INHALATION OF HYPERTONIC SALINE AEROSOL ENHANCES MUCOCILIARY CLEARANCE IN ASTHMATIC AND HEALTHY-SUBJECTS

Hyperosmolarity of the airway surface liquid (ASL) has been proposed a s the stimulus for hyperpnoea-induced asthma We found previously that mucociliary clearance (MCC) was increased after isocapnic hyperventila tion (ISH) with dry air, and we proposed that the increase related to transient hyperosmolarity of the ASL, We investigated the effect of in creasing the osmolarity of the ASL on MCC, by administering an aerosol of concentrated salt solution. MCC was measured using Tc-99m-sulphur colloid, gamma camera and computer analysis in 12 asthmatic and 10 hea lthy subjects on three separate days, involving administration of each of the following: 1) ultrasonically nebulized 14.4% saline; 2) ultras onically nebulized 0.9% saline; and 3) no aerosol intervention (contro l). The (mean+/-SD) volume of nebulized 14.4% saline was 2.2+/-1.2 mL for asthmatics and 3.2+/-0.7 mL for healthy subjects, This:volume was delivered over a period of 5.4+/-1.3 and 6.4+/-0.7 min for asthmatic a nd healthy subjects, respectively. The airway response to 14.4% saline was assessed on a separate visit and the fall in forced expiratory vo lume in one second (FEV(1)) was 22+/-4% in the asthmatic and 3+/-2% in the healthy subjects. Compared to the MCC with the 0.9% saline and co ntrol, the hypertonic aerosol increased MCC in both groups. In asthmat ic subjects, MCC of the whole right lung in 1 h was 68+/-10% with 14.4 % saline vs 44+/-14% with 0.9% saline and 39+/-13% with control. In he althy subjects, MCC of the whole right lung in 1 h was 53+/-12% with 1 4.4% saline vs 41+/-15% with 0.9% saline and 36+/-13% with control. We conclude that an increase in osmolarity of the airway surface liquid increases mucociliary clearance both in asthmatic and healthy subjects . These findings are in keeping with our previous suggestion that the increase in mucociliary clearance after isotonic hyperventilation with dry air is due to a transient hyperosmolarity of the airway surface l iquid.