Pressure. 3. Direct Pressure. Pressure in Human Body. Pressures and Ranges. Effects of Kinetic Energy. Effect of Gravitational Force

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1 3. Direct Fundamental concepts Diaphragm-type pressure transducers Dynamics of catheter-transducer system Catheter-tip pressure transducers Implantable pressure transducers measurements in small vessels measurements in collapsible vessels Tissue pressure measurements Force per area, unit is Pascal (Pa), mmhg, cmh O 1Pa = 1N/m 1mmHg = 133.3Pa 1mmH O = Pa 1mmHg=13.595mmH O Absolute pressure refer to Vacuum = Atmosphere pressure + Gage pressure Gage pressure refer to Atmosphere pressure (1atm=101,35Pa=760mmHg=1033.mmH O) in human body = Gage pressure, generally in Human Body Organs Note Cardiovas Ventricular (VP) Heart contraction and expansion cular Arterial Blood (ABP) Aorta pressure by left ventricle contraction Venous (VP) in vein. Right atrium=central VP Pulmonary Artery (PAP) Lung pressure by right ventricle (PCWP) Microvascular D=0-50μm vessels Respirato Airway (PAW) Due to respiration ry Intrathoracic Due to respiration Urinary Gastrointestinal in stomach and bowels Digestive Intravesical Urine pressure in bladder Intraurethral for urination Others Intracranial (ICP) in skull Intraocular (IOP) in eye Intrauterine (IUP) Amniotic pressure in amnion s and Ranges 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 P gh 1 U const static pressure gravitational kinetic energy potential energy where U: flow velocity P: static pressure ρ: density of fluid g: acceleration of gravity h: height difference in two positions vortex 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 Biomedical Information Technology Lab 1

2 Physiological Reference Point sternum right atrium Blood (BP) Cardiovascular system is divided into systematic circulation and pulmonary circulation connected by veins and arteries on vessel wall when heart pushes out blood Arterial blood pressure Upper arm arterial BP at heart level center of the fourth intercostal space BP Gradient in Cardiovascular System First BP Measurement Stephen Hales 1733 UK 10/16 Direct BP Measurement Catheter and Transducer Fixation Radial artery Stopcock Biomedical Information Technology Lab

3 Arterial Catheter Transducer and Disposable Dome AD Instruments ML T1050 Strain Gauge Transducer Strain of Diaphragm Displacement of diaphragm at a distance r from the center 1 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 3P 1 r R 3r r 8t E 3P Tangential strain 1 t r R r 8t E Silicon Beam Transducer Silicon Diaphragm Biomedical Information Technology Lab 3

4 Capacitive Transducer Capacitive Transducer C A d ε permittivity of the medium ( F/m in air) A area of diaphragm d distance of separation gap Ci V0( t) V e C x jt i d C V e A jt i i Catheter Transducer Model F d x dx m c Kx dt dt F: external force m: mass of fluid in the catheter c: flow resistance K: elastance damping factor Step Response h ln P i1 P i P i1 ln Pi natural frequency f 0 1 h T r K Natural frequency: f 0 l Damping factor: 4l h 3 r K An example: if l = 1.5 m, r = 0.33 mm, K = 33 kpa/m 3, then f 0 = 48 khz and h = transducer 1 f d T Frequency Response Catheter-Tip System amplifier controller connection cable catheter tip Millar Mikro-Tip Catheters Biomedical Information Technology Lab 4

5 Catheter-Tip Sensor Head Fiber-optic Transducer Light source Photo detector Optical fibers Diaphragm Servo-controlled Pipet System Pipet Resistance vs. Difference micropipette counter pressure drive unit inward flow outward flow Intracranial Intraocular Sensor head Configuration of the pressure sensor transponder Schematic of the intraocular pressure monitoring system Implantation scheme Biomedical Information Technology Lab 5

6 Sac Radio Telemetry Capsule stent graft Holowitz and Farrar 196 Balloon Catheter for Collapsible Vessel pressure-volume characteristics Pneumohydraulic Perfusion System regulator sphincter contraction pressure on the esophagus, the anus and the urethra inflated by air the pressure in the balloon will be equilibrated to the surrounding tissue pressure Compressed gas bottle Infusion fluid Interstitial 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 Hypodermic Needle Perspex dome Biomedical Information Technology Lab 6

7 Compartment Esophageal Sphincter Glass capillary transducer Intravenous catheter Meniscus Wick Biomedical Information Technology Lab 7