A new method to diagnose bronchial responsiveness in asthma
Published: September 15, 2021
Asthma is an inflammatory disease of airways characterized by dyspnea, cough and wheeze due to airflow obstruction that is often variable and sometimes responsive to bronchodilators. Spirometry has been the cornerstone to diagnose airflow obstruction in asthma. Improvement in FEV1 and FVC (forced expiratory volume in 1 second and forced vital capacity) obtained from spirometry after using an albuterol inhaler has been widely utilized to demonstrate the presence of reversible airway obstruction in asthma. However, significant improvements in FEV1 and FVC are only observed in about 17% of patients with asthma. Recent studies have documented the presence of significant lung volume abnormalities (air trapping from airway obstruction) utilizing body plethysmography in subjects with asthma despite normal spirometry. Therefore, investigators measured improvement in the residual volume (reduction in the trapped lung volume) as a test to diagnose improvement in airflow obstruction utilizing body plethysmography before and after administration of albuterol.
In a recent study published in The Journal of Allergy and Clinical Immunology: In Practice, Vempilly et al. invited adult patients with physician-diagnosed asthma and experiencing persistent symptoms on treatment for more than 12 months to participate in this prospective study. After obtaining baseline spirometry and lung volume measurements using body plethysmography, patients were given 360 ug of albuterol MDI as a bronchodilator. Following administration of bronchodilator, spirometry and lung volume measurements were repeated to assess improvement in spirometry and lung volumes. The authors also collected information regarding the severity of cough, wheeze, and dyspnea experienced in the two weeks prior to the day of study using a Likert scale.
Among 120 subjects, 76% were women. The mean age was 52 ±15 years. The mean duration of asthma was 16 ± 15 years. The mean residual volume percent improvement measured using body plethysmography was 7.74%. Therefore, by using 7.74% as a measure of significant improvement in residual volume, 37% more patients were diagnosed with responsive airway obstruction than the 20% using spirometry-based criteria. Furthermore, the degree of improvement in residual volume by body plethysmography showed a significant association with the severity of wheeze and dyspnea score. In contrast, there was no such association observed between spirometry and the degree of asthma symptoms. Therefore, the authors concluded that the addition of lung volume improvement utilizing body plethysmography could diagnose significantly more patients with responsive airway obstruction in asthma than with spirometry-based criteria alone. Furthermore, the residual volume improvement can be helpful in assessing the severity of asthma symptoms associated with air trapping. Finally, the number of subjects referred for a methacholine challenge test can be reduced by utilizing this new approach to demonstrate bronchial responsiveness.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.