Does Sleep Suppress the Cough Reflex?
Yes, sleep is known to suppress the cough reflex, with spontaneous cough almost completely abolished during deep sleep stages 3 and 4. 1
Mechanism of Cough Suppression During Sleep
Sleep produces a marked reduction in cough frequency through decreased cough reflex sensitivity. The evidence demonstrates that:
- Spontaneous cough is almost abolished during sleep stages 3 and 4 in patients with lung disease and nocturnal cough 1
- Ambulatory recordings have consistently shown a marked reduction in cough overnight in coughers, asthmatics, and non-coughers 1, 2
- Cough is more difficult to induce during REM sleep compared to slow-wave sleep 3
- The cough reflex is suppressed during sleep, though the expiratory reflex remains less affected 3
Clinical Implications
The suppression of cough during sleep explains why patients cough less at night despite having chronic cough conditions. 1
Key clinical observations include:
- Approximately 50% of patients with chronic cough report sleep disruption due to cough, but cough frequency remains much lower at night than during the day 3
- It is uncommon for healthy people to cough at night 3
- Upon waking, the cough reflex returns to normal sensitivity, which may trigger morning coughing as accumulated mucus and secretions are cleared 2
Important diagnostic considerations:
- A cough that abates overnight may be due to reflux (closure of the lower esophageal sphincter during sleep) 1, 2
- Asthma, infection, or heart failure can cause coughing that wakes patients, indicating these conditions can overcome the normal sleep-related cough suppression 1
- The presence or absence of nocturnal cough is not particularly helpful in establishing the etiology of chronic cough 3
Mechanisms Beyond Simple Reflex Suppression
The suppression involves both reduced exposure to tussive stimuli and decreased cough reflex sensitivity during sleep. 3
- Studies of anesthetized humans demonstrate that the cough reflex is suppressed, suggesting involvement of cortical neural pathways 3
- Most antitussive drugs are sedatives, suggesting that part or all of their action may be through effects on cortical neural pathways similar to sleep 3
- Voluntary control of cough is abolished during sleep, as cough can be voluntarily inhibited or abolished when conscious but this control is lost during sleep 4, 5
Clinical Pitfall to Avoid
Do not assume that absence of nocturnal cough rules out serious pathology. While sleep suppresses cough, conditions that cause cough severe enough to wake patients (asthma, heart failure, infection) warrant immediate investigation. 1 Conversely, the presence of nocturnal cough does not reliably distinguish between different etiologies of chronic cough. 3