Disability and breathlessness in asthmatic patients--a scoring method by repetitive inspiratory effort

Measurement of disability and breathlessness in asthma is important to guide treatment. Using an incentive spirometer, Triflo II (Tyco Healthcare, Mansfield, MA, USA), we developed a three-minute respiratory exercise test (3-MRET) to score the maximal breathing capacity (MBC) and perception of dyspnea (POD) index by means of repetitive inspiratory efforts achieved within 3 minutes. POD index was calculated based on the ratio of breathlessness on visual analogue scale over MBC score. In 175 normal healthy subjects and 158 asthmatic patients of mild (n = 26), moderate (n = 78), and severe (n = 54), severity, the mean (95% CI) MBC scores in mild, moderate, and severe asthma patients were 168 (145-192), 153 (136-169), and 125 (109-142) respectively, and 202 (191-214) in normal subjects (p < 0.001). The mean POD index in mild, moderate, and severe asthma patients was 16 (9-23), 25 (14-37), and 57 (14-100), respectively, and 6 (4-7) in normal subjects (p < 0.001). Intraclass correlation coefficients for MBC score and POD index in 17 asthmatic and 20 normal subjects were high. In 14 asthmatic patients randomized to receiving nebulized beta2-agonist or saline in a cross-over, double-blind study, % forced expiratory volume in one second (FEV1) change correlated with % change in MBC score [r(s) = 0.49, p < 0.01] and POD index [r(s)-0.46, p = 0.012]. In 21 asthmatic and 26 normal subjects, the MBC score and POD index correlated with the walking distance and walking POD index of the six-minute walking test (6MWT). We conclude that 3MRET is discriminative between asthmatic patients of varying severity and normal subjects, is reproducible, is responsive to bronchodilator effect, and is comparable with 6MWT. Taken together, it has the potential to score disability and POD in asthma simply and effectively.