Pressure in Human Body

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Mae Pierce
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1 3. Direct Pressure Fundamental concepts Diaphragm-type pressure transducers Dynamics of catheter-transducer system Catheter-tip pressure transducers Implantable pressure transducers Pressure measurements in small vessels Pressure measurements in collapsible vessels Tissue pressure measurements

Pressure Force per area, unit is Pascal (Pa), mmhg, cmh 2 O 1Pa = 1N/m 2 1mmHg = 133.322Pa 1mmH 2 O = 9.8066Pa 1mmHg=13.

2 Pressure Force per area, unit is Pascal (Pa), mmhg, cmh 2 O 1Pa = 1N/m 2 1mmHg = Pa 1mmH 2 O = Pa 1mmHg=13.595mmH 2 O Absolute pressure refer to Vacuum = Atmosphere pressure + Gage pressure Gage pressure refer to Atmosphere pressure (1atm=101,325Pa=760mmHg= mmH 2 O) Pressure in human body = Gage pressure, generally

3 Pressure in Human Body Organs Pressure Note Cardiovas cular Respirato ry Urinary Digestive Ventricular Pressure (VP) Arterial Blood Pressure (ABP) Venous Pressure (VP) Pulmonary Artery Pressure (PAP) Microvascular Pressure Airway Pressure (PAW) Intrathoracic Pressure Gastrointestinal Pressure Intravesical Pressure Intraurethral Pressure Heart contraction and expansion Aorta pressure by left ventricle contraction Pressure in vein. Right atrium=central VP Lung pressure by right ventricle (PCWP) D=20-250μm vessels Due to respiration Due to respiration Pressure in stomach and bowels Urine pressure in bladder Pressure for urination Others Intracranial Pressure (ICP) Pressure in skull Intraocular Pressure (IOP) Intrauterine Pressure (IUP) Pressure in eye Amniotic pressure in amnion

4 Pressures and Ranges

5 Effects of Kinetic Energy Bernoulli s theorem Total energy per unit volume of fluid in a steady flow of ideal fluid (incompressible and zero viscosity) E static pressure P gh 1 U 2 2 gravitational potential energy const kinetic energy where U: flow velocity P: static pressure ρ: density of fluid g: acceleration of gravity h: height difference in two positions vortex

6 Effect of Gravitational Force Gravitational potential energy ρgh where Gravitational potential ρ: density of fluid ρh h: difference in altitude between these two points g: acceleration due to gravity

7 Physiological Reference Point sternum right atrium center of the fourth intercostal space

veins and arteries Pressure on vessel wall when heart pushes

8 Blood Pressure (BP) Cardiovascular system is divided into systematic circulation and pulmonary circulation connected by veins and arteries Pressure on vessel wall when heart pushes out blood Arterial blood pressure Upper arm arterial BP at heart level

9 BP Gradient in Cardiovascular System

10 First BP Measurement Stephen Hales 1733 UK 10/126

11 Direct BP Measurement

12 Catheter and Transducer Fixation Radial artery Stopcock

13 Arterial Catheter

14 Transducer and Disposable Dome AD Instruments ML T1050

15 Strain Gauge Transducer

Strain of Diaphragm Displacement of diaphragm at a distance r from the center 2 2 2 1 R r r 3 P 16t E Z 3 μ Poisson s ratio R diaphragm radius t

16 Strain of Diaphragm Displacement of diaphragm at a distance r from the center R r r 3 P 16t E Z 3 μ Poisson s ratio R diaphragm radius t diaphragm thickness P pressure difference E Young s modulus Radial strain r 2 3 P r R 3r 8t 2 E 2 3 P Tangential strain r R r t 8t 2 E

17 Silicon Beam Transducer

18 Silicon Diaphragm

85 10-12 F/m in air) A area of diaphragm d

19 Capacitive Transducer C A d ε permittivity of the medium ( F/m in air) A area of diaphragm d distance of separation gap V 0 ( t) C C i x V e i j t d A C V i i e j t

20 Capacitive Transducer

21 Catheter Transducer Model F d x m dt 2 dx c dt 2 F: external force Kx m: mass of fluid in the catheter c: flow resistance K: elastance Natural frequency: f r 2 K l 0 Damping factor: h r 3 4 l K An example: if l = 1.25 m, r = 0.33 mm, K = 33 kpa/m 3, then f 0 = 48 khz and h = 0.085

22 Step Response damping factor h 2 ln P P i 1 i 2 P ln 2 i 1 P i natural frequency f 0 1 T h 2 Pressure transducer 1 f d T

23 Frequency Response

24 Catheter-Tip Pressure System amplifier controller connection cable catheter tip Millar Mikro-Tip Catheters

25 Catheter-Tip Sensor Head

26 Fiber-optic Transducer Light source Photo detector Pressure Optical fibers Diaphragm

27 Servo-controlled Pipet System micropipette counter pressure drive unit

28 Pipet Resistance vs. Pressure Difference inward flow outward flow

29 Intracranial Pressure Sensor head Implantation scheme

30 Intraocular Pressure Configuration of the pressure sensor transponder Schematic of the intraocular pressure monitoring system

31 Sac Pressure stent graft

32 Radio Telemetry Capsule Holowitz and Farrar 1962

33 Balloon Catheter for Collapsible Vessel pressure-volume characteristics inflated by air the pressure in the balloon will be equilibrated to the surrounding tissue pressure

34 Pneumohydraulic Perfusion System Pressure regulator sphincter contraction pressure on the esophagus, the anus and the urethra Compressed gas bottle Infusion fluid

35 Interstitial Pressure Capsules are implanted subcutaneously Tissue and vascular system grow into the inside of the capsule (4w) Hypodermic needle is inserted into the capsule, and fluid pressure is measured by a pressure sensor

36 Perspex dome Hypodermic Needle

37 Compartment Pressure Glass capillary Pressure transducer Intravenous catheter Meniscus Wick

38 Esophageal Sphincter Pressure

Pressure Measurement. Introduction. Engr325 Instrumentation. Dr Curtis Nelson 3/12/18

Pressure Measurement. Introduction. Engr325 Instrumentation. Dr Curtis Nelson 3/12/18 3/12/18 Pressure Measurement Engr325 Instrumentation Dr Curtis Nelson Introduction A cluster of 72 helium-filled balloons over Temecula, California in April of 2003. The helium balloons displace approximately