naw by subtracting R rs, mo from R rs, na. We examined whether changes in R naw occurred when increases in R rs, mo were induced by inhaling histamine aerosol via the mouth with the nose occluded in 11 patients with stable, mild asthma (six males, age 28.1 + 2.1 years, forced expiratory volume in 1 s 97 +6% of predicted, means +SEM). Six of the patients had a history of rhinitis. The patients were first challenged with doubling concentrations of histamine via a dosimeter to establish the dose which reduced the forced expiratory volume in 1 s by ≧ 20%. Two hours later when the forced expiratory volume in 1 s had returned to baseline, they were challenged with saline and again 2 h later with the concentration of histamine that had earlier caused a ≧ 20% fall in the forced expiratory volume is 1 s.

3. Between 0.5 and 10 min after histamine inhalation, a sustained increase in R rs, mo was achieved with mean increases averaging 68–77% above baseline over this period (P <0.001). This was associated with a slower rise in mean R naw which reached a maximum of 53% above baseline at 5 min after histamine inhalation. The rise in R naw varied between patients, but was sustained for 10 min in eight of the patients; the extent of rise was not related to a history of rhinitis.

4. The results suggest that, in some asthmatic patients, bronchoconstriction results in an increase in R naw, probably due to a pulmonary-nasal reflex. Further studies are required to investigate the mechanisms of this increase.

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