1. Chapter 13 Blood Pressure Monitoring

2. Originates from the heart Value depends on 3 factors: cardiac output diameter of arteries the quantity of blood Commonly refers to arterial blood pressure peripheral resistance One of the oldest physiological measurements Powerful risk factor for cardiovascular disease Circulation System

3. AV valve close Aortic valve close Circulation System

4. Definition 단위 면적의 혈관벽에 가해지는 혈액의 힘 continuous : 혈액순환에 있어서 가장 중요함 심장에서 pumping 된 양과 같은 양의 혈액이 인체 각 부분에 전달되어야 함 Why do we need BP? 1) 혈관 질환이나 생리학적 불균형을 알 수 있음 2) cardiac output 의 변화, 혈관저항의 변화, 혈류역학 및 생리학적 변화의 영향을 반영 3) 말초신경 계통의 변화상태를 판단 혈압의 종류 1) 수축기 혈압 (systolic BP) 2) 이완기 혈압 (diastolic BP) 3) 평균 혈압 (mean BP) Blood Pressure

5. Brachial artery is the most common measurement site Close to heart Convenient measurement Other sites are : forearm / radial artery wrist (tends to give higher SP) The most common indirect methods are Auscultation and Oscillometric Measurement of Blood Pressure

6. Invasive (Direct) 측정위치 : brachial, carotid, femoral 정맥압 (CVP, central venous pressure) 동맥압 (RAP, right atrial pressure) Catheter 의 특성이 중요 as short as possible as stiff as possible Noninvasive (Indirect) Use of Korotkoff sound Sphygmomanometer (cuff, pressure gage, pressure bulb, release valve) + sthethoscope Measurement of Blood Pressure

7. Use of Korotkoff sound 1906 년 Russian Physicist 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) Cuff 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 BP,wide cuff width : low BP Indirect Measurement

8. The Korotkoff sounds are auscultated with a stethoscope or microphone (automatic measurement) Korotkoff sounds are generated by the flow of blood and vibrations of the vessel The frequency range of Korotkoff is 15~500 Hz and the accuracy is ± 2mmHg (SP) and ±4mmHg (DP) Korotkoff Method

9. SP and DP are estimated from the amplitudes of the oscillation by using a (proprietary) empirical algorithm. The cuff pressure is deflated either linearly or stepwise. The intra-arterial pulsation is transmitted via cuff to transducer Oscillometric Method

10. Photoplethysmography (PPG) Tonometry Ultrasound Other Noninvasive Methods

11. Components 1) Catheter - semi rigid (filled with saline) - 압력을 측정하는 부위까지 삽입 (balloon tipped catheter) 2) Pressure transducer 3) Monitor 장점 : continuous observation, sampling blood 단점 : technical problems (air bubble, infection) Direct Measurement

12. Extravascular sensor Intravascular sensor Direct Measurement

14. Catheter Model and Fluid Resistance Flow of fluid in a catheter,, is proportional to the pressure difference, Resistance of the tube (friction between the fluid and the inside surface of the tube) radius of the tube viscosity of the fluid length of the tube

15. Inertance and Compliance Inertance ( 유체의 관성 ) Compliance ( 벽의 탄성 ) Volume of expansion 시간당 흐름의 변화를 감지 constant

16. Fluid-Electrical Analogy

17. Catheter Equivalent Circuit radius of the tube viscosity of the fluid length of the tube

18. Frequency Response of a Catheter with a Diaphragm

19. Example #1 Catheter length : 2 meter Radius : 0.46 mm Wall with zero compliance Diaphragm compliance : (water) Compliance of the water in the catheter,

20. Example #2 Compute the transfer gain,

21. Catheter with Pinch, Bubble, and Leak Pinch Bubble Leak Assumption Pinch is a cylindrical shape Compliance of the pinch is neglected as a small quantity Pressure difference inside and outside the catheter

22. Example #3 Example #1 Pinch that reduces the radius by one-half It has a length Calculate pinch compliance, resistance, and frequency response,