Noninvasive ventilation reduces energy expenditure in amyotrophic lateral sclerosis

Abstract

BackgroundAmyotrophic 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).MethodsUsing indirect calorimetry, we measured REE during spontaneous breathing (REESB) and NIV (REENIV) in 16 ALS patients with diaphragmatic dysfunction, during the first 3 months of NIV. Measured values were compared with predicted REE (REEpred)(Harris-Benedict equation).ResultsNIV abolished inspiratory neck muscle activity. Even though our patients were not hypermetabolic, on the contrary, with a REESB that was lower than REEpred (average 11%), NIV did reduce energy expenditure. Indeed, median REENIV, 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 REESB (1197 kcal/24 h, 1054-1402; mean difference 7%; p = 0.03, Wilcoxon). REESB and REENIV were correlated with forced vital capacity and maximal inspiratory pressure.ConclusionsNIV 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.

Macroglossia in advanced amyotrophic lateral sclerosis

“…The higher BMI despite lower energy intake in the more advanced‐stage patients with macroglossia may indicate abnormal central metabolic regulation and an energy imbalance. Macroglossia in advanced ALS may be a result of overfeeding and replacement of the tongue muscle by fat under conditions of extremely low energy expenditure …”

NIV in amyotrophic lateral sclerosis: The ‘when’ and ‘how’ of the matter

“…Recent physiological studies have further refined our knowledge of the benefit of NIV in ALS. By resting accessory muscles, NIV allows a dramatic reduction of energy expenditure (−7% of daily resting energy expenditure), as well as ‘cortical resting’ via decreased premotor cortex activity …”

“…This approach was initially proposed in Duchenne's myopathy in 1994, before being ceased following demonstration of excess mortality in the ‘early NIV’ group . However, several arguments suggest that early ventilation could reduce the respiratory decline in ALS and decrease respiratory work . A large retrospective study and three small series have demonstrated an improvement in survival for patients initiating NIV with VC > 80% predicted, although this effect was not confirmed when sham NIV was used in the control group .…”

Should patients with ALS gain weight during their follow-up?

“…Conversely, NIV may positively affect energy balance [28], with a possible protective effect on peripheral muscle mass.…”

“…A recent study of 10 patients with ALS who had signs of respiratory failure and diaphragmatic dysfunction showed that although resting energy expenditure was below predicted values while breathing spontaneously, noninvasive ventilation (NIV) induced a further median decrease of resting energy expenditure by 7%. The transfer of the respiratory burden from the diaphragm to the accessory inspiratory muscles may be a potent contributor to weight loss, reversible by NIV [28].…”