Representative pulmonary gas exchange abnormalities (GEA) patterns in patients with typical RTT and MeCP2 gene mutation: (a) “low pattern” abnormality; (b) “high pattern” abnormality; (c) “simple mismatch”; and (d) “mixed pattern” abnormality. Ventilation-perfusion () inequalities (i.e., GEA) were detectable in 80.7% of the whole RTT population, whereas only 19.3% of the patients showed a normal gas exchange. A “low” pattern (i.e., 34.8 of all GEA types in RTT) indicates the presence of perfusion in poorly ventilated pulmonary areas; a “high" pattern (i.e., 39.8% of all GEA types) points out the existence of high ventilation in poorly perfused pulmonary areas; a mixed pattern (i.e, 19.6% of all GEA types) is a combination of the former two patterns, while a “simple mismatch” (i.e., 5.9% of GEA types) is a uncoupling, showing a modest fraction of low ratios (1 to 0.1) and a modest fraction of high ratios (1 to 10).
