Abstract
The three respiratory muscle groups are the inspiratory muscles, expiratory muscles, and bulbar-innervated muscles. The inspiratory and expiratory muscles can be assisted or supported indefinitely by applying pressure to the body or airways such that no extent of dysfunction should result in respiratory failure or need to resort to tracheotomy. Inspiratory and expiratory muscle aids are devices and techniques that involve the manual or mechanical application of forces to the body or pressure changes to the airway to assist or substitute for inspiratory or expiratory muscle function. Negative pressure applied to the airway during expiration assists the expiratory muscles for coughing, just as positive pressure applied to the airway during inhalation (noninvasive intermittent positive pressure ventilation [IPPV]) assists inspiratory function [4]. A manual thrust applied to the abdomen during expiration or exsufflation, especially when in combination with mild chest compression, assists expiratory muscle function and increases cough flows. Patients with little or no measurable vital capacity (VC) or any ability to autonomously sustain alveolar ventilation or cough can be managed without invasive tubes using these methods. However, even when inspiratory and expiratory muscles are functional, patients with bulbar-innervated muscle dysfunction to the extent that continuous aspiration of airway secretions results in decrease in an oxyhemoglobin saturation (SpO2) baseline below 95% need to undergo tracheotomy to survive [15]. At the point that this occurs, the patient has usually already lost the ability to speak and swallow food. This essentially only occurs for patients with advanced bulbar amyotrophic lateral sclerosis (ALS) and the occasional patient with spinal muscular atrophy type 1 (SMA1).