21d头低位卧床期间脑底动脉血流动力学的变化_英文_

21d头低位卧床期间脑底动脉血流动力学的变化_英文_ Changes of Human Cerebral Bottom Arter ial Hemodyna mics dur ing 21 d Hea d2do wn Til t( - 6?) Bed2rest 1 1 1 2 3 3YAO Yo ng2jie,WU Xing2yu,SU N Xi2qing,WAN G Zho ng2bo,J IAN G Chang2lin,J IAN G Shi2zho ng (1 . Depart ment of Aerospace Medicine , The Fourt h Military Medical U niversity , Xi’an 710032 ; 2 . Linto ng Sanatorium of Air )Force ,Linto ng 710600 ; 3 . Instit ute of Space Medico2Engineering ,Beijing 100094 Abstract : Object ive To investigate t he change of human cerebral bot to m arterial hemo dynamics during 21 d ( ) simulated weightlessness. Method 21 d - 6?head2dow n tilt bed rest HD Twere used to simulate weight2 ( ) lessness. 6 healt hy male ,aged 24 . 8 ?6 . 1 served as subject s. Systolic bloo d velocit y V , diastolic bloo d ve2 s ( ( ( ) ( ) ) ) locit y V ,mean bloo d velocity V ,p ulsatilit y index P I,resistance index R Iand ot her indices of mid2 dm ( ) () ( ) dle cerebral arteries MCA,anterio r cerebral artery ACAand po sterio r cerebral artery PCAwere mea2 () sured by t ranscranial ult raso und Doppler befo re HD T and o n day 0 D0,1 ,3 ,7 ,10 ,21 of HD T. HU T + 75? 20 min o rt ho static tolerance test s were do ne o n day - 1 ,10 ,and 21 of HD T. Result During HU T + 75?20min o rt ho static tolerance test o n day 10 and 21 of HD T ,t he average standing time were sho rter t han t hat of ( ) t he p re2HD T values P < 0 . 05. On day 3 and 21 of HD T ,Vof right MCA reduced significantly t han p re2 s ( ) HD T P < 0 . 05 o r P < 0 . 01. On day 1 , 3 , 7 , 10 and 21 of HD T , Vof right MCA were o bvio usly lower s ( ) t han t hat o n D0 P < 0 . 05 o r P < 0 . 01. L ef t MCA V o n D0 increased significantly t han t hat of p re2HD T s ( ) ( ) P < 0 . 05,and bot h were significantly higher t han t ho se of t he 3rd day of HD T P < 0 . 01. Right MCA ( Vo n t he 3rd and 21st day of HD T were significantly lower t han t ho se p re2HD T and D0 P < 0 . 05 o r P < m ) ( ) 0 . 01. On day 10 of HD T ,Vof right MCA were significantly reduced t han t hat o n D0 P < 0 . 05. Bot h m ( ) MCA bilateral velocit y difference right V2lef t Vo n t he 3rd , 10t h , 21st day of HD T , and MCA inter2 mm hemisp heric asymmet ry index o n t he 10 t h ,21st day of HD T were significantly lower t han t hat of p re2HD T ( ) P < 0 . 05 o r P < 0 . 01. Concl usion 21 d HD T bed2rest decreased o rt ho static tolerance , Vof bot h side s MCA ,and Vof right MCA . Lower Vof bot h side MCA and t he inter2hemisp heric asymmet ry of MCA m s during HD T maybe respo nsible ,in part ,fo r t he increased risk of o rt ho static intolerance . Key words :weightlessness simulatio n ; cerebral bot to m artery ; hemo dynamics ; t ranscranial Doppler ; o rt ho2 static tolerance 21 d 头低位卧床期间脑底动脉血流动力学的变化. 姚永杰 ,吴兴裕 ,孙喜庆 ,王忠波 ,蒋昌林 ,姜世忠. 航 () 天医学与医学工程 ,2001 ,14 1:11,16 摘要 :目的 观察 21 d 头低位卧床期间脑底动脉血流动力学的变化 。方法 6 名健康男性志愿者 ,年龄 24 . 8 ?6 . 1 岁 ,进行了 21 d HD T - 6?卧床试验 。HD T 前 、HD T 第 10 天及卧床结束时进行了 3 次立位 () () ( ) 耐力检查 。HD T 前 坐位、HD T 即刻 D0、第 1 、3 、7 、10 、21 天用经颅超声多普勒 TCD测量了双侧大 () ( ) ( ) 脑前 ACA、中 MCA、后动脉 PCA的血流动力学指标 。