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OBJECTIVE@#To observe the effect of high positive acceleration (+Gz) environment on dental implant osseointegration in a rabbit model and to investigate its mechanism.@*METHODS@#Forty-eight New Zealand white rabbits were randomly divided into 6 groups. The rabbit's mandibular incisors were extracted and 1 implant was placed in each socket immediately. After 1 week of rest, the rabbits were exposed to a high +Gz environment, 3 times a week. The rabbits were sacrificed at 3 weeks (2 weeks +Gz exposure), 5 weeks (4 weeks +Gz exposure), and 12 weeks (4 weeks +Gz exposure and 7 weeks normal environment) after surgery, respectively. Specimens were harvested for micro-CT scanning, histological analysis, and real-time polymerase chain reaction examination.@*RESULTS@#Compared with those in the control group, the mRNA expression levels of bone morphogenetic protein-2 (BMP-2), osteopontin (OPN), and transforming growth factor-β1 (TGF-β1) were significantly lower (P < 0.05), while the mRNA expression level of receptor activator of nuclear factor κB ligand (RANKL) and the RANKL/osteoprotegerin (OPG) ratio were significantly higher (P < 0.05) at 3 weeks; values of bone volume fraction, trabecular number, bone-implant contact (BIC), and TGF-β1 and OPG mRNA expression levels were significantly lower (P < 0.05), and the value of trabecular separation, RANKL mRNA expression level and RANKL/OPG ratio were significantly higher (P < 0.05) at 5 weeks; and the value of BIC was still significantly lower (P < 0.05) at 12 weeks in the experimental group.@*CONCLUSION@#Early exposure to the high +Gz environment after implant surgery might have an adverse effect on osseointegration, and its mechanism could be related to the inhibition of osteoblast activity and promotion of osteoclast activity.
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Objective To explore the effect of positive acceleration (+Gz) on immune barrier of intestinal mucosa in rats. Methods Thirty two male SD rats were randomly divided into 4 groups (8 each): Group A (control group), Group B (+5Gz group), Group C (+10Gz group) and Group D (repeated exposure group). The animal centrifuge was used to simulate the exposure of acceleration. Group A was no disposed. +5Gz group and +10Gz group were subjected to centrifugal force of +5Gz and +10Gz respectively for 5min; repeated exposure group was continuously exposed to 1.5min under +5Gz value, 2min under +10Gz value and 1.5min under +5Gz. All groups were exposed to the respective acceleration once daily for 5 days. The damage of intestinal mucosa was observed by light microscopy after the experiment was finished, and the content of sIgA in intestinal mucosa was detected by ELISA. Results Except for group A, intestinal mucosal injury was observed in the other three groups. Group D was shown as the most serious one, followed by group C and group B. Compared with group A, the level of sIgA was significantly lower in other three groups (P<0.05). The level of sIgA in group C was significantly lower than that in group B (P<0.05) and higher than that in group D (P<0.05). Conclusion +Gz exposure can result in intestinal injury and weaken the function of immune barrier of intestinal mucosa in rats.
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The prevention of myocardial and brain dysfunction induced by positive acceleration (+Gz) exposure is the focus in the field of aerospace medicine research topic .The characteristics and mechanisms that +Gz exposure caused damages to vital organs such as heart and brain remain to be further elucidated .The research literature about +Gz acceleration exposure-induced heart and brain injuries in experimental animals and its mechanisms at home and abroad was reviewed in this paper .
