Fontan (FTN) circulation is a surgical palliation for single ventricle physiology resulting in venous circulation directed to the pulmonary system in the absence of a subpulmonary (right) ventricle. Patients with FTN may exhibit impaired vascular reactivity and commonly display exercise intolerance, possibly related to an uncoupling of blood flow to oxygen demand. We tested the hypothesis that patients with FTN would exhibit impaired upper limb reactive hyperemia (near infrared spectroscopy, NIRS) compared to age-matched controls (CTL). Twelve patients with FTN (6 females, 6 males, 17±3 yrs) and 9 CTL (6 females, 3 males, 18±4 yrs) were instrumented with NIRS probe on the belly of the flexor digitorum profundus. The hyperemic response was determined over 6 min following rapid deflation of the brachial cuff (6 min circulatory occlusion), Results from repeat testing were averaged and comparisons were made between groups with two-tailed unpaired t-tests. Baseline tissue oxygenation index (TOI) prior to occlusion was not different between FTN (75±5%) and CTL (77±7%, P = 0.2853). TOI desaturation rate during cuff occlusion was also similar between FTN (-0.16 ± 0.08%/s) versus CTL (-0.20 ± 0.07%/s, P = 0.2368). The nadir of TOI during cuff occlusion was also similar between FTN (36±20%) and CTL (31±11%, P = 0.4679). Following cuff release, the rate of TOI recovery was also similar between FTN (2.1±1%/s) and CTL (2.5±0.8%/s, P = 0.4134). Notably, peak TOI following cuff release was attenuated in FTN (83±3%) compared to CTL (88±2%, P = 0.0004). Together, these data illustrate that although resting TOI and rates of TOI reduction and restoration were similar, peak TOI following circulatory cuff occlusion release was blunted in FTN. Thus, young patients with FTN may demonstrate a reduction in peak microvascular reperfusion. 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.
Ali et al. (Fri,) studied this question.