Limiting factors in peak oxygen uptake and the relationship with functional ambulation in ambulating children with spina bifida.

The objective of this study is to interpret the outcomes of peak oxygen uptake (VO(2peak)) in children with SB and explore the relationship between VO(2peak) and functional ambulation using retrospective cross-sectional study. Twenty-three ambulating children with SB participated at Wilhelmina's Children's Hospital Utrecht, the Netherlands. VO(2peak) was measured during a graded treadmill-test. Eschenbacher's and Maninna's algorithm was used to determine limiting factors in reaching low VO(2peak) values. Energy expenditure during locomotion (both O(2) rate and O(2) cost) and percentage of VO(2peak) and HR(peak) were determined during a 6-min walking test (6MWT). Differences between community and normal ambulators were analyzed. VO(2peak), VO(2peak)/kg, HR(peak), RER(peak) and VE (peak) were significantly lower compared to reference values, with significant differences between normal and community ambulators. Limiting factors according to the algorithm were mostly "muscular and/or deconditioning" (47%) and ventilatory "gasexchange" (35%). Distance walked during 6MWT was 48.5% of predicted distance. Both O(2) rate and O(2) cost were high with significant differences between normal and community ambulators [17.6 vs. 21.9 ml/(kg min) and 0.27 vs 0.43 ml/(kg m)]. Also %HR(peak) and %VO(2peak) were significantly higher in community ambulators when compared to normal ambulators (resp. 97.6 vs. 75% and 90.2 vs. 55.9%). VO(2peak) seems to be mostly limited by deconditioning and/or muscular components and possible ventilatory factors. For both peak values and functional ambulation, community ambulators were significantly more impaired than normal ambulators. High energy expenditure, %VO(2peak) and %HR(peak) reflect high level of strain during ambulation in the community ambulators. Future exercise testing in children with SB should include assessment of ventilatory reserve. Exercise training in ambulatory children should focus on increasing both VO(2peak) and muscular endurance, as well as decreasing energy cost of locomotion.