• FEV05
• muscular wakeness
• neuromuscular diseases
• spirometry

Introduction: Spirometry is the most used and available lung function test (PFT); it measures the flows and volumes of air moved during various respiratory maneuvers and can be performed easily from 5-6 years of age. Spirometry can rapidly diagnose respiratory diseases with obstructive or restrictive ventilatory pattern, monitor their course and the effect of therapeutic interventions, and define the patient's prognosis. The correct performance of spirometry requires specific standardisation of the entire procedure updated in 2019 by the American Thoracic Society (ATS) and the European Respiratory Society (ERS). Performing a correct spirometry is not easy and some categories of patients are unable to do it correctly. We focused our attention to patients suffering from neuromuscular diseases (NMDs), which are heterogeneous neurological disorders affecting several neural structures: upper motor neurons, lower motor neurons, peripheral nerves, the neuromuscular junction, and muscles. Respiratory muscle weakness is a major cause of morbidity and mortality in patients with neuromuscular diseases, with a broad range of symptoms and manifestations ranging from recurrent respiratory infections and hypoventilation during sleep to irreversible respiratory failure requiring noninvasive ventilation (NIV) or even tracheostomy. To monitor the respiratory involvement and to support management decisions, PFT are commonly used, including spirometry with Forced Vital Capacity (FVC), Forced Expiratory Volume in the first second (FEV1) and Peak Expiratory Flow Rate (PEF) measurement, maximum inspiratory and expiratory pressure (MIP/MEP) or sniff nasal inspiratory pressure (SNIP) and peak cough flow (PCF). Unfortunately, the correct performance of these tests is often a challenge for these patients because they show difficulty even performing a forced expiration of at least one second during spirometry. Moreover, these tests are designed for school-age children so an early assessment at pre-school age is still difficult to obtain although it would be useful for the early diagnosis of lung disease.
Objective: The primary aim of the study was to evaluate the role of FEV0.5 in patients with neuromuscular diseases, analyzing its correlation with FEV1 and FVC and PEF. The same correlation was also investigated in an equal number of spirometries performed in a matched sample of healthy patients. We also compared their values with those of the neuromuscular patients.
The second objective of the study was to demonstrate that FEV0.5 can be used as an early marker of impaired respiratory function compared to FEV1. To demonstrate this, we analysed the time course of spirometric parameters in patients with neuromuscular diseases who had performed more than one spirometry.
Materials and Methods: In this retrospective observational study, we consulted the clinical records of 40 children (12 Females) aged 4 – 18 years, affected by neuromuscular diseases referred to the pulmonology outpatient service of the Pediatrics Unit of the University Hospital of Pisa, from May 2019 to May 2024, who performed at least 1 acceptable and repeatable spirometry. Their clinical and spirometric data were collected in a proforma. We also included a group of 46 Healthy Children (HC) which performed at least 1 acceptable and repeatable spirometry, selected based on age (5 -18 years) gender (14 Female) and height and evaluated at the pulmonology outpatient service during 2024 for reasons different than lung / lower airways symptoms or morbidity.
Results and Discussion: This is the first study evaluating the role of FEV0.5 in the assessment of respiratory function in patients with neuromuscular diseases, especially those not able to perform an expiration of at least 1 second. Using the Student T-Test, we compared the spirometric parameters (FVC, FEV1, PEF, FEV0,5) of neuromuscular patients with those of healthy patients and for every parameter we found a significant difference (p<0,001 for both absolute measurements and z-score when available). Then we made a linear correlation analysis between FEV0,5 and FEV1, FVC, PEF (expressed in absolute value): using Pearson's correlation coefficient in neuromuscular patients as well in healthy children. We found a highly significant linear correlation between FEV0,5 and other parameters in neuromuscular patients as well as in healthy children (p<0,001). Based on our results, we can state that in patients who are unable to exhale for at least 1 second due to specific pathologies such as NMDs or due to their young age (pre-school patients) it is possible to consider the use of FEV0.5 as a spirometric reference parameter for the study of lung function. To complete our study, in the 15 patients with neuromuscular disease who performed at least three spirometry, we studied their trend over time but we did not find any significant results.
Conclusion: The FEV0.5 is a spirometric parameter easily obtainable in patients with marked muscle weakness including those not able to forcefully exhale for at least one second and may be an acceptable option beyond FEV1 and FVC.
More studies are needed to further elucidate the role and value of FEV0,5 as well as its clinical application.