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Objective To investigate the effect of positive acceleration (+Gz) on monophasic action potential duration of 90%repolarization( MAPD90 ) and transmural dispersion of repolarization ( TDR) in ventricles of rabbits and to explore the cellular electrophysiologic mechanism of tachyarrhythmia induced by positive acceleration .Methods Twenty-four healthy, male New Zealand white rabbits were randomly and equally divided into control group and +Gz group.The +Gz group rabbits were given +8 Gz exposure, 1 min a time, 3 times a day,and a total of 7 days.The two groups were subjec-ted to Holter monitoring at the same time to observe the incidence of tachyarrhythmia .Using the monophasic action potential ( MAP) recording technology , the MAP of the left ventricle was recorded while MAPD 90 and TDR were measured .By using Burst stimulation method , the right ventricular anterior wall of the rabbits was stimulated , and the incidence of tachya-rrhythmia was observed .Results The Holter record showed that the incidence of tachyarrhythmias in +Gz group was 55%(6/11), but the control group did not have any case of tachyarrhythmias .Compared with the control group ,MAPD90 of en-docardial and epicardial cells was significantly decreased in the +Gz group, while MAPD90 of middle myocardial cells did not change significantly ,but TDR was increased obviously .Four rabbits in +Gz group suffered from tachyarrhythmias dur-ing Burst stimulation ,and the incidence of tachyarrhythmias was 40% ( 4/10 ) .Conclusion +Gz exposure can increase the incidence of tachyarrhythmias .The shortened MAPD90 of ventricular muscle cells and the increased TDR may be the cell electrophysiological mechanisms of tachyarrhythmias induced by +Gz.
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Objective To investigate the effect of repeated and prolonged +Gz exposure on endocrine function of vessel in a rabbit model of atherosclerosis. Methods Twenty-four male New Zealand white rabbits were used to establish the model of atherosclerosis, and then randomly divided into control group and +Gz exposure group (12 each). Animals in control group underwent no +Gz exposure, while those in +Gz exposure group underwent +Gz exposure for 4, 8, and 12 weeks respectively (4 animals at each time point), and 4 animals from each group were sacrificed at each time point. The levels of angiotensin II (Ang II), endothelin (ET), heme oxygenase-1 (HO-1), carbon monoxide (CO) and cyclic guanosine-3', 5'-monophosphate (cGMP) were measured by radioimmunoassay and biochemical method, and the ultrastructure of aortic intima was examined by electron microscopy. Results Along with the prolongation of +Gz exposure, the contents of Ang II, ET, HO-1, CO and cGMP were increased in +Gz exposure group (P<0.05), but the increase stopped at the 12th week, and no obvious change in the above indices was observed in control group (P=0.05). The foam cells and collagen content under the aortic intima and in the shallow layer of aortic media were slightly increased in control group, but the foam cells and the interstitial collagen fibers were greatly increased after +Gz exposure for 8 and 12 weeks as compared with that in control group. Conclusion Repeated and prolonged +Gz exposure may induce the production of Ang II and ET, increase the secretion of HO-1, CO and cGMP, thus play a potential role in protecting the vessels from further injuries.
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Objective To investigate the effect of repeated and prolonged +Gz exposure on endocrine function of vessel in a rabbit model of atherosclerosis. Methods Twenty-four male New Zealand white rabbits were used to establish the model of atherosclerosis, and then randomly divided into control group and +Gz exposure group (12 each). Animals in control group underwent no +Gz exposure, while those in +Gz exposure group underwent +Gz exposure for 4, 8, and 12 weeks respectively (4 animals at each time point), and 4 animals from each group were sacrificed at each time point. The levels of angiotensin II (Ang II), endothelin (ET), heme oxygenase-1 (HO-1), carbon monoxide (CO) and cyclic guanosine-3', 5'-monophosphate (cGMP) were measured by radioimmunoassay and biochemical method, and the ultrastructure of aortic intima was examined by electron microscopy. Results Along with the prolongation of +Gz exposure, the contents of Ang II, ET, HO-1, CO and cGMP were increased in +Gz exposure group (P<0.05), but the increase stopped at the 12th week, and no obvious change in the above indices was observed in control group (P=0.05). The foam cells and collagen content under the aortic intima and in the shallow layer of aortic media were slightly increased in control group, but the foam cells and the interstitial collagen fibers were greatly increased after +Gz exposure for 8 and 12 weeks as compared with that in control group. Conclusion Repeated and prolonged +Gz exposure may induce the production of Ang II and ET, increase the secretion of HO-1, CO and cGMP, thus play a potential role in protecting the vessels from further injuries.
