The VO2 time constant of the exercise phase during a 6-minute walk test was significantly delayed in patients with Fontan circulation compared to healthy controls (44 vs 28 seconds, P=0.0002).
Cross-Sectional (n=32)
Do patients with Fontan circulation have delayed VO2 kinetics during the six-minute walk test compared to healthy controls?
Adolescents and young adults with Fontan circulation exhibit significantly delayed VO2 kinetics and reduced exercise capacity during the six-minute walk test compared to healthy controls.
Absolute Event Rate: 44% vs 28%
p-value: p=0.0002
Background: A hallmark feature in individuals with a Fontan circulation (FTN) is reduced exercise tolerance, possibly the result of slower oxygen kinetics. However, the kinetics of oxygen uptake (VO2) in FTN during the six-minute walk test (6MWT) have not been studied. Hypothesis: We tested the hypothesis that VO2 kinetics would be slower in FTN than control (CTL). Methods: 18 adolescents and emerging adults between the ages of 12-23 years old were recruited with FTN (m/f = 9/9; age = 16 ± 4yrs) and compared to similarly age- and sex-matched 14 healthy CTLs (m/f = 7/7, age = 16 ± 4yrs). Each participant performed a 6MWT using a wearable metabolic system (COSMED K5). VO2 kinetics were modeled using mono-exponential curve fitting (Origin, 2024b). Analyses were made using unpaired t-tests with P < 0.05 indicating significance. Results: During walk testing, the highest VO2 achieved was significantly lower in FTN (24 ± 7 ml/kg/min) compared to CTL (32 ± 8 ml/kg/min, P = 0.0040) and FTN also covered a significantly shorter distance (529 ± 79 m) than CTL (645 ± 46 m, P = 0.0001), despite both groups reporting similar perceived exertion scores (FTN: 6 ± 3 vs CTL: 5 ± 2, P = 0.2420). Resting VO2 was not different between FTN (6 ± 2 ml/kg/min) and CTL (5 ± 1 ml/kg/min, P = 0.9305). VO2 amplitude of Phase II was significantly lower in FTN (13 ± 5 ml/kg/min) compared to CTL (21 ± 6 ml/kg/min, P = 0.0007). The VO2 time constant, tau, of the exercise phase was significantly delayed in FTN (44 ± 11 s) compared to CTL (28 ± 8 s, P = 0.0002). Similarly, the tau of the recovery phase was slow in FTN compared to CTL (63 ± 17 s vs 51 ± 9 s, P = 0.0236). Conclusion: VO2 kinetics during the 6MWT in FTN are delayed. Funding: Saskatchewan Centre for Patient Oriented Research, Saskatchewan Health Research Foundation, Heart and Stroke Foundation of Canada, Scottish Rite Charitable Foundation of Canada, Canadian Institute of Health Research) This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Yang et al. (Fri,) conducted a cross-sectional in Fontan circulation (n=32). Six-minute walk test vs. Healthy controls was evaluated on VO2 time constant (tau) of the exercise phase (p=0.0002). The VO2 time constant of the exercise phase during a 6-minute walk test was significantly delayed in patients with Fontan circulation compared to healthy controls (44 vs 28 seconds, P=0.0002).