Medical research: Electrical stimulation helps control bleeding in rats

本期Scientific Reports上发表的一项研究提出，用微秒脉冲对大鼠的静脉和动脉进行电刺激，也许能帮助控制出血和减少不能通过压迫止血的伤口中的失血。还需要进一步的研究来确定该方法对人类患者是否有效，但该方法对于在外伤中或手术过程中控制不能通过压迫止血的出血也许会有用。

用止血带止血在战场上能帮助降低创伤死亡率，但该方法无法用于不能通过压迫止血的出血，包括流入体腔（如腹腔）中的出血，也不能用于躯干与四肢或颈部接合部的伤口。上个世纪70年代，人们发现给一个被夹住的血管施加直流电几分钟时间可诱导产生血栓。然而，这样所导致的热损伤使得该技术无法用在临床实践中。

Yossi Mandel和来自Daniel Palanker实验室的同事将微秒脉冲的电流施加到大鼠的大腿（腹股沟）区域和腹腔内的静脉和动脉上。这样使得这些血管中在几秒内发生血管收缩，但几分钟内血管又扩张回它们的本来大小。增强电流强度，血管被完全地、永久性地阻断。大鼠股动脉和腹部动脉中的血流速度降低，出血被迅速止住，股动脉的失血量与未经处理的大鼠相比减少7倍。作者在血管收缩后长达3.5小时未发现组织受到损伤，尽管还需要进行更长时间的跟踪观察来评估对组织是否会有任何潜在的长期影响。

Vasoconstriction by Electrical Stimulation: New Approach to Control of Non-Compressible Hemorrhage

Non-compressible hemorrhage is the most common preventable cause of death on battlefield and in civilian traumatic injuries. We report the use of microsecond pulses of electric current to induce rapid constriction in femoral and mesenteric arteries and veins in rats. Electrically-induced vasoconstriction could be induced in seconds while blood vessels dilated back to their original size within minutes after stimulation. At higher settings, a blood clotting formed, leading to complete and permanent occlusion of the vessels. The latter regime dramatically decreased the bleeding rate in the injured femoral and mesenteric arteries, with a complete hemorrhage arrest achieved within seconds. The average blood loss from the treated femoral artery during the first minute after injury was about 7 times less than that of a non-treated control. This new treatment modality offers a promising approach to non-damaging control of bleeding during surgery, and to efficient hemorrhage arrest in trauma patients.

Introduction

Trauma is the leading cause of death among US individuals younger than 44 years. Hemorrhagic shock accounts for 30–40 percent of traumatic mortality^{1, 2}. Bleeding is also the most common preventable cause of death on battlefield³. Applications of tourniquets to compressible hemorrhages^{4, 5, 6, 7, 8} caused a marked decrease in limb exsanguinations^{3, 4, 9}. As a result, according to the US army, hemorrhage not amenable to truncal tourniquets (also called non-compressible hemorrhage) is now the leading cause of preventable death³. Part of the non-compressible hemorrhages occur due to bleeding into body cavities (such as the abdomen or chest), while others are caused by wounds in the junction between the trunk and the limbs or neck. The latter ones, called junctional hemorrhages, are recognized as a care gap, and those of the pelvic, buttock and groin area are of highest prevalence¹⁰. Though Combat Gauze™ is endorsed by the US Army for bleeding care in areas not amenable to a tourniquet, it is often ineffective in junctional hemorrhages such as groin, gluteal, axilla, shoulder and others^{9, 4, 3, 10}. A novel mechanical compressing device, the Combat Ready Clamp, was recently introduced into the US Army^{3, 11}, but has not yet been proven clinically. This device cannot be applied to wounds of the head, neck, abdomen and chest.

Effective prevention of blood loss in the pre-hospital arena offers the best opportunity to save soldiers with non-compressible injuries¹², therefore major efforts are undertaken to develop technologies for this unmet need. In early 70 s, it was demonstrated that thrombosis can be induced in a clamped blood vessel by minutes-long application of direct electric current^{13, 14, 15}. However, associated thermal damage precluded the use of this technology in clinical practice. Reduction in blood perfusion during electro-chemotherapy was also noted previously, and it was found to enhance the antitumor effect of the chemotherapy^{16, 17}. More recently, constriction of blood vessels and thrombosis without thermal damage have been achieved with short (μs-ms) electric pulses¹⁸. However, these techniques have not been characterized in mammals, nor have they been evaluated for clinical use in various bleeding scenarios.

Recently we described significant decrease in blood loss from liver injury in rabbits treated by sub-millisecond electrical pulses¹⁹. The current study evaluates the effect of microsecond pulses on blood vessels in two areas non-amenable to truncal tourniquets: the groin area (femoral) and the abdominal cavity (mesenteric). We demonstrate significant vasoconstriction and decrease in blood loss following injury of these blood vessels. These results indicate a possibility of controlling non-compressible hemorrhage using non-thermal pulsed electrical stimulation.

Results

Constriction of femoral and mesenteric blood vessels

Stimulation current was applied to the exposed blood vessel via 2 mm diameter pipette electrode filled with saline, while a large pad return electrode was applied to skin on the back side on the animal via conductive gel. Biphasic (symmetric, anodic-first square) pulses of electric current with duration of 1 μs per phase, amplitude of 250 V and repetition rate of 10 Hz caused, within seconds, a very pronounced local constriction of both femoral (Figure 1a,b) and mesenteric (Figure 1c,d) arteries and veins. Extent of the constriction of femoral vessels in response to 10 seconds long stimulation at 1 Hz repetition rate is plotted in Figure 2, as a function of stimulus amplitude and duration. Vasoconstriction increased with higher pulse amplitude and longer duration for both arteries and veins. For all pulse durations tested, vessels diameter decreased with increasing pulse amplitude along a sigmoid curve, having a response threshold on the lower end, and reaching a minimum size of about 20–25% of the original diameter on the high end (Figure 2). Strength-duration dependence of the 25% and 50% constriction thresholds could be approximated by a power dependence t^−a, where a was approximately 0.3 for femoral arteries and veins (Figure 3). For all pulse durations, lower voltage was required to reach similar constriction in arteries, compared to veins, although the difference decreased at longer durations.