Hyperinflation on chest radiograph as a marker of low adherence to positive airway pressure therapy in the overlap syndrome.

BACKGROUND Positive airway pressure (PAP) in subjects with both obstructive sleep apnea and COPD reduces the risk of pulmonary hypertension, death, and hospitalizations from COPD exacerbations, but adherence to the intervention is low, similar to the experience with noninvasive ventilation in stable COPD. We sought to assess whether hyperinflation on chest radiographs contributes to low adherence to PAP therapy in the overlap syndrome. METHODS Records of patients with a listed diagnosis of COPD at the time of polysomnography were reviewed. Overlap syndrome was diagnosed when COPD was clinically confirmed with spirometry showing a fixed airway obstruction and when the apnea-hypopnea index was ≥ 5. Hyperinflation was evaluated by a review of the right diaphragm height on a lateral chest radiograph. Adherence was assessed clinically or through device download at a 3-month follow-up, and later adherence was assessed by telephone interviews. A receiver operating curve was used to determine whether diaphragm height was associated with adherence. RESULTS Twenty-one of 41 subjects (51%) were considered adherent to PAP therapy at the 3-month visit. Adherent subjects were more overweight compared with non-adherent subjects (body mass index of 36.0 ± 5.7 vs 32.0 ± 5.7 kg/m(2), P = .03), sleepier at the onset (Epworth sleepiness scale score of 13.0 ± 5.8 vs 9.4 ± 5.4, P < .05), and less likely to have hyperinflation as defined by a right diaphragm height ≤ 2.45 cm (33% vs 65%, P = .04). The body mass index and initial sleepiness no longer predicted adherence beyond 3 months, but 35% of subjects with a right diaphragm height ≤ 2.45 cm were adherent beyond 3 months compared with 75% of those with a right diaphragm height > 2.45 cm (P = .04 by Fisher exact test). CONCLUSIONS Hyperinflation is associated with decreased adherence to PAP therapy in the overlap syndrome.