The ability to cough is a natural protective reflex that removes foreign particles and accumulated secretions from the lungs and airways. When respiratory muscles are too weak to generate the necessary force, mucus can build up, leading to serious complications like lung infections and pneumonia. A cough assist machine, formally known as a mechanical insufflator-exsufflator, is a non-invasive device designed to help people clear their airways when their natural cough is insufficient. By simulating the mechanics of a strong, healthy cough, this technology provides an effective method for maintaining respiratory hygiene and lung function at home.
What Cough Assist Machines Are
The term “Cough Assist” is the common name for a device that performs Mechanical Insufflation-Exsufflation (MIE). This machine functions by delivering a controlled, rapid change in air pressure within the lungs to mimic the natural process of a forceful cough. The goal of the device is to mobilize thick secretions from the lower airways up toward the mouth where they can be easily cleared.
The equipment includes a main unit that generates and controls the air pressure, flexible air tubing, and a filter to ensure air hygiene. Air is delivered to the user through a patient interface, such as a close-fitting face mask, a mouthpiece, or an adapter for individuals with a tracheostomy tube.
The Mechanics of Operation
The cough assist machine operates in two distinct, sequential phases to replicate the powerful pressure changes of a voluntary cough. The first phase is the insufflation phase, where the machine delivers a controlled amount of positive pressure air into the lungs. This action effectively inflates the lungs to a greater volume than the patient could achieve alone, pushing air behind any trapped secretions.
The second phase is the exsufflation phase, which follows the inhale almost immediately. The machine rapidly reverses the pressure to a strong negative pressure, essentially creating a vacuum-like pull. This sudden pressure shift generates a high expiratory flow rate, often between 300 to 600 liters per minute, which is comparable to a healthy, unassisted cough.
This rapid expulsion of air provides the shearing force necessary to loosen and pull mucus from the inner walls of the airways. The settings for both the inspiratory (positive) and expiratory (negative) pressures are precisely calibrated by a clinician, typically ranging from +30 to -50 centimeters of water pressure. The quick transition between these two opposing pressures is what makes the mechanical cough effective in clearing deep-seated mucus.
Conditions Requiring Cough Assistance
Patients who rely on this technology share a common issue: a compromised ability to generate the necessary muscle power for a forceful cough. The problem stems from weakened or impaired abdominal and intercostal muscles, which are responsible for creating the sudden, high-pressure expulsion of air during a cough. When a patient’s Peak Cough Flow (PCF) falls below 270 liters per minute, their natural cough is considered ineffective for proper secretion clearance.
The machine is frequently used by individuals with progressive neuromuscular disorders that cause a loss of muscle strength over time. Specific patient populations include:
- Muscular Dystrophy
- Amyotrophic Lateral Sclerosis (ALS)
- Spinal Muscular Atrophy
- Individuals with high-level spinal cord injuries, as nerve signals to the respiratory muscles are disrupted.
For these individuals, using the device is a proactive measure to prevent mucus accumulation and reduce the risk of respiratory infections.
Practical Steps for Using the Machine
The use of the cough assist machine follows a structured procedure to maximize the effectiveness of the treatment. The patient should first be positioned upright, either sitting in a chair or reclined in bed, with their head well-supported to optimize lung expansion. Once the machine is powered on and the prescribed settings are confirmed, the mask or mouthpiece is placed securely over the face, ensuring a tight seal is maintained.
A treatment session consists of several cycles, with each cycle containing the insufflation and exsufflation phases, followed by a brief pause. The machine automatically initiates the positive pressure breath, which the user is encouraged to work with by taking a deep inhale. This is immediately followed by the negative pressure phase, where the user will feel the rapid pull of air, which is the simulated cough.
A common regimen involves completing a set of three to six consecutive cough cycles, followed by a short rest period of about 30 seconds to prevent hyperventilation. This entire sequence may be repeated three to six times, depending on the amount of secretions needing to be cleared. After use, the mask and tubing must be washed with mild soapy water and air-dried to maintain hygiene.