A BREATHING FILTER EXCHANGING HEAT AND MOISTURE PREVENTS ASTHMA INDUCED BY COLD-AIR

In order to devise a protective aid against bronchial obstruction indu ced by cold air, we have tested a breathing filter with heat and moist ure exchanging properties. Nine asthma patients, who all had a history of cold-induced asthma, took part in exercise tests on an ergometer b icycle at a temperature of approximately -10 degrees C, without and wi th a breathing filter. Without a breathing filter, the maximum reducti on in FEV(1) was, on average, 36%. With the breathing filter, the maxi mum reduction in FEV(1) was, on average, 11%. The difference was clear ly significant (P<0.001). A further five cold-sensitive asthmatics per formed similar exercise tests at -10 degrees C on three occasions: 1) without and 2) with a breathing filter as above, and 3) with two breat hing filters connected in parallel: one for inspiration and the other for expiration. Thus, no heat-moisture exchange could take place. The fall in FEV(1) after provocation without a breathing filter and with p arallel breathing filters was similar but attenuated when rebreathing took place through the breathing filter, The results confirm the theor y that in cold/exercise-induced asthma, it is indeed the heat and/or w ater loss from the airways that triggers airway narrowing, and that a heat and moisture exchanging filter has a considerable protective effe ct and can be of value in the treatment of asthma.