结果 卧床第 10 天和卧床结束时 ,受试者立 ( ( ) 位耐力比卧床前显著降低 P < 0 . 05。卧床第 3 天和第 21 天的右侧 MCA 的 V 较卧床前显著降低 P s ( ) < 0 . 05或 P < D0 . 01,卧床第 1 、3 、7 、10 和第 21 天 ,右侧 MCA 的 V显著低于 D0 时 P < 0 . 05 或 P < s ) ( ) 0 . 01。左侧 MCA 的 V 在 D0 时较卧床前和第 3 天显著增加 P < 0 . 05 或 P < 0 . 01。右侧 MCA 的 s ( ( ) V,在第 3 和第 21 天较卧床前显著降低 P < 0 . 05 或 P < 0 . 01,在第 3 、10 、21 天较 D0 显著降低 P < m ) 0 . 05 或 P < 0 . 01。在卧床前 , MCA 右左两侧流速差 BVD 和右左两侧非对称指数 A I 的均数分别为 ( 7 . 0 cm/ s 和 13 . 74 % ,在第 3 、10 、和 21 天 BVD 均数降为负值 ,较卧床前时显著降低 P < 0 . 05 或 P < ) ( ) 0 . 01, A I 在第 10 和 21 天降为负 ,较卧床前显著降低 P < 0 . 05 或 P < 0 . 01。MCA 的其余指标 、ACA 和 PCA 的各指标变化不显著 。结论 21 d 头低位卧床使立位耐力 、双侧 MCA 的 V 和右侧 MCA 的 V s m 显著降低 ; MCA 血流速度降低和不对称变化 ,可能与立位耐力降低有关 。 关键词 :失重模拟 ;脑底动脉 ;血液动力学 ;经颅多普勒 ;立位耐力 () 文章编号 :100220837 20010120011206 中图分类号 : R852 . 22文献标识码 :A 作者地址 :姚永杰. 第四军医大学航空航天医学系 ,西安 710032 2 result s in o rt ho st atic intolerance even synAst ro naut s were expo sed to microgravi2 cope immediately af ter ret ur ning to eart h . t y enviro nment during spaceflight . It of ten But t he underlying mechanisms remain un2 1 ,2 Recieved date :2000204205 clear. In recent years , so me aut ho rs have ( do ne in t he head2dow n po sitio n defecatio ns suggested t hat cerebral vascular adap t atio n ) changes to weightlessness may co nt ribute to were not including . The volunteers wereo rt ho st atic intolerance ,and t he hypot hesis of given a co nt rolled diet acco rding to t he avia2 p rimary impair ment of cerebral vascular au2 to r’s diet standard by nut ritio n docto r . ( to regulatio n occurred befo re syncope cere2 Exa mination of cerebral arterial hemo2 ) brovascular syncope2initiating mechanism dyna mics The indexes of hemo dynamics of were p ut fo rward , but direct experimental ACA , MCA , PCA were measured no ninva2 1 sively by t ranscranial ult raso und Doppler evidences were lacking. Multit udino us TM ( ) st udies co nsidered t hat t he resist ance of cere2 technique Neuro visio n during 0 . 5 h be2 ( ) bral circulatio n was increased during weight2 fo re HD T up right sit ting、and t he first 0 . 5 ( ) lessness o r simulated weightlessness , but t he h of HD T D0、o n t he 1st 、3rd 、7t h 、10t h 、 ( ) and 21st day of HD T. TCD was operated by change of cerebral bloo d flow CB F were 3 ,6 4 uncertain. Wang Desheng et al o b2 special docto r . The TCD p ro be was placed served t he changes in cerebral circulato ry over t he Tempo ral window and fixed at a ( ) f unctio n during head dow n bed rest HD Tco nstant angle and po sitio n to o btain signals fo r 7 d ,t he result s showed t hat CB F velocit y f ro m ACA , MCA and PCA . Ult raso nic co u2 in t he MCA increased t hro ugho ut HD T. In pling agent was applied to t he p ro be . Stated p revio us st udies ,we investigated t he changes tensio n was held bet ween skin and p ro be , so of human CB F by admit t ance r heoencep hlo2 t hat ult raso nic beam can penet rate t hro ugh . ( ) gramp hy during 21 d HD T - 6?, t he re2 Imp ulse repeat f requency was 2 M Hz , and sult s showed t hat CB F were lower and cere2 t he sampling dep t h were : 50 , 60 mm fo rbral vascular resistance were higher t