Background and objective Chronic breathlessness is common and often leads to avoidance of symptomprovoking activities. Expectations of breathlessness influence behaviour and symptom perception, but the accuracy of these expectations remains unclear. The aim of this study was to examine the relationship between expected and experienced breathlessness, the moderating role of mental states, determinants of expectation accuracy and the influence of recent symptoms on future expectations.

Methods In this longitudinal study, 83 participants with chronic breathlessness rated expected and experienced breathlessness (on 0-10 numerical rating scales (NRS)) using a mobile ecological momentary assessment app over 7 days. Associations were analysed using linear and mixed regression models.

Results Expected breathlessness was significantly associated with subsequently experienced breathlessness ([3=0.51, 95% CI 0.35-0.68) but was systematically overestimated (mean +/- SD expected 4.7 +/- 1.9 versus experienced 2.9 +/- 1.7; mean absolute difference 2.0 +/- 1.5). Depressive symptoms attenuated the association ([3=0.40, 95% CI 0.23-0.58), whereas anxiety, wellbeing and self-efficacy were not associated with either the strength or the accuracy of expectations. Expected breathlessness for the upcoming week was strongly related to the experience during the study week ([3=0.85, 95% CI 0.61-1.08, R2=0.48), suggesting recent experience shapes expectations more than expectations predict future breathlessness.

Conclusion Individuals with chronic breathlessness overestimated future breathlessness by a mean of 2 NRS points. Indication of depressive symptoms influenced the strength of the association, but accuracy appears unaffected by mental state indicators. These findings highlight the need to address and recalibrate symptom expectations in clinical care.