Assessing the exertion required to induce breathlessness in a population with advanced cancer: Matching measures to the level of physical function

Background: The aim of the study was to assess four evidence-based assessments utilising exercise challenges that induce breathlessness, each with progressively less demanding levels of exertion, which can be tailored to people with a range of functional capabilities in the setting of advanced cancer for research studies. Functional cut off points for these assessments have not previously been defined. Methods: A cross sectional study of four exercise tests attempted by all participants: 6 min walk test (6MWT); (derived) 2 min walk test (2MWT); arm exercises; and reading numbers aloud. Performance status (Australia-modified Karnofsky Performance Status (AKPS)), baseline breathlessness using the modified Medical Research Council (mMRC) breathlessness scale, and a visual analogue scale of intensity and unpleasantness of breathlessness were measured. Co-morbidity was codified using the Charlson Co-morbidity Index. Percentage of people completing each test by AKPS level of function and baseline mMRC breathlessness scores were quantified. Results: In the 68 participants, poorer function decreased the proportion of people able to complete the exercise tests. For completion rates ≥80%, of 6MWT and 2MWT, only people with an AKPS 70-90 had completion. For arm exercises, this included people with an AKPS as low as ≥50; and for reading numbers, it included people with an AKPS of 40 but not below. Conclusions: Walking tests have poor utility in people with high levels of functional impairment. For people with high levels of dependence, reading numbers should be used in evaluating exercise-induced breathlessness in research studies. These data also suggest that people's exertional limitations have been under-estimated as cancer progresses.