Efficacy of a Heat Exchanger Mask in Cold Exercise-Induced Asthma: Summary
It may be a promising adjunctive therapy for asthmatics that want to work, exercise, or spend time in the cold, particularly for those individuals who still experience symptoms of EIA after pretreatment with albuterol.
One potential explanation for improved exercise lung function with the device is the expiratory resistance afforded by the system. If back pressure increases, one could argue that the improvement in lung function is due to the known beneficial effect of positive end-expiratory pressure on obstructive lung disease. The manufacturer of the device reports unpublished studies demonstrating a pressure drop across the mask during tidal breathing of only 0.5 cm of water (L. Bagby, MBA; September 2003). This pressure difference should increase with an increase in minute ventilation during exercise, but no subjects complained of feeling an increase in breathing resistance during these studies. Source
We chose an inhaled temperature range of – 25 to – 15°C, which is colder than previous studies of mask devices to prevent EIA. We wanted to significantly challenge the device, and it is common to experience these very cold and dry conditions during winter recreation. Further studies might look at two or three different inhaled air temperatures and humidities to ascertain the optimal performance characteristics of this device with respect to symptoms and lung function in asthma.
Exhaled flow rates can vary significantly with lung volume, particularly the FEF25-75. One way to correct for this is by using the ratio of FEF25-75 to FVC. For both studies, this ratio yielded similar results to the FEF25-75 data. The difference in the decline in FEF25-75 when normalized to lung volume was still highly significant in study 1, and suggested a trend toward significance in study 2. This analysis, while not a replacement for lung volume measurement, supports the validity of the FEF25-75 data.
This novel heat exchanger mask is highly effective in blocking cold exercise-induced bronchospasm in a broad population of asthmatics, as demonstrated by changes in FEV1 and FEF25-75. Compared to pretreatment with albuterol, the magnitude of its effect is similar for FEV1 and greater for FEF25-75. This mask promises to be a useful adjunctive therapy for asthmatic patients who work, live, or exercise in cold environments.