Peak VO2Q: A new approach for the interpretation of cardiorespiratory fitness estimates

There are difficulties with the standardisation of interpretative strategies for peak oxygen uptake (peak <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_2}}}$</mml:annotation></mml:semantics> </mml:math> ) related to the quality of reference equations. We aimed to investigate the utility of peak <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>Q</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_2}{\mathrm{Q}}}}$</mml:annotation></mml:semantics> </mml:math> , a novel method reflecting how far a measured value is from the 1st percentile. We retrospectively analysed data from patients referred for a cardiopulmonary exercise test (CPET) at Cambridge University Hospital (CUH) and Royal Papworth Hospital (RPH). Data were included from those 18 years or older. We investigated the stability of the 1st percentile overall, then stratified by sex and age group. We calculated the peak <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>Q</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_2}{\mathrm{Q}}}}$</mml:annotation></mml:semantics> </mml:math> (measured peak <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_2}}}$</mml:annotation></mml:semantics> </mml:math> /1st percentile) and investigated its association with all-cause mortality using Cox regression analysis. Data from 1377 patients were included in the analyses: 590 from CUH (mean age 55.5 (15.4) years, 47% female) and 787 from RPH (mean age 46.1 (15.3) years, 48% female). The 1st percentile value for peak <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_2}}}$</mml:annotation></mml:semantics> </mml:math> was 9.5 mL kg^-1 min^-1 (95% CI: 8.8-9.9) and was consistent across sex and age groups. The mean peak <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>Q</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_2}{\mathrm{Q}}}}$</mml:annotation></mml:semantics> </mml:math> was 2.3 (0.8); it declined with age and was lowest in patients referred for heart transplant. Data on all-cause mortality were available for all patients from CUH. Median follow-up time was 3.8 (2.2-9.6) years, during which time 96 of 590 (16%) patients died. A 1-unit increase in peak <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>Q</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_2}{\mathrm{Q}}}}$</mml:annotation></mml:semantics> </mml:math> was associated with a 60% reduction in risk of all-cause mortality. We propose the peak <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>Q</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_2}{\mathrm{Q}}}}$</mml:annotation></mml:semantics> </mml:math> as an alternative means to interpret cardiorespiratory fitness estimates that does not require reference equations.