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Objective To explore the effect of hyperbaric oxygen (HBO) preconditioning on learning and memory damage induced by high positive acceleration( + Gz) exposure in rats.Methods Thirty-two male Sprague-Dawley rats were randomly divided into four groups with 8 in each group: control group( Con), + Gz group,HBO group and HBO-+ Gz group.Rats of Con group were given 5d( 1 ATA ,21% O2, 1h/d); Rats of + Gz group was exposed to + 10Gz for 5 min; HBO group were only given 5d (2.5 ATA, 100% O2,1 h/d); HBO-+ Gz group were given HBO 5 consecutive days,and then suffered +Gz exposure.Morris water maze was used to observe the navigation and probe capabilities of rats.Results In the spatial acquisition test,there exist significant difference among these groups(F(3.28) = 5.325, P＜ 0.01 ).Compared with the control group, the escape latency increased significantly in the + Gz group and HBO-+ Gz group (P＜0.05) while had no difference in HBO group.HBO-+ Gz group had significantly shorter escape latency than + Gz group (P＜0.05).In the probe test,compared with the control group, + Gz group and HBO-+ Gz group had a longer percentage in the target quadrant( (43.71 ± 3.29 ) %vs (28.65 ±1.00)%, P＜0.05;(43.71 ±3.29)% vs (37.17 ±0.98)%, P＜0.05)),and HBO-+Gz group was better than + Gz group.Conclusion HBO preconditioning may have a protective effect on the impairment of learning and memory caused by + Gz exposure in rats.
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Pilots are usually under various different mechanical loads during flights, which can affect their musculoskeletal and cardiovascular system and even bring them injuries. Biomechanics mainly studies the mechanics and mechanobiology in medicine and biology. Aviation biomechanics studies the physiological response to different complicated mechanical loads during flights and the countermeasures. The research fields of aviation biomechanics include: mechanical loads on human body injury and related countermeasures, durative loads, vibration and noise on the physiological effects of human body and related comtermeasures, etc.
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BACKGROUND: The physiological change of positive acceleration is primarily focused on the hydrostatic column effects that are associated with acceleration exposures. IOP values during positive acceleration is reduced according to this theory. However, the first trial of IOP measurement during positive acceleration showed that there were no significant changes in IOP values during the +2G phase of parabolic flight. In addition, IOP study during centrifuge exposures showed that there were significant increases in IOP during +2Gz and +3Gz. Therefore, the purpose of this study is to investigate the effect of positive acceleration on IOP. METHODS: The data from 4 normal subjects (2 men and 2 women) were included in this study. The baseline IOPs of subjects were within normal range. The subjects did not wear anti-G suits and use anti-G maneuver during the acceleration exposure. Pressure phosphene tonometer was used to measure IOP. To minimize the difference between the Goldmann tonometer and the pressure phosphene tonometer, IOPs were measured in subjects for 1 week prior to this study. IOP measurements of protocol 1 were obtained with pressure phosphene tonometer at +1Gz (baseline), +2Gz, +3Gz, +4Gz, and again at +1Gz (post). IOP measurements of protocol 2 were obtained at + 1Gz (baseline), +3Gz, and again at +1Gz (post). IOP measurements of protocol 3 were obtained at + 1Gz (baseline), +4Gz, and again at +1Gz (post). A total of 55 IOP measurements for each subject were made. RESULTS: The result showed that there was a significant difference in the means of IOP in protocol 1, 2, and 3 (P<0.05). But, they did not show an increasing or decreasing trend according to increase in acceleration. In particular, subject 1 showed that there was significant decrease of IOP in protocol 1, 2, and 3 compared to the baseline IOP measurements during positive acceleration(P<0.05). Based on symptom questionnaire and VTR review, variable body contractions may affect the IOP measurements during acceleration. There were significant differences in the means of IOP among variable body contractions in subject 1 when compared to the baseline IOP measurements. CONCLUSIONS:Persistent decreases of IOP in subject 1 suggest that the mechanism of IOP changes under positive acceleration could be explained by the hydrostatic column effect. In addition, interpretation for IOP measurements under positive acceleration should be cautious due to variable muscle contraction.
