- For patients with a bulbar form, slow vital capacity > 60% of theoretical value or, if spirometry not assessable (severe bulbar disability), patient should not have significant abnormality in both nocturnal capnography and nocturnal oximetry (median pCO2 (carbon dioxide partial pressure ) < 52 mmHg, SaO2 (arterial oxygen saturation ) < 90% less than 5% of the time during night) less than 3 months prior inclusion.