Bronchodilatory effects of ipratropium bromide in patients with tetraplegia

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.

Bronchodilator effects of ipratropium bromide and albuterol sulfate among subjects with tetraplegia

OBJECTIVE

In addition to lung volume restriction, persons with chronic tetraplegia demonstrate obstructive airway physiology evinced by pharmacologically-induced bronchodilation. We previously found independent evidence that anticholinergic agents (ipratropium bromide; IB) and beta-2 adrenergic agonists (albuterol sulfate; AS) were associated with significant bronchodilation in subjects with tetraplegia as determined via spirometry or body plethysmography. Direct comparison of these two classes of agents has received little attention.

METHODS

Twelve subjects with chronic tetraplegia completed single dose treatment on alternate days with nebulized IB or AS. Patients underwent pre- and 30-minute post-bronchodilator spirometry, body plethysmography, and impulse oscillation system (IOS) in accordance with established protocols.

RESULTS

Spirometry and specific airway conductance revealed significant bronchodilator responsiveness following both IB and AS. As determined by increases in specific airway conductance post-bronchodilator, IB tended toward greater bronchodilation than AS (71% vs. 47%). IOS revealed a greater reduction in central airway resistance (R20) following IB compared to AS (22% vs. 9%, P < 0.01). A greater number of subjects exhibited a clinically significant reduction in R20 following IB compared to AS (58% vs. 8%, P < 0.01).

CONCLUSION

Among subjects with tetraplegia, both IB and AS elicit significant bronchodilation, although the magnitude of the bronchodilator response is greater following IB. This lends support to theory of overriding cholinergic airway tone in tetraplegia. The IOS findings further suggest that the predominant site of action of IB is upon the larger central airways congruent with findings in able-bodied subjects.

Respiratory problems and management in people with spinal cord injury

Spinal cord injury (SCI) is characterised by profound respiratory compromise secondary to the level of loss of motor, sensory and autonomic control associated with the injury. This review aims to detail these anatomical and physiological changes after SCI, and outline their impact on respiratory function. Injury-related impairments in strength substantially alter pulmonary mechanics, which in turn affect respiratory management and care. Options for treatments must therefore be considered in light of these limitations.

KEY POINTS

Respiratory impairment following spinal cord injury (SCI) is more severe in high cervical injuries, and is characterised by low lung volumes and a weak cough secondary to respiratory muscle weakness.Autonomic dysfunction and early-onset sleep disordered breathing compound this respiratory compromise.The mainstays of management following acute high cervical SCI are tracheostomy and ventilation, with noninvasive ventilation and assisted coughing techniques being important in lower cervical and thoracic level injuries.Prompt investigation to ascertain the extent of the SCI and associated injuries, and appropriate subsequent management are important to improve outcomes.

EDUCATIONAL AIMS

To describe the anatomical and physiological changes after SCI and their impact on respiratory function.To describe the changes in respiratory mechanics seen in cervical SCI and how these changes affect treatments.To discuss the relationship between injury level and respiratory compromise following SCI, and describe those at increased risk of respiratory complications.To present the current treatment options available and their supporting evidence.

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.

The impact of spinal cord injury on breathing during sleep

The prevalence of sleep disordered breathing (SDB) following spinal cord injury (SCI) is considerably greater than in the general population. While the literature on this topic is still relatively small, and in some cases contradictory, a few general conclusions can be drawn. First, while both central and obstructive sleep apnea (OSA) has been reported after SCI, OSA appears to be more common. Second, SDB after SCI likely reflects a complex interplay between multiple factors including body mass, lung volume, autonomic function, sleep position, and respiratory neuroplasticity. It is not yet possible to pinpoint a "primary factor" which will predispose an individual with SCI to SDB, and the underlying mechanisms may change during progression from acute to chronic injury. Given the prevalence and potential health implications of SDB in the SCI population, we suggest that additional studies aimed at defining the underlying mechanisms are warranted.

Management of acute spinal cord injury in the neurocritical care unit

Acute spinal cord injury (SCI) is associated with widespread disturbances not only affecting neurologic function but also leading to hemodynamic instability and respiratory failure. Traumatic SCI rarely occurs in isolation, and frequently is accompanied by trauma to other organ systems. Management of individuals with SCI is complex, requiring aggressive monitoring and prompt treatment when complications arise. Typically this level of care is provided in the neurocritical care unit. This article reviews the pathophysiology of the neurologic, cardiovascular, and pulmonary derangements following traumatic SCI and their management in the critical care setting.

