Volume 3 • Issue 2 • 1000147 J Pulmon Resp Med ISSN: 2161-105X JPRM, an open access journal Chen et al., J Pulmon Resp Med 2013, 3:2 DOI: 10.4172/2161-105X.1000147 Research Article Open Access Postural Change of FVC in Patients with Neuromuscular Disease: Relation to Initiating Non-Invasive Ventilation Joe Chen 1 , Nathan Nguyen 2 , Matt Soong 2 and Ahmet Baydur 1 * 1 Division of Pulmonary and Critical Care Medicine 2 Division of General Medicine, Keck School of Medicine, University of Southern California, USA Abstract 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 fow (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 signifcance between cohorts. There was a negative correlation between %ΔFVC (sit-sup) and FVC sit (% 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 signifcantly 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. *Corresponding author: Baydur A, Division of Pulmonary and Critical Care Medicine, Keck School of Medicine, University of Southern California, IRD 723, 2020 Zonal Avenue, Los Angeles, CA 90033, USA, E-mail: baydur@usc.edu Received April 04, 2013; Accepted May 06, 2013; Published May 08, 2013 Citation: Chen J, Nguyen N, Soong M, Baydur A (2013) Postural Change of FVC in Patients with Neuromuscular Disease: Relation to Initiating Non-Invasive Ventilation. J Pulmon Resp Med 3: 147. doi:10.4172/2161-105X. 1000147 Copyright: © 2013 Chen J, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Keywords: Postural change in vital capacity; Assisted ventilation; Neuromuscular disorders Introduction Te forced vital capacity (FVC) and maximal respiratory pressures are commonly used to assess respiratory muscle strength in patients with neuromuscular disorders (NMD) [1-4]. Te FVC and lung volumes decrease with progression of the disease. Orthopnea is associated with diaphragmatic weakness or paralysis [3]. Indications for initiation of non-invasive ventilation (NIV) include dyspnea, orthopnea, drowsiness, decreased cognitive function, hypercapnia, and decline in FVC to usually below 50% predicted [4]. Respiratory muscle weakness can also be assessed by measuring the diference in FVC between sitting and supine positions (FVC sit and FVC sup , respectively) [5-14], a more sensitive index than upright FVC. In normal subjects, vital capacity changes insignifcantly (about 5%) upon assuming the supine position [5-9], while greater decreases in VC have been documented in patients with NMD [10-13]. Te value of this index as it relates to the need for NIV, however, has not been assessed. Te forced expiratory fow (FEF) has been used to quantify the individual’s ability to cough and eliminate airway secretions. Postural change in FEF, however, has also not been assessed in relation to initiating NIV. Tis retrospective exploratory study aimed to assess the relationship of the postural changes in FVC and FEF with initiation of NIV in patients with NMD. Methods The records of patients with NMD evaluated in the outpatient respiratory clinic at Keck Medical Center, University of Southern California between January 1998 and June 2011 were reviewed. Spirometric values obtained closest to the time of initiating NIV were recorded. Patients who could not perform spirometry according to ATS/ERS criteria were excluded [14]. Individuals with difficulty in clearing airway secretions and/or who exhibited seated forced expiratory flow rates (FEFs) less than or equal to 160 L/min were provided cough-assist devices, and their caregivers instructed in the provision of mechanical and manual cough techniques [15]. The study was approved by the Institutional Review Board of the University of Southern California Health Sciences Campus (IRB Proposal #HS-13-00080). Patients underwent spirometry (Medgraphics Elite Dx, St. Paul, Minnesota) in seated and supine postures while seated comfortably in a reclining chair that could be converted into a horizontal position. Maximal inspiratory and expiratory pressure measurements (Pimax and Pemax, respectively), available in 8 SB and 6 NIV subjects, were measured in seated position according to the method of Black and Hyatt [16,17]. Arterial blood gases were obtained in the seated position while breathing room air (Rapidlab 1265, Siemens, Tarreytown, NY). Reference values for FEV 1 and FVC were from Morris et al. [18], and Forced Expiratory Flow (FEF) from Te National Health and Nutrition Examination Survey (NHANES) III [19]. Te change in FVC between seated (sit) and supine (sup) positions was expressed as %ΔFVC(sit – sup) = [{FVC(L) sit – FVC(L) sup }/FVC(L) sit ]. Te postural change in FEF was expressed as % ΔFEF(sit – sup) = [{FEF(L/sec) sit – FEF(L/sec) sup }/FEF(L/sec) sit ]. Statistical Analysis Because of non-normal distribution of subjects, tabulated values were expressed as median and Interquantile Range (IQR). Comparison J o u r n a l o f P u l m o n a r y & R e s p i r a t o r y M e d i c i n e ISSN: 2161-105X Journal of Pulmonary & Respiratory Medicine