Joe Chen, Nathan Nguyen, Matt Soong and Ahmet Baydur
Background: Forced Vital Capacity (FVC) has been used to assess respiratory muscle strength in patients with Neuromuscular Disease (NMD). However, postural changes to FVC have not been assessed in relation to the start of Non-Invasive Ventilation (NIV). This study aims to assess the changes to postural FVC for indications of NIV.
Methods: The records of spirometry performed in seated and supine posture were retrospectively reviewed in 33 patients with NMD [18 breathing spontaneously (SB), 15 receiving NIV]. The change in FVC (in L) between seated (sit) and supine (sup) positions was expressed as %⊗ FVC (sit – sup) = [{FVC(L)sit – FVC(L)sup}/FVC(L)sit]. The postural change in forced expiratory flow (FEF), % FEF (sit – sup) was similarly computed.
Results: %ΔFVC (sit – sup) in patients receiving NIV exceeded the %ΔFVC (sit – sup) of SB patients by 14-fold (p = 0.001). %ΔFEF (sit–sup) however, did not reach statistical significance between cohorts. There was a negative correlation between %ΔFVC (sit-sup) and FVCsit(% pred) (R = -0.40, p = 0.02), and a direct correlation between %ΔFVC(sit-sup) and %ΔFEF(sit-sup) (R = 0.72, p<0.0001) amongst all patients.
Conclusions: Postural change of FVC in patients with neuromuscular disease placed on noninvasive ventilation is significantly greater than in those still able to breathe spontaneously. A prospective longitudinal study designed to assess the predictive value of ΔFVC (sit – sup), and if possible, a threshold value for initiating NIV may provide a guideline more precise than the seated FVC.
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