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.

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

The role of airway inflammation in mediating airflow obstruction in persons with chronic traumatic tetraplegia is unknown. Measurement of the fraction of exhaled nitric oxide (FeNO) affords a validated noninvasive technique for gauging the airway inflammatory response in asthma, although it has never been assessed in persons with tetraplegia. This study was designed to determine the FeNO in individuals with chronic tetraplegia compared with that in patients with mild asthma and healthy able-bodied individuals. Nine subjects with chronic tetraplegia, seven subjects with mild asthma, and seven matched healthy able-bodied controls were included in this prospective, observational, pilot study. All subjects were nonsmokers and clinically stable at the time of study. Spirometry was performed on all participants at baseline. FENO was determined online by a commercially available closed circuit, chemiluminescence method, using a single-breath technique. Subjects with tetraplegia had significantly higher values of FeNO than controls (17.72 +/- 3.9 ppb vs. 10.37 +/- 4.9 ppb; P < or = 0.01), as did subjects with asthma (20.23 +/- 4.64 ppb vs. 10.37 +/- 4.9 ppb, P < or = 0.001). There was no significant difference in FeNO between subjects with tetraplegia and those with asthma (17.72 +/- 3.9 ppb vs. 20.23 +/- 4.64 ppb, P < or = 0.27). Individuals with chronic tetraplegia have FeNO levels that are comparable to that seen in mild asthmatics and higher than that in healthy able-bodied controls. The clinical relevance of this observation has yet to be determined.

Pulmonary function and spinal cord injury

Injury to the cervical and upper thoracic spinal cord disrupts function of inspiratory and expiratory muscles, as reflected by reduction in spirometric and lung volume parameters and static mouth pressures. In association, subjects with tetraplegia have decreased chest wall and lung compliance, increased abdominal wall compliance, and rib cage stiffness with paradoxical chest wall movements, all of which contribute to an increase in the work of breathing. Expiratory muscle function is more compromised than inspiratory muscle function among subjects with tetraplegia and high paraplegia, which can result in ineffective cough and propensity to mucus retention and atelectasis. Subjects with tetraplegia also demonstrate heightened vagal activity with reduction in baseline airway caliber, findings attributed to loss of sympathetic innervation to the lungs. Significant increase in airway caliber following inhalation of ipratropium bromide, an anticholinergic agent, suggests that reduction in airway caliber is not due to acquired airway fibrosis stemming from repeated infections or to abnormal hysteresis secondary to chronic inability of subjects to inhale to predicted total lung capacity. Reduced baseline airway caliber possibly explains why subjects with tetraplegia exhibit airway hyperresponsiveness to methacholine and ultrasonically nebulized distilled water. While it has been well demonstrated that bilateral phrenic nerve pacing or stimulation through intramuscular diaphragmatic electrodes improves inspiratory muscle function, it remains unclear if inspiratory muscle training improves pulmonary function. Recent findings suggest that expiratory muscle training, electrical stimulation of expiratory muscles and administration of a long-acting beta(2)-agonist (salmeterol) improve physiological parameters and cough. It is unknown if baseline bronchoconstriction in tetraplegia contributes to respiratory symptoms, of if the chronic administration of a bronchodilator reduces the work of breathing and/or improves respiratory symptoms. Less is known regarding the benefits of treatment of obstructive sleep apnea, despite evidence indicating that the prevalence of this condition in persons with tetraplegia is far greater than that encountered in able-bodied individuals.

Respiratory management during the first five days after spinal cord injury

Respiratory complications are the most common cause of morbidity and mortality in acute spinal cord injury (SCI), with an incidence of 36% to 83%. Eighty percent of deaths in patients hospitalized with cervical SCI are secondary to pulmonary dysfunction, with pneumonia the cause in 50% of the cases. The number of respiratory complications during the acute hospital stay contributes significantly to the length of hospital stay and cost. Four factors (use of mechanical ventilation, pneumonia, the need for surgery, and use of tracheostomy) explain nearly 60% of hospital costs and may be as important a predictor of hospital cost as level of injury. Atelectasis (36.4%), pneumonia (31.4%), and ventilatory failure (22.6%) are the most common complications during the first 5 days after injury. Ventilatory failure occurs on average 4.5 days after injury. Transfer to an SCI center specializing in acute management of tetraplegia has been shown to significantly reduce the number of respiratory complications. This review concentrates on the first 5 days after injury, focusing on complications, predictive factors, prevention, and management of those complications.

