A mechanical cough assist device helps people who cannot generate enough force to cough effectively. This inability to clear the airways of mucus and secretions can lead to recurrent respiratory infections and lung complications. The device provides a non-invasive way to simulate a strong, natural cough, which is necessary for maintaining healthy lungs.
Defining the Mechanical Insufflator-Exsufflator
The cough assist machine is formally known as a Mechanical Insufflator-Exsufflator (MIE). This instrumental airway clearance technique replaces the function of weakened respiratory muscles by mechanically delivering air pressure changes. The compact device compresses ambient air and delivers it through flexible tubing. The patient interface connects to the tubing and can be a face mask, a mouthpiece, or a tracheostomy tube adapter. The MIE is a preferred method for secretion clearance because it is more comfortable than traditional invasive suctioning techniques.
The Physics of Assisted Coughing
The core of the MIE’s function involves two distinct, rapid phases: insufflation and exsufflation. Insufflation is the first phase, where the device delivers positive pressure to the lungs, simulating the deep breath taken right before a cough. This positive pressure is typically set to a range of +30 to +60 cm H₂O, which maximizes lung volume and helps to loosen secretions from the airway walls.
This inspiratory phase is immediately followed by a rapid shift to the exsufflation phase, which applies negative pressure to the airways. This sudden reversal of pressure simulates the explosive, high-velocity force of an actual cough, moving the loosened mucus out of the lungs. The negative pressure usually mirrors the positive pressure, often set between -30 and -60 cm H₂O.
The goal of this powerful pressure change is to generate a high Peak Cough Flow (PCF), the speed of air expulsion necessary to effectively clear secretions. A PCF below 270 L/min is often a warning sign, and the MIE aims to boost this flow to a sufficient level, sometimes achieving 300-600 L/min.
Patient Populations Who Rely on This Therapy
The mechanical insufflator-exsufflator is primarily indicated for patients with weak inspiratory and expiratory muscles. These individuals cannot generate the muscular strength required for a productive cough, leading to secretion retention. The most common conditions requiring this therapy are neuromuscular disorders that cause progressive muscle weakness.
Neuromuscular Conditions
Specific examples include Amyotrophic Lateral Sclerosis (ALS), Muscular Dystrophy (MD), and spinal cord injuries (SCI). Patients with these conditions experience a loss of the muscle function needed for forced expiration, making them susceptible to respiratory complications like pneumonia. The device is also used for patients with other neurological disorders that impair the respiratory muscles, such as post-polio syndrome. Regular use helps prevent lung collapse, known as atelectasis, and maintains the range of motion of the chest wall. This therapy is intended to reduce hospitalizations and the need for more invasive long-term ventilation.
Administering a Cough Assist Session
A cough assist session is a structured procedure that requires careful setup and monitoring, often guided by a respiratory therapist or physician. The appropriate interface—mask, mouthpiece, or tracheostomy adapter—is secured to the patient to ensure an airtight seal, which is necessary for the pressure changes to be effective. The initial settings for pressure often start low, around +10/-10 or +15/-15 cm H₂O, to allow the patient to acclimate to the sensation.
The pressures are then gradually and individually titrated based on patient comfort and the effectiveness of secretion clearance, typically aiming for the therapeutic range of +/-40 cm H₂O. A treatment session for an adult usually involves performing four to six consecutive cough cycles. A single cough cycle consists of the insufflation phase, the exsufflation phase, and a brief pause.
This sequence of cycles is then repeated for multiple sessions, with four to six sessions commonly performed during one treatment period. A short rest period, often around 30 seconds, is included between sessions to prevent patient fatigue. The frequency of treatment is often two to three times per day, with increased frequency during times of illness or high secretion production.