Noninvasive ventilation reduces energy expenditure in amyotrophic lateral sclerosis

BACKGROUND: Amyotrophic lateral sclerosis (ALS) leads to chronic respiratory failure. Diaphragmatic dysfunction, a major driver of dyspnea and mortality, is associated with a shift of the burden of ventilation to extradiaphragmatic inspiratory muscles, including neck muscles. Besides, energy expenditure is often abnormally high in ALS, and this is associated with a negative prognostic value. We hypothesized that noninvasive ventilation (NIV) would relieve inspiratory neck muscles and reduce resting energy expenditure (REE). METHODS: Using indirect calorimetry, we measured REE during spontaneous breathing (REE(SB)) and NIV (REE(NIV)) in 16 ALS patients with diaphragmatic dysfunction, during the first 3 months of NIV. Measured values were compared with predicted REE (REE(pred))(Harris-Benedict equation). RESULTS: NIV abolished inspiratory neck muscle activity. Even though our patients were not hypermetabolic, on the contrary, with a REE(SB) that was lower than REE(pred) (average 11%), NIV did reduce energy expenditure. Indeed, median REE(NIV,) in this population with a mean body mass index of 21.4 kg.m(-2), was 1149 kcal/24 h [interquartile 970-1309], lower than REE(SB) (1197 kcal/24 h, 1054-1402; mean difference 7%; p = 0.03, Wilcoxon). REE(SB) and REE(NIV) were correlated with forced vital capacity and maximal inspiratory pressure. CONCLUSIONS: NIV can reduce energy expenditure in ALS patients probably by alleviating the ventilatory burden imposed on inspiratory neck muscles to compensate diaphragm weakness. It remains to be elucidated whether or not, in which population, and to what extent, NIV can be beneficial in ALS through the corresponding reduction in energy expenditure.