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2013 Senior Design: MEEG401/BMEG450 mySpirometer: An Educational Tool to Study Respiratory Function m = Bachelor of Mechanical Engineering b = Bachelor of Biomedical Engineering e = Bachelor of Electrical Engineering Ian Beringerᵐ Stacy Handᵇ, Chris Mayᵇ, Tonghua Liᵉ, Ling Liᵉ, Tim Baranᵐ Background Prototype Testing and Validation Final Prototype National Instruments : A producer of scientific testing equipment involved in developing interactive educational programs and equipment to make science education portable and fun. Ambition: Extend their products to teach about the respiratory system and assist in the diagnosis of respiratory conditions in third world countries. Spirometry: The evaluation of respiratory function using a spirometer—a device used to measure lung volumes and flow rate of expired and inspired air. Fig. 1: Students utilizing the myDAQ [2] Project Scope The team has designed an educational program and spirometer that is able to interface with the myDAQ whilst teach about lung function as well as provide diagnostic feedback to meet the needs of the sponsor. It is designed to easily and accurately measure necessary pulmonary functions in both classroom and clinical settings. Design Requirements Based on conversations with the sponsor and research on spirometry standards, the requirements were established to be the following: Spirometer: Measure volume and flow rate of air inspired and expired air, be compatible with the myDAQ, have a low manufacturing cost, be hygienic. LabVIEW Program: Contain interactive features, be attractive, contain interface to educate students about lung functions and interface for diagnostic functions. Fig. 2: Mechanical Spirometer [1] Fig. 3: Electrical Interface [1] Fig. 4: LabVIEW Program [1] The final prototype is the union of three main components: Mechanical Spirometer- Using a 1400x200 wire mesh that acts to create two distinct pressure chambers, a pressure gradient , proportional to the effect induced by Darcy’s Law, is produced as a person inhales and exhales. Electrical Interface- Integrates the spirometer with the myDAQ. Utilizes a pressure sensor capable of converting the pressure gradient to a voltage. Maximizes accuracy of the signal. LabVIEW Program- Converts voltage to flow rate and volume. Creates an interactive, educational environment for high school students to learn about lung function. Prototype Construction: Mechanical Spirometer produced by FDM 3D printing, and coated with 100% acetone. Electrical components soldered to prototype board. Calibration Linear relationship between flow rate and voltage Slope and baseline voltage determined, and used to calibrate the program. Testing and Validation Tested according to spirometry standards set by the American Thoracic Society. Tests for accuracy and range conducted with a source of known flow-rate varying from 0-14L/s. Set-up shown in figure 10. Physiological Tests: 5 Subjects were tested performing maximum inhale and exhale. Accuracy calculated according to expected values from standards. 1 Mechanical Metric Concept Generation Volume 2 Want/Need/Constraint Metric and Target Value Interactive Program/ Display Functional Spirometer Contains interactive features, 90% find it attractive, easy to use, and understand. Conduct measurements from: 0-30 sec, 0-8L volume, 0.5-12.0L/s flow rate 3 Accuracy Less than 3% error in volume measurements, less than 5% error in flow rate measurements 4 Compatible with myDAQ Yes 5 Easily Assembled <1 minute for assembly 6 Hygienic Meets industry standard for hygiene 7 Durable <12000 cycles to failure 8 Small Size Within 8”x8”x8” footprint -- Low Manufacturing Cost <$40/unit -- Ergonomic 90% find spirometer comfortable -- Safe No sharp corners, <1 open wired connection Table 1: Condensed ranked wants, needs, constraints, and coinciding metrics and target values. [1] Description Value Slope 6.981 Baseline Voltage 31.95 R^2 Value 0.9971 Table 2: Calibration Values [1] Fig. 12: Test set-up, known flow. [1] Flow Rate Rank Fig. 11: Final Prototype [1] Time Fig. 5: 1st Generation [1] Fig. 6: 2nd Generation [1] Fig. 7: 3rd Generation [1] Electrical Fig 8: 1st and 2nd Generation [1] The design process of the three main components was highly iterative. Some of the major changes are highlighted below. Mechanical: From 1st to 3rd generation, the spirometer airways were increased in diameter, the mouthpiece changed from threaded to pressed fit, and a handle containing the PCB board was added. Electrical: From 1st to 2nd generation, four op-amps and multiple capacitors were replaced by one 4-in-1 op-amp, LabVIEW Fig. 9: 2nd Generation [1] decreasing cost. LabVIEW: From 1st to 3rd generation, the user interface became more comprehensive while still maintaining ease of use and functionality. Fig. 10: 3rd Generation [1] Spirometry Standards mySpirometer Range 0-8L >8 L Accuracy +/- 3% 5-10% Range 0.5-12.0 L/s >12.0 L/s Accuracy +/- 5% 5-10% Range 0-30 sec >30 sec Accuracy 2% <1% Table 3: mySpirometer accuracy and range tests compared to ATS Spirometry Standards. [1] [3] Fig. 13: mySpirometer Volume vs. Time, and Volume vs. Flow Rate Test. [1] Fig. 14: Vernier Spirometer Volume vs. Time Test. [4] Acknowledgements & References The mySpirometer team would like to thank National Instruments, Sam Strickling, Dr. Anita Singh, Dr. Jennifer Buckley, Dr. Antony Beris, Dr. Roger Stahl, and Prof. Dyer Harris. [1] – “mySpirometer: An edcucational tool…”. Beringer, Hand, et al. [2] – “National Instruments myDAQ”. National Instruments. [3] – “Spirometry Standards”. American Thorasic Society [4] – “Vernier/Biopac, Inc. Spirometer Interface”. Vernier and Biopac. Inc.