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APS Refresher Course Mechanics of Breathing John B. West, MD, PhD, Dsc UCSD School of Medicine Experimental Biology

Students seem to be much less prepared for mechanics than they were 40 years ago. Apparently elementary physics now receives less attention in college and high school. I grew up building radios, and notions of pressure, flow and resistance are ingrained. Today's kids simply plug in electronic components.

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APS Refresher Course Mechanics of Breathing John B. West, MD, PhD, Dsc UCSD School of Medicine Experimental Biology

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    1. APS Refresher Course Mechanics of Breathing John B. West, MD, PhD, Dsc UCSD School of Medicine Experimental Biology 2008 April 5, 2008

    2. Students seem to be much less prepared for mechanics than they were 40 years ago

    3. Apparently elementary physics now receives less attention in college and high school

    4. I grew up building radios, and notions of pressure, flow and resistance are ingrained. Today’s kids simply plug in electronic components

    5. Two examples of confusion from this year’s teaching

    6. In a demonstration with a lung in a Lucite box, a water manometer showed the box pressure. One student was confused about whether the pressure indicated on the manometer was above or below atmospheric pressure

    7. Another example on the mechanics of the pulmonary circulation

    8. An embolism completely blocks blood flow to one lobe of the lung. Which of the following is FALSE? A. Vascular resistance of the non-occluded lung is decreased. B. Vascular resistance of the overall lung is decreased. C. Alveolar Po2 in the occluded lobe is increased. D. If total ventilation and blood flow remain constant, arterial Po2 will fall. E. After 3 days, the compliance of the occluded lobe will be reduced.

    9. B is a false statement. If a large part of the circulation is blocked the overall vascular resistance must increase. Astonishingly some students cannot see this. (They argue that recruitment and distension of vessels in the non-embolized area will result in a reduced overall resistance)

    10. Because some students are so ill-prepared for the simple physical concepts, we now include a short primer before the lecture notes

    15. Our physiology course has two lectures on mechanics, one on statics, and the other on dynamics. We also have a demonstration on pressure-volume behavior of a rabbit lung, and three small-group discussions covering some of the material.

    16. Topics in the first lecture include Muscles of respiration Inspiration Expiration Elastic properties of the lung Pressure-volume curve Compliance Surface tension Regional differences of ventilation Airway closure Elastic properties of the chest wall

    17. Here are some of the slides in the first lecture taken from my book

    24. Topics in the second lecture include Airway resistance Laminar and turbulent flow Measurement of resistance Pressures in the breathing cycle Factors determining resistance Dynamic compression Causes of uneven ventilation Tissue resistance Work of breathing Work done on the lung Total work of breathing

    25. Here are some of the slides in the second lecture

    32. Conclusions Students are less well-prepared to understand simple physical principles than they were a few years ago We now include a short primer at the beginning of the course Mechanics of breathing remains a very difficult topic for some students

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