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

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1 J B iom ed Eng 2002; 19 (1) ( ) 2 ( ) 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 ) 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 ) 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

2 1 49 [ 1 2 ] P2V [ 1 ] Hoffler [ 1 ] ( ) ( L ow er body negative p ressu re LBN P) (r= P < ) [ 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

3 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) 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% m lgkg [ 7 ] [ 3 4 ] BP 75 kg 75 m lgkg : 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) LBN P cm 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 m in LBN P 3 m in 5 m in LBN P 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) : (n= 5) : HR bpm; SBP mmh g; M A P mmh g : HR 74 bpm; SBP mmh g;m A P mmh g NO T E: basic values in hum an test (n= 5) : HR bpm; SBP mmh g;m A P mmh g. ues in study: HR 74 bpm; SBP mmh g;m A P mmh g basic val2

4 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

5 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 ] ) [ ] S I 20% ; 20% 40% [ ] 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 ; 25% LB2.. N P HR 116 bpm SBP 97 mm H g S I % 15% Res 1970; 26 (6) 1069 ( ) 1994; 22 (5) 524 W eissler [ 9 ] W arren LBN P [ 1 3 ] LB2 blockade. N P 1992; 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) 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) ; 12 (4) 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.. : 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 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) : 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 ; 18 (5) 318 ( : )