Could peak oxygen uptake be estimated from proposed equations based on the six-minute walk test in chronic heart...

To evaluate the agreement between the measured peak oxygen uptake (VO₂peak) and the VO₂peak estimated by four prediction equations based on the six-minute walk test (6MWT) in chronic heart failure patients.

Thirty-six chronic heart failure patients underwent cardiopulmonary exercise testing and the 6MWT to assess their VO₂peak. Four previously published equations that include the variable six-minute walk distance were used to estimate the VO₂peak: Cahalin, 1996a (1); Cahalin, 1996b (2); Ross, 2010 (3); and Adedoyin, 2010 (4). The agreement between the VO₂peak in the cardiopulmonary exercise testing and the estimated values was assessed using the Bland-Altman method. A p-value of <0.05 was considered statistically significant.

All estimated VO₂peak values presented moderate correlation (ranging from 0.55 to 0.70; p<0.001) with measured VO₂peak values. Equations 2, 3, and 4 underestimated the VO₂peak by 30%, 15.2%, and 51.2%, respectively, showing significant differences from the actual VO₂peak measured in the cardiopulmonary exercise testing (p<0.0001 for all), and the limits of agreement were elevated. The VO₂peak estimated by equation 1 was similar to that measured by the cardiopulmonary exercise testing, and despite the agreement, bias increased as VO₂peak increased.

Only equation 1 showed estimated VO₂peak similar to the measured VO₂peak; however, a large limits of agreement range (∼3 METs) does not allow its use to estimate maximal VO₂peak.