Effects of a Tailored Physical Activity Intervention on Cardiovascular Structure and Function in Individuals With Spinal Cord Injury

Feasibility of a community-based structured exercise program for persons with spinal cord injury

OBJECTIVES

(1) Examine the feasibility of a community-based exercise intervention for persons with spinal cord injury and (2) compare the cardiorespiratory fitness, skeletal muscle strength, and psychosocial well-being of participants in the intervention group versus control group.

DESIGN

Community-based pilot randomized controlled trial. Setting: Accessible community-based health and wellness center. Participants: Thirty-two sedentary community-dwelling adults with any level of spinal cord injury. Interventions: Participants were randomized to a 36-session/12-week community-based exercise program (intervention; EG) or to a 36-session/12-week physical activity education group (control; CG). Outcome measures: Primary outcome measures included cardiorespiratory fitness measured by a VO2peak test, a composite score of four upper extremity musculoskeletal strength 1-repetition maximum exercises, and feasibility measured by EG participants' adherence and exercise intensity achieved during the program. EG participants' acceptance of the program was also evaluated using a self-reported satisfaction scale. Self-efficacy, motivation, pain, and goal performance and satisfaction were secondary outcome measures. Adherence and acceptability were also measured.

RESULTS

Fifteen participants (n = 15) completed the community-based exercise intervention and seventeen (n = 17) completed the education program. While no statistically significant differences were found, the EG experienced changes of moderate effect size in cardiorespiratory fitness, strength, motivation, and satisfaction with their goals. The EG attended, on average, two sessions per week. The community-based exercise intervention was highly accepted by and satisfying for participants to engage in.

CONCLUSIONS

The EG had improvements in the two primary measures, cardiorespiratory fitness and musculoskeletal strength, following the intervention. The community-based exercise intervention was feasible and accepted by participants.

Acute intermittent hypoxia elicits sympathetic neuroplasticity independent of peripheral chemoreflex activation and spinal cord tissue hypoxia in a rodent model of high-thoracic spinal cord injury

The loss of medullary control of spinal circuits controlling the heart and blood vessels is a unifying mechanism linking both hemodynamic instability and the risk for cardiovascular diseases (CVD) following spinal cord injury (SCI). As such, new avenues to regulate sympathetic activity are essential to mitigate CVD in this population. Acute intermittent hypoxia (AIH) induces a type of neuroplasticity known as long-term facilitation (LTF), a persistent increase in nerve activity post-AIH in spinal motor circuits. Whether LTF occurs within the sympathetic circuit following SCI is largely unknown. We aimed to test whether AIH elicits sympathetic LTF (i.e., sLTF) and attenuates hypoactivity in sub-lesional splanchnic sympathetic circuits in a male rat model of SCI. In 3 experimental series, we tested whether 1) high-thoracic contusion SCI induces hypoactivity in splanchnic sympathetic nerve activity, 2) AIH elicits sLTF following SCI, and 3) sLTF requires carotid chemoreflex activation or spinal cord tissue hypoxia. Our results indicate that a single-session of AIH therapy (10 × 1 min of FiO2 = 0.1, interspersed with 2 min of FiO2 = 1.0) delivered at 2 weeks following SCI attenuates SCI-induced sympathetic hypoactivity by eliciting sLTF 90 min post-treatment that is independent of peripheral chemoreflex activation and/or spinal cord hypoxia. These findings advance our mechanistic understanding of AIH in the field and yield new insights into factors underpinning AIH-induced sLTF following SCI in a rat model. Our findings also set the stage for the chronic application of AIH to alleviate secondary complications resulting from sympathetic hypoactivity following SCI.

Exercise and aerobic capacity in individuals with spinal cord injury: A systematic review with meta-analysis and meta-regression

BACKGROUND

A low level of cardiorespiratory fitness [CRF; defined as peak oxygen uptake ([Formula: see text]O2peak) or peak power output (PPO)] is a widely reported consequence of spinal cord injury (SCI) and a major risk factor associated with chronic disease. However, CRF can be modified by exercise. This systematic review with meta-analysis and meta-regression aimed to assess whether certain SCI characteristics and/or specific exercise considerations are moderators of changes in CRF.