Determinants of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/FVC in chronic spinal cord injury

OBJECTIVE

To assess factors that influence pulmonary function, because respiratory system dysfunction is common in chronic spinal cord injury (SCI).

DESIGN

Cross-sectional cohort study.

SETTING

Veterans Affairs Boston SCI service and the community.

PARTICIPANTS

Between 1994 and 2003, 339 white men with chronic SCI completed a respiratory questionnaire and underwent spirometry.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Forced expiratory volume in 1 second (FEV(1)), forced vital capacity (FVC), and FEV(1)/FVC.

RESULTS

Adjusting for SCI level and completeness, FEV(1) (-21.0 mL/y; 95% confidence interval [CI], -26.3 to -15.7 mL/y) and FVC (-17.2 mL/y; 95% CI, -23.7 to -10.8 mL/y) declined with age. Lifetime cigarette use was also associated with a decrease in FEV(1) (-3.8 mL/pack-year; 95% CI, -6.5 to -1.1 mL/pack-year), and persistent wheeze and elevated body mass index were associated with a lower FEV(1)/FVC. A greater maximal inspiratory pressure (MIP) was associated with a greater FEV(1) and FVC. FEV(1) significantly decreased with injury duration (-6.1 mL/y; 95% CI, -11.7 to -0.6 mL/y), with the greatest decrement in the most neurologically impaired. The most neurologically impaired also had a greater FEV(1)/FVC, and their FEV(1) and FVC were less affected by age and smoking.

CONCLUSIONS

Smoking, persistent wheeze, obesity, and MIP, in addition to SCI level and completeness, were significant determinants of pulmonary function. In SCI, FEV(1), FVC, and FEV(1)/FVC may be less sensitive to factors associated with change in airway size and not reliably detect the severity of airflow obstruction.

Infusion of neostigmine-glycopyrrolate for bowel evacuation in persons with spinal cord injury

Defecatory complications are common after spinal cord injury (SCI) and have been attributed, in part, to an imbalance of the autonomic nervous system between parasympathetic and sympathetic effects on the colon. Because parasympathetic (i.e., cholinergic) input to the bowel may be downregulated after SCI, it was hypothesized that neostigmine, a medication that increases cholinergic tone by blocking the metabolism of acetylcholine, might promote bowel evacuation in these persons. Since neostigmine is known to cause bradycardia and bronchoconstriction, we also assessed whether these side-effects could be prevented by coadministration of neostigmine with glycopyrrolate, an anticholinergic agent that has limited activity on the muscarinic receptors of the colon. The hypothesis was tested in 13 persons with SCI in whom videofluoroscopy was carried out after instillation of a barium oatmeal paste into the rectum and descending colon. On separate days, subjects received, in a randomized, blinded design, one of three intravenous infusates (normal saline, 2 mg neostigmine, or 2 mg neostigmine + 0.4 mg glycopyrrolate). The effect of these infusates on bowel evacuation of the barium paste, heart rate, and airway resistance was determined. Both neostigmine and neostigmine + glycopyrrolate resulted in prompt bowel evacuation. The nadir heart rate was lower after neostigmine alone than with the combination. Neostigmine administration increased both total and central airway resistance, an effect that was not observed with the coadministration of glycopyrrolate. Other side-effects of neostigmine and the combination of drugs included muscle fasciculations and dry mouth, both of which were mild and short-lived. Abdominal cramping was noted in subjects with spinal cord lesions below thoracic level 10. These results indicated that neostigmine/glycopyrrolate administration is safe and well tolerated in persons with chronic SCI.

Assessment of airway caliber and bronchodilator responsiveness in subjects with spinal cord injury

STUDY OBJECTIVES

Previous spirometric findings among subjects with chronic tetraplegia that reduction in FEV1 and maximal forced expiratory flow, mid-expiratory phase (FEF(25-75%)) correlated with airway hyperresponsiveness to histamine, and that many of these subjects exhibited significant bronchodilator responsiveness, suggested that baseline airway caliber was low in this population. To better evaluate airway dynamics in patients with spinal cord injury, we used body plethysmography to determine specific airway conductance (sGaw), a less effort-dependent and more reflective surrogate marker of airway caliber.

DESIGN

Cohort study.

