The “Complex Restrictive” Pulmonary Function Pattern: Clinical and Radiologic Analysis of a Common but Previously Undescribed Restrictive Pattern

Background Most patients with restriction have a pulmonary function test (PFT) pattern in which total lung capacity (TLC), FVC, and FEV₁ are reduced to a similar degree. This pattern is called “simple restriction” (SR). In contrast, we commonly observe a pattern in which FVC percent predicted (_pp) is disproportionately reduced relative to TLC_pp. This pattern is termed “complex restriction” (CR), and we attempted to characterize its clinical, radiologic, and physiologic features. Methods This study reviewed PFT results of patients tested between November 2009 and June 2013 who had restriction (TLC less than the lower limit of normal). SR was defined as TLC_pp-FVC_pp ≤ 10%, and CR was stratified into four classes based on TLC_pp-FVC_pp discrepancy: Class 1 CR, TLC_pp-FVC_pp > 10% and ≤ 15%; Class 2 CR, TLC_pp-FVC_pp > 15% and ≤20%; Class 3 CR, TLC_pp-FVC_pp > 20% and ≤ 25%; and Class 4 CR, TLC_pp-FVC_pp > 25%. The medical records of 150 randomly selected patients with SR and 50 patients from each CR class were reviewed. Results Of 39,277 PFTs completed, we identified 4,532 patients (11.5%) with restriction: 2,407 (6.1%) with SR, 1,614 (4.1%) with CR, and 511 (1.3%) with a mixed pattern. Patients with CR were younger, were more often women, and had a higher prevalence of neuromuscular disease, BMI > 40 kg/m² or < 18.5 kg/m², diaphragmatic dysfunction, bronchiectasis, CT mosaic attenuation, and pulmonary hypertension (P <.0001, <.0001, <.001,.004,.0008,.002,.008,.009,.053, and.01, respectively) and a lower prevalence of interstitial lung disease (P <.0001). Conclusions CR is a common PFT pattern with distinct clinical features. The associated clinical entities share impaired lung emptying (eg, neuromuscular disease, occult obstruction, chest wall limitation). Clinicians should be aware of this novel PFT pattern and how it shapes the differential diagnosis.