Adaptive servoventilation in treatment of sleep-disordered breathing

Breathing is a process that is tightly controlled by a system of feedback loops that produce a relatively constant output of minute ventilation. Response of the medullary respiratory center to stimuli of peripheral and central chemoreceptors, several types of lung receptors, and respiratory muscle afferents assure that serum P_AO₂ and P_ACO₂ stay within a narrow physiological range. Like any other system controlled by feedback loops, breathing has the potential to become unstable. Cheyne–Stokes breathing pattern (CSBP), a form of central sleep apnea (CSA) characterized by cyclic episodes of hypopnea/apnea alternating with periods of hyperpnea that is frequently found in patients with congestive heart failure (CHF) and stroke, is a reflection of such an instability of the respiratory system. Under other circumstances, erratic behavior of the medullary control center may lead to intermittent centrally mediated apneas. A range of therapies, including oxygen supplementation, carbon dioxide supplementation, continuous positive airway pressure (CPAP), and various forms of noninvasive positive pressure ventilation, have been employed in the treatment of the various CSA syndromes. Here, we describe adaptive servoventilation (ASV) and its applications (Figure 1).