han MCA ,55,65 mm fo r ACA , 60,70 mm fo r t ho se p re2HD T ,and t he p ro blem of asymme2 PCA . Fo r each subject and fo r each bloo d 7 vessel , t he same“Doppler window ”and t he t ry of cerebral circulatio n was discussed. In same dep t h and angle were used fo r repeated t his paper , t herefo re , we o bserved t he measurement s. This window was identified changes of hemo dynamics of ACA ,MCA and ( ) PCA during 21 d HD T - 6?by t ranscra2 and mar ked o n t he skin . Auto matically calcu2 ( ) ( nial ult raso und Doppler TCDtechnique . lated indexes were : V,V,V, P I , P I = V s d m s ) ( ) - V/ V, R I , R I = V- V/ V. Manual2 d m s d s Method ly calculated indexes were : V/ V, bilateral sd () (velocit y difference BVDof MCA , BVD = Subjects Six healt hy male subject s ) right V- lef t V, and inter2Hemisp heric m m ?6 . 1 year , averagewit h mean age of 24 . 8 ( ) ( asymmet ry index A Iof MCA ,A I = right height of 168 . 1 ?3 . 4 cm ,and mean weight) ( V- lef t V3 200/ right V+ lef t m m m of 52 . 9 ?7 . 9 kg participated t his st udy. The8 ) subject s were examined by using medical his2 V. Arterial bloo d p ressure in lef t m to ry and a p hysical examinatio n , elect rocar2 brachial artery were reco rded every mo r ning dio grap hy , and echocardio grap hy et al . No ( ) ?30,7?00during HD T.6 subject had chro nic o r acute medical p ro b2 Tilt tests To investigate o rt ho st atic in2 lems. Befo re t he experiment , t he p urpo se of tolerance ,tilt test s were perfo r med : o n D22 , t he experiment and det ail of t he p rocess of D10 of HD T , and immediately af ter t he end t he HD T were explained to t hem all . of HD T perio d ; each of t hese tilt test s was (perfo r med at t he same time in t he day 8?00 Experimental procedure and hea d2do wn ) ,11?00. The seco nd and t he t hird tilt test stilt Subject s were ho spitalized in a special were do ne af ter t he indexes of hemo dynamics ( ) Air Fo rce sanato rium Linto ng , China fo r of ACA ,MCA , PCA had been measured. Tilt 28 d ,including 4 d ambulato ry co nt rol w hen t he subject s equilibrated to t he st andardized test p rotocol co nsisted of tilting t he subject to ( ) diet ,21 d HD T - 6?,and 3 d of po st HD T + 75?in 3 s af ter 15 min in ho rizo ntal po si2 recovery. Roo m temperat ure was maintained tio n. The + 75?po sitio n was maintained fo rat 19 ?,23 ?and roo m lighting was main2 20 min o r until a p re2syncopal o r syncopal tained 07 ?00 , 22 ?00 everyday . During 7 state ensued. During t hese tilt test s , EC G ( ) HD T - 6?perio d , t he subject s remained and arterial bloo d p ressure were reco rded. head2dow n wit ho ut interrup tio n : all testing , Data analysis and statistics All data eating , drinking , washing , and pissing were were exp ressed as x ?s . A General Linear ? ) 2 lef t MCA day was signifiMo dels ANOVA regressio n mo del was used < 0 . 01 . Vof s to deter mine t he significance of difference cantly higher o n D0 t han t ho se of p re2HD T bet ween CB F parameters during HD T and ( ) levels P < 0 . 