| Background: when battleplane or space shuttle accelerates, pilots or astronaut could be exposed to rather high +Gz acceleration defined as acceleration along foot-to-head direction. The blood of the body will be redistributed and flow toward the direction of inertia force, to the lower body, which could produces cerebral ischemia and even loss of consciousness (G-LOC). G-LOC is a severe threat to aviation safeies. In addition, the tolerance of +Gz is decreased if–Gz, 0Gz suddenly switch to +Gz during the fly, which is called as―push-pull effect, PPE‖. Therefore, in this situation,G-LOC phenomenon more easily happened comparing with pure +Gz. At present,the preventive methds against +Gz mainly adopt anti-G devices and anti-G straining maneuvers (AGSM) to maintain the blood supply of brain against G-LOC during +Gz acceleration. Unfortunately, currently available methods against G-LOC do not result in sufficient symptomatic improvement. So, it is a so urgent task to explor novel, convenient and effective methord against G-LOC.Our previous studies have demonstrated that electroacupuncture (EA) could mimic cerebral ischemia pretreatment to enhance brain tolerance of ischemia. Cerebral ischemia is main factor to cause G-LOC. Consequently, it is reasonable to speculate that EA can reduce the occurrence of G-LOC by enhancing the cerebral tolerance to hypoperfusion/ischemia. The present study is to explore different schemes of EA against G-LOC mimicked by a combination of using tilt table and lower body negative pressure (LBNP). Furthermore, in human centrifuge, we further test effect of EA against G-LOC during +Gz acceleration and PPM. The studies could provide novel insight and theoretical evidence for further elucidation of the effectiveness of EA.Part 1 Electroacupuncture could ameliorates G-LOC in a combination of tilt table and lower body negative pressureMethods1. The prevention effect of G-LOC by a single 30 min EA performed before the head-up tiltTo ensure the best comparison, a randomized, controlled, crossover design was taken in the protocol 1, in which every volunteer was tested 3 times. Twenty healthy volunteers were randomly allocated to the Con, Acupoint and Non-acupoint groups. Con group: non-acupoint; Acupoint: bilateral EA at the Neiguan (PC 6), volunteers were subjected to head-up tilt (HUT) /LBNP test immediately after a single 30 min EA treatment; Non-acupoint: bilateral EA at a non-acupoint of both shoulders. Blood pressure, heart rate, heart rate variability (HRV), plasma catecholamine, bispectral index (BIS) and cerebral blood flow velocity (CBFVmax) were measured.2. The prevention effect of G-LOC by the EA performed at the beginning of the head-up tiltTo ensure the best comparison, a randomized, controlled, crossover design was taken in the protocol 2, in which every volunteer was tested 3 times. Ten healthy volunteers were randomly allocated to the Con, Acupoint and Non-acupoint groups. Con group: non-acupoint; Acupoint: bilateral EA at the Neiguan (PC 6), volunteers were subjected to HUT/LBNP test while receiving EA; Non-acupoint: bilateral EA at a non-acupoint of both shoulders. Blood pressure, heart rate, heart rate variability (HRV), plasma catecholamine, bispectral index (BIS) and cerebral blood flow velocity (CBFVmax) were measured.3. The prevention effect of G-LOC by the EA was performed for 5d before head-up tilt improves G-LOCTwenty volunteers were randomly divided into EA group and Control group. Ten volunteers were tested after repeated bilateral EA at the Neiguan for 30 minutes daily for 5 consecutive days, with final pretreatment 24 hours prior to the HUT /LBNP test (EA). The other 10 volunteers were treated with no acupuncture prior to the HUT/LBNP test (Con). Blood pressure, heart rate, heart rate variability (HRV), bispectral index (BIS) and cerebral blood flow velocity (CBFVmax) were measured.Results1. When the single 30min EA was performed immediately before HUT and LBNP (protocol 1) compared to control and non-acupoint, the orthostatic tolerance time in acupoint group was significant longer than that in the Con group and Non-acupoint group. EA also could increase stroke volume (SV) and middle cerebral artery maximum velocity (Vmax) and velocity time integral (VTI) in the supine position compared to the Con and non-Acupoint. EA at acupoint decreased the high-frequency ranges of R-R interval and increased the low-frequency ranges of R-R interval in the supine position. The plasma noradrenalin and adrenalin concentration increased from baseline 20 min after EA stimulation at acupoint and continuously increased during HUT and LBNP (P<0.05 compared with control and non-acupoint). The BIS in acupoint group was significant better than that in the Con group and Non-acupoint group.2. When the single EA was performed during HUT/LBNP (protocol 2), the orthostatic tolerance time in acupoint group was significant longer than that in the Con group and Non-acupoint group. EA with acupoint blunted the decrease of SV during HUT/LBNP (P<0.05 compared with Con and non-acupoint). The Vmax and VTI in acupoint group was significant increase than that in the Con group and Non-acupoint group. EA at acupoint decreased the high-frequency ranges of R-R interval and increased the low-frequency ranges of R-R interval in the supine position. The plasma noradrenalin and adrenalin concentration increased from baseline 20 min after EA stimulation at acupoint and continuously increased during HUT and LBNP (P<0.05 compared with control and non-acupoint). The BIS in acupoint group was significant better than that in the Con group and Non-acupoint group.3. After the repeated EA pretreatment (protocol 3), the orthostatic tolerance time in acupoint group was significant longer than that in the Con group and Non-acupoint group. Repeated EA at acupoint also blunted the decrease of Vmax and VTI at 10min after HUT and LBNP compared with Con. However, SV, HRV showed no significant differences during HUT and LBNP between any two groups.Part 2 Electroacupuncture could ameliorates G-LOC in human centrifugeMethods1. EA could ameliorates +Gz exposure in human centrifuge Via randomized, controlled, and crossover fashion. Seven healthy volunteers were randomly allocated to the Con group and EA group. Con group: non-acupoint; EA: bilateral EA at the Zusanli (ST 36), Mean heart rate (MAR), heart rate variability (HRV), +Gz tolerance, peripheral light loss (PLL), plasma catecholamine and bispectral index (BIS) were measured.2. EA could ameliorates PPE in human centrifage Via randomized, controlled, and crossover fashion. Seven healthy volunteers were randomly allocated to the Con group, EA. Con group: non-acupoint; EA: bilateral EA at the Zusanli (ST 36), +Gz tolerance, Mean heart rate (MAR) and heart rate variability (HRV) were measured.Results1. In +Gz exposure, the +Gz tolerance in EA group (4.7±0.2Gz) was significant longer than that in the Con group (3.9±0.1Gz); The PLL time in EA group was significant longer than that in the Con group. According to the HRV, low frequency (LF)/high frequency (HF) in Con group was significantly less than EA. However, MHR, BIS and plasma noradrenalin and adrenalin concentration showed, there was no significant difference between in Con and EA.2. In PPE, the +Gz tolerance in EA group (3.57±0.2Gz) was significant longer than that in the Con group (2.75±0.09Gz); According to the HRV, low frequency (LF)/high frequency (HF) in Con group was significantly less than EA. However, BIS showed, there was no significant difference between in Con and EA.ConclusionSingle and repeated EA pretreatment at Neiguan and Zisanli are both highly effective in improving orthostatic tolerance. Activating peripheral sympathetic nervous system and improving cardiac and brain function are largely responsible for improved orthostatic tolerance after the single EA, whereas the repeated EA improved orthostatic tolerance primarily via increasing brain ischemia tolerance. It suggested that EA can increase +Gz tolerance. EA pretreatment represents a novel potential prophylaxis against G-LOC.
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