Cardiovascular Health and Exercise Following Spinal Cord Injury
Approximately 40,000 Canadians live with spinal cord injury (SCI) with roughly 1,050 new cases per year in Canada (Rick Hansen Spinal Cord Injury Registry 2004). In the United States, there are approximately 12,000 cases of SCI per annum (Foundation for Spinal Cord Injury Prevention 2009, Myers et al 2012). The majority of SCIs (80%) occur in individuals who are under 30 years of age (ICORD 2003, Rick Hansen Spinal Cord Injury Registry 2004). Persons with SCI currently have an increased life expectancy owing to improvements in medical treatment (Rick Hansen Spinal Cord Injury Registry 2004), and therefore, are susceptible to the same chronic conditions across the lifespan as able-bodied persons. In fact, cardiovascular disease (CVD) is the leading cause of mortality in both able-bodied individuals and persons with SCI (Whiteneck et al 1992). Unfortunately, there is considerable evidence indicating an earlier onset and/or prevalence of various chronic diseases (including CVD, type II diabetes, and osteoporosis) in persons with SCI (Yekutiel et al 1989, Whiteneck et al 1992, DeVivo et al 1993, Bauman et al 1999b, Groah et al 2001, Garshick et al 2005, Warburton et al 2007b). The prevalence rate of symptomatic CVD in SCI is 30–50% in comparison to 5%–10% in the general able-bodied population (Myers et al 2007). Moreover, the prevalence of asymptomatic CVD has been estimated to be 60%–70% in persons with SCI (Bauman et al 1993, Bauman et al 1994). It also appears that persons with SCI have increased CVD-related mortality rates and those with tetraplegia experience mortality at earlier ages in comparison to able-bodied individuals (Whiteneck et al 1992, DeVivo et al 1999, Myers et al 2007).These are alarming statistics, which place a significant burden upon the patient, his/her family, and society as a whole.
The separation of the autonomic nervous system from the superior brain centres after injury (exacerbated in lesions above T6) results in a series of changes that markedly affect the cardio-metabolic health of persons with SCI (Bravo et al 2004). Adrenergic dysfunction, poor diet, and physical inactivity are thought to play key roles in the elevated risk for CVD in SCI (Bravo et al 2004, Warburton et al 2007b).
Physical inactivity is a major independent risk factor for CVD and premature mortality (Warburton et al 2006, Warburton et al 2010). Unfortunately, physical inactivity and marked deconditioning are highly prevalent among persons with SCI (Jacobs and Nash 2004). Also, it appears that the ordinary activities of daily living are not adequate to maintain cardiovascular fitness in persons with SCI (Hoffman 1986). It is likely that low levels of physical activity and fitness (as a result of wheelchair dependency) explain (in part) the increased risk for CVD (Myers et al 2007). Marked inactivity associated with SCI has been associated with lower high-density lipoprotein (HDL) cholesterol (Schmid et al 2000, Manns et al 2005); elevated low-density lipoprotein (LDL) cholesterol (Schmid et al 2000); triglycerides (Schmid et al 2000, Manns et al 2005); total cholesterol levels (Schmid et al 2000); abnormal glucose homeostasis (Elder et al 2004, Manns et al 2005); increased adiposity (Elder et al 2004, Manns et al 2005);and excessive reductions in aerobic fitness (Schmid et al 2000, Manns et al 2005).It is important to note that SCI presents an additional risk for CVD above that seen in able-bodied individuals owing to the marked decrease in physical activity and injury-related changes in metabolic function (Bravo et al 2004). Moreover, a reduction in cardiovascular fitness may also lead to a vicious cycle of further decline leading to a reduction in functional capacity and the ability to live an independent lifestyle. Based on the available literature, it is clear that effective exercise interventions are required to slow the progression of multiple risk factors for CVD and other chronic diseases (e.g. obesity, type 2 diabetes) in persons with SCI.
The current chapter summarizes and updates the literature regarding the risk for CVD in persons with SCI. This chapter also critically evaluates the level of evidence regarding the effectiveness of varied forms of exercise rehabilitation in increasing cardiovascular fitness and attenuating the risk for CVD in persons with SCI. Table 1 contains a definition of the commonly used terms and/or abbreviations in this chapter.
Warburton DER, Sproule S, Krassioukov A, Eng JJ (2012). Cardiovascular Health and Exercise Following Spinal Cord Injury. In Eng JJ, Teasell RW, Miller WC, Wolfe DL, Townson AF, Hsieh JTC, Connolly SJ, Noonan V, Mehta S, Sakakibara BM, Boily K, editors. Spinal Cord Injury Rehabilitation Evidence. Version 4.0. Vancouver: p 1-43.