Exhaled nitric oxide levels are elevated in persons with tetraplegia and comparable to that in mild asthmatics

Systemic and Pulmonary Inflammation/Oxidative Damage: Implications of General and Respiratory Muscle Training in Chronic Spinal-Cord-Injured Patients

Chronic spinal cord injury affects several respiratory-function-related parameters, such as a decrease in respiratory volumes associated with weakness and a tendency to fibrosis of the perithoracic muscles, a predominance of vagal over sympathetic action inducing airway obstructions, and a difficulty in mobilizing secretions. Altogether, these changes result in both restrictive and obstructive patterns. Moreover, low pulmonary ventilation and reduced cardiovascular system functionality (low venous return and right stroke volume) will hinder adequate alveolar recruitment and low O₂ diffusion, leading to a drop in peak physical performance. In addition to the functional effects described above, systemic and localized effects on this organ chronically increase oxidative damage and tissue inflammation. This narrative review describes both the deleterious effects of chronic spinal cord injury on the functional effects of the respiratory system as well as the role of oxidative damage/inflammation in this clinical context. In addition, the evidence for the effect of general and respiratory muscular training on the skeletal muscle as a possible preventive and treatment strategy for both functional effects and underlying tissue mechanisms is summarized.

Inflammation and Oxidative Stress as Common Mechanisms of Pulmonary, Autonomic and Musculoskeletal Dysfunction after Spinal Cord Injury

Simple Summary

When a spinal cord injury occurs, the neurons that regulate our voluntary movements, those involved in environment and somatic perception and those that regulate vegetative functions are affected. Once neuronal damage is established, the cells of other tissues are also affected in their functions, altering the interaction between organs and altering the proper functioning of the organism. Multiple studies in animal models, as well as in humans, have recognized as factors involved in organ damage the imbalance between the formation of highly reactive molecules called pro-oxidants and defensive mechanisms called antioxidants. Closely associated with this phenomenon, the inflammatory response is also pathologically activated. In this narrative review, we have analyzed the information involving these pathological processes at the level of the lung, the autonomic nervous system and the skeletal musculature after spinal cord injury. Knowing the abnormal functioning mechanisms that occur after a spinal cord injury not only offers a better understanding of the organic events but also offers future possibilities for therapeutic interventions that may benefit the thousands of patients suffering this pathology.

Abstract

One of the etiopathogenic factors frequently associated with generalized organ damage after spinal cord injury corresponds to the imbalance of the redox state and inflammation, particularly of the respiratory, autonomic and musculoskeletal systems. Our goal in this review was to gain a better understanding of this phenomenon by reviewing both animal and human studies. At the respiratory level, the presence of tissue damage is notable in situations that require increased ventilation due to lower thoracic distensibility and alveolar inflammation caused by higher levels of leptin as a result of increased fatty tissue. Increased airway reactivity, due to loss of sympathetic innervation, and levels of nitric oxide in exhaled air that are similar to those seen in asthmatic patients have also been reported. In addition, the loss of autonomic control efficiency leads to an uncontrolled release of catecholamines and glucocorticoids that induce immunosuppression, as well as a predisposition to autoimmune reactions. Simultaneously, blood pressure regulation is altered with vascular damage and atherogenesis associated with oxidative damage. At the muscular level, chronically elevated levels of prooxidants and lipoperoxidation associated with myofibrillar atrophy are described, with no reduction or reversibility of this process through antioxidant supplementation.

