Cough and sleep are vital functions. The effects of
cough on sleep and vice versa are important for a number of reasons. Sleep disruption is common in patients with
cough and is often the reason why they seek medical attention. Sleep suppresses
cough and the
biological mechanisms for this action are poorly understood.
Cough has recently been reported as a presenting symptom of
obstructive sleep apnea. It is uncommon for healthy people to
cough at night; however, approximately 50% of patients with
chronic cough report sleep disruption due to
cough.
Cough frequency is much lower at night than during the day. There is reduced exposure to tussive stimuli at night and decreased
cough reflex sensitivity.
Cough is more difficult to induce in REM sleep compared to slow-wave sleep. Studies of anesthetized humans have shown that the
cough reflex is suppressed; however, the expiratory reflex is less affected. The sleep-
cough interaction has implications for the physician. The measurement of
cough frequency with 24-h ambulatory
cough monitors in patients with
chronic cough suggests that the presence or absence of nocturnal
cough is not helpful in establishing the etiology. Nocturnal
cough may be a useful outcome parameter for clinical trials of
antitussive drugs since it is under less voluntary control than daytime
cough. Most
antitussive drugs are
sedatives. This suggests that part or all of their action may be through an effect on cortical neural pathways. Unexplained
chronic cough has recently been reported as a presenting feature of
obstructive sleep apnea. Patients are likely to be female and report
gastroesophageal reflux and
rhinitis.
Continuous positive airway pressure therapy is effective in alleviating
cough. Greater awareness of this condition is needed.