Ventilation

Question 1

What does ventilation refer to?

Answer 1

the amount of air entering and leaving the lungs per minute

Question 2

What is alveolar ventrilation?

Answer 2

the amount of air actually exchanging with the blood

Question 3

Is CO2 concentration in alveolar gas directly or inversely proportional to ventilation?

Answer 3

inversely - if you increase ventilation you blow off extra CO2 and CO2 concentration decreases

Question 4

What is the amount of a breath that DOESN”T reach the alveoli?

Answer 4

the anatomic dead space

Question 5

How does physiologic dead space differ from anatomic dead space?

Answer 5

the anatomic dead space is the amount of a breath not reaching the alveoli

physiologic dead space is the amount of a breath that doesn’t get exchanged with the blood (higher than the anatomic dead space)

Question 6

Which part of the lung is ventilated the best?

Answer 6

the lower regions are ventilated better than the upper regions

Question 7

WHat are three causes of a decrease in ventilation?

Answer 7

opiates or other drugs
brain damage
breathholding

Question 8

What is the amount of air inspired and expired in a routine breath? What’s the average?

Answer 8

tidal volume

usually around 500 mL

Question 9

What is total lung volume uusally? How about total lung capcity?

Answer 9

total lung volume is usually about 4000 mL but the total lung capacity is around 7000 mL

Question 10

What is the vital capacity? What is the average?

Answer 10

the maximum volume of air that can be exhaled after a maximum inspiration

usually about 6000 mL

Question 11

WHat is left after you exhale out the vital capacity? What is the average?

Answer 11

the residual volume

usually about 1500 mL

Question 12

What is the difference between residual volume and functional residual capacity? What is the average?

Answer 12

residual volume is what’s left after a forced expiration

functional residual capacity is the amount remaining after a typical expiration - usually 2500 mL

Question 13

Can we dirctly measure the functional residual capacity?

Answer 13

Nope - we have to do it indirectly with a gas dilution technique

Question 14

Describe the gas dilution technique.

Answer 14

Use helium since it doesn’t diffuse into the blood at all.

Have a fixed volume of helium. have the person breath it in - the concentration of the helium will decrease in direct proportion to the added lung volume to the system

Question 15

What’s the other way we can measure functional residual capacity?

Answer 15

with a plethysmograph, which is a closed box that measures pressure changes and measures volumes based on P1 x V1 = P2 x V2

Question 16

What is total ventilation?

Answer 16

the amount of air entering and leaving the lung each minute

Question 17

What is an average total ventilation?

Answer 17

500 mL x 15 breaths/min = 7500 mL/min

Question 18

Of the average 500 mL that enters the lungs per breath, how much actually reacehs the alveoli

Answer 18

350 mL (150 mL in the dead space)

Question 19

Thus, what is an average ALVEOLAR ventilation rate?

Answer 19

350 ml x 15 breaths/min - 5250 mL/min

Question 20

We can’t measure alveolar ventilation directly, so how do we do it?

Answer 20

We calculate it by the amount of the CO2 in the exhaled air divided by the fraciotnal concentration of CO2 in the expired air (since basically all the CO2 coming out has to come from the avoleoli)

Va = Vco2/Pco2 x K (a constant)

Question 21

How do we calculate ANATOMICAL dead space volumes?

Answer 21

Nitrogen washout

You breath in pure O2. This means any expired N2 must come from the lungs

Volume of expired gas is plotted vs N2 concentration in the expired gas

at first you’ll only have O2 coming out because there;s only pure O2 in the dead space, but then as you continue breathing, N2 concentration in the expired gas will increase until it’s constant.

The volume at the half-way point is the dead space volume

Question 22

How do we calculate PHYSIOLOGICAL dead space?

Answer 22

You take the fraction of CO2 in expired gas and compare it to alveolar gas

Vd/Vt = (PAco2 - PEco2)/PAco2