In the present article, we discuss some of the clinical applications for an adaptive servoventilation (ASV). Potential applications include hybrid sleep-related breathing disorders (SRBDs) associated with conventional positive airway pressure (PAP) treatment of OSA and complex or central SRBDs in patients with congestive heart failure (CHF); cerebrovascular, neuromuscular, and neurologic disorders; and sojourn at high altitude. In most cases, however, prospective randomized controlled studies are needed to determine whether ASV devices will enhance the clinical outcomes of these disorders. We have successfully used these devices in three types of SRBDs, including CHF with predominant central sleep apnea (CSA)/Hunter-Cheyne-Stokes breathing (HCSB), sleep apnea induced by long-term opioid medication use, and persistent complex sleep apnea (CompSA) in which OSA coexists with one or more of the following: treatment-emergent CSA, CSA due to high-altitude periodic breathing (PB), CSA due to a medical disorder without HCSB , CSA with HCSB , or primary CSA.

We emphasize the absence in most cases of randomized controlled trials with ASV devices and that in some of the aforementioned SRBDs, conventional PAP devices with or without an oxygen bleed (and in particular, bilevel devices with a backup rate) may be effective and could be used. However, differences exist between conventional PAP and ASV devices that could be anticipated to improve longterm outcome. In contrast to ASV technology, bilevel devices generally use fixed pressure support values and backup rates. Thus, minute ventilation (MV) cannot fall below a fixed value and, hence, could be excessive, augmenting hypocapnia and promoting rather than suppressing CSA. Furthermore, during crescendo episodes of HCSB, the patient may perceive excess ventilation as uncomfortable and thereby curtail adherence. In addition to the lack of variation in MV, bilevel devices with fixed inspiratory and expiratory pressures may increase intrathoracic pressure, and the effect on cardiac hemodynamics can be unpredictable, particularly in patients with CHF. Depending on the existing operating point on the Starling curve, the reduction in preload and afterload could decrease cardiac output rather than augment it.

Patients with CHF frequently suffer from CompSA, predominantly CSA/HCSB and components of OSA.

Moreover, the proportion of CSA/HCSB vs OSA contributing to the overall apnea-hypopnea index (AHI) may vary with body position, time during the night, and sleep state. In a large number of these patients, CSA is not suppressed with CPAP use, and we recommend ASV therapy. CPAP, however, is the treatment of choice in patients with heart failure and exclusively (or perhaps predominantly) OSA, although CSA may emerge with the use of this therapeutic modality as we observed in an early study. In a study comprising 192 patients, the prevalence of CompSA was estimated at 15%.

The patients demonstrating CompSA were found to exhibit heightened CO2 chemosensitivity, which has been shown to predispose to PB by increasing loop gain. In as many as 53% of patients with CHF and heart failure with reduced ejection fraction (HFrEF), CSA is not suppressed during the first night of CPAP titration, and this finding usually persists, with prevalence declining only slightly to 43% at 3 months. At present, it is not possible to accurately predict whether a given patient will exhibit CSA/HCSB on CPAP. One study found that a low Paco2 may be a surrogate for high loop gain and CPAP nonresponsive- ness, but this was not an invariable relationship. Further prospective studies phenotyping patients with heart failure are needed to determine whether high loop gain and low Paco2 reliably predict CPAP nonresponse and obviate the need for a trial of CPAP titration. At present, we recommend continued use of CPAP only in patients in whom CSA is suppressed during the initial titration. We recommend ASV titration when CSA/HCSB persists during the initial CPAP titration because we believe that continued use could be detri- mental. To emphasize, even though a small proportion of patients with CHF will exhibit resolution of CSA/HCSB over time when central events are not initially suppressed by CPAP therapy, the high failure rate (43% at 3 months) and the inability to predict long-term success suggest that it is not beneficial to recommend CPAP therapy if the AHI does not fall to , 15/h on the first night of titration.

There are many short- and long-term observational studies of ASV devices used to treat sleep apnea in HFrEF and heart failure with preserved ejection fraction. The following discussion by Health&Care Pharmacy concentrates on the studies that make specific points of greatest importance to the clinician.

Teschler et al19 were the first to report using an ASV device (the MV-targeted ResMed-AutoSet CS) to treat CSA/HCSB in patients with CHF. The patients underwent 5 nights of polysomnography (PSG): a baseline night without treatment followed by 4 nights titrated with (in random order) oxygen, CPAP, bilevel PAP-spontaneous/timed (S/T), and ASV. The most effective modality was ASV, with the mean