Biomarkers of inflammation in persons with chronic tetraplegia

In addition to lung volume restriction, individuals with chronic tetraplegia exhibit reduced airway caliber and bronchodilator responsiveness similar to persons with asthma. In asthma, airflow obstruction is closely linked to airway inflammation. Conversely, little is known regarding the airway inflammatory response in tetraplegia. To compare levels of biomarkers of inflammation in exhaled breath condensate (EBC) and serum in subjects with chronic tetraplegia, mild asthma, and able-bodied controls.Prospective, observational pilot study. Thirty-four subjects participated: tetraplegia (n = 12), asthma (n = 12), controls (n = 10). Biomarkers in EBC [8-isoprostane (8-IP), leukotriene B4 (LT-B4), prostaglandin E2 (PG-E2), tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6)] and serum (8-IP, LT-B4, TNF-α, IL-6) were determined using commercially available EIA kits (Cayman Chemical Company, Ann Arbor, MI). Separate, one-way ANOVA with Bonferroni's post-hoc analyses were performed to determine group differences in demographic and dependent variables [EBC and serum biomarkers, fractional exhaled nitric oxide (FeNO), pulmonary function parameters, and specific airway conductance (sGaw)]. The tetraplegia group had significantly elevated 8-IP levels in EBC compared to the asthma (68 ± 38 versus 21 ± 13 pg ml(-1); p < 0.001) and control groups (22 ± 13 pg ml(-1); p < 0.01), respectively. FeNO levels were significantly elevated in the asthma compared to the control group (26 ± 18 versus 11 ± 4 ppb; p < 0.05), and trended higher than levels in the tetraplegia group (15 ± 6; p = 0.08). Levels of serum biomarkers did not differ significantly among groups. Through analysis of EBC, levels of 8-IP were significantly elevated compared to levels found in individuals with mild asthma and healthy controls. Further studies are needed to extend upon these preliminary findings that suggest the presence of airway inflammation in subjects with chronic tetraplegia, and how this relates to pulmonary dysfunction in this population.

A center's experience: pulmonary function in spinal cord injury

Traumatic spinal cord injury (SCI) is associated with significant psychological and physical challenges. A multidisciplinary approach to management is essential to ensure recovery during the acute phase, and comprehensive rehabilitative strategies are necessary to foster independence and quality of life throughout the chronic phase of injury. Complications that beset these individuals are often a unique consequence of SCI, and knowledge of the effects of SCI upon organ systems is essential for appropriate management. According to the National SCI Statistical Center (NSCISC), as of 2010 there were an estimated 265,000 persons living with SCI in the United States, with approximately 12,000 incidence cases annually. Although life expectancy for newly injured individuals with SCI is markedly reduced, persons with chronic SCI are expected to live about as long as individuals without SCI; however, longevity varies inversely with level of injury. Since 2005, 56 % of persons with SCI are tetraplegic, and due to paralysis of respiratory muscles, these individuals may be especially prone to pulmonary complications, which remain a major cause of mortality among persons with chronic SCI. We at the VA Rehabilitation Research and Development Center of Excellence for the Medical Consequences of SCI at the James J. Peters VA Medical Center have devoted more than 25 years to the study of secondary medical conditions that complicate SCI. Herein, we review pulmonary research at the Center, both our past and future endeavors, which form an integral part of our multidisciplinary approach toward achieving a greater understanding of and improving care for veterans with SCI.

Pilot study: elevated circulating levels of the proinflammatory cytokine macrophage migration inhibitory factor in patients with chronic spinal cord injury

OBJECTIVE

To test the hypothesis that the proinflammatory cytokine macrophage migration inhibitory factor (MIF) is elevated in the circulation of patients with chronic spinal cord injury (SCI) relative to uninjured subjects, and secondarily to identify additional immune mediators that are elevated in subjects with chronic SCI.

DESIGN

Prospective, observational pilot study.

SETTING

Outpatient clinic of a department of physical medicine and rehabilitation and research institute in an academic medical center.

PARTICIPANTS

Individuals with chronic (>1y from initial injury) SCI (n=22) and age- and sex-matched uninjured subjects (n=19).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Plasma levels of MIF, as determined by a commercially available multiplex suspension immunoassay. The relationship between MIF levels and clinical/demographic variables was also examined. As a secondary outcome, we evaluated other cytokines, chemokines, and growth factors.

