APS Refresher Course APS Refresher Course

Mechanics of BreathingMechanics of Breathing

John B. West, MD, PhD, DscJohn B. West, MD, PhD, DscUCSD School of MedicineUCSD School of Medicine

Experimental Biology 2008Experimental Biology 2008April 5, 2008April 5, 2008

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

Apparently elementary Apparently elementary physics now receives physics now receives

less attention in college less attention in college and high schooland high school

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

Two examples of Two examples of confusion from this confusion from this

year’s teachingyear’s teaching

In a demonstration with a lung in In a demonstration with a lung in a Lucite box, a water manometer a Lucite box, a water manometer showed the box pressure. One showed the box pressure. One

student was confused about student was confused about whether the pressure indicated whether the pressure indicated

on the manometer was above or on the manometer was above or

below atmospheric pressurebelow atmospheric pressure

Another example on the Another example on the mechanics of the mechanics of the

pulmonary circulationpulmonary circulation

An embolism completely blocks blood An embolism completely blocks blood flow to one lobe of the lung. Which of flow to one lobe of the lung. Which of

the following is the following is FALSEFALSE??

A.A. Vascular resistance of the non-Vascular resistance of the non-occluded lung is decreased.occluded lung is decreased.

B.B. Vascular resistance of the Vascular resistance of the overall lung is decreased.overall lung is decreased.

C.C. Alveolar PoAlveolar Po22 in the occluded in the occluded lobe is increased.lobe is increased.

D.D. If total ventilation and blood If total ventilation and blood flow remain constant, arterial Poflow remain constant, arterial Po22 will fall. will fall.

E.E. After 3 days, the compliance of After 3 days, the compliance of the occluded lobe will be reduced.the occluded lobe will be reduced.

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

reduced overall resistance) reduced overall resistance)

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

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

material.material.

Topics in the first lecture includeTopics in the first lecture include

Muscles of respirationMuscles of respiration Inspiration Inspiration Expiration ExpirationElastic properties of the lungElastic properties of the lung Pressure-volume curve Pressure-volume curve Compliance Compliance Surface tension Surface tensionRegional differences of ventilationRegional differences of ventilation Airway closure Airway closureElastic properties of the chest wallElastic properties of the chest wall

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

taken from my booktaken from my book

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

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

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

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

Topics in the second lecture includeTopics in the second lecture include

Airway resistance Airway resistance Laminar and turbulent flow Laminar and turbulent flow Measurement of resistance Measurement of resistance Pressures in the breathing cycle Pressures in the breathing cycle Factors determining resistance Factors determining resistance Dynamic compression Dynamic compressionCauses of uneven ventilationCauses of uneven ventilationTissue resistanceTissue resistanceWork of breathingWork of breathing Work done on the lung Work done on the lung Total work of breathing Total work of breathing

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

lecturelecture

Figure 7-12

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

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

Figure 7-14From 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 7-17From J.B. West, Respiratory Physiology: The Essentials (8th ed.), 2008, used with permission by Lippincott Williams & Wilkins

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

ConclusionsConclusions

1)1) Students are less well-prepared Students are less well-prepared to understand simple physical to understand simple physical principles than they were a few principles than they were a few years agoyears ago

2)2) We now include a short primer at We now include a short primer at the beginning of the coursethe beginning of the course

3)3) Mechanics of breathing remains a Mechanics of breathing remains a very difficult topic for some very difficult topic for some studentsstudents