SETTING

Veterans Affairs medical center.

PARTICIPANTS

Thirty clinically stable subjects with chronic spinal cord injury, including 15 subjects with tetraplegia (injury at C4-C7) and 15 subjects with low paraplegia (injury below T7), participated in the study. Fifteen able-bodied individuals served as a control group.

INTERVENTIONS

Subjects underwent baseline assessment of spirometric and body plethysmographic parameters. Repeat measurements were performed among subjects with tetraplegia and paraplegia before and 30 min after receiving aerosolized ipratropium bromide (2.5 mL 0.02% solution; 12 subjects) or normal saline solution (2.5 mL; 6 subjects).

MEASUREMENTS AND RESULTS

We found that subjects with tetraplegia had significantly reduced mean values for sGaw (0.16 cm H2O/s), total lung capacity, FVC, FEV1, and FEF(25-75%) compared to subjects in the other two groups. Subjects with tetraplegia who received ipratropium bromide experienced significant increases in sGaw (135%), FEV1 (12%; 260 mL), and FEF(25-75%) (27%). Significant, though far smaller, increases in sGaw (19%) were found among subjects with paraplegia. No discernable change in any pulmonary function parameter was found following the administration of normal saline solution.

CONCLUSIONS

Subjects with tetraplegia, as opposed to those with low paraplegia, have reduced baseline airway caliber due to heightened vagomotor airway tone, which we hypothesize is the result of the interruption of sympathetic innervation to the lungs, and/or from low circulating epinephrine levels.

Lung mechanics in individuals with spinal cord injury: effects of injury level and posture

Individuals with spinal cord injury (SCI) exhibit reduced lung volumes and flow rates as a result of respiratory muscle weakness. These features have not, however, been investigated in relation to the combined effects of injury level and posture. Changes in forced vital capacity (FVC), forced expiratory volume in 1 s (FEV(1)), FEV(1)/FVC, forced expiratory flow at 50% vital capacity (FEF(50)), inspiratory capacity (IC), and expiratory reserve volume (ERV) were assessed by injury level in the seated and supine positions in 74 individuals with SCI. The main findings were 1) FVC, FEV(1), and IC increased with descending SCI level down to T(10), below which they tended to level off; 2) supine values of FVC and FEV(1) tended to be larger in the supine compared with the seated posture down to injury level T(1), caudad to which they were less than when seated; 3) IC increased proportionately more down to injury level L(1), below which it declined slightly and plateaued; 4) ERV was measurable even at high cervical injuries, was generally smaller in the supine position, reached peak values in both positions at T(10) injury level, and then rapidly declined at lower levels; 5) when subjects were separated according to current, former, and never smokers, only formerly smoking paraplegic individuals demonstrated spirometric values significantly less than paraplegic individuals who never smoked. Changes in spirometric measurements in SCI are dependent on injury level and posture. These findings support the concept that the increase in vital capacity in supine position is related to the effect of gravity on abdominal contents and increase in IC.

Airway hyperreactivity in subjects with tetraplegia is associated with reduced baseline airway caliber

OBJECTIVES

We administered aerosolized histamine to 32 subjects with tetraplegia to determine whether there were differences in spirometric and/or lung volume parameters between responders and nonresponders.

RESULTS

Baseline pulmonary function parameters revealed mild to moderate restrictive dysfunction. We found that 25 subjects (78%) were hyperreactive to histamine (mean provocative concentration of a substance causing a 20% fall in FEV(1) [PC(20)], 1.77 mg/mL). Responders (PC(20), < 8 mg/mL) had significantly lower values for forced expiratory flow between 25% and 75% of the outflow curve (FEF(25-75)), FEF(25-75) percent predicted, and FEF(25-75)/FVC ratio. Among all 32 subjects, the natural logarithmic transformation performed on PC(20) values (lnPC(20)) correlated with FEF(25-75) percent predicted, FEV(1) percent predicted, and FEF(25-75)/FVC ratio but not with FVC percent predicted. Responders with PC(20) values < 2 mg/mL (n = 13) had significantly reduced values for FVC, FVC percent predicted, FEV(1), and FEV(1) percent predicted compared to those with PC(20) values between 2 mg/mL and 8 mg/mL. In addition, among responders, there was a significant correlation between lnPC(20) and FVC percent predicted. A significant relationship was found between maximal inspiratory pressure (PImax) and both FEV(1) percent predicted and FEF(25-75) percent predicted, but not between lnPC(20) and either PImax or maximal expiratory pressure (PEmax).

