Table 2.
Pulmonary gas exchange abnormality (GEA) in patients with typical Rett syndrome (n = 228): relationships between lung ventilation-perfusion (V/Q) inequalities patterns and respiratory variables.
| Variables | Pulmonary ventilation/perfusion (V/Q) patterns in typical Rett syndrome | P value (ANOVA) | ||||
|---|---|---|---|---|---|---|
| No mismatch (N = 44) | “Low” (N = 64) | “High” (N = 73) | “Mixed” (N = 36) | “Simple” Mismatch (N = 11) | ||
| V tot (L/min) | 6.74 ± 2.87a | 5.26 ± 2.08a,b | 9.71 ± 5.60b,c,d | 6.07 ± 2.46c | 6.3 ± 1.46d | <0.001 |
| Respiratory rate (breaths/min) | 27.4 ± 6.9 | 25.9 ± 9.1 | 30.4 ± 8.0 | 26.7 ± 8.3 | 27.1 ± 9.0 | 0.162 |
| Alveolar vent. (L/min) | 4.22 ± 2.60a | 3.14 ± 1.80a,b | 6.93 ± 4.80a,b,c,d | 4.01 ± 2.2c | 4.23 ± 1.30d | <0.001 |
| PaO2 (mmHg) | 95.4 ± 15.2a,b | 85.7 ± 15.7a,d | 92.2 ± 12.4c,d | 83.9 ± 16.9b,c | 89.8 ± 3.6 | 0.025 |
| Std. PaO2 (mmHg)* | 87.6 ± 14.4 | 81.2 ± 14.9 | 87.3 ± 11.2 | 78.7 ± 20.3 | 88.8 ± 6.5 | 0.082 |
| PaCO2 (mmHg) | 35.3 ± 8.5 | 36.3 ± 7.9 | 37.0 ± 6.6 | 36.9 ± 6.9 | 39.4 ± 3.7 | 0.753 |
| Blood pH | 7.429 ± 0.05 | 7.436 ± 0.05 | 7.417 ± 0.04 | 7.422 ± 0.04 | 7.413 ± 0.01 | 0.462 |
| (A-a) O2 (mmHg) | 14.1 ± 7.9a,b,c,d,e | 25.1 ± 11.3a,b,d | 27.8 ± 10.8a,c,d | 36.9 ± 10.8a,b,c,d,e | 19.4 ± 2.6b,c,d,e | <0.001 |
| Bohr's DS % V t | 45.0 ± 19.4a,c,d | 41.2 ± 15.7b,c,d | 55.4 ± 10.8c | 54.7 ± 15.5a,b,d | 41.8 ± 9.5a,c,d | <0.001 |
| Q s/Q t (%) | 6.3 ± 2.9 | 24.3 ± 2.9 | 8.3 ± 7.2 | 19.4 ± 8.9 | 21.6 ± 15.1 | 0.224 |
| V O2 (mL/min) | 137.8 ± 63.5a | 89.5 ± 58.3a,b,c,d | 181 ± 132b,c,d | 88.6 ± 29.7d,e | 164.8 ± 20.8e | <0.001 |
| V CO2 (mL/min) | 148 ± 78 | 126 ± 58a,e | 193 ± 146a,b | 117 ± 55b,e | 174 ± 59e | 0.015 |
| Respiratory ratio | 1.12 ± 0.43a | 1.72 ± 0.77a,b,c,d | 1.09 ± 0.30b | 1.37 ± 0.59c | 1.04 ± 0.25d | <0.001 |
Data are expressed as means ± SD. Bold characters indicate statistical significant differences; superscript letters indicate significant pairwise post hoc differences; V tot: total ventilation; (A-a) O2: Bohr's DS: physiological dead space, as calculated by the Bohr equation, which, by quantifying the ratio of physiological dead space to the total tidal volume (V d/V t = PaCO2 − PaCO2/PaCO2), gives an indication of the extent of wasted ventilation; (A-a) O2: O2 alveolar-arterial gradient; V t: tidal volume; Q s/Q t: pulmonary functional shunting; V O2: oxygen uptake; V CO2: carbon dioxide production; *values were calculated according to the formula by Sorbini et al. accounting for hypocapnia: standard PaO2 = 1.66 × PaCO2 + PaO2 − 66.4 [52]; respiratory ratio: respiratory exchange ratio, that is, V CO2/V O2. See text for further methodology details.