Cheyne-Stokes respiration (CSR)-central sleep apnea (CSA) is a common breathing disorder in 25 to 40% of patients with chronic heart failure (CHF). In such patients, ventilation is destabilized by a combination of high controller gain (increased carbon dioxide responsiveness), hypocapnia resulting from lung edema (high filling pressures), and a long circulation time. CSR-CSA may contribute to disease progression by exposing the failing ventricle to intermittent hypoxia, arousals from sleep, and surges in sympathetic nervous system activity and BP. Ultimately, the presence of CSR-CSA and its adverse effects confer an increased risk of mortality in CHF patients independent of underlying cardiac function.
Treatment of CSR-CSA with continuous positive airway pressure (CPAP) has been demonstrated to stabilize ventilation, attenuate sympathetic activation, and improve left ventricular function in patients with CHF and CSR-CSA. In the largest trial of CPAP in CHF patients with CSR-CSA (Canadian Trial of Continuous Positive Airway Pressure for Patients With Central Sleep Apnea and Heart Failure [CANPAP]), the investigators found only a 50% reduction in the apnea-hypopnea index (AHI) [apneas and hypopneas per hour of sleep] and no beneficial effects on prognosis offered by My Canadian Pharmacy www.my-medstore-canada.net. However, a stratified analysis of the CANPAP trial demonstrated that increases in left ventricular ejection fraction and transplant-free survival were greater in those CHF patients in whom CPAP suppressed CSR-CSA than in the control group. These data suggest that a reduction in AHI in response to CPAP is a predictor of improved cardiovascular outcome in CHF patients with CSR-CSA.
As a large proportion of CPAP-treated CHF patients with CSR-CSA have residual apneas and hy-popneas, and suppression of CSR-CSA appears to be a possible mechanism by which positive airway pressure support can improve cardiovascular outcome in CHF patients, conventional CPAP may not be the optimal therapeutic approach in these patients. Therefore, devices that suppress CSR-CSA more effectively are needed.
One such approach is flow-targeted dynamic bilevel positive airway pressure (BPAP) support (BiPAP autoSV; Respironics; Murrysville, PA), which has been developed to normalize breathing in patients with both obstructive sleep apnea and CSR-CSA. The flow-targeted dynamic BPAP device provides a minimum expiratory positive airway pressure (EPAP) to maintain upper-airway patency and eliminate obstructive apneas and hypopneas. In addition, the device modulates inspiratory positive airway pressure (IPAP) in order to maintain a target inspiratory airflow and eliminate central apneas and hypop-neas. In this first clinical evaluation of flow-targeted dynamic BPAP, our objective was to test the hypothesis that it effectively suppresses CSR-CSA in CHF patients in whom CSR-CSA persisted using conventional CPAP or BPAP therapy.