Christopher R. West

Influence of the neurological level of spinal cord injury on cardiovascular outcomes in humans: a meta-analysis

Background:Although motor and sensory deficits following spinal cord injury (SCI) are well known, there are still contrasting reports on how SCI affects baseline cardiovascular (CV) parameters and other autonomic functions.Study design:Meta-analysis is performed.Objectives:To examine the effect of injury level on supine and seated CV function in individuals with SCI.Methods:A total of 98 studies representing 1968 individuals were retrieved for analysis. Systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) were abstracted from the studies and compared between four groups according to the neurological lesion level, cervical (C) SCI (C4-C8), high-thoracic (HT) SCI (T1-T6), low-thoracic lumbar (LTL) SCI (below T6) and able-bodied (AB) controls.Results:In the supine position, SBP, DBP and HR were lower in C compared with HT, LTL and AB (all P<0.04). In the seated position, SBP and DBP were significantly lower in C compared with LTL and AB (all P<0.003) and HR was significantly lower in C compared with LTL only (P=0.01). A final finding was that C exhibited a lower resting SBP in the seated compared with the supine position (P<0.001).Conclusion:Individuals with SCI exhibit a lesion-dependent impairment in resting CV function, whereby those with the highest injury had the greatest degree of CV dysfunction. A further finding was that individuals with a C injury exhibited a lower resting SBP in the seated vs supine position. Thus, clinicians and researchers should consider lesion level and body position when measuring and interpreting CV parameters in individuals with SCI.

Peripheral vascular function in spinal cord injury: a systematic review

Background:During the past 20 years, significant advances in patient care have resulted in individuals with spinal cord injury (SCI) living longer than before. As lifespan increases, cardiovascular complications are emerging as the leading cause of mortality in this population, and individuals with SCI develop cardiovascular disease at younger ages than their able-bodied counterparts. To address this increasing clinical challenge, several recent studies investigated the central cardiovascular adaptations that occur following SCI. However, a somewhat less recognized component of cardiovascular dysfunction in this population is the peripheral vascular adaptations that also occur as a result of SCI.Study design:Literature review.Objective:To present a comprehensive overview of changes in arterial structure and function, which occur after SCI.Setting:Canada.Methods:A systematic literature review was conducted to extract studies that incorporated measures of arterial structure or function after SCI in animals or humans.Results:Individuals with SCI exhibit vascular dysfunction below the lesion that is characterized by a reduction in conduit artery diameter and blood flow, increased shear rate and leg vascular resistance, and adrenoceptor hyper-responsiveness. There is also recent alarming evidence for central arterial stiffening in individuals with SCI.Conclusion:Although physical deconditioning is the primary candidate responsible for the maladaptive remodeling of the peripheral vasculature after SCI, there is emerging evidence that blood pressure oscillations, such as those occurring in the large majority of individuals with SCI, also exacerbates vascular dysfunction in this population.

Resting cardiopulmonary function in Paralympic athletes with cervical spinal cord injury

PURPOSE The purposes of this study were to describe resting cardiopulmonary function in highly trained athletes with cervical spinal cord injury (SCI) and to compare the data with able-bodied (AB) control subjects. METHODS Twelve Paralympic wheelchair rugby players with cervical SCI (injury level = C5-C7) and 12 AB controls matched for age, stature, and body mass were assessed for pulmonary function using spirometry, body plethysmography, and maximal inspiratory and expiratory mouth pressures; diaphragm function using magnetic stimulation of the phrenic nerves; and cardiac function using transthoracic echocardiography. RESULTS Total lung capacity, vital capacity, inspiratory reserve volume, and expiratory reserve volume were lower in SCI compared with AB (P < 0.01), whereas residual volume was elevated in SCI (P = 0.022). Airway resistance and maximal inspiratory mouth pressure were not different between groups (P > 0.41), whereas maximal expiratory mouth pressure, maximal transdiaphragmatic pressure, and twitch transdiaphragmatic pressure were lower in SCI (P < 0.01). Percent predicted total lung capacity was significantly correlated with maximal transdiaphragmatic pressure in SCI (r = 0.74), suggesting that the pulmonary restriction was a result of diaphragm weakness. Left ventricular mass, ejection fraction, stroke volume, and cardiac output were lower in SCI (P < 0.04), but early and late filling velocities during diastole were not different between groups (P > 0.05). CONCLUSIONS Highly trained athletes with cervical SCI exhibit a restrictive pulmonary defect, weakness of the expiratory and diaphragm muscles, atrophy of the heart, and reduced systolic cardiac function.