METHODS AND FINDINGS

Databases (MEDLINE, EMBASE, CENTRAL, and Web of Science) were searched from inception to March 2023. A primary meta-analysis was conducted including randomised controlled trials (RCTs; exercise interventions lasting >2 weeks relative to control groups). A secondary meta-analysis pooled independent exercise interventions >2 weeks from longitudinal pre-post and RCT studies to explore whether subgroup differences in injury characteristics and/or exercise intervention parameters explained CRF changes. Further analyses included cohort, cross-sectional, and observational study designs. Outcome measures of interest were absolute (A[Formula: see text]O2peak) or relative [Formula: see text]O2peak (R[Formula: see text]O2peak), and/or PPO. Bias/quality was assessed via The Cochrane Risk of Bias 2 and the National Institute of Health Quality Assessment Tools. Certainty of the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. Random effects models were used in all meta-analyses and meta-regressions. Of 21,020 identified records, 120 studies comprising 29 RCTs, 67 pre-post studies, 11 cohort, 7 cross-sectional, and 6 observational studies were included. The primary meta-analysis revealed significant improvements in A[Formula: see text]O2peak [0.16 (0.07, 0.25) L/min], R[Formula: see text]O2peak [2.9 (1.8, 3.9) mL/kg/min], and PPO [9 (5, 14) W] with exercise, relative to controls (p < 0.001). Ninety-six studies (117 independent exercise interventions comprising 1,331 adults with SCI) were included in the secondary, pooled meta-analysis which demonstrated significant increases in A[Formula: see text]O2peak [0.22 (0.17, 0.26) L/min], R[Formula: see text]O2peak [2.8 (2.2, 3.3) mL/kg/min], and PPO [11 (9, 13) W] (p < 0.001) following exercise interventions. There were subgroup differences for R[Formula: see text]O2peak based on exercise modality (p = 0.002) and intervention length (p = 0.01), but there were no differences for A[Formula: see text]O2peak. There were subgroup differences (p ≤ 0.018) for PPO based on time since injury, neurological level of injury, exercise modality, and frequency. The meta-regression found that studies with a higher mean age of participants were associated with smaller changes in A[Formula: see text]O2peak and R[Formula: see text]O2peak (p < 0.10). GRADE indicated a moderate level of certainty in the estimated effect for R[Formula: see text]O2peak, but low levels for A[Formula: see text]O2peak and PPO. This review may be limited by the small number of RCTs, which prevented a subgroup analysis within this specific study design.

CONCLUSIONS

Our primary meta-analysis confirms that performing exercise >2 weeks results in significant improvements to A[Formula: see text]O2peak, R[Formula: see text]O2peak, and PPO in individuals with SCI. The pooled meta-analysis subgroup comparisons identified that exercise interventions lasting up to 12 weeks yield the greatest change in R[Formula: see text]O2peak. Upper-body aerobic exercise and resistance training also appear the most effective at improving R[Formula: see text]O2peak and PPO. Furthermore, acutely injured, individuals with paraplegia, exercising for ≥3 sessions/week will likely experience the greatest change in PPO. Ageing seemingly diminishes the adaptive CRF responses to exercise training in individuals with SCI.

REGISTRATION

PROSPERO: CRD42018104342.

Exercise Training Does Not Attenuate Cardiac Atrophy or Loss of Function in Individuals With Acute Spinal Cord Injury: A Pilot Study

OBJECTIVE

To investigate the effects of 2 modes of exercise training, upper-body alone, and the addition of electrical stimulation of the lower body, to attenuate cardiac atrophy and loss of function in individuals with acute spinal cord injury (SCI).

DESIGN

Randomized controlled trial.

SETTING

Rehabilitation Hospital.

PARTICIPANTS

Volunteers (N=27; 5 women, 22 men) who were <24 months post SCI.

INTERVENTIONS

Volunteers completed either 6 months of no structured exercise (Control), arm rowing (AO), or a combination of arm rowing with electrical stimulation of lower body paralyzed muscle (functional electrical stimulation [FES] rowing).

MAIN OUTCOME MEASURES

Transthoracic echocardiography was performed on each subject prior to and 6 months after the intervention. The relations between time since injury and exercise type to cardiac structure and function were assessed via 2-way repeated-measures analysis of variance and with multilevel linear regression.

RESULTS

Time since injury was significantly associated with a continuous decline in cardiac structure and systolic function, specifically, a reduction in left ventricular mass (0.197 g/month; P=.049), internal diameter during systole (0.255 mm/month; P<.001), and diastole (0.217 mm/month; P=.019), as well as cardiac output (0.048 L/month, P=.019), and left ventricular percent shortening (0.256 %/month; P=.027). These associations were not differentially affected by exercise (Control vs AO vs FES, P>.05).

CONCLUSIONS

These results indicate that within the subacute phase of recovery from SCI there is a linear loss of left ventricular cardiac structure and systolic function that is not attenuated by current rehabilitative aerobic exercise practices. Reductions in cardiac structure and function may increase the risk of cardiovascular disease in individuals with SCI and warrants further interventions to prevent cardiac decline.

Spinal cord injury impairs cardiac function due to impaired bulbospinal sympathetic control

Spinal cord injury chronically alters cardiac structure and function and is associated with increased odds for cardiovascular disease. Here, we investigate the cardiac consequences of spinal cord injury on the acute-to-chronic continuum, and the contribution of altered bulbospinal sympathetic control to the decline in cardiac function following spinal cord injury. By combining experimental rat models of spinal cord injury with prospective clinical studies, we demonstrate that spinal cord injury causes a rapid and sustained reduction in left ventricular contractile function that precedes structural changes. In rodents, we experimentally demonstrate that this decline in left ventricular contractile function following spinal cord injury is underpinned by interrupted bulbospinal sympathetic control. In humans, we find that activation of the sympathetic circuitry below the level of spinal cord injury causes an immediate increase in systolic function. Our findings highlight the importance for early interventions to mitigate the cardiac functional decline following spinal cord injury.

By combining experimental models with prospective clinical studies, the authors show that spinal cord injury causes a rapid reduction in cardiac function that precedes structural changes, and that the loss of descending sympathetic control is the major cause of reduced cardiac function following spinal cord injury.