Comparison of Slow and Forced Vital Capacity on Ability to Evaluate Respiratory Function in Bulbar-Involved Amyotrophic Lateral Sclerosis

Abstract

Background and ObjectiveThe percent-predicted forced vital capacity (FVC%) in the pulmonary function test (PFT) is generally used to evaluate the respiratory function in amyotrophic lateral sclerosis (ALS). The slow vital capacity (SVC) is another method to evaluate the respiratory function. Some neurologists found that the FVC% was not reflective of respiratory symptoms and the percent-predicted SVC (SVC%) was found to be higher in some patients with bulbar-onset ALS. We aimed to compare the percent predicted SVC (SVC%) with FVC% in evaluating the respiratory function and investigate the associations between the associations between clinical characteristics and the difference between the SVC% and the FVC% (SVC%-FVC%) in bulbar-involved ALS patients.MethodThis prospective study included patients with bulbar-involved ALS who visited the Peking University Third Hospital between October 2020 and November 2021. They underwent comprehensive clinical assessments, including bulbar symptom assessments, revised ALS functional rating scale (ALSFRS-R), Rasch-Built Overall Amyotrophic Lateral Sclerosis Disability Scale (Roads), and PFTs. The group differences were analyzed using parametric and non-parametric tests.ResultsA total of 59 participants were initially enrolled, and 51 of them were included in the final analysis. In patients with bulbar-involved ALS, the SVC% (73.82 ± 21.95%) was significantly higher (p = 0.013) than the FVC% (71.42 ± 23.15%). After controlling for other relevant variables, a partial correlation analysis showed a significant correlation (r = −0.352, p = 0.041) between ALSFRS-R1 score and SVC%-FVC%.ConclusionOur prospective study found that the SVC% was significantly higher and more reflective of actual respiratory function than the FVC% in patients with bulbar-involved ALS. Furthermore, the severity of dysarthria was found to be positively correlated with SVC%-FVC%, providing a clinical marker for predicting SVC%-FVC%.

Evaluation of arterial blood gas parameters as prognostic markers in amyotrophic lateral sclerosis

“…However, this analysis is complicated to design without any bias as spirometry would not be possible for some subtypes of patients for whom we obviously need an alternative mode of lung function evaluation. The lack of predictive value reported here in bulbar patients also limits the use of ABG in this specific subpopulation, in which spirometry, and especially SVC, still should be prioritized [16].…”

“…This difference might be explained by a lack of statistical power, as the number of bulbar forms was lower, or could reflect a real difference in the relevance of ABG parameters between the two forms, as observed in our survival analysis. Selection bias or incorrect FVC due to the difficulty in performing spirometry in bulbar forms can also not be ruled out [16].…”

Application of respiratory function tests in patients with neurological diseases

“…21,69,70 Diaphragmatic strength can also be evaluated using slow VC or the difference between the FVC values measured in supine and sitting positions in situations where the above-mentioned tests for evaluating diaphragm strength are not available or where patients with neurological disease present with significant orofacial weakness. [71][72][73] VC, MIP, and MEP can also be used to predict the need for endotracheal intubation and mechanical ventilation by applying the following criteria: VC, MIP, and MEP <20 mL/kg, 30 cmH 2 O, and 40 cmH 2 O, respectively, or decreases by more than 30%. 74 Respiratory function tests are also considered for weaning off mechanical ventilation.…”