Patients with complex congenital heart disease have slower calf muscle oxygenation during exercise

Background: Peripheral muscle factors are presumed to be contributors to the reduced exercise capacity incongenital heart disease (CHD), but the underlying mechanisms are poorly understood. The aim was to investigate if muscle oxygenation, at rest and during exercise, and the resting blood flow in the calf muscle is impaired in adults with complex CHD in comparison to controls. Method: Seventy-four adults with complex CHD (35.6 ± 14.3 years, females n = 22 [30%], males n = 52 [70%]) and seventy-four age and sex matched subjects were recruited. Muscle oxygenation was successfully determined using near-infrared spectroscopy on the medial portion of m. gastrocnemius in 63 patients and 67 controls. Measurements were made at rest, during venous occlusion to estimate blood flow (indicated by slope increase of total haemoglobin, HbT), and post arterial occlusion. Additionally, measurements were made at the onset of isotonic unilateral heel-lifts to exhaustion and during recovery post exercise. Results: Adults with CHD had a slower desaturation rate at exercise onset (-7.7 ± 4.3%StO2x3.5sec-1 vs. -11.7 ± 5.8%StO2x3.5sec-1, p < 0.001) a slower half recovery time (28.6 ± 21.2s vs. 16.8 ± 11.1s, p < 0.001) and a slower resaturation rate post exercise in comparison to the control subjects (3.9 ± 3.7%StO2x3.5sec-1 vs. 6.1 ± 3.8%StO2x3.5sec-1, p = 0.002). In contrast, there were no differences in muscle oxygen kinetics at rest. Conclusion: Slower muscle oxygenation kinetics during muscle exercise found in adults with complex CHD may give insight to the mechanisms for the reduced exercise capacity commonly found in this population. This finding may also provide implications for design of exercise training programs targeting muscle function for these patients.