05,and also significantly high2 () baseline values p re2HD To r D0 values. Sta2 ( er t han t ho se o n t he 3rd day of HD T P < tistical significance was set at P < 0 . 05 . The ) 0 . 01. Right MCA Vof t he 3rd and 21st m statistical sof t ware was SPSS27 . 5 fo r win2 day of HD T were significant lower t han p re2 dows. ( ) HD T and o n D0 P < 0 . 05 o r P < 0 . 01. On day 10 of HD T , Vof right MCA were sig2 m Result ( nificantly lower t han t ho se o n D0 P < ) 0 . 05 . Bot h MCA bilateral velocit y differ2 Changes of hemodyna mics of human ( ) ence right V- lef t Vo n t he 3rd , 10t h , m m cerebral bottom arteries 21st day of HD T ,and MCA inter2hemisp her2 1 . Changes of CB F parameters of MCA . ic asymmet ry index o n t he 10t h ,21st day of On day 3 and 21 of HD T , Vof right MCA s HD T were significantly lower t han t ho se p re2reduced significantly f ro m t he p re2HD T level ( ) HD T P < 0 . 05 o r P < 0 . 01. The analysis ( ) P < 0 . 05 o r P < 0 . 01. On day 1 ,3 ,7 ,10 showed no significant difference fo r lef t V mand 21 of HD T ,Vof right MCA were o bvi2 s and V,V/ V, R I , P I bet ween t he t wo sides d sd ( o usly lower t han t ho se o n D0 P < 0 . 05 o r P ( ) during 21 d HD T Table 1. Ta ble 1 Changes of blood f lo w velocity of MCA in subjects during HD T( ?x ?s , n = 6) index gro up D0 D1 D3 D7 D10 D21 p re2HD T V right 93 . 8 73 . 6 102 . 3 89 . 3 77 . 9 86 . 8 86 . 4 s?3 ????3 3 ?? ?9 . 6?14 . 8?18 . 1 ?16 . 5 ?23 . 5 ?22 . 1 ?18 . 6 ()cm/ s 80 . 3 96 . 9 87 . 8 77 . 8 84 . 5 85 . 7 84 . 9 lef t 3???19 . 9 ?20 . 2 ?13 . 9?25 . 9?27 . 1?20 . 5?19 . 2 58 . 2 47 . 9 V right 56 . 4 55 . 4 53 . 4 54 . 1 46 . 2 m3 ???3 3 ?? ?11 . 8 ()?11 . 5 cm/ s ?8 . 9?13 . 5?15 . 1?15 . 7 ?14 . 2 58 . 2 48 . 7 lef t 48 . 2 54 . 1 49 . 5 52 . 0 51 . 9 ?13 . 5?12 . 2 ?9 . 3?15 . 7?15 . 7?12 . 8?10 . 4 37 . 9 34 . 9 V 39 . 4 39 . 9 37 . 9 34 . 9 33 . 3 right d ?12 . 7?9 . 5() cm/ s ?12 . 6?10 . 8?9 . 7?12 . 1?12 . 2 39 . 9 35 . 4 lef t 33 . 3 39 . 1 32 . 9 36 . 2 35 . 9 ?10 . 8?9 . 6 ?7 . 8?10 . 3?10 . 1?9 . 0?6 . 7 1 . 62 1 . 81 V / V right 1 . 81 1 . 78 1 . 78 1 . 68 1 . 81 sd ?0 . 24?0 . 10 ?0 . 41?0 . 12?0 . 05?0 . 15?0 . 25 1 . 72 1 . 87 1 . 72 1 . 83 1 . 64 1 . 74 1 . 75 lef t ?0 . 22?0 . 21 ?0 . 15?0 . 11?0 . 10?0 . 09?0 . 11 0 . 63 0 . 56 R I right 0 . 58 0 . 56 0 . 56 0 . 60 0 . 56 ?0 . 10?0 . 03 ?0 . 14?0 . 04?0 . 01?0 . 05?0 . 09 0 . 59 0 . 54 lef t 0 . 59 0 . 55 0 . 61 0 . 58 0 . 57 ?0 . 07?0 . 07 ?0 . 06?0 . 03?0 . 04?0 . 03?0 . 03 1 . 14 0 . 91 1 . 00 0 . 91 0 . 92 1 . 03 0 . 93 P I right ?0 . 34?0 . 09 ?0 . 38?0 . 10?0 . 04?0 . 17?0 . 23 1 . 00 0 . 87 lef t 0 . 99 0 . 89 1 . 05 0 . 95 0 . 93 ?0 . 19?0 . 18 ?0 . 09?0 . 16?0 . 08?0 . 13?0 . 09 - 0 . 5 2 . 0 7 . 0 0 - 2 . 5 - 2 . 0 - 5 . 5 BDV 33?10 . 6 3 3 ?5 . 7 ?5 . 7 () ?6 . 0?6 . 9?8 . 2cm/ s ?6 . 2 2 . 1 0 . 62 - 5 . 11 13 . 74 0 . 60 10 . 93 A I - 15 . 10 33 3?13 . 6 ?25 . 5?20 . 4 ?11 . 6 ( )% ?11 . 6?14 . 8?10 . 3 Note : 3 P < 0 . 05 , 3 3 P < 0 . 01 ,as co mpared wit h p re2HD T ; ? P < 0 . 05 , ?? P < 0 . 