Six minute walk distance in a multicenter study of healthy subjects aged 40-80 years in spain and south america

Background: The six-minute walk distance (6MWD) predicted values have been derived from small cohorts mostly from single countries. Objective: To investigate differences between countries and identify new reference values to improve 6MWD interpretation. Methods: We studied 444 subjects (238 males) from 7 countries (10 centers) ranging from 40 to 80 years old. We measured the 6MWD, height, weight, spirometry,, heart rate (HR), the maximum HR during the 6MWT/the predicted maximum HR (%PredMaxHR), Borg dyspnea and oxygen saturation. Results: The mean 6MWD was 571 (90) m (range 380-782). Males walked 30 m more than females (p <0.001). A multiple regression model for the 6MWD included age, gender, height, weight, and %PredMaxHR (Radj= 0.38, p <0.001), but there was variability across centers (Radj= 0.09-0.73) and its routine use is not recommended. Age had a great impact in 6MWD independent of the centers, declining significantly in the older population (p <0.001). Age-specific reference standards 6MWD were constructed for male and female adults. Conclusion: In healthy subjects, there are geographic variations in 6MWD and caution must be taken when using existing predictive equations. The present work provides new 6MWD standard curves that could be useful in the care of adult patients with chronic diseases. Word count: 200