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

Students seem to be much less prepared for mechanics than they were 40 years ago 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 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. Todays kids simply plug in electronic components I grew up building radios, and notions of pressure, flow and resistance are ingrained. Todays kids simply plug in electronic components

Two examples of confusion from this years teaching Two examples of confusion from this years teaching

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 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

Another example on the mechanics of the pulmonary circulation Another example on the mechanics of the pulmonary circulation

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. A.Vascular resistance of the non- occluded lung is decreased. B.Vascular resistance of the overall lung is decreased. B.Vascular resistance of the overall lung is decreased. C.Alveolar Po 2 in the occluded lobe is increased. C.Alveolar Po 2 in the occluded lobe is increased. D.If total ventilation and blood flow remain constant, arterial Po 2 will fall. D.If total ventilation and blood flow remain constant, arterial Po 2 will fall. E.After 3 days, the compliance of the occluded lobe will be reduced. E.After 3 days, the compliance of the occluded lobe will be reduced.

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) 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)

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

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. 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.

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 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

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

Figure 7-1 From J.B. West, Respiratory Physiology: The Essentials (8 th ed.), 2008, used with permission by Lippincott Williams & Wilkins

Figure 7-3 From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

Figure 7-7 From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

Figure 7-5 From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

Figure 7-10 From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

Figure 7-11 From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

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 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

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

Figure 7-12 From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

Figure 7-13 From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

Figure 7-14 From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

Figure 7-16 From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

Figure 7-17 From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

Figure 7-18 From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

Conclusions 1) Students are less well-prepared to understand simple physical principles than they were a few years ago 2) We now include a short primer at the beginning of the course 3) Mechanics of breathing remains a very difficult topic for some students