Electrical stimulation (ES) has been used since the 1960s to enhance healing of various chronic wounds including pressure ulcers 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 ulcer prevention post SCI.
Given that the primary cause of pressure ulcers 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 ulcers 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 ulcer prevention (Levine et al. 1990; Bogie et al. 1995; 2000; 2006).
Several articles were found that 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 change in ischial pressure reduction. 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 seat 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.
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 relief. They found that an on-off ES ratio of 1:4 seconds (versus 1:1 seconds) provided better IT pressure relief (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 relief 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).
It is encouraging that study subjects scored the usability of the ES shorts as satisfactory (Smit et al. 2013a) as this represents progress for the feasibility of ES in clinical and daily living situations. 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 relief 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 relieving movements making ES potentially more effective for pressure relief 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.
There is level 2 evidence (from one prospective controlled trial and one cohort study; 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 pressures post SCI.
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 a 1993; Bogie & Triolo 2003) that electrical stimulation may increase tissue oxygenation post SCI.
Electrical stimulation likely decreases ischial pressures.
Electrical stimulation may increase blood flow to tissues.
Electrical stimulation likely increases tissue oxygenation.
Electrical stimulation likely helps to prevent pressure ulcer formation or progression by reducing ischial pressures and increasing tissue oxygenation.