Pulmonary 4 - Lecture 26

Question 1

What is the combined gas law?

Answer 1

PV/T1 = PV/T2

• Pressure is proportional to temp
• volume is proportional to temp
• volume & pressure are inversely related

Question 2

What does the sum of the partial pressures & partial volumes of a gas equal?

Answer 2

Equals the total pressure & total volume

Question 3

What airways do not participate in gas exchange?

O2, N2, and Water vapor in humidified air remains unchanged until gas reaches what?

Answer 3

CONDUCTING AIRWAYS!

Unchanged until it reaches the ALVEOLUS
respiratory zone

Question 4

What kind of relationship exists between CO2 and ventilation?

As ventilation increases, what happens to CO2 content?

Answer 4

INVERSE

As ventilation increases, CO2 content decreases

Question 5

What are the regional differences in ventilation? What are the 2 reasons?

Answer 5

The base has higher ventilation than the apex

1. Gravitational Effects
2. Variable Resistance/Compliance of alveolar units

Question 6

What is the PO2 equation?

The PAO2 equation?

Answer 6

PIO2 = (Patm - Pwater)x FO2

PAO2 = PIO2 - PACO2 / R

Question 7

What is a normal PA02?

Answer 7

95-100 cmH20

Question 8

1.What is the PAO2 if you breathe 100% oxygen and the PACO2 is 45 mmHg (R=0.8)

Answer 8

PIO2 = (760 -47 mmhg) X 1.0
= 713 mmHG

PAO2 = 713 mmHg – 45 mmHg / 0.8 
PAO2 = 657 mmHg

Question 9

2. What is the PAO2 if you breath 40% oxygen and the PACO2 is 60 mmHG (R=0.8)

Answer 9

PIO2 = (760 mmHG – 47 mmHg) X 0.4
= 285 mmHg

PAO2 = 285 mmHg – 60 mmHg / 0.8
= 210 mmHg
 expect this in the arterial blood

Question 10

What determines the fraction of Alveolar CO2 (partial pressure)?
2 things

Answer 10

1. Metabolism

2. Rate of elimination (ventilation)

Question 11

If alveolar CO2 is high, is ventilation high or low?

Answer 11

LOW

Question 12

If you increase ventilation by 2, how does CO2 change?

Answer 12

Decreases by 2

Question 13

What did radioactive Xenon studies determine about inspired air?

Answer 13

Showed that air is distributed more to the base of the lung

Question 14

Why does the base of the lung receive the most air?

Answer 14

1. 5 lobes form a triangular structure so widest part is at the BASE - anatomically more alveoli
2. at FRC the base of the lung is MORE COMPLIANT than apex

Question 15

Because the Pleural Pressure & Translung pressure is greater at the APEX in an upright position, why is there still LESS air into the apex?

Answer 15

The Alveoli units at the apex are LESS COMPLIANT

-AT the top:
the alveoli are already slightly open since they are in a more negative pleural pressure, but because they are LOWER in compliance
they receive LESS VOLUME of the ventilation as compared to the base of the lung

Question 16

When are the Base Alveoli completely collapsed and thus the units of airflow at the APEX are higher than those at the base?

Answer 16

LOW VOLUMES

Question 17

The time constant is determined by what? What does a longer time constant represent?

Answer 17

T = R * C
Resistance & Compliance

Longer Time constant = slow emptying/filling

Question 18

What are normal inspiratory & expiratory times?

Answer 18

Normal inspiratory time: 2 s

Normal expiratory time: 3s

Question 19

If Resistance increases how does the Time Constant change?

If compliance decreases?

Answer 19

1. SLOWER FILLING, incomplete filling at 2 s
2. Incomplete filling in 2s
   - fills FASTER but incompletely filled (since it is stiffer) so a smaller portion ventilated

Question 20

If you decrease compliance and keep resistance constant, what happens to the time constant/ filling and ventilation?

Answer 20

FILLS FASTER! BUT INCOMPLETELY filled so a smaller proportion of the ventilation!!!
- affects whether the lung is evenly ventilated

Question 21

What does the single nitrogen test show?

State the 4 events

Answer 21

At uniform ventilation, N2 and lung volume is constant

1. N2 fixed at zero as dead spaces full of O2 empty
2. Rapid Upswing in N2 as alveolar regions in the BASE OF THE LUNG empty
3. Aveolar Plateau - equal emptying of all lung zones from base to apex
4. 2nd increase in N2 due to slow emptying alveoli!!!

Question 22

What is the equation for ventilation?

Answer 22

Ventilation = Frequency * Tidal Volume

Question 23

The tidal volume first fills what space?

Answer 23

Dead space filled first (VD) then the alveolar space (VA)

Vtotal = f * (VD + VA) = f * VT

Question 24

What is the first air to reach the deep alveoli during inspiration?

Answer 24

Dirty air from previous exhalation

Question 25

What ventilation does not contribute to gas exchange?

Answer 25

Dead space ventilation

D= f*VD

Question 26

What is the alveolar ventilation equation?

Answer 26

VA = f*VA
OR

VA = f * (Vt - VD)

Question 27

What does the single breath Nitrogen washout determine?

Answer 27

Anatomical Dead Space

“Fowler’s Method”

Question 28

What measures Anatomic Dead Space? Physiological dead space?

Answer 28

1. Anatomic = Fowler’s Nitrogen Washout

2. Bohr’s method

Question 29

What is physiological dead space?

Answer 29

Total volume that does not participate in gas exchange =

Anatomical Dead Space + ventilated Alveoli that are not perfused (ex: lung emboli –> vessels are obstructed and alveolar regions not perfused)

Question 30

When do physiologically dead spaces become larger than anatomical dead spaces? Are these usually equal?

Answer 30

DISEASES

• usually equal

Question 31

What is the normal ratio of VD/Vt?

Answer 31

0.2 - 0.35

Question 32

What does the expired fraction of CO2 X the exhaled tidal volume equal?

Answer 32

Vt * Fe = (Vt - VD) * FA

VD/Vt = PaCO2 - PCO2 / PaCO2

PaCO2 = arterial CO2
FA = alveolar CO2 fraction
Fe = expired fraction of CO2

Question 33

What are the two components of tidal volume?

Answer 33

1. Dead space

2. Alveolar Ventilation

Question 34

How does one increase alveolar ventilation?
1. Increase Frequency of breathing
OR
2. Increase Tidal Volume

Answer 34

Increasing Tidal Volume is more effective than an increase in the frequency of breathing