Physical Exercise Is Safe for Fontan Patients in Hypoxia

Objectives: Activities with hypoxia exposure such as mountain hiking or especially traveling by planes become more usual in our everyday life. In healthy individuals, hypoxia leads to vasoconstriction in the pulmonary arteries resulting in increased pulmonary blood pressure (pbP). In patients with a Fontan circulation, the pulmonary blood flow (pbF) plays an important role, since a subpulmonary pump does not exist. Hypothetically, higher pbP leads to a lower pbF and a reduced physical capacity resulting in potentially life-threatening situations. So far, sufficient data are missing leaving patients and families uncertain about exposure to hypoxia. Our study investigates physical capacity and endurance performance in both normoxia and hypoxia.

Methods: Twenty teenagers and young adults (age 18.4 [14;31] years) with Fontan circulation and 20 sex-, age-, and body mass index-matched healthy subjects underwent a cardiopulmonary exercise test and an endurance exercise on a cycle ergometer in both normoxia and normobaric hypoxia (≙ an altitude of 2,500 m above sea level [a.s.l.]) using a ramp protocol until exhaustion. We demonstrate spiroergometric data, ECG, blood pressure, capillary lactate, O₂ saturation (SpO₂), and blood gas analysis. After a 4-hour break, subjects underwent a 1-hour aerobic exercise with constant workload under the individually VT1. The same protocols were used in normoxia and 2 weeks later in hypoxia.

Results: Fontan patients achieved a maximal workload of 1.8 W/kg in normoxia compared with 1.6 W/kg in hypoxia. In normoxia, peak oxygen uptake (VO_2peak) in Fontan patients was 62% of the VO_2peak of healthy controls with a maximum workload of 56% of healthy subjects. In hypoxia, they reached 61% of the VO_2peak with a maximum workload of 55% of the controls. Overall, lactate at VO_2peak was significantly lower in Fontan patients than in controls (55% in normoxia and 52% in hypoxia), interestingly, increasing already on lower workload levels. At rest, SpO₂ was significantly lower in Fontan patients both in normoxia and hypoxia with a larger drop of saturations on maximum workload.

Conclusion: The physical capacity in patients with Fontan circulation in normoxia and hypoxia was significantly impaired, compared with healthy controls. There was no critical situation due to hypoxic conditions. Contrary to our hypothesis, the influence of hypoxia on maximum and endurance physical exercise was similar in Fontan and control patients. Hypoxia exposure equivalent to altitudes of 2,500 m a.s.l. seems to be safe for Fontan patients.

Supported by Innovationspreis NRW 2016 Stiftung KinderHerz