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Humans , Male , Acceleration , Intraocular Pressure , Muscle Contraction , Phosphenes , Reference Values , Surveys and QuestionnairesABSTRACT
Objective To observe changes of expression level of HSP70 protein in rat hippocampus after exposure to +Gz of different magnitudes and to investigate the machanism of HSP70 protein induced by +Gz exposure.Method One hundred rats were divided into: control group,+2 Gz group,+6 Gz group and +10 Gz group.The experimental rats were exposed to +2 Gz,+6 Gz and +10 Gz for 3 min respectively.The rats were killed 6 h,1 d,2 d,4 d,6 d after exposure and brain specimens were made for examination under microscope.The changes of HSP70 protein expression level were determined with immunohistochemical technology.Result The HSP70 protein expression level in the 3 experimental groups were significantly higher than that in control group.It began to rise 6 h after exposure,reached the peak after 1 d,and resumed to normal 6 d after exposure.The expression level was the highest in +6 Gz group and the lowest in +10 Gz group.Conclusion +Gz exposure can induce obvious changes of HSP70 protein expression level and the most prominent changes are found in rats after exposure to +6 Gz group.
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Objective To investigate changes of learning ability and somatostatin (SS) changes after positive acceleration (+Gz) exposures. Mehtod Eighty male SD rats were randomly divided into 3groups: control group(Con), +6 Gz/3 min group ( +6 Gz), and +10 Gz/3 min group ( +10 Gz),8 rats in each group. Changes of learning ability in rats were observed at 0 d, 2 d, 4 d and 6 d after + Gz exposure. SS in hippocampus was measured by RIA at 0 d, 2 d and 4 d after + Gz exposures ( there were 8 rats every time, in each group). Result In Y-maze test,number of correct response decreased significantly (P ＜0.01 ), and total reaction time increased significantly(P ＜0.01 ) in +6Gz and +10 Gz groups as compared with control group; number of correct response and total reaction time in +10 Gz group changed significantly at 0 d(P ＜0.01 or P ＜0.05) as compared with +6Gz group. RIA showed that, content of SS in hippocampus declined at 0 d and 2 d(P ＜0.05 or P ＜0.01) in +6 Gz and + 10 Gz groups as compared with control group. Conclusion + Gz exposure could impair learning ability of rats, and inhibit expression of SS in hippocampus.
