Differences in cerebral and muscle oxygenation patterns during exercise in children with univentricular heart after Fontan operation compared to healthy peers.

BACKGROUND

We assess whether the lower exercise tolerance in children with univentricular heart (UVH) after Fontan operation is associated with altered peripheral muscular and cerebral tissue oxygenation.

METHODS

18 children with UVH and 20 healthy subjects performed an incremental ramp exercise test. Changes in the cerebral and muscular pattern of oxygenated (O2Hb) and deoxygenated hemoglobin (HHb) and local tissue oxygenation (TOI) were analyzed by means of Near Infrared Spectroscopy (NIRS). Correlations between arterial saturation during exercise and tissue oxygenation were evaluated.

RESULTS

In UVH, maximal oxygen consumption (VO2peak/kg, 28.9 ± 7.9 vs. 46.3 ± 11.9 ml/min/kg, P < 0.001), heart rate (HRpeak, 168 ± 13 vs. 193 ± 12 bpm, P < 0.001) and load (Ppeak, 73 ± 19 vs. 133 ± 68 W, P < 0.001) were lower, VE/VCO2 slope was higher (34.5 ± 5.9 vs. 27.1 ± 3.9, P < 0.001). A faster and steeper course up to the same level of HHb and absent increase in O2Hb was seen at cerebral level in UVH; tissue oxygenation index (TOI) demonstrated a steady decrease from the start of exercise. At the muscular level, HHb curve has a similar pattern compared to controls, with an early cessation. O2Hb has a similar pattern, but with early discontinuation at a higher O2Hb-level. Muscular TOI has the same course throughout exercise, starting from a lower level. Lower arterial saturation and higher age correlated with lower VO2peak; higher amplitude of muscular TOI and lower amplitude cerebral TOI correlated with higher VO2peak.

CONCLUSION

Children after Fontan procedure have different oxygenation mechanisms at muscular and cerebral level. This reflects a different balance between O2 supply to O2 demand which might contribute to the reduced exercise tolerance in this patient population.