Dyspnea During Night-Time and at Early Morning in Patients with Stable COPD is Associated with Supine Tidal Expiratory Flow Limitation

RATIONALE: Patients with chronic obstructive pulmonary disorder (COPD) complain of various COPD-related symptoms with different daily frequencies. During the night-time and at early morning, dyspnea is often reported and may predict an increased risk of COPD exacerbation and hospitalization and all-cause mortality. The aim of the study was to assess the underlying mechanisms of this symptom, seeking functional biomarkers of its occurrence. METHODS: Stable COPD patients with moderate-to-severe airflow obstruction and without confounding comorbidities underwent extensive baseline function respiratory tests. Spirometry, maximal flow-volume curves, lung volumes, and lung diffusion capacity parameters were obtained. Inspiratory capacity was also measured both in seated and supine positions. Forced oscillation technique (FOT) and negative expiratory pressure (NEP) method were used to establish the presence of tidal expiratory flow limitation (EFL) during recumbency. Questionnaires for recording COPD-related symptoms were administered. Sleep-related disturbances reported by the patients were also registered. RESULTS: Forty-two consecutive COPD patients aged 65±9 completed the protocol. They were divided, according to the absence (NFL) or presence (FL) of supine EFL, in NFL group (n=17) and FL group (n=25). FL COPD patients had more severe airflow obstruction (FEV(1)= 46.4±19.4 vs 65.1±12.5% pred., p<0.01) and they showed no increase of supine IC in contrast with NFL COPD patients (ΔIC= 0.080±0.18 vs 0.390±0.28 L, p<0.01). Dyspnea either during night-time and at early morning was significantly more reported in FL COPD patients than in NFL COPD patients (p<0.05) and in those with less than 10% increase in supine IC (p<0.05). CONCLUSION: Supine EFL is frequently associated with both night-time and early morning dyspnea, suggesting that the development of recumbent dynamic pulmonary hyperinflation, heralded by the lack of increment of IC in supine position, is a pivotal mechanism of this symptom. No or trivial increase in supine IC may indicate the occurrence of dyspnea under these conditions.