Continuous Positive Airway Pressure Versus Noninvasive Ventilation in Patients With Overlap Syndrome (OS)

Chronic obstructive pulmonary disease (COPD) is a leading cause of disability and death worldwide. Acute exacerbations of COPD (AECOPD), in particular, serve as marker of an accelerated disease course and thus herald an increased risk of not only repetitive AECOPD episodes but also deteriorating pulmonary function and death (2). Obstructive sleep apnea (OSA), when it occurs in combination with COPD, is an increasingly recognized contributor to AECOPD episodes. OSA consists of repetitive sleep-related partial loss of airway caliber arising from increased transmural pressures which favor luminal collapse. OSA is estimated to afflict 4 to 9% of the populations, a prevalence which is anticipated to climb hand-in-hand with the rising incidence of obesity.

The combination of the two disorders, which has been arbitrarily labeled as Overlap Syndrome (OS), has been linked with greater elevations in arterial carbon dioxide tensions and pulmonary vascular resistance and lower arterial oxygen tensions than is seen with either of its component disorders in isolation. Elevated pulmonary artery pressures may progress to cause cor pulmonale, a process whereby compensatory right ventricle remodeling, hypertrophy, and eventually, florid heart failure. In the setting of OSA, the therapeutic gold standard is nightly continuous positive airway pressure (CPAP). Essentially, CPAP machines function by administering a single continuous positive pressure airflow to the person's airway via an appropriately fitted nasal mask. The applied pressure stents open partially occluded airway segments during sleep. Though effective in OSA and OS, it is increasingly realized that for OS patients there may exist a reduction not only in airway patency but also in ventilatory drive when sleeping such that means to augment per breath volumes may attain incremental benefits to the use of CPAP alone. Although CPAP is ineffective in COPD, Bipap has shown benefit suggesting that patient with OSA and COPD may derive an improvement in health-related outcomes by using a ventilation modality which addresses both of the underlying conditions.

Bipap functions by combining the single flow in CPAP with a second inspiratory pressure assist which not only overcomes sleep-related airway resistance but also increases the magnitude of each breath resulting in lower diurnal carbon dioxide tensions and pulmonary artery pressures. Bipap may harbor a mortality benefit in COPD; but the study results are conflicting. It is unclear if Bipap is more effective at treating OSA than usual CPAP. However, it is in the setting of OS that Bipap may assume a prominent role through its ability to address both disorders; CPAP for the OSA portion and an inspiratory pressure assist to ameliorate the COPD piece. Thus far no study has been conducted to address whether OS may derive a particular benefit from Bipap or, more specifically, examine whether Bipap may diminish the risk of AECOPD, or heart failure-related hospitalizations.