To evaluate whether cardiac output manipulation via a cardiac pacemaker can stabilise ventilation.

Many patients with heart failure exhibit a distinctive abnormal cyclical breathing pattern, 'periodic breathing'. This means that patients have a worse prognosis and they have debilitating symptoms including breathlessness, fatigue and disrupted sleep. Many of these patients also have cardiac pacemakers fitted, to improve their heart function. We have discovered a new physiological mechanism linking the heart and lungs, and have shown that by changing the programmed settings of a cardiac pacemakers, we can change a patient's breathing. If we increase the programmed pacing heart rate, we increase the rate of delivery of carbon dioxide to the lungs temporarily, which increases ventilation. When we reduce the programmed pacing heart rate, the converse happens. We aim to demonstrate this phenomenon scientifically, and to use this information to stabilise periodic breathing in heart failure patients using pacemakers. We then plan to continue to investigate whether we can show that sleep quality is improved in heart failure patients with periodic breathing, by our pacing protocol.

Inclusion Criteria:

• Patients with cardiac pacemakers implanted on standard clinical grounds, and either normal left ventricular systolic function (as assessed by echocardiogram) or impaired left ventricular systolic function and stable breathing patterns (as assessed by screening in outpatients' clinic).

Exclusion Criteria:

• Patients with atrial fibrillation with a ventricular rate of >70 bpm will be excluded.
• Patients with implantable cardiac defibrillators with anti-tachycardia therapy set at an unusually low rate (<120 bpm), because it would limit the ability to vary the heart rate during the experiment.
• Patients with significant respiratory disease (FEV1 <50% predicted) will be excluded, as will patients with any condition that who have any condition precluding them from lying comfortably on a bed for 90 minutes.
• Patients who have had a recent deterioration in condition i.e. admission in previous six weeks, those in a brittle condition and those who have end-stage renal failure requiring haemodialysis.