Sleep apnea is a heterogeneous group of conditions that may be attributable to a wide array of underlying conditions, with varying contributions of obstructive or central sleep-disordered breathing. The spectrum from obstructive sleep apnea (OSA) to central sleep apnea (CSA) includes mixed sleep apnea, treatment-emergent CSA (TECSA), and Cheyne-Stokes respiration (CSR).1 The pathophysiologic causes of CSA can be attributed to delayed cardiopulmonary circulation in heart failure, decreased brainstem ventilatory response due to stroke, blunting of central chemoreceptors in chronic opioid use, and/or stimulation of the Hering-Breuer reflex from activation of pulmonary stretch receptors after initiating positive airway pressure (PAP) for treatment of OSA.2,3 Medications are commonly implicated in many forms of sleep-disordered breathing; importantly, opioids and benzodiazepines may blunt the respiratory drive, leading to CSA, and/or impair upper airway patency, resulting in or worsening OSA.
Continuous positive airway pressure (CPAP) therapy is largely ineffective in correcting CSA or improving outcomes and is often poorly tolerated in these patients.4 Adaptive servo-ventilation (ASV) is a form of bilevel PAP (BPAP) therapy that delivers variable adjusting pressure support, primarily to treat CSA. PAP also may relieve upper airway obstructions, thereby effectively treating any comorbid obstructive component. ASV has been well documented to improve sleep-related disorders and improve apnea-hypopnea index (AHI) in patients with CSA. However, longitudinal data have demonstrated increased mortality in patients with heart failure with reduced ejection fraction (HFrEF) who were treated with ASV.5 Since the SERVE-HF trial results came to light in 2015, there has been no consensus regarding the optimal use, if any, of ASV therapy.6-8 This is partly related to the inability to fully explain the study’s major findings, which were unexpected at the time, and partly due to the absence of similar relevant mortality data in patients with CSA but without HFrEF.
TECSA may present in some patients with OSA who are new to PAP therapy. These events are frequently seen during PAP titration sleep studies, though patients can also experience significant TECSA shortly after initiating home PAP therapy. TECSA is felt to result from a combination of stimulating pulmonary stretch receptors and lowering arterial carbon dioxide below the apneic threshold. Chemoreceptors located in the medulla respond by attenuating the respiratory drive.9 Previous studies have shown most cases of mild TECSA resolve over time with CPAP treatment. However, in patients with persistent or worsening TECSA, ASV may be considered as an alternative to CPAP.
The prevalence of OSA in the veteran population is estimated to be as high as 60%, considerably higher than the general population estimation.10 Patients with more significant comorbidities may also experience a higher frequency of central events. Patients with CSA have also been shown to have a higher risk for cardiac-related hospital admissions, providing plausible justification for correcting CSA.10
In the current study, we aim to characterize the group of patients using ASV therapy in the modern era. We will assess the objective efficacy and adherence of ASV therapy in patients with primarily CSA compared with those having primarily OSA (ie, TECSA). Secondarily, we aim to identify baseline clinical and polysomnographic features that may be predictive of ASV adherence, as a surrogate for subjective benefit.11 In the wake of the SERVE-HF study, the sleep medicine community has paused prescribing ASV therapy for CSA. We hope to provide more perspective on the treatment of veterans with CSA and identify the patient groups that would benefit most from ASV therapy.