Efficacy of a Heat Exchanger Mask in Cold Exercise-Induced Asthma: Methods
Spirometry was performed at 5, 15, and 30 min after exercise, and subjects were rescued with albuterol if they demonstrated a > 40% decline in FEV1 at any time.
The primary outcome for both studies was the maximum postexercise percentage decline in FEV1. Secondary outcomes included the percentage decline in maximum mid-expiratory flow (FEF25-75), FEF25-75/FVC ratio, and for study 1, the presence or absence of EIA as defined by a decline in FEV1 > 10%. The maximal percentage decrease in lung function was expressed as a mean ± SE. Data from two exercise visits within a study were compared by applying the Wilcoxon signed-rank test to the percentage of maximal decline in lung function. In study 1, the McNemar test was used to compare placebo and active device exercises with respect to the presence of EIA. so
Study 1 enrolled 13 subjects, and study 2 enrolled 5 subjects. All subjects met inclusion and exclusion criteria, and no subjects dropped out. Of the 15 people who participated in one or both studies, 9 were women, and the average age of participants was 29 years (Table 1). Mean baseline FEV1 was 3.24 ± 0.17 L (88 ± 4.0% of predicted).
Study 1 subjects demonstrated improved lung function after exercise with the active device, compared to placebo (Fig 2). The mean fall in FEV1 was 19 ± 4.9% with placebo and 4.3 ± 1.6% with the active device (p = 0.0002). The mean fall in FEF25-75 was 31 ± 5.7% with placebo and 4.7 ± 1.7% with the active device (p = 0.0002). Since exhaled flow rates can vary significantly with lung volume, particularly the FEF25-75, we calculated the decrease in the ratio FEF25-75 to FVC with exercise. For study 1, the mean percentage decrease in the FEF25-75/FVC ratio was 21 ± 4.3% with placebo exercise and 0.4 ± 1.7% with the PRHE mask exercise (p = 0.0002). Thus, the difference in the decline in FEF25-75 when normalized to lung volume was still highly significant.
During the placebo device exercise, 6 of 13 subjects demonstrated EIA by a fall in FEV1 > 10% from baseline. Of those six subjects, two had a > 40% fall in FEV1, necessitating early rescue with albuterol. However, during exercise with the active device, only one of these six subject demonstrated EIA (p = 0.0253) and no subjects required albuterol rescue.
Table 1—Subject Characteristics
|Subject No.t||Sex||yr||Baseline FEVb L||Prebronchodilator FEV1 % of Predicted, %||Methacholine PC20, mg/mL|
Figure 2. Individual changes in FEV1 with cold air exercise in study 1. Solid bars represent the placebo exercise; striped bars represent the active device exercise. The active heat exchanger mask is highly effective, particularly in subjects demonstrating a > 10% decline in FEV1 with placebo exercise.