Control of blood flow in patients with a Fontan circulation during high-intensity dynamic handgrip exercise

Patients with a Fontan (FTN) circulation exhibit vascular dysfunction characterized by reduced nitric oxide bioavailability, impaired endothelium-dependent vasodilation, and abnormal vascular reactivity. However, the kinetics of forearm blood flow during exercise in FTN remains unknown. We tested the hypothesis that forearm blood flow kinetics during the transition from rest to high-intensity (40% maximum voluntary contraction) dynamic handgrip exercise would be slower in FTN compared to healthy control (CTL) participants. Patients with FTN (9M/9F, mean(SD), 16(4) yrs) and similar age- and sex-matched CTL (7M/6F, 17(4) yrs, P = 0.614) performed 3 bouts of exercise lasting 5 min with a 2:2-s contraction:relaxation duty-cycle. Brachial artery diameter and velocity were recorded using a linear array Doppler ultrasound to determine mean forearm blood flow. Beat-by-beat blood flow from each trial for each subject was interpolated to 1-s time bins, time-aligned, and averaged to yield a single response profile, then binned into 5-s averages. Blood flow kinetics were determined using a mono-exponential model with time delay, fit to the first 3 min of exercise. Data were compared using two-tailed unpaired t-tests. Baseline forearm blood flow was similar between groups (FTN: 28(15) mL/min vs. CTL: 34(12) mL/min, P = 0.184). Patients with FTN and CTL had a similar time delay (FTN: 5(13) s vs. CTL: 2(6) s, P = 0.441), time constant (τ, FTN: 28(15) s vs. CTL: 30(12) s, P = 0.652), and mean response time (τ + time delay, FTN: 32(24) s vs. CTL: 32(12) s, P = 0.939). The amplitude of change in forearm blood flow (FTN: 29(10) mL/min vs. CTL: 45(25) mL/min, P = 0.030) and steady-state blood flow (FTN: 56(22) mL/min vs. CTL: 79(31) mL/min, P = 0.028) were lower in FTN compared to CTL, owing to differences in absolute grip strength. Within the exercise transient, FTN had a 19% smaller increase in blood velocity and a 79% smaller reduction in artery diameter compared to CTL. These findings suggest that while forearm blood flow kinetics are preserved in FTN, the underlying determinants of blood flow differ. Funding: Saskatchewan Centre for Patient-Oriented Research, Canadian Institute of Health Research, Scottish Rite Charitable Foundation of Canada, Heart and Stroke Foundation of Canada 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.