Respiratory motor function in seated and supine positions in individuals with chronic spinal cord injury
Introduction
Respiratory dysfunction is a major cause of morbidity and mortality in patients with SCI (Center, 2013, Garshick et al., 2005). Individuals with SCI are also at increased risk of sleep disordered breathing (Burns et al., 2000). Major causes of such dysfunction are respiratory motor control deficits associated with paresis, paralysis and spasticity of trunk and respiratory muscles (Gracies, 2005, Ovechkin et al., 2010, Schilero et al., 2009, Terson de Paleville et al., 2011). In general clinical practice and research the pulmonary function test (PFT) is used to evaluate respiratory motor function. In people with SCI, this test includes spirometrical and maximum airway pressure measures acquired with the test subject in the seated position (American Thoracic Society/European Respiratory Society, 2002, Brusasco et al., 2005, Jain et al., 2006, Miller et al., 2005, Stolzmann et al., 2008). While normative values are corrected for age, height, gender and race, they may also vary depending on body position (Manning et al., 1999, Segizbaeva et al., 2013) and functional capacity of the respiratory muscles (Rehder, 1998). It has been shown that healthy individuals exhibit significantly lower spirometrical and airway pressure outcomes in supine compared to seated position (Badr et al., 2002, Meysman and Vincken, 1998, Navajas et al., 1988, Vilke et al., 2000). It is not clear how postural changes affect respiratory function in individuals with SCI. In contrast to healthy controls, individuals with chronic SCI showed higher FVC and FEV1 outcomes in supine compared to seated position (Chen et al., 1990, Estenne and De Troyer, 1987, Maeda et al., 1990). However, it has been shown that paraplegic patients with thoracic SCI can reach higher spirometrical values in seated position (Baydur et al., 2001). The dynamics of the maximum airway pressure measures in response to the seated-to-supine postural change in SCI population are less known. Compared to supine position, individuals with acute tetraplegic injury exhibited higher PEmax and PImax outcomes in the semirecumbent position (Alvisi et al., 2012). At the same time, significant seated-to-supine decrease in PEmax has been found in the group of patients with motor-complete and incomplete cervical SCI (Sankari et al., 2014). Therefore, since postural factors may have differential impacts in healthy individuals and persons with SCI, it suggests that neurological level and severity of SCI may have complex effects on postural variations in spirometrical and maximum airway pressure measures. This study was undertaken to investigate the impact of postural changes on spirometrical and maximum airway pressure measures in patients with motor-complete and motor-incomplete chronic SCI.
Section snippets
Neurological assessment
The study was approved by the University of Louisville Institutional Review Board in compliance with all the institutional and federal regulations concerning the ethical use of human volunteers for research studies. Neurological level and clinical severity of the spinal cord lesion were determined using the American Spinal Cord Injury Association Impairment Scale (AIS) according to the International Standards for the Neurological Classification of Spinal Cord Injury (ISNCSCI) (Kirshblum et al.,
Results
When analyzed for all participants (n = 27), ranges of seated-to-supine change in PFT values for FVC and FEV1 varied from −7.5% to +29.8% and from −15.3% to +30.9%; whereas for PEmax and PImax those changes varied from −48.2% to +35.4% and from −38.8% to +36.4%, respectively. When analyzed in all subjects, only PEmax was decreased significantly in the supine as compared to seated position (p = .011). In the complete group (n = 13), FVC were increased (p = .007) and PEmax were decreased (p = .031);
Discussion
The major conclusion of the current study is that PFT measures assessed in seated and supine positions in patients with chronic SCI depend on severity and neurological level of SCI, and that these postural effects vary in specific respiratory tasks. Our findings indicate that spirometrical (FVC and FEV1) and airway pressure (PEmax and PImax) measures exhibit differential dynamics when posture is changed from seated to supine position. In contrast to subjects with motor-complete SCI, those with
Conclusion
The effects of posture on respiratory function after SCI can depend on specificity of the respiratory tasks and are greater in those with higher neurological injury level and bigger loss of motor function. Both biomechanical and neuromuscular issues are candidate mechanisms for this observation. Therefore, additional studies are warranted to develop methods for evaluation and improving respiratory and trunk motor control and thereby reduce disability due to SCI-induced respiratory
Acknowledgements
This work was supported by University of Louisville/IRIG; Kentucky Spinal Cord and Head Injury Research Trust 9-10A; Christopher and Dana Reeve Foundation OA2-0802; Craig H. Neilsen Foundation 1000056824; and National Institutes of Health 1RO1HL103750 grants.
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