Physiology II

Question 1

How is the “volume of the physiologic dead space” estimated?

Answer 1

(Pco2 of systemic arterial blood - Pco2 of mixed expired air)*(tidal volume/Pco2 of systemic arterial blood)

or tidal volume times the dilution of alveolar Pco2 by dead space air (which contributes no CO2)

Question 2

What is ventilation rate?

Answer 2

the volume of air moved into and out of the lungs per unit time

Question 3

What are some ways to express ventilation rate?

Answer 3

• minute ventilation

- alveolar ventilation

Question 4

What is minute ventilation?

Answer 4

the total rate of air movement into and out of the lungs

Question 5

What is the eqn. for minute ventilation?

Answer 5

tidal volume*(Breaths/min)

Question 6

How is alveolar ventilation different from minute ventilation?

Answer 6

alveolar corrects from the physiological dead space

Question 7

What is the eqn for alveolar ventilation?

Answer 7

(tidal volume - physiologic dead space)* (breaths/min)

or

Vco2(Rate of CO2 production) * K (863mmHg) / PAco2(alveolar PCo2)

Question 8

So Pco2 can be predicted using what two variables?

Answer 8

1) rate of CO2 production (Vco2)

2) alveolar ventilation (which excretes the produced co2)

Question 9

T or F. If CO2 production (Vco2) is constant, then PAco2 is determined by alveolar ventilation

Answer 9

T.

Question 10

Arterial Pco2 always equals alveolar Pco2. Why?

Answer 10

CO2 always equilibrates between pulmonary capillary blood and alveolar gas

Question 11

In asthma are FEV1 and FVC decreased or increased?

Answer 11

both decrease but FEV1 is decreased more so the ratio decreases as well (typical of obstructive disease where airway resistance is increased)

Question 12

How do FEV1 and FVC change in restrictive disease?

Answer 12

both decrease but FEV1 is decreased LESS so the ratio increases

Question 13

For a given pressure the volume of a lung is larger during expiration than inspiration. Why?

Answer 13

Hysteresis. Compliance is higher during expiration

Question 14

What is responsible for hysteresis?

Answer 14

difference in surface tension at the liquid-air interface of the air-filled lung

Question 15

So why is compliance less during inspiration?

Answer 15

when the lung volume is small, more tension is required to overcome surface tension

Question 16

When is surfactant active, inspiration or expiration?

Answer 16

inspiration

Question 17

What creates the negative pressure of the intrapleural space?

Answer 17

two opposing forces pulling on the space, the lungs tend to collapse and the chest wall tends to pull out

NOTE: this negative pressure helps keep the chest wall from popping out of place or the lungs from collapsing

Question 18

What is a consequence of pneumothorax?

Answer 18

the lung collapses because its no longer opposed by the IP vacuum

Question 19

How does emphysema affect lung compliance?

Answer 19

Increases it (fibrosis decreases it)

Question 20

T or F. In emphysema, the tendency for the lungs to collapse is less than for the chest wall to expand

Answer 20

T. So the body compensates with increased lung volumes (seeks a HIGHER FRC)

fibrosis is the opposite (seeks a lower FRC)

Question 21

What is the eqn for collapsing pressure on alveoli by surface tension?

Answer 21

P=2T/r (this equals the pressure needed to keep it from collapsing)

Question 22

When an alveoli collapses it is known as _____

Answer 22

Atelectasis

Question 23

What is the most important constituent of surfactant?

Answer 23

dipalmitoyl phosphatidylcholine (DPPC)

Question 24

When does surfactant production begin in gestation?

Answer 24

as early as 24 weeks

Question 25

What is the eqn for transmural pressure?

Answer 25

Palveolar- Pip

Question 26

Why is Pip negative?

Answer 26

The opposing forces of the lungs trying to collapse and the chest wall trying to expand create a negative pressure. This negative pressure keeps the lungs inflated

Question 27

When does Palveolar become less than Patm and thus drive air entering the lung?

Answer 27

halfway through inspiration

Question 28

During inspiration, Pip becomes even more negative. Why?

Answer 28

1) as lung volume increases, the elastic recoil of the lungs also increases and pull more against the IP space
2) airways and alveolar pressures become negative

Question 29

T or F. Alveolar pressure is negative during expiration

Answer 29

F.

Question 30

During forced expiration, the alveolar pressure becomes very positive. Why doesnt the lung collapse?

Answer 30

As long as transmural pressure remains positive the lungs stay open

Question 31

What is a possible consequence of forced expiration in someone with emphysema?

Answer 31

The positive alveolar pressures generated may cause the lungs to collapse

Question 32

Why would the lungs collapse during forced expiration in emphysema?

Answer 32

Pip raises to the same value as a normal person (~+20) but because elastic recoil is gone, alveolar pressure and airway pressure are lower than normal. The alveoli can remain open at a relatively normal transmural pressure but the larger airways cannot maintain the positive transmural gradient

Question 33

How do emphysema patients combat the potential for airway collapse upon expiration?

Answer 33

They expire slow and with pursed lips to raise airway pressure

Question 34

What is the eqn for converting partial pressure of a gas to conc of gas in liquid phase?

Answer 34

Cx= Px*Solubility constant

Question 35

What is the driving force for diffusion of gas?

Answer 35

partial pressure difference of the gas across the membrane

Question 36

Which diffuses more readily, Co2 or O2?

Answer 36

Co2 by up to 20x

Question 37

What forms of gas contribute to its partial pressure?

Answer 37

Only dissolved forms (i.e. not Hb bound, protein bound, etc.)

Question 38

What is the only constituent of air NOT bound in any form in blood?

Answer 38

Nitrogen