Cardiovascular Function in Individuals with Incomplete Spinal Cord Injury: A Systematic Review

BACKGROUND There is a clear relationship between the neurological level of spinal cord injury (SCI) and cardiovascular function; however, the relationship between completeness of injury and cardiovascular function is less straightforward. Traditionally completeness of injury has referred to neurological (motor/sensory) completeness. Recently, a number of studies have started to investigate autonomic completeness of injury. OBJECTIVE To investigate the relationships between cardiovascular function and neurological and autonomic completeness of injury. METHODS A literature search was conducted in November 2012 through MEDLINE, Embase, and CINAHL. Twenty-one studies were included in this review. RESULTS In acute SCI, there is no clear consensus about whether resting heart rate (HR), blood pressure (BP), or prevalence of BP abnormalities differs between neurologically complete and incomplete SCI. In chronic SCI, there is limited evidence that there is less prevalence of autonomic dysreflexia and improved heart rate variability in response to provocation in neurologically incomplete SCI; however, resting HR and BP appear similar between neurologically complete and incomplete SCI. There is growing evidence that BP and HR at rest and during orthostasis is enhanced in autonomically incomplete SCI. Numerous studies report that neurological completeness does not agree with autonomic completeness of injury. CONCLUSIONS For acute SCI, there is no clear consensus whether cardiovascular function differs between complete and incomplete. For chronic SCI, the studies to date suggest that autonomic completeness of SCI is more strongly related to cardiovascular function than neurological completeness of injury. Thus, clinicians and scientists should account for autonomic completeness of injury when assessing cardiovascular function in SCI.

Autonomic cardiovascular control in Paralympic athletes with spinal cord injury.

INTRODUCTION Disruption of autonomic control after spinal cord injury (SCI) results in life-threatening cardiovascular dysfunctions and impaired endurance performance; hence, an improved ability to recognize those at risk of autonomic disturbances is of critical clinical and sporting importance. PURPOSE The objective of this study is to assess the effect of neurological level, along with motor, sensory, and autonomic completeness of injury, on cardiovascular control in Paralympic athletes with SCI. METHODS Fifty-two highly trained male Paralympic athletes (age, 34.8 ± 7.1 yr) from 14 countries with chronic SCI (C2-L2) completed three experimental trials. During trial 1, motor and sensory functions were assessed according to the American Spinal Injury Association Impairment Scale. During trial 2, autonomic function was assessed via sympathetic skin responses (SSR). During trial 3, cardiovascular control was assessed via the beat-by-beat blood pressure response to orthostatic challenge. RESULTS Athletes with cervical SCI exhibited the lowest seated blood pressure and the most severe orthostatic hypotension (P < 0.025). There were no differences in cardiovascular function between athletes with different American Spinal Injury Association Impairment Scale grades (P > 0.96). Conversely, those with the lowest SSR scores exhibited the lowest seated blood pressure and the most severe orthostatic hypotension (P < 0.002). Linear regression demonstrated that the combined model of neurological level and autonomic completeness of SCI explained the most variance in all blood pressure indices. CONCLUSION We demonstrate for the first time that neurological level and SSR score provide the optimal combination of assessments to identify those at risk of abnormal cardiovascular control. We advocate the use of autonomic testing in the clinical and sporting classification of SCI athletes.

No effect of arm-crank exercise on diaphragmatic fatigue or ventilatory constraint in Paralympic athletes with cervical spinal cord injury.

Cervical spinal cord injury (CSCI) results in a decrease in the capacity of the lungs and chest wall for pressure, volume, and airflow generation. We asked whether such impairments might increase the potential for exercise-induced diaphragmatic fatigue and mechanical ventilatory constraint in this population. Seven Paralympic wheelchair rugby players (mean + or - SD peak oxygen uptake = 16.9 + or - 4.9 ml x kg(-1) x min(-1)) with traumatic CSCI (C(5)-C(7)) performed arm-crank exercise to the limit of tolerance at 90% of their predetermined peak work rate. Diaphragm function was assessed before and 15 and 30 min after exercise by measuring the twitch transdiaphragmatic pressure (P(di,tw)) response to bilateral anterolateral magnetic stimulation of the phrenic nerves. Ventilatory constraint was assessed by measuring the tidal flow volume responses to exercise in relation to the maximal flow volume envelope. P(di,tw) was not different from baseline at any time after exercise (unpotentiated P(di,tw) = 19.3 + or - 5.6 cmH(2)O at baseline, 19.8 + or - 5.0 cmH(2)O at 15 min after exercise, and 19.4 + or - 5.7 cmH(2)O at 30 min after exercise; P = 0.16). During exercise, there was a sudden, sustained rise in operating lung volumes and an eightfold increase in the work of breathing. However, only two subjects showed expiratory flow limitation, and there was substantial capacity to increase both flow and volume (<50% of maximal breathing reserve). In conclusion, highly trained athletes with CSCI do not develop exercise-induced diaphragmatic fatigue and rarely reach mechanical ventilatory constraint.