01 ,as co r mpared wit h D0 2 . Changes of CB F parameters of ACA lessness st ate , hydro st atic fo rce disappears , and PCA . There were no significant change fluids shif t toward t he head and to rso . These in V, V, V, V/ V, R I and P I in bot h make int racranial p ressure to rise ,brain bloo d s m d sd ( flow slow ness , and hemo dynamics cerebral sides during 21d HD T bed rest Table 2 and bot to m arteries to change . In p revio us st ud2 ) 3. ies ,impedance and admit tance r heoencep hlo2 3 . The change of SB P ,DB P and MB P in grap hic technique were used to measure t he brachial artery were not significant during change of CB F. Broad applicatio n of t hese t he w hole HD T. means was hard due to it ’s localizatio n . Results of orthostatic tolerance Transcranial ult raso und Doppler technique is On D22 , all subject s passed t he 20 min a new met ho d fo r t he st udy of cerebral circu2 + 75?tilt test , wit ho ut interrup tio n . During latio n in aero space medicine . This no ninva2 t he tilt test s o n D10 and immediately af ter sive technique is safe and can be repeated f re2 t he end of HD T bed rest ,all t he subject s p re2 has been used during parabolic , and quently sented p resyncopal o r syncopal symp to ms , ot her weightlessness simula2 flight and such as cold sweat ,pallo r , nausea , vo miting , 1 ,3 ,9 ,11 and so o n . The average standing times were tio ns. 13 . 87 ?5 . 77 min and 14 . 95 ?3 . 23 min re2 of right MCA o n D0In t his st udy , V s spectively , bot h of t hem were sho rter t han was higher t han t he p re2HD T value , t ho ugh ( ) t he p re2HD T value P < 0 . 05. not st atistically significant . O n day 3 and 21 of HD T , Vof right MCA reduced signifi2 s Discussion cantly f ro m t he p re2HD T value . As fo r Vof s t he lef t side ,o nly t he value o n D0 was signif2 O n t he eart h ,bloo d tends to pool in t he icantly higher t han t ho se of p re2HD T value . vascular bed of t he dependent po sitio n of t he Right MCA Vo n t he 3rd and 21st day of bo dy due to t he hydro st atic fo rce generated m HD T were significantly lower t han p re2HD T by gravit y. When ast ro naut s enter weight2 x? ?s , n = 6) Changes of blood f lo w velocity of ACA in subjects during HD T( Ta ble 2 index gro up p re HD T D0 D1 D3 D7 D10 D21 V right 52 . 9 45 . 7 46 . 9 51 . 8 41 . 9 59 . 9 49 . 9 s () cm/ s ?14 . 2?7 . 5?14 . 7?4 . 3?6 . 0?12 . 6?10 . 4 lef t 44 . 9 47 . 8 44 . 1 53 . 2 47 . 4 57 . 4 57 . 9 ?14 . 8?4 . 3?13 . 7?10 . 1?8 . 1?10 . 5?14 . 0V right 30 . 4 28 . 3 28 . 0 33 . 0 28 . 5 37 . 4 30 . 8 m ()cm/ s ?6 . 4?4 . 6?7 . 5?1 . 3?3 . 7?10 . 8?5 . 8 lef t 27 . 5 30 . 0 28 . 3 33 . 3 29 . 5 32 . 4 37 . 0 ?6 . 8?4 . 4?11 . 0?3 . 8?5 . 3?7 . 7?12 . 0V right 21 . 0 20 . 8 19 . 5 25 . 0 22 . 5 27 . 5 22 . 9 d () cm/ s ?4 . 5?4 . 7?4 . 8?1 . 5?4 . 3?10 . 1?5 . 3 lef t 20 . 0 22 . 1 21 . 7 24 . 2 22 . 5 21 . 5 26 . 5 ?2 . 5?7 . 1?10 . 4?1 . 4?5 . 2?6 . 3?11 . 5V / V right 2 . 57 2 . 24 2 . 44 2 . 07 1 . 89 2 . 30 2 . 23 sd ?0 . 78?0 . 41?0 . 71?0 . 17?0 . 28?0 . 46?0 . 51 2 . 21 2 . 35 2 . 18 2 . 21 2 . 16 2 . 76 2 . 35 lef t ?0 . 51?0 . 72?0 . 40?0 . 45?0 . 43?0 . 45?0 . 57R I right 0 . 59 0 . 54 0 . 56 0 . 51 0 . 46 0 . 55 0 . 53 ?0 . 