Efficacy of a Heat Exchanger Mask in Cold Exercise-Induced Asthma
Exercise-induced asthma (EIA) is present in up to 90% of all patients with asthma, and exercise is one of the most common precipitants of acute asthma. While pre-exercise inhalation therapy aimed at reducing EIA may help significantly, many patients are left with limitations in their ability to exercise, particularly in cold weather, and some patients prefer minimizing pharmacologic approaches to treatment. Even in mild asthma, multiple medications may be needed to control EIA, and with high levels of exercise patients may still have incomplete symptom control.
The mechanism of EIA has been well studied but is still incompletely understood. The magnitude of temperature difference and increase in minute ventilation in asthmatics is related to the degree of bronchospasm in a dose-dependent fashion. Increases in ventilation that occur with exercise cause airway cooling as well as increased water loss from the bronchial epithelium, leading to local increases in mucus osmolarity. While the exact mechanism is unclear, it has been shown that mast cells, independent of IgE, release histamine in response to increased osmolarity. Source
Some studies’ support the theory that it is this airway drying and increase in osmolarity that are responsible for exercise-induced bronchoconstriction. Other data suggest that airway cooling followed by rapid rewarming caused by bronchial hyperemia leads to airway wall edema and bronchoconstriction.’’ While the exact mechanisms are not fully elucidated, recent evidence suggests that dry air is more important than cold air temperature in causing EIA. The purpose of this study was to evaluate a new heat exchanger device built into a mask (Qxtec Personal Respiratory Heat Exchanger [PRHE]; AllergyZone, LLC; Louisville, KY) that warms and humidifies inspired air, with regard to decrements in lung function with exercise in cold air.
All subjects gave consent to participate in this Institutional Review Board-approved protocol. There were two studies. In study 1, 13 subjects with asthma symptoms during cold air exercise were recruited. Inclusion criteria included a postbron-chodilator FEV1 > 70% predicted and a methacholine challenge test with a provocative concentration of methacholine resulting in a 20% drop in FEV1 < 8 mg/mL.