7. Respiration Type Principle Rotameter Rotation of a rotor Volumeter Rotation of a rotor Pneumotachograph Air resistance Venturi tube Dynamic pressure Hot-wire anemometer Heat dissipation Time-of-flight flowmeter Traveling time Ultrasonic flowmeter Sound velocity Vortex flowmeter Generated vortices Turbulent flowmeter Pressure drop Wright respirometer Rotameter the revolution of the rotor responds to the air flow one direction Dräger volumeter Volumeter Fleisch Pneumotachograph Wire screen Pressure drop Poiseuille's Law η=fluid viscosity Metal foil parallel lumen two direction avoid water condensation Turbulent Flowmeter To differential pressure gauge Flow-through tube Cylindrical chamber To differential pressure gauge Bernoulli s theorem P const This geometry produces turbulent Q flow, and causes a pressure drop proportional to the square of the Flow-through tube flow rate between the upstream Cross-sectional and downstream tubes. P Q area A 1 A 1 U ρ: density U: velocity P: pressure Venturi Tube 1 A P 1 U A 1 The pressure difference is proportional to the square of the flow velocity. To differential pressure gauge Biomedical Information Technology Lab 1
Hot-wire Anemometer Servo-control Circuits for Hot-wire Anemometer Constant wire temperature Tw: wire temperature Tg: gas temperature d: diameter of the wire l: length of the wire α: heat transfer coefficient k: thermal conductivity of gas Tw Tg H dl( T w Tg ) N u k / d n Nu A BU T H U )( T w T ) ( a b g Heat dissipation: H RI Nusselt Number 0.17 Wire support The gas flow velocity is estimated by the amount of heat transfer from the wire to the gas, and the temperature difference between the wire and gas temperatures. the ratio of convective to conductive heat transfer Constant temperature difference between the wire and the gas Bidirectional Hot-wire Anemometer pulsed-wire technique Time-of-flight Flowmeter Flow velocity is measured by introducing a tracer into the upstream and detecting it in the downstream. When the separation between the introducing and detecting sites is known, flow velocity can be determined by the time-of-flight of the tracer. The most convenient tracer is a heated gas bolus. (flow velocity) Pulsed wire Sensor wire Pulsed wire Sensor wire (flow direction) Parallel arrangement Right-angle arrangement Time Course of Time-of-flight Flowmeter a short pulse current is applied to the wire Pulsed-wire Time-of-flight Gas Flowmeter elevates then decreases due to the heat dissipation from the wire to the gas detecting ambient temperature fluctuation The heated gas bolus moves downstream and reaches the sensor wire increases due to the heated gas bolus hitting the sensor wire Mosse and Roberts 1987 Biomedical Information Technology Lab
Sing-around Method Time-of-flight Flowmeter Using Singaround Method a signal detected by the detecting (sensor) wire triggers the next pulse applied to the heating (pulsed) wire frequency output is proportional to the flow velocity switch the transducers and measure the transit-time difference for N sing-around loops up and down stream measures the total time it takes to complete the N sing-around loops Transit time of downstream sound wave Ultrasonic Flowmeter D t1 c U cos Transit time of upstream sound wave D t c U cos θ=0 Diagonal Beam Ultrasonic Flowmeter Head cross section Short ultrasonic pulse trains are transmitted downstream and upstream simultaneously at 500 Hz Diagonal Coaxial c t c U D cos D cos U: flow velocity c: sound velocity D: distance between two crystals θ: beam angle with respect to the flow Δϕ: phase difference θ=0 Cylindrical T=ultrasonic transceiver Ultrasonic transmission channel Long tube termination Buess et al. 1986 Cylindrical Shell Ultrasonic Flowmeter Head Kármán Vortex Flowmeter predominant shedding frequency StU f d U: flow velocity d: diameter of the vortex generator S t : Strouhal number, a dimensionless number describing oscillating flow mechanisms Biomedical Information Technology Lab 3
