Ischemic preconditioning (IPC) was first described in 1986 as a vascular stimulus to protect vital organs from ischemic injury and has been extensively studied in animal models and humans for its potential to promote cardioprotection from ischemia (see review by Heusch et al. [
44]). Since IPC was first described over three decades ago, other groups have shown that IPC, when applied to the arm or leg (known as remote ischemic preconditioning, or RIPC) of healthy individuals with a standard blood pressure cuff inflated to 225 mmHg for 5 min on-off intervals, can promote muscle fatigue resistance [
45], increase athletic performance [
46‐
49], and promote motor learning [
50]. It is important to note that in most of these studies, the effect sizes of RIPC to promote athletic performance are relatively small (improvements between 2 and 5%); however, these studies were performed in young, healthy individuals; thus, a ceiling effect likely exists. Recently, the effects of RIPC on motor function and muscle performance in patient populations with reduced physical capacity (chronic stroke survivors) were examined for the first time, and those studies showed the positive effects of RIPC to promote strength [
51••] and reduce neuromuscular fatigue [
52••] far exceed those reported in healthy volunteers and occur in as little as 2 weeks [
52••]. Furthermore, in chronic stroke, individuals with the slowest self-selected walking speed and largest strength deficits tended to show the most improvement in muscle strength following RIPC [
51•]. Despite these promising results, the effects of RIPC on physical function and measures of frailty in the elderly population are still largely unknown. However, these previous findings, coupled with the fact that RIPC is low risk, low cost, easy to perform, and well tolerated makes RIPC an attractive alternative to traditional aerobic exercise to improve functional capacity in the frail patient in the preoperative period.
The underlying mechanisms of RIPC are inherently complex and involve neuronal, humoral, and local pathways [
53,
54]. It is accepted that ischemia and subsequent reperfusion of a remote limb causes the release of cardioprotective substances, as evidenced by the fact that organ protection is observed in animals that have received blood transfusions from preconditioned donors [
55]. It is hypothesized that organ protection from RIPC may depend on improvements in vascular function as RIPC has been shown to improve brachial artery flow-mediated dilation (FMD) in humans [
56] and our own preliminary data shows that RIPC improves brachial artery FMD in chronic stroke survivors. Further, RIPC has been demonstrated to reduce the rate of acute kidney injury following cardiac surgery [
57]; therefore, RIPC may not only decrease frailty and improve postoperative physical function but may also have more broad beneficial effects on cardiovascular health as well. Although it is well established that RIPC improves vascular endothelial function (FMD) and prevents end-organ damage in the perioperative period, whether preoperative RIPC can prevent postoperative vascular dysfunction or increase functional capacity remains unknown.