11?0 . 08?0 . 13?0 . 04?0 . 07?0 . 11?0 . 10 0 . 53 0 . 53 0 . 53 0 . 53 0 . 52 0 . 63 0 . 55 lef t ?0 . 11?0 . 19?0 . 09?0 . 11?0 . 09?0 . 07?0 . 10 1 . 03 0 . 89 0 . 96 0 . 81 0 . 69 0 . 91 0 . 88 P I right ?0 . 33?0 . 22?0 . 33?0 . 10?0 . 16?0 . 26?0 . 26 lef t 0 . 86 0 . 91 0 . 85 0 . 86 0 . 85 1 . 14 0 . 90 ?0 . 25?0 . 41?0 . 21?0 . 24?0 . 22?0 . 21?0 . 27 Ta ble 3 Changes of blood f lo w velocity of PCA in subjects during HD T( x ?s , n = 6) ? index gro up p re HD T D0 D1 D3 D7 D10 D21 V right 44 . 9 40 . 4 40 . 4 41 . 2 34 . 9 40 . 4 46 . 4 s () cm/ s ?13 . 3?8 . 7?7 . 4?6 . 6?9 . 3?9 . 9?7 . 6 40 . 4 45 . 7 36 . 6 39 . 9 37 . 0 45 . 7 40 . 9 lef t ?7 . 2?7 . 2?8 . 6?2 . 5?6 . 6?9 . 7?4 . 2V right 27 . 4 25 . 4 25 . 0 25 . 6 22 . 5 24 . 5 26 . 0 m ()cm/ s ?8 . 4?5 . 8?5 . 9?2 . 4?4 . 7?4 . 8?5 . 8 lef t 24 . 5 26 . 7 24 . 2 26 . 7 23 . 3 27 . 1 23 . 5 ?3 . 7?3 . 4?4 . 6?2 . 9?5 . 2?7 . 0?2 . 9V 19 . 5 19 . 2 19 . 5 19 . 4 18 . 0 17 . 5 17 . 5 right d ()cm/ s ?6 . 7?5 . 6?5 . 7?1 . 3?3 . 3?1 . 8?5 . 0 17 . 5 18 . 3 17 . 9 20 . 8 17 . 5 18 . 8 16 . 5 lef t ?1 . 8?3 . 0?4 . 0?3 . 8?4 . 2?5 . 9?4 . 5V / V right 2 . 36 2 . 22 2 . 18 2 . 12 1 . 94 2 . 29 2 . 77 sd ?0 . 35?0 . 60?0 . 63?0 . 24?0 . 35?0 . 34?0 . 60 lef t 2 . 30 2 . 52 2 . 09 1 . 96 2 . 16 2 . 57 2 . 64 ?0 . 22?0 . 37?0 . 53?0 . 42?0 . 30?0 . 56?0 . 81R I right 0 . 57 0 . 52 0 . 51 0 . 52 0 . 47 0 . 56 0 . 63 ?0 . 07?0 . 11?0 . 12?0 . 05?0 . 12?0 . 06?0 . 07 0 . 56 0 . 60 0 . 50 0 . 48 0 . 53 0 . 59 0 . 59 lef t ?0 . 04?0 . 06?0 . 13?0 . 11?0 . 06?0 . 09?0 . 12P I right 0 . 94 0 . 88 0 . 86 0 . 84 0 . 74 0 . 92 1 . 15 ?0 . 17?0 . 27?0 . 32?0 . 14?0 . 24?0 . 14?0 . 27 0 . 93 1 . 02 0 . 77 0 . 73 0 . 86 1 . 03 1 . 06 lef t ?0 . 12?0 . 16?0 . 28?0 . 25?0 . 19?0 . 26?0 . 36 and D0 values. O n day 10 of HD T , Vining HD T in t his st udy. This wo uld decrease m bloo d velocit y and bloo d flow . It is also po ssi2 right MCA was significantly reduced f ro m ble t hat t he increased cerebral veno us and t hat of D0 value ,but Vof t he lef t MCA did m capillary p ressures co uld elicit a dilatio n re2 not show t hese changes. Due to t he abo ve spo nse in t he larger cerebral vessels , such as changes ,BVD and A I of MCA at p re2HD T t he MCA , to maintain CB F w hile velocit y is were 7 . 0 cm/ s and 13 . 74 % respectively ,it 3 reduced . As o bserved in t his st udy , all t he showed t hat Vin right MCA were higher m subject s p resented p resyncopal o r syncopal t han t ho se in t he lef t o ne . During t he HD T , symp to ms during t he tilt test s o n D10 and o n day 10 and 21 of HD T ,bot h BVD and A I immediately af ter t he end of HD T perio d , dropped to negative values ,and were signifi2 w hich means o rt ho st atic intolerance were o b2 cantly lower t han t he p re2HD T values ,Vin m served. The adap tatio n changes of cerebral right MCA were lower t han t ho se in t he bot to m arteries hemo dynamics were parallel lef t . It showed t hat , bloo d flow velocities in to o rt ho static intolerance . Expo sure to MCA were enhanced at t he begining of weightlessness o r simulated