Electrical Stimulation
Electrical stimulation (ES) has been used since the 1960s to enhance healing of various chronic wounds including pressure injuries in both able-bodied and SCI individuals (Kloth & Feeder 1988; Baker et al. 1996; Bogie et al. 2000). More recently, ES has been studied to assess its potential for pressure injury prevention post SCI.
Given that the primary cause of pressure injuries is postulated as externally applied pressure over bony prominences such as the IT (Bogie et al. 1995), researchers have studied the role of ES in reducing ischial pressures and redistributing seating interface pressures towards prevention (Bogie et al. 2006). ES-related prevention of pressure injuries in individuals with SCI are directed at skin versus muscle stimulation, dynamic versus long-term effects and surface versus implanted devices (Levine et al. 1990; Bogie et al. 2000; Bogie et al. 2006).
ES also has the ability to change blood flow to skin and muscle. Bogie et al. (2006) state that with increasing interface pressures over bony prominences, regional blood flow is adversely affected. By reducing IT pressure, regional blood flow could be improved and in turn, tissue health could be useful in pressure injury prevention (Levine et al. 1990; Bogie et al. 1995; 2000; 2006).
Smith et al. (2016) completed a literature review focused on electrical stimulation use for prevention of pressure injuries (n=34). In their review the authors noted variability in the studies with stimulation frequencies, intensities, pulse duration, stimulation parameters and sites. These findings are consistent with the systematic review completed by Liu et al. (2014) related to electrical stimulation in the prevention and treatment of pressure injuries (n=16). (The findings related to treatment from the Liu et al. review are highlighted in the related section of this chapter). Smit et al. report that there wasn’t evidence to support that electrical stimulation prevents pressure injury development, however, they do suggest there is moderate evidence to support positive changes in blood flow and/or oxygenation, muscle volume and ischial tuberosity pressure related to use of electrical stimulation for prevention.
Discussion
Several articles examined the effects of ES on ischial pressure. Ferguson et al. (1992) used functional electrical stimulation (FES) on the quadriceps of restrained lower legs in seated SCI subjects and found a significant reduction in ischial pressure. However, the authors were not able to provide recommendations for stimulation frequency and duration parameters based just on this small (N=9) preliminary study. Bogie and Triolo (2003) studied changes in interface pressure distribution at the support/surface interface following eight weeks of gluteal neuromuscular electrical stimulation (NMES) delivered via an implanted neuroprosthesis. With NMES, mean ischial regional interface pressure tended towards a uniform decrease in post-exercise pressures (p<0.01).
Liu et al. (2006b) studied the effects of ES delivered via an implanted sacral anterior root stimulator on sitting surface interface pressure distribution. With ES functional magnetic stimulation of the S2 nerve root, sufficient to result in gluteal muscle contraction, there was an average decrease of 33% in peak pressure (p<0.01) and a 38% decrease in gradient peak pressure (p<0.05) at the IT of the seated participants. Liu et al. (2015) compared sitting surface pressure changes across 3 ES modalities; 1) functional magnetic stimulation (FMS), 2) Fintech-Brindley sacral anterior root stimulator implant (SARS), and 3) surface functional electrical stimulation (FES). They found that during stimulation there was a significant decrease in peak pressures and in the gradient at peak pressures at the ischial tuberosities for all modalities.
Smit et al. (2013a) sought to understand the effect of varying ES parameters applied for three hours to the gluteal and hamstring muscles via a custom-made electrode garment (i.e., shorts) with built-in electrodes to achieve IT pressure reduction. They found that an on-off ES ratio of 1:4 seconds provided better IT pressure reduction (versus 1:1 seconds) (32% reduction; p=0.04) without marked muscle fatigue. Study subjects also provided feedback that the ES shorts were satisfactory for daily use. An earlier study revealed that ES of the gluteal muscles alone and in combination with the hamstring muscles both provided pressure reduction around the IT (Smit et al. 2012); the latter was more effective (p=0.01). When stimulating the gluteal muscles alone, there was no reported difference between two different stimulation protocols on decreased interface pressure in seated people with SCI (van Londen et al. 2008).
Despite the usability of the ES shorts reported by Smit et al. (2013a), Smit et al. (2013b) found that ES-induced muscle activation was not as effective as pressure redistribution movements on IT pressure, and on blood flow and oxygenation of the gluteal and hamstring muscles. However, the frequency of ES is much higher and more reliable than the performance of pressure reduction movements making ES potentially more effective for pressure reduction in the long term. Gyawali et al. (2011) did present evidence to show that intermittent ES resulted in some improved tissue oxygenation in addition to significant pressure redistribution in loaded muscles of individuals with SCI. Mawson et al. (1993; N=29) also found that sacral tissue oxygen levels were 35% higher (p<0.001) after 30 minutes of high voltage pulsed galvanic stimulation.
Conclusion
There is level 2 evidence (from two prospective controlled trials and one cohort study: Lui et al. 2015; Lui et al. 2006b; Ferguson et al. 1992); supported by level 4 evidence (from five pre-post studies, and two case series studies: Smit et al. 2012, 2013a, 2013b; Gyawali et a. 2011; Bogie & Triolo 2003; Van London et al. 2008; Liu et al. 2006a) that electrical stimulation decreases ischial peak pressures during stimulation.
There is level 4 evidence (from one pre-post study: Bogie & Triolo 2003) that electrical stimulation may increase blood flow at sacral and gluteal areas post SCI.
There is level 2 evidence (from two prospective controlled trials and one pre-post study: Lui et al. 2006a; Mawson et al. 1993; Bogie & Triolo 2003) that electrical stimulation may increase tissue oxygenation post-SCI.
