A six-minute walk test for assessing exercise tolerance in severely ill children

The primary objective of this study was to compare exercise tolerance, heart rate, and oxyhemoglobin saturation (Sao2) between a traditional progressive maximal exercise test and a self-paced, 6-minute walk test in severely ill children.

Seventeen patients (9 to 19 years of age) performed a progressive maximal exercise test on a cycle ergometer and a self-paced, 6-minute walk test as part of the evaluation for possible heart, lung, or combined heart and lung transplantation. Physical work capacity and peak oxygen uptake were measured during the progressive cycle test. The walk test was performed in a hospital corridor, with patients trying to cover as much distance as possible in 6 minutes at their own pace. Oxyhemoglobin saturation and heart rate were monitored continuously by pulse oximetry and compared between the two tests.

The distance walked in 6 minutes correlated with peak oxygen uptake (r = 0.70, p < 0.01) and physical work capacity (r = 0.64, p < 0.005). The minimum (Min) Sao2 on the bike test correlated significantly with Min Sao2 on the walk test (r = 0.82, p < 0.001), with 11 of 17 patients having a lower Min Sao2 on the walk test than the bike test (mean Min Sao2, 84% and 86%, respectively). The peak heart rate did not correlate significantly between the bike and walk tests (r = 0.25), although significantly lower (p < 0.01) values were observed on the walk (148 beats/min) than bike (169 beats/min) test.

The results suggest that the 6-minute self-paced walk test may provide an alternative method for assessing functional capacity in severely ill children, and that Sao2 measured during progressive exercise testing on a cycle ergometer may not reflect the degree of oxyhemoglobin desaturation during self-paced walking in some patients with severe cardiopulmonary disease.