Swirler Swirlmeter Thermal sensor Spirometry amplifier swirl producing component sensor meter body deswirl component Swirl flow When the gas passes through the blades, it spins forming vortices. The vortices is detected by a thermal sensor, and the gas flow rate is determined by the number of vortices passing at the sensor in a unit time interval. Objective To assess ventilatory function of the lung To assess ventilatory capacity: Forced Vital Capacity (FVC) Maximum Voluntary Ventilation (MVV) To assess airway obstruction: Forced Expiratory Volume in the 1st second (FEV1) Forced Expiratory Flow from 5% to 75% of vital capacity (FEF5-75%) Peak Expiratory Flow Rate (PEFR) Benedict-Roth Spirometer Bell the elevation of the bell is proportional to the expired air into the bell. Bell Displacement Measurement Plastic bell oxygen uptake measurement Water seal CO absorber Pure oxygen Rotating drum Water seal Pen the displacement of the bell or bellows is detected electronically. Mouth piece Counter weight to balance atmospheric pressure Respiration Linear potentiometer Bellows for Dry Spirometer various bellows are used instead of water seals light-weight portable instruments SpiroTech S780 CareFusion Corp. Spirometers Rolling seal type Straight bellows type Wedge type SuperSpiro Micro Medical Ltd. Biomedical Information Technology Lab 4
Hand Held Spirometer For a confined gas held at a constant temperature, pv = constant Boyle's law Body Plethysmographies the lung volume change is measured by the volume change of the body Mouthpiece P P V L P 0 P V L V0 P 0 V V L Spirobank FutureMed America Inc. IQspiro Digital Spirometer Midmark Corp. V 0 Detecting pressure change while maintain constant volume P P 0 Detecting volume change while maintaining constant pressure gas volume in the lung V V L P 0 P Closed-circuit system Body Plethysmograph Inductance Plethysmography Elite Body Plethysmography System Medical Graphics Corp. R measures the changes in thoracic and abdominal cross-sectional area. Lung volume change V K R K A 1 A Impedance Pneumography Sensitivity of Impedance Pneumography at Different Somatotype ΔZ/ΔV in human Ohms/Liter of air breathed Rib number 0-100kHz 5-500uA Baker and Geddes 1970 Z 453.3W V 1.084 (Ω/L) Two-electrode system Four-electrode system ΔZ/ΔV in dog Ohms/Liter of air breathed W: body weight (kg) Biomedical Information Technology Lab 5
Impedance Pneumogram and Spirometric Record Baker 1979 Oxygen-uptake in Exercise Essential function: Ventilation Circulation Metabolism ΔV respired volume change The maximum capacity of oxygen transport limits the maximum work load ΔZ Oxygen-uptake is the most important parameter Also known as VO, ventilation of oxygen. A measure of how much oxygen your body is consuming at any given time. Unit: ml/min, L/min of oxygen consumed. transthoracic impedance change Portable Oxygen-uptake Measurement A hood covers the head, a servo controlled blower draws outside air through the hood, adjusting its volume flow in order to keep the oxygen concentration in the hood constant. The flow rate of the blower is measured with a flowmeter, and oxygen concentration is measured by an oxygen meter. Continuous Oxygen-uptake Measurement A mask covers subject s head, fresh air is drawn into the mask. A pump adjusts air flow Q to keep the oxygen concentration in the mask constant. CO out Second mixing chamber with metal meshes and a honeycomb CO in Oxygen-uptake: Q VO Q CO in C Oout Respiratory Monitoring Objective = detection of abnormal respirations Central sleep apnoea = brain's respiratory control centers malfunction Obstructive sleep apnoea = obstruction of the upper airway Small tidal volume (<500ml or 7ml/kg bodyweight) Low respiration rate (<1-0 bpm) Oronasal sensors: Temperature Pressure Hot-wire anemometer Ultrasound Moisture Airflow Sensors Wearable during sleep Disposable sensors available Airflow - thermistor Snore - microphone Biomedical Information Technology Lab 6