Blood Pressure. Hsiao-Lung Chan, Ph.D. Dept Electrical Engineering Chang Gung University, Taiwan

Transcription

1 Bood Pressure Hsiao-Lung Chan, Ph.D. Dept Eectrica Engineering Chang Gung University, Taiwan

2 Bood pressure traves from aorta toward smaer vesses 2

3 Bood pressure 3

4 Hagen-Poiseuie s equation Assumed a Newtonian, or uniform, fuid with aminar, or smooth, fow Q: fow R: fuid resistance η: fuid viscosity 4

5 systemic vascuar resistance MAP: mean arteria pressure CO: cardiac output SVR: systemic vascuar resistance CVP: centra venous pressure measured in thoracic vena cava, an approximation of pressure in right atrium 5

6 Cardiac catherterization 6

7 Cardiac output ( 心輸出量 ) Cardiac output (CO) = heart rate (HR) stroke voume (SV) Exampe Stroke voume Voume of ejected bood from the ventrices (about 80 ml/beat) Average resting heart rate 70 beats/min Cardiac output = = 5,600 ml/min = 5.6 L/min Heavy exercise increases both HR and SV, and CO can increase to as high as 25 L/min. 7

8 CO measurement by thermodiution Cod saine is injected into right atrium Temperature change in arteria circuation is measured using a thermistor attached to a catheter in pumonary artery 8

9 CO by thermodiution (cont.) If cardiac output is reduced, the bous takes onger to pass through the heart. Heathy patients with norma cardiac output have ess area under temperature versus time curve, than unheathy patients with some type of coronary insufficiency. 9

10 CO by thermodiution (cont.) CO V I ( T B TI ) K1K Area 2 3 (m /s) V I, injectate voume T B, bood temperature of pumonary artery T I, injectate temperature K 1, density factor (injectate/bood) K 2, catheter manufacturer s computation constant 10

11 Vita signs Norma adut ranges for the five vita signs Bood pressure: <120 mmhg systoic,, <80 mmhg diastoic Respiratory rate: breaths/min Heart rate: bpm at rest Temperature: F Arteria saturation of oxygen: % 11

12 Bood pressure cassification Contro of bood pressure is critica because BP predicts cardiovascuar risk. For every 20 mmhg systoic or 10 mmhg diastoic increase, the mortaity from both ischemic heart disease and stroke doubes 12

13 Bood pressure measurement Invasive, continuous BP During surgery, continuous BP monitoring is indicated for cardiac patients and hypertensive patients Discrete, noninvasive BP Systoic & diastoic BPs Continuous, noninvasive BP 13

14 Intraarteria pressure transducer system 14

15 Intraarteria pressure transducer system (Extravascuar bood pressure measurement) Saine-heparin soution 15

16 Pressure sensor components: a diaphragm, strain gauge, and Wheatstone bridge R 1 =R 2, R 3 = initia strain gauge resistance 16

17 Strain guage A A A A A R stretched ) 2 ( ) ( ) ( A stretched A ) ( R A R 2 2 dispacement dispacement 17

18 Intravascuar sensors Detection of pressure in the catheter tip without the use of iquid-couping system High-frequency response Eiminate time deay Bonding strain-gage systems onto a fexibe diaphragm at catheter tip Fiber-optic microtip sensor 18

19 Fiber-optic pressure sensor: Avaiabe for magnetic resonance imaging 19

20 Discrete, noninvasive BP: auscutation method Russian army surgeon Nikoai Korotkoff discovered pressure markers during cuff defation sphygmomanometer Pressure in units of miimeters of mercury (mm Hg) 760 mm Hg = 1 atmosphere (atm) = 101,325 Pascas (Pa) 20

21 Principe of discrete, noninvasive BP Cuff Occuded bood vesse ( Korotkoff sounds ) 21

22 Discrete noninvasive BP: osciometry method Bioengineer and physician Maynard Mike Ramsey III deveoped the first automated BP monitor by anayzing pressure pusations over the brachia artery is defated Mean arteria pressure occurred when peakto-peak ampitude of pusation is maxima 22

23 Osciometry system diagram sphygmomanometer 23

24 24

25 Measurement equivaency of BP 25

26 Continuous noninvasive bood pressure measurement (NIBP) Arteria tonometer 26

27 Continuous NIBP IEEE Engineering in Medicine and Bioogy Magazine,

28 Continuous NIBP (cont.) IEEE Engineering in Medicine and Bioogy Magazine,

29 Reference G. D. Baura, Medica device technoogies, Esevier Inc., JG. Webster, Medica Instrumentation, appication and design, 3rd, Houghton Miffin, JJ.Carr, JM.Brown, Introduction to Biomedica Equipment Technoogy, 4nd Edition, Prentice-Ha, 2000.