J B iom ed Eng 2002; 19 (1) 48 52 3 1 2 1 2 2 1 ( 100084) 2 ( 710032) M elch io r (1994) ( ) 15% ; 5% LBN P HR BP The Changes of Card iova scular Respon se to O rthosta tic Stress Caused by Hypovolem ia Inuced by W e ightlessness: A Sim ula tion Study Hao W e iya 1 Ba i J ing 1 Zhang L ifan 2 W u X ingyu 2 1 (D ep artm ent of E lectrical E ng ineering T sing hua U niversity B eij ing 100084) 2 (D ep artm ent of A erosp ace M ed icine T he F ou rth M ilitary M ed ical U niversity X i an 710032) Abstract W e introduced the m ethod of computer in the studies of gravitational physio logy. Based on w o rk of M elch io r (1994) w e developed a m athem atical model that can be used to sim ulate cardiovascular re2 sponses to o rtho static stress (low er body negative p ressure LBN P). T he model includes 7 sub2models: the redis2 tribution of blood the filling of left ventricle left ventricle w o rk ing peripheral circulation contro l of heart rate (HR ) contro l of peripheral resistance and contro l of venous tone. T hen w e sim ulated the changes of blood p res2 sure (BP) and heart rate during low er body negative p ressure and the results agreed w ell w ith the results of our hum an experim enṫ By using the developed model w e also sim ulated the effects of hypovo lem ia on the BP HR and shock index during o rtho static stresṡ T he results indicate that the cardiovascular responses to o r2 tho static stress change significantly w hen the decrease of blood vo lum e is mo re than 15% of the to tal blood vo l2 um e. How ever if the amount of the decrease of blood vo lum e is less than 5% of the to tal blood vo lum e HR and BP could be m aintained in no rm al range by the regulation of baro reflex during LBN P. O ur results sug2 gest that hypovo lem ia m ay be the m ain cause of o rtho static into lerance induced by w eigh tlessnesṡ Key words Computer W eigh tlessness Cardiovascular system M athem atical model 1 (B lood p ressu re BP) [ 1 ] : (Cardiovascu lar decondition ing) 3 (200105) 1G
1 49 [ 1 2 ] P2V [ 1 ] Hoffler [ 1 ] ( ) ( L ow er body negative p ressu re LBN P) (r= - 0. 54 P < 0. 005) [ 1 ] (2) [ 6 ] 2 (3) 2. 1 LBN P LBN P M elch io r [ 3 ] (1994) [ 4 ] (CN S) CN S 7 : d [ 3 ( 1) ] t (t2d) P (t2d) ( t2d) (1) 2 P trans V P trans : 2 V m + Π arctan [ Π trans C 0 P ] S (t) = 1 T 2 V c t- d [P (Σ) - P n ] e - (t- d- Σ) gt c d Σ (2) m + - V = 2 V m - Π arctan [ Π (1) : Σ ; P (Σ) trans C 0 P ] 2 V m - ( P (Σ) V P trans M A P; : V m + CV P ) ; P n ( ; V m - P trans M A P CV P) ; T c (1) P2V M o reno [ 5 ] (1970) 1 F ig 1 Block diagram of human cardiovascular simulation model
50 19 H R m ax- H R m in H R = H R m in+ (3) 1+ e S (t) gs 0 : HR m in HRm ax ; S0 [ 8 9 ] [ 7 S ] (4) 2. 2 2. 2. 1 LBN P LBN P V T H O + V H UL + V A B D + V PB + V T H I + V CA L + V F T = V b (5) LBN P (4) : V b ( CV P) LBN P 7% (LV EDV ) 8% 70 80 m lgkg [ 7 ] [ 3 4 ] BP 75 kg 75 m lgkg : 5 625 m l (SBP DBP ) (M A P ) HR (0% 25% ) LBN P CV P T PR (0 220 mm H g) HR SBP DBP HR T PR [ 10 ] (Shock index S I; S I= HR gsbp) CV P 2. 3 ( 1mm H g) 5 24. 3 5. 0 LBN P 168. 45 6. 28 cm 55. 31 6. 47 kg V T H O + V H UL + V A B D + V PB + V T H I+ V CA L + V FT = 0 (4) : V THO V HUL V ABD V PB V TH I V CAL ; 10 s V FT 3 m in 1 2 3 m in LBN P 3 m in 5 m in 2. 