Asthma is an obstructive airway disease characterized by reduced FEVI, FVC and FEV1/FVC% ratio with reversibility to bronchodilators. There is another pattern called pseudo-restrictive pattern with reduced FVC, normal to high FEV1/FVC% ratio, high RV and normal to high TLC have been described. Objective: To evaluate the prevalence and possible mechanism of restrictive physiology in patients with asthma in our hospital.
A retrospective review of an outpatient cohort who were referred for pulmonary function tests with a diagnosis of asthma from 1995 to 2009. We defined restriction as FVC < 80%, FEV1/FVC% > 70%, DLCO > 70% and a normal chest radiograph. Patients with restrictive lung disease and chest wall abnormalities were excluded.
A total of 2181 patients were evaluated. Restrictive pattern was noted in 32 patients. 22 of 32 patients had high RV (2 L, 113%), normal to low TLC (4.71 L, 90.5%) and low FEF 25–75 % (60%). This was suggestive of pseudo-restriction (small airways disease with hyperinflation). . The remaining 10 patients had a “True restrictive pattern” defined by RV and TLC ≤ 80% predicted. (Mean RV 1.6 L, 80%, Mean TLC 4.78, 78%). Mean BMI in pseudo-restriction group was 32 and in the true restrictive group was 37.5.
The restrictive pattern is an uncommon spirometric manifestation of asthma (1.5%). Small airways disease with hyperinflation may account for this pseudo-restrictive pattern. Small airway closure without apparent air trapping is the basis for the true restrictive pattern; perhaps an elevated closing capacity in the face of moderately severe obesity may explain this observation.
Restrictive impairment in patients with asthma. Respiratory Medicine, Volume 101, Issue 2, Pages 272–276. A. Miller, A. Palecki
Gill K, Miller A. True restrictive impairment in bronchial asthma. AJRCM 1999;159:A652.
Patients with asthma presenting with restrictive pattern on spirometry need to be further evaluated by lung volumes. The spirometry in Obesity and asthma should be interpreted with caution.
Murali Krishna Chelikani, No Financial Disclosure Information; No Product/Research Disclosure Information