CPAP therapy is the most common and effective treatment for obstructive sleep apnea (OSA). This medical device delivers a constant stream of pressurized air through a mask to keep the airway open, eliminating the pauses in breathing that characterize OSA. While CPAP significantly improves sleep quality, some users experience side effects like a persistent cough. A CPAP-induced cough often indicates irritation in the respiratory system, suggesting a simple adjustment to the machine’s settings or equipment is needed. Understanding the specific causes, from air quality issues to pressure settings, is the first step toward resolving the discomfort.
Addressing Dryness and Air Quality
The continuous flow of air from the CPAP machine can rapidly dry out the delicate mucous membranes of the nose, throat, and upper airways. This dryness irritates the throat, triggering a reflexive cough as the body attempts to restore moisture. Using a heated humidifier, which is built into most modern CPAP units, is the primary method to combat this effect by adding warmth and moisture to the pressurized air. Users should experiment with the humidity settings to find a level that provides comfort, as a setting that is too low will not adequately moisten the air.
A secondary effect of using a humidifier can be a phenomenon known as “rainout,” which occurs when the warm, moist air cools down as it travels through the tubing to the mask. This cooling causes the moisture to condense into water droplets that collect in the hose and mask. Inhaling these cold water droplets can lead to an abrupt sputtering, gurgling, or gagging sensation that triggers a cough reflex. Solutions include using a heated hose, which maintains the air temperature throughout the length of the tube, or insulating the standard tubing with a fabric cover.
Mouth breathing while using a nasal mask or nasal pillows is a common cause of dryness. An ill-fitting mask that allows air to leak also contributes to this issue. Mask leaks allow humidified air to escape, replacing it with the drier room air, which bypasses the natural filtration of the nasal passages. When pressurized air blows out of a leak, it can irritate the back of the throat and cause coughing. Solutions include using a chin strap to keep the mouth closed or switching to a full-face mask.
Identifying Incorrect Pressure Settings
The pressure of the air delivered by the CPAP machine can be a source of coughing, independent of humidity or mask fit. If the prescribed pressure is set too high, the forceful stream of air can be uncomfortable. This excessive pressure makes it difficult to exhale naturally against the resistance, often causing a reflexive cough. High pressure may also force air down the esophagus and into the stomach, a condition called aerophagia. Aerophagia causes bloating and discomfort that can further contribute to coughing.
To ease the sensation of high pressure upon initiating therapy, most modern machines include a “ramp” feature. The ramp allows the machine to start at a lower, more tolerable pressure, often around 4 cmH2O. Pressure then gradually increases to the prescribed therapeutic setting over a set period. Properly setting the ramp ensures the user is asleep before the full therapeutic pressure is reached, preventing a sudden blast of air that could trigger a cough.
Many CPAP devices incorporate Expiratory Pressure Relief (EPR) technology to improve breathing comfort. This feature automatically lowers the pressure during the exhalation phase of the breathing cycle. By reducing the pressure when the user breathes out, EPR makes the breathing sensation feel more natural. This reduction minimizes the effort and resistance that might otherwise lead to a forceful cough.
Equipment Hygiene and Contamination
A cough can signal the inhalation of contaminants built up within the CPAP equipment. The warm, moist environment created by the humidifier and breath is a breeding ground for mold, mildew, and bacteria. If the water tank, tubing, or mask are not cleaned regularly, the pressurized air can aerosolize these contaminants. Inhaling mold spores or bacteria acts as a direct respiratory irritant, leading to coughing or allergy-like symptoms.
The humidifier water chamber should be emptied daily and cleaned with mild soap and warm water to prevent microorganism growth. The air intake filter on the CPAP machine also requires regular checking and replacement. A clogged or dirty filter recirculates dust, pet dander, pollen, or other environmental allergens present in the room. Inhaling these allergens irritates the sensitive lining of the respiratory tract, mimicking cold or allergy symptoms, including a persistent cough.
Exacerbation of Existing Health Conditions
CPAP therapy may not be the root cause of the cough but rather a trigger that amplifies an underlying medical issue. Gastroesophageal Reflux Disease (GERD), or chronic acid reflux, can be exacerbated by the positive pressure from the CPAP machine. The air pressure can sometimes push stomach acid back up the esophagus, particularly if the user lies down shortly after eating. This acid irritation in the throat and upper airway leads to a nocturnal cough.
A cough may also stem from pre-existing sinus congestion or post-nasal drip. The forced CPAP air can dry out the sinuses or push excess mucus down the back of the throat. This drainage irritates the throat lining, leading to a tickle and subsequent cough. If a persistent cough remains after addressing all equipment and setting variables, consult a physician or sleep specialist for medical evaluation.