2. 2 LBN P - 30-50 - 70 mm H g (M ean circu lato ry filling p ressu re M CFP ) M CFP (CV P ) 3 (Sup ine2lbn P) : 5 m in CV P (LV EDV ) 3. 1 L BNP LBN P (mmh g) 1 L BNP Table 1 Changes of heart rate and blood pressure by computer simulation vs human- test dur ing L BNP HR change (bpm ) SBP change (mmh g) M A P change (mmh g) 230 8. 27 3. 55 10 2 8. 57 7. 29 28. 05 24. 04 3. 16 23. 08 250 15. 19 4. 15 16 212. 78 5. 64 212. 41 25. 04 3. 99 24. 74 270 26. 67 10. 16 21 217. 52 1. 73 215. 11 25. 64 3. 08 26. 09 : (n= 5) : HR 68. 87 10. 93 bpm; SBP 120. 087 11. 13 mmh g; M A P 86. 17 6. 54 mmh g : HR 74 bpm; SBP 116. 99 mmh g;m A P 95. 04 mmh g NO T E: basic values in hum an test (n= 5) : HR 68. 87 10. 93 bpm; SBP 120. 087 11. 13 mmh g;m A P 86. 17 6. 54 mmh g. ues in study: HR 74 bpm; SBP 116. 99 mmh g;m A P 95. 04 mmh g basic val2
1 51 LNBP HR ( 1) LBN P SBP M A P LNBP HR ; ( 1) LBN P HR 2 ( 5% ) HR LBN P LBN P ; 15% ; LBN P LBN P HR Po lese 5% LBN P 0 HR 76 bpm ; LBN P 220mm [ 11 ] (1992) H g HR 88 bpm 20% LBN P 0 2 L BNP F ig 2 Simulation results of blood pressure changes dur ing stepped L BNP exposure HR 96 bpm ; LBN P 220 mm H g HR 132 bpm (2) SBP ( 2) < 10% LBN P SBP > 15% SBP LBN P LBN P < 15% LBN P DBP ; DBP LBN P 3. 2 L BNP (3) LBN P 3 m in 10% 15% HR BP S I ( 3) : 3 F ig 3 The effects of hypovolem ia on HR BP and SI changes dur ing supine-l NBP
52 19 S I (< 10% ) LNBP (S I< 1) ; ( 20% ) LBN P 4 [ 7 ] 5% [ 7 ] 15% 10% 15% S I [ 1 2 (S I> 1 ; S I> 2 ] ) [ 10 12 ] S I 20% ; 20% 40% [ 10 12 ] 20% LBN P (LBN P 0) HR 96 bpm SBP 104 mm H gdbp 78 mm H g S I< 1 (0. 92) P ress 1996 6312674 2 ; 25% LB2.. N P HR 116 bpm SBP 97 mm H g S I 1. 19 5% 15% Res 1970; 26 (6) 1069 ( ) 1994; 22 (5) 524 W eissler [ 9 ] W arren LBN P [ 1 3 ] LB2 blockade. N P 1992; 63 467 LBN P ( ) 1 W atenpaugh D E H argens A R. The cardiovascular system in m icrogravity. In: F regly M J and B latteis CM eds. H andbook of Physio logy: Environm ental Physio logy. g : The Gravitational Environm ent 1: M icrogravity. N ew Yo rk: O xfo rd U niversity 1998; 11 (2) 378 3 M elchio r FM Srinivasan RS Thullier PH et al. Sim ulation of cardiovascular response to low er body negative p ressure from 0 to 240 mmh g. J A pp l Physio l 1994; 77 (2) 630 4.. 1999; 12 (4) 262 5 M o reno A H Katz A I Go ld RV et al. M echanics of distension of dog veins and o ther very th in2w alled tubular structures. C irc 6 Bai J L in H Zhou X. A study of Op tim al Configuration and Contro l of M ulti2cham ber Balloon fo r IABP. A nn B iom ed Eng 7.. : 1992 1552244 8 M elchio r FM Srinivasan RS Charles JB. O n m athem atical modeling of hum an cardiovascular system fo r of o r2 tho static response. Am J Pysio l 1992; 262 (6) H 1920 9 Boyers D G Cuthbertson JG L uetscher JA. Sim ulation of the hum an cardiovascular system: a modelw ith no rm al responses to change of po sture blood lo ss transfusion and autonom ic Sim ulation 1972; 18 (2) 197 10.. : 1995 21232 11 Po lese A Sandler HD M ontgom ery L. H emodynam ic re2 sponse to seated and sup ine low er body negative p ressure com 2 parison w ith + Gz acceleration. A viat Space Environ M ed 12.. 1998; 18 (5) 318 ( : 2000210216)