weightlessness HD T ,but during t he w hole HD T it was low2 can cause o rt ho static intolerance ,t he po ssible er t han t he p re2HD T value , t he degree of p hysiolo gical mechanism of o rt ho static intol2drop was greater o n t he right side ,t he reaso n 1 ,2 erance may include: decreased plasmawere still unknow n ,may be t he reactivities to volume , mo dificatio n of volume regulating HD T of bot h sides MCA are different . There ho r mo nes ,decreased efficiency of t he baro re2 may be several po ssible explanatio ns fo r t he flex co nt rol , change of cardiovascular f unc2 drop of cerebral bloo d velocit y of MCA we tio ns , at rop hy of skeletal muscle , increased o bserved. Wit h head2dow n tilt o r weightless2 lower limb veno us co mpliance ,and mo difica2 ness , int racranial p ressure and , t herefo re , tio n of t he arteries. Previo us wo r ks indicated cerebral veno us p ressure may increase mo re t hat no single f acto r can explain t he cause of t han arterial p ressure do se , and t he arterial po stflight o rt ho static intolerance ,so it is now p ressure in subject s were not significant dur2 well recognized t hat multiple mechanisms rule during micro gravit y expo sure , especially might acco unt fo r it . The o rt ho st atic intoler2 t he relatio nship bet ween o rt ho st atic intoler2 ance o bserved in ast ro naus o n ret ur ning to ance and asymmet ry of cerebral circulatio n . eart h and in subject s af ter p rolo nged bed rest [ Ref e rence ] may be at t ributable to t he decreased and t he asymmet rical changes of CB F velocities of 1 Watenpaugh D E , Hargens AR. The cardiovascular system in MCA during HD T. There is no direct o bser2 microgravit yM . In : Fre gly MJ , CM Blat tis , eds. Handboo k vatio n , alt ho ugh , relating t he o rt ho static in2 of p hysiology : Enviro nmental p hysiology. New Yo r k : Oxfo rd U niversit y Press ,1996 :631,674 tolerance wit h hemo dynamic changes in cere2 2 Blo mqvist C G ,Buckey J C , Gaff ney FA , et al . Mechanism of bral circulatio n . The result s of t his wo r k po st2flight o rt ho static intolerance J . J Graviatio nal Ph ysiol , st ro ngly suppo rt t he hypot hesis of cere2 ( ) 1994 ,1 1:122,124 3 Kawal Y ,Murt hy G , Watenpaugh D E , et al . Cerebral bloo d bro vascular syncope - initiating mechanism . 5 flow velocit y in humans expo sed to 24 h of head2down tilt SH EN X Y et al repo rted t hat cere2( ) J . J A ppl Physiol ,1993 ,74 6:3046,3051 bral bloo d inrush time were extended , cere2 WAN G Desheng , XIAN G Qiulu , SHEN Xianyun , et al . 4 Changes in cerebral circulatio n f unctio n during heat down bed bral vascular resistance were increased , and rest fo r 7 days J . S pace Medicine & Medical Engineering , CB F were reduced by impedance technique ( ) 1998 ,11 4:273,276 ) ( during head2dow n tilt - 15?bed rest fo r 4 汪德生 ,向求鲁 ,沈羡云 , 等. 头低位卧床 7 天脑循环功能6 h . ZHAO GX et al fo und t hat carotid was( ) 的变化J . 