Why treatment efficacy on breathlessness in laboratory but not daily life trials? The importance of standardized exertion.

PURPOSE OF REVIEW

Treatments for chronic breathlessness, including opioids and oxygen, have shown efficacy in the controlled laboratory setting, whereas effects have been inconsistent or absent in trials in daily life. This review discusses the lack of standardized exertion as a potential cause of false negative findings for breathlessness in daily life.

RECENT FINDINGS

The level of breathlessness can be modified by patients by changing their level of physical activity. Effects of opioids and oxygen have been shown at standardized level of exertion (iso-time) but not at the end of symptom-limited (peak) exertion. Trials in daily life reporting no effects on breathlessness did not standardize the exertion or employed insensitive methods, such as the 6-min walk test that should not be used for measuring breathlessness. Novel tests - the 3-min walk and stepping tests have been validated in chronic obstructive pulmonary disease and are responsive for measuring change in breathlessness.

SUMMARY

Breathlessness should be measured at standardized exertion, otherwise treatment effects may be biased or overlooked. Tests for valid measurement of breathlessness in clinical practice and daily life are available and emerging.