Does the application of blood flow restriction during walking exercise influence the accuracy of indirect calorimetry?

Objectives: Identify whether the application of blood flow restriction (BFR) during walking influences fraction of expired oxygen (F_eO₂) and carbon dioxide (F_eCO₂) measures, key variables in the calculation of oxygen consumption (V̇O₂) via indirect calorimetry. Design: Randomised cross-over. Methods: On separate visits, sixteen participants completed four experimental sessions (order randomised), each comprising 10 min of treadmill exercise; i.e., with or without BFR (60% arterial occlusion pressure) combined with two different intensity levels (100% or 120% comfortable walking speed). For data analysis, walking speeds within the same condition (with or without BFR) were pooled, and the speed variance was controlled within the statistical model. The F_eO₂, F_eCO₂, V̇O₂, volume of carbon dioxide production, minute ventilation (V̇E) and respiratory exchange ratio were extracted from the metabolic cart from the fifth min of the exercise period to the 3 min post-exercise. Measures were averaged across 2 min increments during exercise and 1 min increments post-exercise. Results: Condition × time interactions were observed for F_eO₂ (p < 0.01) and F_eCO₂ (p < 0.01). Post hoc analysis identified within the BFR condition an increase in F_eO₂ (p < 0.01) during the exercise period and for 2 min post-exercise, while F_eCO₂ was decreased (p < 0.01) during the exercise period and 1 min post-exercise. A main effect of BFR and time was observed for V̇E (p ≤ 0.044) and V̇O₂ (p ≤ 0.01). Conclusions: The increase of F_eO₂ and decrease of FeCO₂ during BFR walking likely reduces the validity of V̇O₂ values calculated via indirect calorimetry.