航天医学与医学工程 ,1998 ,11 4:273,2765 SHEN Xianyun , XIAN G Qiulu , M EN G J ingrui . Changes of distended , and mean CB F velocit y increased cerebral impedance during 4 ho urs head2down tilt bed rest f ro m t he p re2HD T value , and t ho se changes ( ) J . Chinese S pace Science and Technology ,1992 ,12 2: 66 were o bvio usly alo ng wit h t he p rocess of ,71 12 沈羡云 ,向求鲁 ,孟京瑞. 4 小时头低位卧床期间脑阻抗图HD T time ; ZHAN G L N et made rat s al ( ) 的变化J . 中国空间科学技术 ,1992 ,12 2:66,71to be kep t in a t ail2suspended po sitio n fo r 4 ZHAO Guo xuan , HU Suwei , P EI J ingshen . Individual differ2 6 weeks to investigate t he effect s of simulated ence of carotid bloo d flow in respo nse - 15?to head2down tilt ( ) J . Chinese Jo urnal of Aviatio n Medicine , 1994 , 5 2 : 85 , weightlessness o n co nt ractile respo nsiveness 89 of t he basilar artery. Respo nses of perf used 赵国璇 ,胡素伟 , 裴静琛. 颈动脉血流对头低位 - 15?反应isolated basilar rings to vario us vasoco nst ric2 ( ) 的个体差异J . 中华航空医学杂志 ,1994 ,5 2:85,89YAO Yo ngjie , WU Xingyu , L I Mingdeng , et al . Changes of to r subst ances were examined. He fo und t hat 7 human cerebral bloo d flow during 21 d - 6?head2down tilt maximal iso met ric co nt ractile respo nses to bed rest and t he relatio nship wit h o rt ho static tolerance J . ( ) Chinese Jo urnal of Aero space Medicine , 1998 , 9 4 : 205 , KCL , arginine vasop ressin , o r 52hydro x2 208 yt ryp tamine were significantly enhanced in 姚永杰 ,吴兴裕 ,李明登 ,等. 21 天头低位卧床期间脑血流arterial isolated rings. Ot her st udies showed 的变化及其与立位耐力的关系J . 中华航空航天医学杂t hat CB F were increased during HD T , and ( ) 志 ,1998 ,9 4:205,208 周永昌 ,郭万学. 超声医学M . 第三版. 北京 : 科学技术出t here was po sitive co rrelatio n bet ween mean 8 版社 ,1998 :266,277CB F velocit y and co mp uted encep halic arter2 Hu Z ,Zhao G , Xiao Z , et al . Different respo nses of cerebral 10 3 ,4 ,10 vessels to - 30?head2down tilt in human J . Aviat S pace En2 repo rted 9 ies p ressure. Sat ake etal ( ) viro n Med ,1999 ,70 7:674,680 t hat CB F of cerebellum and basilar ganglio n Satake H ,ko nishi T , Kanwashima T , et al . Int rocranial bloo d were enhanced during HD T as co mpared flow measured wit h singel p hoto n emissio n co mp uter to mog2 10 ( ) rap hy SP EC Tduring t ransient - 6?head down tilt J . Avi 2 wit h p re2HD T values. At t he same time , in at Space Enviro n Med ,1994 ,65 :117,122o ur p revio us st udies , we investigated t he Frey MA ,Mader T H ,Bagian J P , et al . Cerebral bloo d veloci2 changes of human CB F by admit tance t y and ot her cardiovascular respo nses to 2 d of head2down tilt 11 r heoencep hlo grap hy during 21 d HD T , t he ( ) J . J A ppl Physiol ,1993 ,74 1:319,25ZHAN G L ening ,MA J in , ZHAN G Lifan , et al . Vasoco nt ric2 result s showed t hat CB F were lower and t he to r respo nsiveness of rat basilar artey enhanced by simulated 12 dep ressed degree was greater fo r lef t t han fo r weightlessnessJ . S pace Medicine & Medical Engineering , 7 right . The differences bet ween o ur result s ( ) 1999 ,12 1:10,13 张乐宁 ,马进 ,张立藩 , 等. 模拟失重可引起大鼠基底动脉and ot her st udies may be related to differ2 ( ) 收缩反应性增强J . 航天医学与医学工程 , 1999 , 12 1 :ences in t he techniques used o r t he times of 10,13measurement s. Thus ,mo re experiment s were needed to st udy t he changes of CB F and it ’s