In this single-center, prospective, double-blind, placebo controlled randomized clinical study, we demonstrated that TEAS on FeiShu (BL13) and ZuSanLi (ST36) could be a non-invasive complementary treatment to reduce lung injury following tourniquet-induced extremity ischemia-reperfusion in patients undergoing lower extremity surgery.
Limb ischemia-reperfusion injury is a common pathophysiological process mediated by multiple mechanisms and pathways. The application of tourniquet in lower extremity surgery causes limb ischemia-reperfusion injury, and at the same time, it also causes multiple distant organ damage, among which the lung is one of the most susceptible and harmful organs to insult due to their high perfusion, large contact area with air and sensitivity to inflammatory mediators such as oxygen free radicals. Many clinical studies have documented that the electric acupuncture treatment increases pulmonary ventilation and the mechanism is related with its effect of relieving local inflammation and mitigating small airway stenosis[20, 21]. Our previous research also demonstrated that electric stimulation at FeiShu (BL13) and ZuSanLi (ST36) acupoints could alleviate endotoxin shock-induced acute lung injury by reducing oxidative stress injury in rabbits. In the traditional Chinese Medicine theory, ZuSanLi (ST36) acupoint is highly praised in health care and clinical treatment for modulating the Qi-blood balance. Recent study proved that acupuncture at ZuSanLi (ST36) could alleviate neuroinflammation and persistent pain. In addition, FeiShu (BL13) locates along the sides of spine and close to the lungs, is the major acupoint for treating lung diseases. Study has shown that FeiShu acupoint application of cold asthma recipe has a greater advantage of absorption into blood circulation and lung distribution over non-FeiShu acupoint application. Thus, we hypothesized that TEAS at FeiShu (BL13) and ZuSanLi (ST36) acupoints could protect the lungs from tourniquet related I/R injury.
Increased pulmonary vascular permeability is usually considered the major pathological feature of limb I/R-induced lung injury, leading to ventilation dysfunction. A-aDO2 and RI can evaluate the pulmonary ventilation function reliably. In addition, A-aDO2 is a sensitive indicator of pulmonary diffusion function and pulmonary gas exchange efficiency in the early stage of ventilation insufficiency[24, 25]. OI indicates the lung ventilation function and oxygen utilization, is directly proportional to lung function. In our study, the decreased OI and the increased A-aDO2 and RI indicate the dysfunction of ventilation and oxygenation. Compared with the control group, TEAS could reduce the dysfunction of lung ventilation and oxygenation 4 h after removing the tourniquet(T4), which proves the exact efficacy on reducing lung injury.
The major pathological changes of limb I/R induced lung injury include extensive damage to alveolar epithelium and pulmonary vascular endothelium. However, the exact mechanism of the target cell injury remains unknown. Oxygen free radicals and lipid peroxidation damage are key factors in pathophysiological mechanism of ischemic damage. On the one hand, the integrity of cell ultrastructures and ion selectivity are destroyed by peroxidation with membrane unsaturated fatty acids; on the other hand, changes to the microenvironment of membrane binding enzyme receptors causes a series of irreversible degeneration such as intracellular calcium overload, thus resulting in the destruction of cell structure and function. MDA is a lipid peroxidation product of oxygen free radicals, indicating oxidative damage in pulmonary inflammation. SOD is an important enzyme for decomposing the oxygen free radicals and protects cells from injury. Studies have shown that electrical stimulation could increase SOD activity, reduce ROS production and regulate balance of oxidation-antioxidation system[29, 30]. The current data also suggests that TEAS increases the ability to scavenge the oxygen free radicals. Nitric oxide (NO), a pulmonary vasodilator, is proved to perform vital functions in inhibiting platelet adhesion and maintaining the endothelial structure and function. Endothelin-1 (ET-1) is an endogenous vasoconstrictor peptide that contributes to reducing endothelial injury. In this study, there is no significant difference between control group and TEAS group, suggesting that TEAS might have less impact on pulmonary vascular permeability. During the reperfusion following severe ischemia or hypoxia, a large amount of superoxide is generated from xanthine under the action of XOD, and polymorphonuclearneutrophils (PMN) accumulate in large quantities. PMN highly express myeloperoxidase (MPO), which reflects the aggregation of PMN in tissue. Nevertheless, excessive activation of PMNs contributes to inflammatory reaction further causes tissue injury. However, we did not observe obvious change in XOD or MPO when compared with the control group, maybe because the damage was relatively mild. Furthermore, various proinflammatory cytokines are released during inflammatory reaction induced by limb I/R, mediating systemic inflammatory reaction and causing organ damage. In our study, the plasma levels of ICAM-L IL-6 IL-8 IL-10 and TNF-a were increased after tourniquet release, while TEAS could reverse the inflammatory response. These results demonstrate that TEAS significantly reduces inflammation and increases the ability to scavenge the oxygen free radicals.
HO-1, expressed in almost all mammals, is considered as an early endogenous protective kinase. HO-1 serves as a protective gene with anti-inflammatory and anti-apoptotic properties, and has protective functions in several models of organ injury[35, 36]. Our previous study showed that HO-1/carbon monoxide protects lipopolysaccharide-exposed alveolar macrophages by reducing ROS generation. Research shows that activation of PKC-a/HO-1 signaling pathway increases SOD activity and diminishes ROS content in LPS-activated alveolar macrophage cells. Thus, the results in this study suggest that HO-1 is upregulated in lung injury and TEAS has a protective effect against I/R injury by possibly upregulating HO-1 expression.
We have several advantages in this study. First, it is a double-blind, placebo controlled randomized clinical study. Secondly, we use the blood gas data and several inflammatory and lung injury markers as objective indicators to evaluate the lung injury. Finally, we explore the potential mechanism for TEAS, providing a basis for further research. However, our research still has some limitations. One is the small sample size, and the other is that the mechanism of limb I/R-induced lung injury has not been fully elucidated yet. More basic and large sample clinical studies are needed in this field.