Characterization of acute ischemia‐related physiological responses associated with remote ischemic preconditioning: a randomized controlled, crossover human study

Remote Ischemic Preconditioning (RIPC) is emerging as a new noninvasive intervention that has the potential to protect a number of organs against ischemia-reperfusion (IR) injury. The standard protocols normally used to deliver RIPC involve a number of cycles of inflation of a blood pressure (BP) cuff on the arm and/or leg to an inflation pressure of 200 mmHg followed by cuff deflation for a short period of time. There is little evidence to support what limb (upper or lower) or cuff inflation pressures are most effective to deliver this intervention without causing undue discomfort/pain in nonanesthetized humans. In this preliminary study, a dose-response assessment was performed using a range of cuff inflation pressures (140, 160, and 180 mmHg) to induce limb ischemia in upper and lower limbs. Physiological changes in the occluded limb and any pain/discomfort associated with RIPC with each cuff inflation pressure were determined. Results showed that ischemia can be induced in the upper limb at much lower cuff inflation pressures compared with the standard 200 mmHg pressure generally used for RIPC, provided the cuff inflation pressure is ~30 mmHg higher than the resting systolic BP. In the lower limb, a higher inflation pressure, (~55 mmHg > resting systolic BP), is required to induce ischemia. Cyclical changes in capillary blood O2, CO2, and lactate levels during the RIPC stimulus were observed. RIPC at higher cuff inflation pressures of 160 and 180 mmHg was better tolerated in the upper limb. In summary, limb ischemia for RIPC can be more easily induced at lower pressures and is much better tolerated in the upper limb in young healthy individuals. However, whether benefits of RIPC can also be derived with protocols delivered to the upper limb using lower cuff inflation pressures and with lesser discomfort compared to the lower limb, remains to be investigated.