Abstract
Purpose: Oxygen uptake efficiency slope (OUES), defined as the slope of the linear relationship between oxygen uptake and the semilog transformed ventilation rate measured during an incremental exercise test, may have prognostic utility. The objective of this investigation was to examine the relationship between assessments of OUES and all-cause mortality in a cohort of apparently healthy adults.
Methods: The sample included 2220 apparently healthy adults (48% females) with a mean age of 44.7 +/- 12.9 yr who performed cardiopulmonary exercise testing. The OUES was calculated from the entire test, using data from the initial 50% (OUES50) and 75% (OUES75) of test time, and normalized to body surface area. Cox proportional hazard models assessed the relationship between measures of OUES and mortality. Prognostic peak oxygen uptake (V[spacing dot above]O2peak) and OUES models were compared using the concordance index.
Results: There were 310 deaths (29% females) over a follow-up period of 19.8 +/- 11.1 yr. For males, OUES, OUES75, and normalized OUES had an inverse association with mortality, even after adjusting for traditional risk factors (P < .05). For females, only the unadjusted OUES, OUES75, and normalized OUES models were associated with mortality (P < .05). The concordance index values indicated that unadjusted OUES50 and OUES75 models had lower discrimination than the unadjusted OUES and V[spacing dot above]O2peak models (P < .05). Furthermore, OUES did not complement the fully adjusted V[spacing dot above]O2peak model (P >= .32).
Conclusions: Assessments of OUES are related to all-cause mortality in males but not in females. These findings suggest that OUES can have prognostic utility in apparently healthy males. Moreover, submaximal determinations of OUES could have value when measuring V[spacing dot above]O2peak is not feasible.