PROVISION OF FUNCTIONAL MOBILITY
Mobility assistive technology has recently been reviewed in progressive NMD (215). Generally, antigravity quadriceps are required for community ambulation in childhood NMD. Short distance ambulation may be achieved by some patients with more severe weakness using KAFO bracing with or without a walker. Such orthotic intervention is often provided to children with SMA type III, Severe Childhood Autosomal Recessive Muscular Dystrophy (SCARMD), CMD, DMD, and BMD during adulthood. Children with DMD SMA type II, CMD, congenital myopathies, some myasthenic syndromes, and more severe HMSNs utilize power mobility devices for functional mobility. Generally, children can be taught to safely operate a power wheelchair when they are at the developmental age of approximately 2 years (216,217). The initial power wheelchair prescription needs to consider the natural history of the NMD condition over the following five years as some children will subsequently develop the need for a power recline system and the chair needs to be able to accommodate such a recline or be retrofit. In more severe disability, the power wheelchair electronics should be sufficiently sophisticated to incorporate alternative drive control systems, environmental control adaptations, and possibly communication systems in patients who are unable to vocalize.
ROBOTICS AND ASSISTIVE TECHNOLOGY TO IMPROVE UPPER LIMB FUNCTION
The state of the art in therapeutic and assistive robots and orthoses for the upper and lower extremity in neuromuscular disorders has been recently reviewed by Rahman and colleagues (218). As an example, a novel, articulated upper extremity orthosis, the Wilmington Robotic EXo-skeleton (WREX), helps people with NMD overcome upper limb movement deficits secondary to weakness. The WREX uses elastic bands to negate the effects of gravity; it allows a person with neuromuscular weakness to move their arm in three dimensions. The WREX can be fixed on a brace for ambulatory patients and on the wheelchair for nonambulatory patients. The WREX provided an increase in functionality and improved the quality of life of the patients. The JACO™ robotic arm (Kinova; Innovations Health, Roseville, California) uses the joystick as a controller for patients with distal hand function allowing operation of a power chair. The arm is mounted on the chair and provides reach in multiple dimensions and functional grasp.
Pulmonary complications are recognized as the leading cause of mortality in childhood NMD. Respiratory insufficiency in NMD results from a number of factors, including: (a) respiratory muscle weakness and fatigue; (b) alteration of respiratory system mechanics; and (c) impairment of a central control of respiration. Progressive muscle weakness and fatigue lead to restrictive lung disease and ultimately to hypoventilation, hypercarbia, and respiratory failure. Increase in elastic load on respiratory muscles occurs because of chest wall stiffness, airway secretions, and ineffective cough mechanism. This may result in atelectasis and increased airway resistance, and kyphoscoliosis can further alter respiratory mechanics. Defects in central control of respiration may be secondary to hypoxemia and hypercarbia, associated with severe restrictive lung disease. Significant nocturnal decreases in partial pressure of oxygen, as well as elevations in arterial partial pressure of carbon dioxide occur in more severe restrictive lung disease. Hypercapnia or hypoxemia occurring at night may have a role in reducing daytime central respiratory drive. A chronic increase in the bicarbonate pool may blunt the stimulus to breathe, generated by respiratory acidosis and perpetuates the hypercapnic state. Expiratory muscle weakness may produce ineffective cough, problems with clearance of secretions, and predispose patients to pulmonary infections.
Respiratory failure may present acutely or insidiously. Respiratory difficulties in the delivery room or early infancy may be seen in acute infantile type I SMA, myotubular myopathy, congenital hypomyelinating neuropathy, congenital infantile myasthenia, congenital myotonic muscular dystrophy, transitory neonatal myasthenia, and severe neurogenic arthrogryposis. In most other childhood NMDs, the respiratory insufficiency develops more insidiously unless an acute decompensation occurs from an event such as an aspiration episode or acute onset of weakness, as seen in Guillain-Barre syndrome, botulism, and myasthenic syndromes. Signs and symptoms of significant respiratory difficulties may include subcostal retractions, accessory respiratory muscle recruitment, nasal flaring, exertional dyspnea or dyspnea at rest, orthopnea, generalized fatigue, and paradoxic breathing patterns. A history of nightmares, morning headaches, and daytime drowsiness may indicate nocturnal hypoventilation with sleep disordered breathing. Pulmonary function tests have been used to help in the decision-making process regarding the institution of mechanical ventilation. In a study of 53 patients with proximal myopathy, hypercapnia occurred when the MIP was less than 30% of predicted and when vital capacity was less than 55% of predicted (219). Other authors (220,221) have noted lower values for vital capacity measurements in their patients with DMD at the time they require institution of mechanical ventilatory support. Hahn and colleagues (222) have reported the predicted value of maximal static airway pressures in predicting impending respiratory failure. Splaingard (223) reviewed a series of 40 patients with a diverse group of NMD conditions. They noted that all their patients who required mechanical ventilation had a vital capacity of 25% or less with at least one of the following associated findings: (a) PaCOz greater than 55 mmHg; (b) recurrent atelectasis or pneumonia; (c) moderate dyspnea at rest; or (d) congestive heart failure.
Noninvasive forms of both positive and negative pressure ventilation are being increasingly applied to children with NMDs (Figure 18.15). Initially, patients may require ventilatory support for only part of the day. Noninvasive nocturnal ventilation has become a widely accepted clinical practice, providing ventilatory assistance for patients while sleeping and allowing them to breathe on their own during the day. Intermittent ventilation may ameliorate symptoms of respiratory failure, reduce hypercarbia, increase oxygenation (even during periods off the ventilator), and prolong survival in patients with NMD. The long-term use of noninvasive ventilation (see Figure 18.12) may be associated with fewer complications than ventilation via a tracheostomy; however, bulbar muscle function should be adequate for safe swallowing (184). Ventilatory support has allowed prolonged survival and acceptable quality of life in SMA I, SMA II, and DMD (221,224-226).
FIGURE 18.15 Noninvasive ventilatory support using BIPAP and nasal pillows mask interface in young adult with DMD.
Improved pulmonary toilet and clearance of secretions can be achieved with assisted cough, deep breathing and set-up spirometry, percussion and postural drainage, and in more severe cases, the additional use of interpulmonary percussive ventilation (IPV), given two to three times daily.