Making strange, prolonged humming or groaning sounds while asleep is a recognized, though relatively uncommon, phenomenon. These involuntary noises can be startling or confusing to a sleeping partner, who typically reports the sound to the person producing it. The sound is generally described as a monotonous, low-pitched vocalization that occurs rhythmically. This nocturnal vocalization is distinct from other common sleep disturbances and is usually not noticed by the sleeper. This unique pattern of noise is linked to an underlying sleep-related breathing event.
What Is Catathrenia?
The official term for this sleep-related groaning or humming is Catathrenia, which is classified as a sleep-related breathing disorder. The condition is characterized by episodes of repetitive, loud moaning that can last from a few seconds to nearly a minute. Catathrenia most frequently occurs during Rapid Eye Movement (REM) sleep, but episodes can also be observed during Non-REM (NREM) sleep.
Catathrenia is often mistaken for snoring or sleep talking. The key distinction is that Catathrenia only occurs during exhalation (breathing out). Snoring, by contrast, is a sound created by vibrating tissues during inhalation (breathing in). Catathrenia is also separate from sleep apnea, which involves a complete cessation or significant reduction of airflow. The groaning sounds can reach volumes up to 75 decibels, making them highly disruptive to bed partners.
How the Noise Is Physically Produced
The physiological mechanism behind the characteristic humming sound involves a specific action within the respiratory system, particularly the vocal cords. An episode of Catathrenia begins with the sleeper taking an unusually deep breath. Following this deep inhalation, the breath is temporarily held against a partially or fully closed glottis. The glottis is the part of the larynx that contains the vocal cords.
The humming or groaning sound is produced during a forced, prolonged exhalation against this restricted airway. As air is pushed out, the closed or nearly closed vocal cords vibrate slowly, creating the low-pitched, monotonous noise. This process is essentially the opposite of speech, which is a controlled, conscious vocalization. The prolonged exhalation can slow the overall breathing rate, typically without causing a significant drop in blood oxygen levels. The sound’s regular harmonic pattern distinguishes it from the irregular sound of snoring.
Primary Factors That May Trigger Catathrenia
The precise origin of Catathrenia remains largely unknown, making it an idiopathic condition in many cases. Research has pointed to several potential underlying factors. One theory suggests the condition may arise from abnormalities in the brain’s respiratory control center, specifically malfunctioning neurons in the medulla oblongata. This malfunction could lead to the prolonged exhalation pattern that characterizes the disorder.
Anatomical factors in the upper airway are also considered a possible cause. Individuals with Catathrenia often have smaller-than-average jaws and narrow upper airways. This increased upper airway resistance may prompt the body to use forced exhalation to clear the airways, leading to the groan. This anatomical link suggests a mechanical component, similar to other sleep-disordered breathing conditions.
A possible genetic component exists, as some people report a family history of nocturnal groaning. While Catathrenia is not classified as a psychological disorder, stress or anxiety may trigger episodes, though this link lacks strong clinical support. The disorder is also sometimes associated with other parasomnias like sleepwalking, particularly when cases begin in childhood or adolescence.
Steps for Diagnosis and Treatment
If nocturnal groaning is persistent and disruptive, consulting a sleep specialist is the appropriate first step. Diagnosis relies primarily on a comprehensive evaluation that includes an overnight sleep study, known as polysomnography. This study monitors breathing, brain activity, muscle tone, and heart rate during sleep. This helps confirm the expiratory nature of the sound and rule out other conditions like sleep apnea. Audio recordings are helpful during the diagnostic process to verify the characteristic monotonous sound.
Treatment is recommended when the groaning significantly affects the sleeper’s quality of life or severely disrupts the bed partner’s sleep. The most common and effective treatment is the use of a Continuous Positive Airway Pressure (CPAP) device. The mild air pressure delivered by the CPAP machine helps keep the upper airway open during exhalation, which can reduce or eliminate the episodes.
Other management strategies include the use of oral appliances, designed to reposition the jaw and tongue to prevent airway collapse. In rare cases involving significant anatomical obstruction, surgery, such as tonsillectomy, may be considered to open the airway. Behavioral modifications, like deep breathing exercises or yoga, have also been suggested as complementary approaches to manage symptoms.