An early study of ASV 9 showed similar short-term effects to CPAP therapy, but over 6 months apnoeas and hyponoeas were suppressed better by ASV.Īlthough there is no doubt that NIV is gold-standard therapy in acute hypercapnic exacerbations of COPD, results from trials of domiciliary NIV in COPD have been more mixed. As shown in Fig 1, ASV aims to smooth out the waxing–waning pattern of CSR by increasing inspiratory positive airway pressure support when ventilatory effort falls and reducing it again to a pre-set minimum level as ventilatory effort increases. 8 The mode of adaptive servo-ventilation (ASV) has been developed to deal primarily with central sleep apnoea and/or CSR, but also incorporates positive pressure during expiration so that obstructive episodes can also be obviated. This can be complicated by swings in intrathoracic pressure caused by OSAs, which reduce pre-load, and high levels of oxidative stress.Īlthough continuous positive airway pressure therapy (CPAP) can address obstructive events, there have been no rigorous long-term trials of CPAP in patients with heart failure and OSA, and a randomised controlled trial of CPAP 7 in CSA did not show favourable effects, other than in a post-hoc analysis, where benefit was seen in those patients in whom CPAP suppressed apnoea and hypopnoeas. 6 Moreover, these forms of sleep-disordered breathing can be associated with intermittent hypoxaemia and surges of catecholamines, which further compromise left ventricular function. Either OSA or central sleep-disordered breathing (CSA) can occur in approximately half of patients with mild to severe chronic heart failure (CHF). More recently, it has been shown that not only Cheyne Stokes respiration (CSR) is present in those with milder heart failure, but also that other forms of sleep-disordered breathing, such as obstructive sleep apnoea (OSA), are common. Previously, it was felt that periodic breathing and/or a Cheyne Stokes pattern of waxing and waning ventilation was a characteristic of end-stage heart failure, NYHA grade 4. Approximately 70% of those individuals have mild heart failure, New York Heart Association (NYHA) grade 2. NIV is less successful in dealing with acute and chronic hypoxaemic respiratory failure because it does not address causes of hypoxaemia, such as ventilation–perfusion mismatch or diffusion difficulties, although NIV can offload the work of breathing (see, ‘Palliation of breathlessness’, below) and buy time for other therapies to take effect.Īdaptive servo-ventilation in chronic heart failureĪpproximately 1–2% of the population have heart failure, with the prevalence increasing as the population ages. 4, 5 All these clinical situations exemplify the pathophysiological vicious cycle of an overloaded respiratory system, leading first to nocturnal hypoventilation and then overt diurnal ventilatory failure. For chronic application, there are extensive case-series data on the use of NIV in chronic restrictive disorders (eg chest wall and neuromuscular disease), 2 with one randomised controlled trial (RCT) showing improved survival in patients with motor neurone disease of approximately 7 months, 3 and other cohort series showing a major increase in survival in patients with Duchenne muscular dystrophy treated with NIV. The evidence base (Box 1) for non-invasive positive-pressure ventilation (NIV) is now extensive, particularly in acute ventilatory failure, where there is evidence from randomised controlled trials and meta-analysis 1 to support the first-line use of NIV in acute acidotic hypercapnic exacerbations of chronic obstructive pulmonary disease (COPD), and to wean patients with COPD off invasive ventilation. Although negative-pressure ventilation has a long history, being used extensively during the poliomyelitis epidemics of the previous century, current delivery of non-invasive ventilation in acute and chronic circumstances is predominantly via positive-pressure systems. In contrast to invasive ventilation, which is delivered by an endotracheal tube or tracheostomy, non-invasive ventilation is applied either by positive pressure through a mask or nasal and/or oral interface, or via negative pressure supplied round the chest wall with a shell or body-encompassing tank ventilator. Definitions and indications for non-invasive ventilation
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