Use of Diaphragmatic Ultrasound to evaluate respiratory function in patients with Amyotrophic Lateral Sclerosis

Introduction: Pulmonary Function Tests (PFT) are commonly used to monitor respiratory function in patients with Amyotrophic Lateral Sclerosis (ALS). However, these may be difficult to perform for patients with bulbar involvement or advanced stages of the disease. Aim: Our aim is to analyze the relationship between Diaphragmatic Ultrasound (DU) and PFT and to assess its utility to detect ventilatory failure and need for NIVM. Methods: We carried out a prospective study from January to November 2022 including ALS patients not under NIMV. They underwent a DU and PFT every 3 months. DU included: diaphragmatic excursion in sniff test (ExST) and deep breathing (ExDB); end-inhalation (IDT) and end-expiration (EDT) diaphragmatic thickness. Diaphragmatic thickness fraction (DTF) was calculated. PFT included: FVC seated and decubitus, maximum inhalatory pressure (MIP) and arterial blood gas analysis (ABG). NIMV indication was also analyzed. Results: Ten patients were included. A strong correlation was found between FVC and both IDT (r= 0,89, p= 0,003) and ExDB (r=0,9, p= 0,014). Also between MIP and both IDT (r=0,95, p=0,004) and EDT (r=0,92, p=0,008). Regarding ABG, strong reverse correlation was found between Base Excess (BE) and HCO3-, and DTF (r=-0,81, p= 0,004), ExDB (r=-0,8, p= 0,016), ExST (r=-0,74, p=0,015) and IDT (r=0,76, p=0,011). HCO3- inversely correlates with ExDB (r=-0,79, p=0,021), IDT (r=-0,77, p=0,009), DTF (r=-0,75, p=0,012) and ExST (r=-0,72, p=0,019). 30% of patients were unable to complete PFT due to bulbar affection. Conclusions: There is a significant correlation between PFT, ABG (FVC, MIP, BE and HCO3-) and DU. DU is useful in patients unable to perform PFT.