PhysicsinMedicine.pptVIP

Physics in Medicine PH3708 Dr R.J. Stewart Scope of Module Cardio-vascular system Fluid flow in pipes, circulation system, pressure Membranes Osmosis and solute transport Transmission of electrical signals Nerves, ECG Optical Fibres and Endoscopy Scope of Module Ultrasound Imaging and Doppler measurements Radioisotope imaging and radiology X-ray generation and imaging NMR imaging Module Resources Web Page: http://www.rdg.ac.uk/physicsnet/units/3/ph3708/ph3708.htm Books: Good general books: “Physics of the Body”, Cameron, Skofronick and Grant “Medical Physics”, J.A. Pope Other more specialised books are given in the unit description and will be referred to where necessary Cardiovascular System Physics of the Body, Cameron, Skofronick and Grant, Ch. 8 In considering the circulation of blood, one essentially considers the flow of a viscous fluid through pipes of different diameters Define: Viscosity: arises from frictional forces associated with the flow of one layer of liquid over another Viscosity Consider a circular cross section pipe: Flow through pipe due to pressure difference Assume: flow at walls of pipe = 0, maximum in the centre (arrows in figure represent velocity) Frictional force per unit area, F, proportional to the velocity gradient Viscosity Viscosity The slower moving fluid outside the central (shaded) region exerts a viscous drag across the cylindrical surface at radius r. For a length Δx of pipe the area of surface is 2πrΔx. The force points in the opposite direction to the direction of fluid motion and is of magnitude 2πrΔx η |dv/dr| 2r 2a Volume Flow Rate The average flow from the heart is the stroke volume (the volume of blood ejected in each beat) x number of beats per second. This is ~ 60 (ml/beat) x 80 (beats/min) = 4800 ml/min Volume Flow Rate Poiseulle’s Equation Volume flow rate, Q, related to pressure difference DP, length l and radius a by: l a P1 P2 DP= P1 - P2 Volume Flow Rate Often convenient to define a resistance, R to fl