ressure Sensors (Blood ressure)
irculation System AV valve close Aortic valve close
Blood ressure Definition 단위면적의혈관벽에가해지는혈액의힘 continuous : 혈액순환에있어서가장중요함심장에서 pumping된양과같은양의혈액이인체각부분에전달되어야함 Why do we need B? 1) 혈관질환이나생리학적불균형을알수있음 ) cardiac output의변화, 혈관저항의변화, 혈류역학및생리학적변화의영향을반영 3) 말초신경계통의변화상태를판단 혈압의종류 1) 수축기혈압 (systolic B) ) 이완기혈압 (diastolic B) 3) 평균혈압 (mean B) Mean 1 T T 0 pdt systolic diastolic 3
Measurement of Blood ressure Invasive (Direct) 측정위치 : brachial, carotid, femoral 정맥압 (V, central venous pressure) 동맥압 (RA, right atrial pressure) atheter의특성이중요 as short as possible as stiff as possible Noninvasive (Indirect) Use of Korotkoff sound Sphygmomanometer (cuff, pressure gage, pressure bulb, release valve) + sthethoscope
Indirect Measurement of Blood ressure Use of Korotkoff sound 1906 년 Russian hysicist Korotkoff : 5 phase of korotkoff sound (400 500Hz) I - V : first appearance of sound - silence 장점 : safe (no side effect) easy to measure 단점 : not accurate not continuous difference between observers instrument error (incorrect size of cuff) uff size AHA (american heart association) cuff width = 40% of the arm circumference bladder length = should cover 80% of the arm circumference 3mmHg/sec of slope thin cuff width : high B, wide cuff width : low B
Indirect Measurement of Blood ressure hotoplethysmography (G) Ultrasound Tonometry 6
Indirect Measurement Korotkoff Sound The frequency range of Korotkoff is 15~5 00 Hz and the accuracy is ± mmhg (S) and ±4mmHg (D) Korotkoff sounds are generated by the flow of blood and vibratio ns of the vessel The Korotkoff sounds are auscultate d with a stethoscope or microphone (automatic measurement) 7
Indirect Measurement Oscillometric Method The cuff pressure is deflated either linearly or stepwise. The intra-arterial pulsation i s transmitted via cuff to tra nsducer S and D are estimated from the amplitudes of the oscillation by usi ng a (proprietary) empirical algorithm. 8
Direct Measurement of Blood ressure omponents 1) atheter - semi rigid (filled with saline) - 압력을측정하는부위까지삽입 (balloon tipped catheter) ) ressure transducer 3) Monitor 장점 : continuous observation, sampling blood 단점 : technical problems (air bubble, infection)
Sensor System for Direct Measurement 혈관외센서시스템 Three-way stopcock 과도자 (catheter) 및압력센서로구성센서는격막의변위를휘트스톤브리지형태의스트레인게이지에서전기신호로변환 혈관내센서압력발생원과센서소자간연결유체가불필요시스템주파수특성이우수한반면여러번사용이불가능하고높은단가. - 광섬유를이용한혈관내압력센서 우측의끝에얇은금속막이센서는혈관에삽입되며압력이걸리면 (b) 와같은가파른광반사신호의변화가나타난다
Modeling of atheter 도자시스템의입구에압력이증가하면, 도자내로센서를향해유체의흐름이발생된다. 이러한유체의흐름이격막을휘어지게하고, 이것이전기기계시스템에의해감지되며, 결과적으로발생된전기신호는증폭기를통해증폭된다. 유체가충만되어있는도자는관성, 마찰그리고탄성을가지고있으며, 이것들이각각이너턴스 (inertance), 저항 (resistance) R, 및컴플라이언스 (compliance) 로나타낼수있다.
atheter Model and Fluid Resistance Flow of fluid in a catheter,, is proportional to the pressure difference, f p p p 1 p p R f v Ri R Resistance of the tube (friction between the fluid and the inside surface of the tube) 8l R 4 r : l : r : viscosity of the fluid length of the tube radius of the tube
Inertance and ompliance Inertance ( 유체의관성 ) L df dt constant ompliance ( 벽의탄성 ) vol p vol t t 0 fdt 1 t t 0 fdt Volume of expansion 시간당흐름의변화를감지
Fourier Analysis of B Waveform
atheter Equivalent ircuit 15 0.5310 VOL v 1 t t idt 0 L m A L r v L di dt : l : r : viscosity of the fluid length of the tube radius of the tube
AT MEAS G D D f fl j R f j G 1 1 Frequency Response of a atheter with a Diaphragm
Example #1 atheter length : meter Radius : 0.46 mm Wall with zero compliance Diaphragm compliance :.0410 0.001Ns / m 1g / cm 3 (water) 15 5 m / N R L 3 4 10 5 8 0.001 / 0.4610 11.37410 Ns / m 3 3 9 10 / 0.4610 3.00810 VOL r l 3 6 3 0.4610 1.3310 m 6 3 6 3 1.3310 m 10 ml / m 1. ml VOL 33 ompliance of the water in the catheter, 15 15 5 0.5310 1.33ml 0.704 10 m N /
D D AT MEAS f fl j R f j G 1 1 ompute the transfer gain, G G 34dB 4. 173.8 Example #
atheter with inch, Bubble, and Leak inch Assumption l p l inch is a cylindrical shape ompliance of the pinch is neglected as a small quantity R Leak 8 l r p 4 p R H L F H H l r p p ressure difference inside and outside the catheter Bubble 8 5 1.010 m N B VOLB / G MEAS AT R EQ jrh feq j RH feq jrh feq jfleq j RH f EQ R EQ R R EQ D B
Example #3 Example #1 inch that reduces the radius by one-half It has a length l p 1cm alculate pinch compliance, resistance, and frequency response, G R 8 0.001 0.01 0.310 3 4 9.09910 9 Ns / m 5 L 3 10 0.01 0.310 3 60.10 6
Frequency Bands for B Measurements 평균혈압측정 : 혈압파형에서기본파의 10 배고조파까지수용 ( 약 0Hz) 만으로가능 미분파형측정 : 0 배고조파까지수용할경우 5% 오차이내로재생가능 파형의완벽한측정 : 진폭및위상특성이공히우수할것이요구되나, 진폭특성이우선