Stable Cytokine Network during Hypoxia and Exercise in Patients with Fontan Circulation

Area of Science:

• Cardiovascular Physiology
• Exercise Immunology
• Environmental Medicine

Background:

• Patients with Fontan circulation are advised to avoid hypoxia due to presumed vulnerability.
• Low-grade inflammation is reported in this population, potentially influenced by hypoxia and exercise.
• The interaction between hypoxia and exercise on inflammatory signaling is not well understood.

Purpose of the Study:

• To investigate the effects of moderate normobaric hypoxia combined with submaximal exercise on systemic inflammation in stable Fontan circulation patients.
• To challenge assumptions of latent immune vulnerability in this population.
• To assess the safety of controlled hypoxic exposure in Fontan patients.

Main Methods:

• Eighteen stable Fontan circulation patients underwent submaximal cycling tests under normoxia and moderate hypoxia (FiO₂ ≈ 15%).
• Venous blood was sampled at rest and peak exercise to analyze cytokines, adipo-myokines, and immune cell indices.
• Data were analyzed to compare inflammatory markers between normoxic and hypoxic conditions.

Main Results:

• Exercise increased white blood cell (WBC) counts mildly under both conditions, but cytokine concentrations remained stable.
• Irisin levels increased after normoxic exercise but not hypoxic exercise; asprosin showed no significant changes.
• No systemic immune activation was observed in response to combined hypoxia and exercise.

Conclusions:

• Moderate normobaric hypoxia with submaximal exercise does not induce systemic immune activation in stable Fontan circulation patients.
• These findings challenge the notion of inherent immune vulnerability in this population.
• Controlled hypoxic exposure appears safe for stable Fontan patients under the tested conditions.