The evolution of inspiratory muscle fatigue compared to the quadriceps in patients with acquired muscle weakness in the intensive care unit

ICU-acquired weakness affects both respiratory and locomotor muscles. Current understanding of short-term evolution of different muscle impairments is limited. Anatomically distinct, inspiratory and locomotor muscles may exhibit varying levels of fatigability in the context of acquired weakness. We postulate that, owing to differences in anatomy and physiology, inspiratory muscles may experience less fatigue compared to quadriceps muscles. In our single-center study, we enrolled 20 patients with concurrent weakness in inspiratory and locomotor muscles following invasive mechanical ventilation in the ICU. Weakness was defined by an MRC score<48/60 and a Maximal Inspiratory Pressure (MIP)≤ 30cmH2O. The fatigue test consisted of 10 contractions at 100% of the maximal voluntary force (MVV). Inspiratory and quadriceps MVV were determined based on the best of 5 measurements of MIP and quadriceps dynamometry. Subsequently, patients performed 10 contractions at 100% of their MVV, with a 10-second rest between each contraction. Three MVV measurements were taken 1 minute after the effort. The mean age of the patients was 61±8 years, with a mean MIP of 38±18cmH2O and a mean Quadriceps Dynamometry of 135±90N at the time of measurement. We found a statistical interaction between muscle group and fatigue throughout time (p=0.003). No difference was observed in inspiratory MVV (p= 0.45) or Quadriceps MVV (p=0.1) after 1 minute of recovery. These findings suggest a similar level of fatigability in both muscle group among patients with acquired muscle weakness in the ICU.