CONCLUSIONS

These findings demonstrate that subjects with tetraplegia who exhibit airway hyperreactivity (AHR) have reduced baseline airway caliber and that lower values for lnPC(20) are associated with parallel reductions in surrogate spirometric indexes of airway size (FEV(1) percent predicted and FEF(25-75) percent predicted) and airway size relative to lung size (FEF(25-75)/FVC ratio). The absence of an association between lnPC(20) and FVC percent predicted for the entire group or between lnPC(20) and either PImax or PEmax indicates that reduced lung volumes secondary to respiratory muscle weakness cannot explain the mechanism(s) underlying AHR. Among responders, however, a possible role for reduction in lung volume, as it pertains to increasing AHR, cannot be excluded. Proposed mechanisms for reduced baseline airway caliber relative to lung size in subjects with tetraplegia include unopposed parasympathetic activity secondary to the loss of sympathetic innervation to the lungs and/or the inability to stretch airway smooth muscle with deep inhalation.

Effects of a beta2-agonist on airway hyperreactivity in subjects with cervical spinal cord injury

STUDY OBJECTIVE

Aerosolized ipratropium bromide or orally administered baclofen or oxybutynin chloride (Ditropan) block methacholine-associated airway hyperreactivity in subjects with chronic cervical spinal cord injury (SCI), whereas these agents do not inhibit airway hyperreactivity associated with the inhalation of histamine. The present study was performed to determine whether pretreatment with a beta2-agonist attenuates airway hyperresponsiveness in these subjects.

PARTICIPANTS

Subjects with chronic cervical SCI previously demonstrating airway hyperreactivity were challenged with methacholine (n = 9) or histamine (n = 16) alone and, on a separate day, 25 min following inhalation of nebulized metaproterenol sulfate.

RESULTS

Inhalation of the beta2-agonist was associated with an increase in provocative concentration causing a 20% decrease in FEV1 (PC20) values (geometric mean) from 1.01+/-2.76 to 20.54+/-6.24 mg/mL for methacholine and from 2.29+/-2.26 to 19.82+/-5.93 mg/mL for histamine. No correlation was found between specific PC20 values for individual subjects and percentage improvement in FEV1 (liter) following inhalation of metaproterenol sulfate and between PC20 values and baseline FEV1 percent.

CONCLUSION

These data, combined with findings that patients with chronic high cervical SCI experience increased breathlessness following exposure to exogenous agents, suggest that long-term prophylactic beta2-agonist therapy may reduce respiratory symptoms associated with airway hyperreactivity in these patients.

A crash course in spinal cord injury

The complex management issues related to spinal cord injury traditionally have been the purview of physical medicine and rehabilitation specialists. However, changes in the healthcare system now offer primary care physicians an expanded role in helping affected patients live a healthier and more functional life. With proper understanding of the mechanisms of spinal cord injury, primary care physicians can become important members of the medical management team. Dr Yu presents a comprehensive overview of medical care issues and common complications in spinal cord injury.

Airway hyperresponsiveness to methacholine in subjects with spinal cord injury

Previously, we found that never-smokers with quadriplegia were hyperresponsive to aerosolized methacholine. To further explore the phenomenon, we compared responsiveness to methacholine in never-smokers with that of smokers and ex-smokers. We also evaluated responsiveness in subjects with high paraplegia (lesions at T-1 to T-6) or low paraplegia (lesions at T-7 and below). We found that smokers and ex-smokers with quadriplegia were hyperresponsive to methacholine (provocative concentration causing a 20% fall in FEV1 = 1.9 mg/mL), and that the response was comparable to that found in never-smokers, revealing that hyperresponsiveness among never-smokers cannot be attributed to preinjury airway hyperreactivity that precluded cigarette use. In contrast, subjects with low paraplegia were not hyperresponsive to methacholine. Among subjects with high paraplegia, the three subjects demonstrating airway hyperresponsiveness had significantly lower FEV1 (percent predicted). The findings support the hypothesis that airway hyperresponsiveness in subjects with quadriplegia represents loss of sympathetic innervation of the lung, thereby leaving intact unopposed bronchoconstrictor cholinergic activity. However, reduced lung volumes in these subjects also suggest the possibility that airway hyperresponsiveness is due to loss of ability to stretch airway smooth muscle by deep breathing.