Passive hind-limb cycling improves cardiac function and reduces cardiovascular disease risk in experimental spinal cord injury

Using a wide array of experimental approaches, we demonstrate for the first time that spinal cord injury is associated with a rapid and sustained impairment in cardiac structure and function that is present as early as 1 week post‐injury. We provide novel data demonstrating that spinal cord injury elicits an altered Starling curve and myocardial fibrosis. The latter of these may be secondary to an up‐regulation of transforming growth factor beta‐1 and mothers against decapentaplegic homolog 3 mRNA, both of which form part of a well‐known fibrotic signalling pathway. Passive hind‐limb cycling averts the spinal cord injury‐induced impairments in cardiac structure and function, prevents myocardial fibrosis and improves blood lipid profiles. Passive lower‐limb cycling represents an elegant, cost‐effective and widely accessible therapeutic strategy that may reduce the clinical cardiovascular burden imposed by spinal cord injury and other neurological disorders.

Effects of inspiratory muscle training on exercise responses in Paralympic athletes with cervical spinal cord injury

We asked whether specific inspiratory muscle training (IMT) improves respiratory structure and function and peak exercise responses in highly trained athletes with cervical spinal cord injury (SCI). Ten Paralympic wheelchair rugby players with motor‐complete SCI (C5‐C7) were paired by functional classification then randomly assigned to an IMT or placebo group. Diaphragm thickness (B‐mode ultrasonography), respiratory function [spirometry and maximum static inspiratory (PI,max) and expiratory (PE,max) pressures], chronic activity‐related dyspnea (Baseline and Transition Dyspnea Indices), and physiological responses to incremental arm‐crank exercise were assessed before and after 6 weeks of pressure threshold IMT or sham bronchodilator treatment. Compared to placebo, the IMT group showed significant increases in diaphragm thickness (P = 0.001) and PI,max (P = 0.016). There was a significant increase in tidal volume at peak exercise in IMT vs placebo (P = 0.048) and a strong trend toward an increase in peak work rate (P = 0.081, partial eta‐squared = 0.33) and peak oxygen uptake (P = 0.077, partial eta‐squared = 0.34). No other indices changed post‐intervention. In conclusion, IMT resulted in significant diaphragmatic hypertrophy and increased inspiratory muscle strength in highly trained athletes with cervical SCI. The strong trend, with large observed effect, toward an increase in peak aerobic performance suggests IMT may provide a useful adjunct to training in this population.

Effects of abdominal binding on cardiorespiratory function in cervical spinal cord injury

We asked whether abdominal binding improves cardiorespiratory function in individuals with cervical spinal cord injury (SCI). 13 participants with chronic SCI (C(5)-C(7)) and 8 able-bodied controls were exposed to varying degrees of elastic abdominal compression (unbound [UB], loose-bound [LB], and tight-bound [TB]) while seated. In SCI, TB increased vital capacity (14%), expiratory flow throughout vital capacity (15%), inspiratory capacity (21%), and maximal expiratory mouth pressure (25%). In contrast, TB reduced residual volume (-34%) and functional residual capacity (-23%). TB increased tidal and twitch transdiaphragmatic pressures (∼45%), primarily by increasing the gastric pressure contributions. TB increased cardiac output (28%), systolic mitral annular velocity (22%), and late-diastolic mitral annular velocity (50%). Selected measures of cardiorespiratory function improved with LB, but the changes were less compared to TB. In able-bodied, changes were inconsistent and always less than in SCI. In conclusion, abdominal-binding improved cardiorespiratory function in low-cervical SCI by optimising operating lung volumes, increasing expiratory flow, enhancing diaphragmatic pressure production, and improving left-ventricular function.

Effects of exercise on fitness and health of adults with spinal cord injury A systematic review

Objective: To synthesize and appraise research testing the effects of exercise interventions on fitness, cardiometabolic health, and bone health among adults with spinal cord injury (SCI). Methods: Electronic databases were searched (1980–2016). Included studies employed exercise interventions for a period ≥2 weeks, involved adults with acute or chronic SCI, and measured fitness (cardiorespiratory fitness, power output, or muscle strength), cardiometabolic health (body composition or cardiovascular risk factors), or bone health outcomes. Evidence was synthesized and appraised using Grading of Recommendations Assessment, Development, and Evaluation (GRADE). Results: A total of 211 studies met the inclusion criteria (22 acute, 189 chronic). For chronic SCI, GRADE confidence ratings were moderate to high for evidence showing exercise can improve all of the reviewed outcomes except bone health. For acute SCI, GRADE ratings were very low for all outcomes. For chronic SCI, there was low to moderate confidence in the evidence showing that 2–3 sessions/week of upper body aerobic exercise at a moderate to vigorous intensity for 20–40 minutes, plus upper body strength exercise (3 sets of 10 repetitions at 50%–80% 1-repetition maximum for all large muscle groups), can improve cardiorespiratory fitness, power output, and muscle strength. For chronic SCI, there was low to moderate confidence in the evidence showing that 3–5 sessions per week of upper body aerobic exercise at a moderate to vigorous intensity for 20–44 minutes can improve cardiorespiratory fitness, muscle strength, body composition, and cardiovascular risk. Conclusions: Exercise improves fitness and cardiometabolic health of adults with chronic SCI. The evidence on effective exercise types, frequencies, intensities, and durations should be used to formulate exercise guidelines for adults with SCI.