Chronobiology in breathlessness across 24 h in people with persistent breathlessness

To the Editor:

Breathlessness is associated with impaired quality of life, comorbidities, more frequent hospitalisation and premature mortality. Breathlessness leads to people avoiding things that trigger their breathlessness, such as physical activity [1–3].

The intensity of breathlessness varies over time both as exacerbations of the underlying aetiologies and among individuals with “stable” disease [4]. A definition of clinically important variability of breathlessness is lacking, and reports of daily symptom variability differ substantially between studies [4–6]. Approximately 44% experience symptom variability during the day [4–6]. Breathlessness intensity is highest on waking, continuing through people's morning routines and tapering later in the day [4]. Daytime symptoms are associated with poorer quality of life and higher anxiety [4, 7–10].