Maximal exercise oxygen pulse as a predictor of mortality among male veterans referred for exercise testing

Abstract

Background

Maximal oxygen pulse (O₂ pulse) mirrors the stroke volume response to exercise, and should therefore be a strong predictor of mortality. Limited and conflicting data are, however, available on this issue.

Methods

Nine hundred forty-eight participants, classified as those with cardiopulmonary disease (CPD) and those without (non-CPD), underwent cardiopulmonary exercise testing (CPX) for clinical reasons between 1993 and 2003. The ability of maximal O₂ pulse and maximal oxygen uptake (peak VO₂) to predict mortality was investigated using proportional hazards and Akaike information criterion analyses. All-cause mortality was the endpoint.

Results

Over a mean follow-up of 6.3 ± 3.2 years, there were 126 deaths. Maximal O₂ pulse, expressed in either absolute or relative to age-predicted terms, and peak VO₂ were significant and independent predictors of mortality in those with and without CPD (P < 0.04). Akaike information criterion analysis revealed that the model including both maximal O₂ pulse and peak VO₂ had the highest accuracy for predicting mortality. The optimal cut-points for O₂ pulse and peak VO₂ (< 12; ≥ 12 ml/beat and < 16; ≥ 16 ml/(kg · min) respectively) were established by the area under the receiver-operating-characteristic curve. The relative risks of mortality were 3.4 and 2.2 (CPD and non-CPD, respectively) among participants with both maximal O₂ pulse and peak VO₂ responses below these cut-points compared with participants with both responses above these cut-points.

Conclusion

These results indicate that maximal O₂ pulse is a significant predictor of mortality in patients with and without CPD. The addition of absolute and relative O₂ pulse data provides complementary information for risk-stratifying heterogeneous participants referred for CPX and should be routinely included in the CPX report.