Mechanisms of Action of Adaptive Servoventilation

It is known that a significant proportion of patients with heart failure have sleep disordered breathing (SDB). Some of these patients will have Central Sleep Apnoea which is one form of SDB. The SERVE-HF study aims to look at the effect of a breathing support machine, or ventilator called Adaptive Servo-ventilation (ASV) on mortality in heart failure patients with central sleep apnoea. In this related sub-study the investigators want to look at how the ASV machine has its effect. The investigators will be carrying out tests in the laboratory to measure various aspects of the way that breathing is controlled to measure the effect that ASV has on patients. In addition measurements looking at activity levels will be made using an actiwatch device worn by patients for 14 consecutive days and nights. Healthy controls will be recruited to all parts of this protocol (ie measurements at baseline and 3 months) to allow comparison of data between patients and controls.