Criteria for the determination of maximal oxygen uptake in patients newly diagnosed with cancer: Baseline data from the randomized controlled trial of physical training and cancer (Phys-Can)

Abstract

Introduction Maximal oxygen uptake (VO _2max) is a measure of cardiorespiratory fitness often used to monitor changes in fitness during and after treatment in cancer patients. There is, however, limited knowledge in how criteria verifying VO _2max work for patients newly diagnosed with cancer. Therefore, the aim of this study was to describe the prevalence of fulfillment of typical criteria verifying VO _2max and to investigate the associations between the criteria and the test leader's evaluation whether a test was performed “to exhaustion”. An additional aim was to establish new cut-points within the associated criteria. Methods From the Phys-Can randomized controlled trial, 535 patients (59 ±12 years) newly diagnosed with breast (79%), prostate (17%) or colorectal cancer (4%) performed an incremental VO _2max test on a treadmill. The test was performed before starting (neo-)adjuvant treatment and an exercise intervention. Fulfillment of different cut-points within typical criteria verifying VO _2max was described. The dependent key variables included in the initial bivariate analysis were achievement of a VO _2 plateau, peak values for maximal heart rate, respiratory exchange ratio (RER), the patients' rating of perceived exertion on Borg's scale6-20 and peak breathing frequency (fR). A receiver operating characteristic analysis was performed to establish cut-points for variables associated with the test leader's evaluation. Last, a cross-validation of the cut-points found in the receiver operating characteristic analysis was performed on a comparable sample of cancer patients (n = 80). Results The criteria RERpeak (<0.001), Borg's RPE (<0.001) and fR peak (p = 0.018) were associated with the test leader's evaluation of whether a test was defined as “to exhaustion”. The cut-points that best predicted the test leader's evaluation were RER ≥ 1.14, RPE ≥ 18 and fR ≥ 40. Maximal heart rate and VO _2 plateau was not associated with the test leader's evaluation. Conclusion We recommend a focus on RER (in the range between ≥1.1 and ≥1.15) and RPE (≥17 or ≥18) in addition to the test leader's evaluation. Additionally, a fR peak of ≥40 breaths/min may be a cut-point to help the test leader evaluate the degree of exhaustion. However, more research is needed to verify our findings, and to investigate how these criteria will work within a population that are undergoing or finished with cancer treatment.