Chest
Recent Advances in Chest MedicineRecent Advances in Respiratory Care for Neuromuscular Disease
Section snippets
Impact of Ventilatory Support on Survival
Long-term ventilation has an established track record in the management of patients with ventilatory failure due to neuromuscular disease (NMD), having gained currency at the time of the poliomyelitis epidemics in the middle of the last century. Many of the old polio patients received treatment with either negative pressure or tracheostomy ventilation, and it was not until the early 1980s that noninvasive ventilation (NIV) with a mask was pioneered by Rideau et al1 in France and subsequently by
Why Does NIV Work?
At first sight, it is surprising that a treatment applied at night can have the sustained effect of correcting arterial blood gas tensions during the day. Over the years, it has been hypothesized that this improvement is mediated by a number of possible mechanisms. Hill8 has suggested that NIV may work by (1) improving ventilatory mechanics, (2) resting fatigued respiratory muscles thereby improving strength and endurance, or (3) enhancing ventilatory sensitivity to CO2. In addition,
When to Start NIV
Having demonstrated benefit, the next step is to determine the most appropriate time to start NIV therapy. Possible reasons for starting NIV therapy are shown in Table 1. For illustrative purposes, the timing of the introduction of NIV therapy in patients with DMD and amyotrophic lateral sclerosis (ALS) will be considered.
DMD
The natural history of DMD is more predictable than that of many neuromuscular conditions. Loss of lung volume is seen particularly after the initiation of wheelchair use; increasing hypoxemic dips are seen during sleep in subsequent teenage years,11, 12 and respiratory failure occurs between 18 and 20 years of age, on average. The typical evolution of these changes and the possible times for initiating NIV therapy are shown in Figure 2. An FVC of < 1 L is a predictor of poor outcome, with a
ALS
Respiratory muscle function is a key determinant of quality of life and survival in ALS patients. Oppenheimer and colleagues18, 19 showed that ALS patients were happier to receive NIV compared to tracheotomy ventilation, with the latter usually started as an emergency. His team demonstrated18, 19 that NIV therapy offers many advantages over invasive ventilation and could be employed unless bulbar weakness was severe. Earlier uncontrolled studies20, 21 had shown that assisted ventilation extends
Combination of Inspiratory and Expiratory Muscle Assist Devices
Bach23 has long championed the role of cough-assistance devices such as the cough in-exsufflator to augment cough peak flow.24 In combination with NIV therapy, these devices may reduce pulmonary morbidity.25, 26 The timing of the application of cough-assist devices in the natural history of the diseases may be as important as NIV therapy, in that the weakening of the expiratory muscles may parallel that of the inspiratory muscles in some patients and may even precede that of the inspiratory
Impact of NIV on Chest Wall and Lung Development
The chest wall develops abnormally in patients with some congenital NMDs, such as type 1 spinal muscular atrophy and some inherited myopathies. In patients with type 1 spinal muscular atrophy, the relative preservation of diaphragm strength in the face of marked weakness of the intercostals commonly leads to a characteristic sternal recession and a small bell-shaped chest. These chest wall deformities in turn restrict pulmonary development. Over and above this effect on thoracic configuration,
Cardiac Effects
A number of neuromuscular disorders are associated with cardiomyopathy and/or conduction defects. In DMD patients, cardiac involvement is inevitable, and approximately 10% of patients die from a left ventricular cardiomyopathy. Clearly, the consequences of cardiac disease are worsened by hypoxemia and hypercapnia. Thus, NIV therapy can have direct cardioprotective effects. In addition, positive intrathoracic pressure has an afterload-reducing effect on the left ventricle. Most NMD patients are
When to Stop NIV Therapy
While a proportion of patients remains stable for many years while receiving NIV therapy, increasing muscle weakness in patients with some conditions means that individuals become more dependent on ventilatory support during the day. This can occur quite rapidly over months in ALS patients, or over 5 to ≥ 10 years in DMD patients. Some choose to continue mask ventilation diurnally, but if buccal strength is reasonably preserved, mouthpiece intermittent ventilation is an effective alternative
Translating Results Into Clinical Practice
Reversing the consequences of respiratory failure with NIV improves the prognosis and quality of life in patients with NMD. Nevertheless, there is evidence that NIV therapy is not being provided to all patients who might benefit from it. The recent Eurovent survey34 of home mechanical ventilation in Europe showed a huge variation in the likelihood of patients with NMD receiving domiciliary ventilatory support, despite the fact that the prevalence of these conditions is unlikely to vary
Conclusion
In the world of oncology, an extension in survival by many years in a previously lethal condition would be met with acclaim. Such gains have been made with the use of long-term NIV therapy in patients with a range of neuromuscular conditions that hitherto were associated with premature death; even when survival is not prolonged, such as occurs in ALS patients with severe bulbar involvement, NIV therapy may still improve quality of life. This significant impact on the natural history of NMD has
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Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).
Dr. Simonds has received research grants from Breas Medical, Sweden (£150,00, 2004–2007) and ResMed UK, Oxfordshire (£62,000, 2004–2006), who manufacture noninvasive ventilators. She is an Advisory Committee member on sleep-disordered breathing in heart failure (ResMed): 1,000 euros.
This article is a based on the Margaret Pfrommer Honor lecture delivered at the American College of Chest Physicians meeting in Montreal, November 2005, in honor of this pioneer of assistive technology, researcher, champion of independent living, and patient advocate, who herself was a long-term poliomyelitis survivor and user of assisted ventilation. The work is also dedicated to the memory of Dr. Tony Oppenheimer who did so much to advance the care of ventilator-dependent patients, particularly those with amyotrophic lateral sclerosis.