Abstract
Purpose: The cardiorespiratory optimal point (COP) is the minimum ventilatory equivalent for oxygen. The COP can be determined during a submaximal incremental exercise test. Reflecting the optimal interaction between the respiratory and cardiovascular systems, COP may have prognostic utility. The aim of this investigation was to determine the relationship between COP and all-cause mortality in a cohort of apparently healthy adults.
Methods: The sample included 3160 apparently healthy adults (46% females) with a mean age of 44.0 +/- 12.5 yr who performed a cardiopulmonary exercise test. Cox proportional hazards models were performed to assess the relationship between COP and mortality risk. Prognostic peak oxygen uptake (V[spacing dot above]O2peak) and COP models were compared using the concordance index.
Results: There were 558 deaths (31% females) over a follow-up period of 23.0 +/- 11.9 yr. For males, all Cox proportional hazards models, including the model adjusted for traditional risk factors and V[spacing dot above]O2peak, had a positive association with risk for mortality (P < .05). For females, only the unadjusted COP model was associated with risk for mortality (P < .05). The concordance index values indicated that unadjusted COP models had lower discrimination compared with unadjusted V[spacing dot above]O2peak models (P < .05) and V[spacing dot above]O2peak did not complement COP models (P >= .13).
Conclusions: Cardiorespiratory optimal point is related to all-cause mortality in males but not females. These findings suggest that a determination of COP can have prognostic utility in apparently healthy males aged 18-85 yr, which may be relevant when a maximal exercise test is not feasible or desirable.