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BACKGROUND: Pilots of tactical aircraft are exposed to sustained accelerations ranging from -1Gz to +9Gz. Pilots are routinely exposed to +2 and +3Gz. It has been known that chronic elevations in intraocular pressure (IOP) are associated with the development of visual impairments, which could lead to a damage of optic nerve fibers with subsequent visual field defects. This IOP alteration may be caused by body fluid shifts resulting from acceleration forces. The IOP, theoretically, will be increased under negative Gz acceleration resulting from cephalad shift of body fluid and should not be increased under positive Gz accelerations according to hydrostatic column effects. However, there is little research regarding intraocular pressure changes during acceleration forces. Therefore, this study was designed to evaluate IOP effects of exposure to +2 Gz, +3 Gz, and -1Gz environments. METHODS: Intraocular pressures were measured on 3 subjects (2 men and 1 woman) during +2Gz, +3Gz, and -1Gz centrifuge exposures on the Dynamic Environment Simulator (DES) centrifuge. Two IOP measurements were obtained with the Ocuton S self-tonometer at +1Gz (Pre-baseline), +2Gz, +3Gz, -1Gz, and again at +1Gz (Post-baseline). A total 60 measures were obtained under +1Gz, + 2Gz, + 3Gz, and -1Gz. RESULTS: The result showed that there was a significant difference in the means for percent change of IOP from pre-baseline to +2Gz, +3Gz, and -1Gz. The mean IOP increased by 19.5% during +2Gz acceleration when compared to pre-baseline (16.3 vs. 19.5 mmHg, P=0.0001). The mean IOP of +3Gz level was 30.2% higher than that of pre-baseline level (16.3 vs. 21.2 mmHg, P=0.0001). The mean of IOP increased 127.9% during -1Gz when compared to baseline values (16.3 vs. 37.1 mmHg, P=0.0001). However, there was no significant difference in IOP between pre-baseline and post-baseline (16.3 vs. 16.0 mmHg, P=0.4261). There were significant differences, in percent change from pre-baseline, among the +2Gz, +3Gz, and -1Gz conditions {F (2,18)=152.05, P=0.0001}. There was a significant difference in the means of IOP at +2Gz and -1Gz (19.5 vs. 37.1 mmHg, P=0.0001). There was a significant difference in the means of IOP at +3Gz and -1Gz (21.2 vs. 37.1 mmHg, P=0.0001). There was a marginal significance in the means of IOP at +2Gz and +3Gz (P=0.0321). CONCLUSION: The conclusion of this study was that significant increases in IOP were found during +2Gz and +3Gz as well as -1Gz when compared to pre-baseline IOP values. These findings suggest that a rise of IOP during +2Gz and +3Gz cannot be explained by the hydrostatic column effects that are associated with acceleration exposure.
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Humans , Male , Acceleration , Aircraft , Body Fluids , Intraocular Pressure , Optic Nerve , Vision Disorders , Visual FieldsABSTRACT
Objective To study the changes of mRNA expression of heat shock protein 70 (HSP70) in the rat brain exposed to repeated +Gz. Method The mRNA expression levels of HSP70 in rat brain were measured by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). Result The HSP70 mRNA expression levels in rat brains taken 30 min and 6 h after repeated +Gz exposures were significantly higher than those in control group, while the difference between the levels of control group and those of experimental rat brains taken 24 h after +Gz exposure was not significant. Conclusion It is suggested that HSP70 mRNA expression in rat brain can be induced by repeated +Gz exposures and the increased HSP70 mRNA expression may play an important role in self-protection against brain damage induced by+Gz exposures.
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To study changes in mRNA expression of induced nitric oxide synthase (iNOS) in the brain of rat repeatedly exposed to +Gz, and to explore the prevention and treatment effect of basis fibroblast growth factor (bFGF) and radix salviae miltiorrhizae (RSM) on the brain injury induced by repeated +Gz exposures. The mRNA expression levels of iNOS in brain were measured by semi quantitative reverse transcription polymerase chain reaction (RT PCR). The results showed the iNOS mRNA expression level in brain of rats repeatedly exposed to +Gz was significantly higher than that of control, but bFGF and RSM could alleviate the expression change of iNOS. It suggested that the iNOS mRNA expression in rat brain was induced by repeated +Gz exposures and it might play an important role in the pathologic course of brain damage induced by +Gz exposures.The bFGF and RSM possessed prevention and treatment on the brain injury induced by repeated +Gz exposures.
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0.05) were found in ejection fraction (EF), fractional shortening of left ventricle (DD), blood flow velocity through aortic valve, blood flow velocity through pulmonary valve, E peak velocity of mitral valve, left atrial end-systolic anterior-posterior diameter, left ventricular end-systolic anterior-posterior diameter, left ventricular end-systolic left-right diameter and left ventricular end-diastolic left-right diameter after 2-4 hours of +Gz exposure. A peak velocity in mitral valve slightly increased (P