RESULTS

Plasma MIF levels were significantly higher in subjects with chronic SCI than in control subjects (P<.001). Elevated MIF levels were not correlated significantly with any one clinical or demographic characteristic. Subjects with SCI also exhibited significantly higher plasma levels of monokine induced by interferon-gamma/chemokine C-X-C motif ligand 9 (P<.03), macrophage colony stimulating factor (P<.035), interleukin-3 (P<.044), and stem cell growth factor beta (SCGF-β) (P<.016). Among subjects with SCI, the levels of SCGF-β increased with the time from initial injury.

CONCLUSIONS

These data confirm the hypothesis that MIF is elevated in subjects with chronic SCI and identify additional novel immune mediators that are also elevated in these subjects. This study suggests the importance of examining the potential functional roles of MIF and other immune factors in subjects with chronic SCI.

Bronchial hyperresponsiveness testing in athletes of the Swiss Paralympic team

BACKGROUND

The aim of this study was to assess airway hyperresponsiveness to eucapnic voluntary hyperventilation and dry powder mannitol challenge in athletes aiming to participate at the Paralympic Games 2008 in Beijing, especially in athletes with spinal cord injury.

METHODS

Forty-four athletes with a disability (27 with paraplegia (group 1), 3 with tetraplegia (group 2) and 14 with other disabilities such as blindness or single limb amputations (group 3) performed spirometry, skin prick testing, measurement of exhaled nitric oxide, eucapnic voluntary hyperventilation challenge test (EVH) and mannitol challenge test (MCT). A fall in FEV1 of ≥10% in either challenge test was deemed positive for exercise-induced bronchoconstriction.

RESULTS

Fourteen (32%) athletes were atopic and 7 (16%) had a history of physician-diagnosed asthma. Absolute lung function values were significantly lower in patients of group 1 and 2 compared to group 3. Nine (20%) athletes were positive to EVH (8 paraplegics, 1 tetraplegic), and 8 (18%) athletes were positive to MCT (7 paraplegics, 1 tetraplegic). Fourteen (22.7%) subjects were positive to at least one challenge; only three athletes were positive to both tests. None of the athletes in group 3 had a positive test. Both challenge tests showed a significant association with physician-diagnosed asthma status (p = 0.0001). The positive and negative predictive value to diagnose physician-diagnosed asthma was 89% and 91% for EHV, and 75% and 86% for MCT, respectively.

CONCLUSION

EVH and MCT can be used to identify, but especially exclude asthma in Paralympic athletes.

31st g. Heiner sell lectureship: secondary medical consequences of spinal cord injury

Persons with spinal cord injury (SCI) have secondary medical consequences of paralysis and/or the consequences of extreme inactivity. The metabolic changes that result from reduced activity include insulin resistance with carbohydrate disorders and dyslipidemia. A higher prevalence of coronary artery calcification was found in persons with SCI than that in matched able-bodied controls. A depression in anabolic hormones, circulating testosterone and growth hormone, has been described. Adverse soft tissue body composition changes of increased adiposity and reduced skeletal muscle are appreciated. Immobilization is the cause for sublesional disuse osteoporosis with an associated increased risk of fragility fracture. Bowel dysmotility affects all segments of the gastrointestinal tract, with an interest in better defining and addressing gastroesophageal reflux disease and difficulty with evacuation. Developing and testing more effective approaches to cleanse the bowel for elective colonoscopy are being evaluated. The extent of respiratory dysfunction depends on the level and completeness of SCI. Individuals with higher spinal lesions have both restrictive and obstructive airway disease. Pharmacological approaches and expiratory muscle training are being studied as interventions to improve pulmonary function and cough strength with the objective of reducing pulmonary complications. Persons with spinal lesions above the 6th thoracic level lack both cardiac and peripheral vascular mechanisms to maintain blood pressure, and they are frequently hypotensive, with even worse hypotension with upright posture. Persistent and/or orthostatic hypotension may predispose those with SCI to cognitive impairments. The safety and efficacy of anti-hypotensive agents to normalize blood pressure in persons with higher level cord lesions is being investigated.