The Impact of Respiratory Function on Functionality and Mortality in ALS Patients

<b>Objective:</b> To investigate the relationship between respiratory function, functionality, and mortality in amyotrophic lateral sclerosis (ALS) patients and to determine which respiratory parameters show the strongest correlation with functionality and mortality. <b>Methods:</b> The study was conducted in Rio Grande do Norte, Northeast Brazil, between January 2018 and December 2023. This was a retrospective cohort, following individuals with ALS who were evaluated at the University Laboratory. <b>Results:</b> A total of 74 ALS patients were included in the analysis, with a mean age of 55.7 ± 13.5 years. Most were male (66.2%) and predominantly presented with spinal-onset ALS (51.3%). Respiratory variables (except peak expiratory flow (PEF)) showed a weak but significant inverse correlation with mortality (FVC% predicted (r_pb = -0.260; <i>p</i> < 0.001), SNIP (r_pb = -0.235; <i>p</i> = 0.001), MEP (r_pb = -0.207; <i>p</i> = 0.007), MIP (r_pb = -0.198; <i>p</i> = 0.009), and PEF% predicted (r_pb = -0.156; <i>p</i> = 0.013)). When analyzing their correlation with ALSFRS-R, all variables showed a significant positive correlation (ranging from weak to moderate) with functionality. A reduction of one unit in the respiratory variables PEF% of predicted, maximal inspiratory pressure (MIP), and sniff nasal inspiratory pressure (SNIP) increased the risk of death by an average of 300% (OR = 2.99; 95% CI: 2.05-4.35), 2% (OR = 1.02; 95% CI: 1.01-1.03), and 1% (OR = 1.01; 95% CI: 1.00-1.02), respectively. <b>Conclusions:</b> Our findings suggest that direct measurements of respiratory function and muscle strength, particularly PEF and SNIP, may serve as more useful markers to guide early interventions such as non-invasive ventilation, thereby improving quality of life and potentially prolonging survival.