Residual Volume Responsiveness Testing May Improve the Detection of Reversible Airway Obstruction in Asthma.

BACKGROUND

Residual volume responsiveness to bronchodilator administration has been observed in subjects with chronic obstructive pulmonary disease. However, the prevalence of residual volume (RV) responsiveness has not been formally studied in asthma.

OBJECTIVE

To identify the prevalence and magnitude of RV responsiveness in asthma.

METHODS

Physician-diagnosed adult subjects with asthma on treatment for >12 months were prospectively recruited to perform spirometry and measurement of lung volumes using body plethysmography before and after administration of 360 μg of albuterol.

RESULTS

Among 120 subjects, 76% were women. The ethnic composition was 64% Caucasian, 32% Hispanic, and 13% African American. The mean age was 52 ± 15 years. The mean duration of asthma was 16 ± 15 years. The mean RV% responsiveness was -7.74 ± 14. Whereas patients with the lowest baseline forced expiratory volume in 1 second (FEV1) value showed the highest mean responsiveness (P = .001), the baseline RV value had minimal influence on RV responsiveness. Using -7.74% to define significant RV responsiveness, and ≥12% and ≥200 mL to define significant FEV1 responsiveness, more subjects showed isolated RV responsiveness (37%) compared with 6% with isolated FEV1 responsiveness and 14% with both FEV1 and RV responsiveness (P = .04). There was a minimal correlation between FEV1 responsiveness and RV responsiveness (r = 0.17, P = .06). The RV responsiveness was significantly associated with the wheeze score (P = .006) and dyspnea score (P = .029).

CONCLUSION

The addition of RV responsiveness testing to spirometry based responsiveness testing can improve the identification of reversible airway obstruction in asthma. RV responsiveness may be useful in monitoring symptoms associated with air trapping in asthma.