Trachte: Ventilation

Question 1

What is ventilation?

Answer 1

how oxygen gets to the alveoli

Question 2

What causes hypoxia?

Answer 2

A reduction in ventilation

Question 3

What are three causes of hypoxia?

Answer 3

1. Drugs (opiates)
2. Brain damage
3. Breath holding

Question 4

What is tidal volume?

Answer 4

The amount of air inspired and expired in routine breathing

Question 5

How much air is normally expired/inspired (tidal volume)?

Answer 5

500 ml

Question 6

What is total long volume?

Answer 6

4000 ml

Question 7

What is total lung capacity?

Answer 7

7000 ml

Question 8

What is the vital capacity?

Answer 8

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

Question 9

What is vital capacity usually equal to?

Answer 9

6000 ml

Question 10

What is the residual volume?

Answer 10

The amount remaining in the lungs after a maximal expiration

Question 11

What is the residual volume usually equal to?

Answer 11

1500 ml

Question 12

What is the functional residual capacity?

Answer 12

Amount remaining after a typical exhalation

Question 13

What is the normal functional residual capacity?

Answer 13

2500 ml

Question 14

How do you measure the functional residual capacity?

Answer 14

You can’t measure it directly but you can calculate it using:

a gas dilution technique

Plethysmograph

Question 15

What is a gas dilution technique?

Answer 15

Take a spirometer w/ a known amt of helium. Ask the pt to breathe starting from the functional residual capacity (volume of air left in the lung after a normal breath out). Measure the new helium concentration once the He settles into the lungs.

Calculate FRC using FRC = ((C1xv1)/C2) - V1

Question 16

What is a plethysmograph?

Answer 16

Measure pressure in a box of fixed volume surrounding an individual.

P1 x V1 = P2 x V2
Change in volume = V2- V1

Question 17

What is total ventilation?

Answer 17

Amount of air entering and leaving the lung each minute

Question 18

What is typical ventilation/minute?

Answer 18

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

Question 19

How much of each breath reaches the alveoli?

Answer 19

350 ml of each breath

Question 20

How much of each breath remains in the anatomic dead space?

Answer 20

150 ml

Question 21

What is typical alveolar ventilation?

Answer 21

350 ml x 15 b/min = 5250- ml/min

Question 22

How can you calculate alveolar ventilation?

Answer 22

Take the amount of CO2 in the exhaled air divided by the fractional concentration of CO2 in the expired air

Va = VCO2/PCO2 x K

Question 23

What happens if there is an increase in alveolar ventilation?

Answer 23

If Va increases and VCO2 stays the same, then PCO2 HAS TO BE lowered.

Question 24

How do you measure dead space volume?

Answer 24

By breathing pure O2!

The expired gas is plotted vs N2 in expired gas. The N2 concentration increases with expiration until it reaches a peak.

Question 25

How do you calculate dead space?

Answer 25

By finding the MIDPOINT N2 concentration such that the volume above and below this point are EQUAL.

THE MIDPOINT represents the VOLUME of the anatomic dead space.

The MIDPOINT represents the midpoint in the transition from dead space to alveolar ventilation.

Question 26

How do you calculate physiological dead space?

Answer 26

By taking the fraction of CO2 in expired gas and comparing it to alveolar gas

Question 27

What is the Bohr equation?

Answer 27

Used to calculate physiological dead space

Vd/VT= (PAco2- PEco2)/ PAco2

Question 28

What are regional differences in ventilation?

Answer 28

LOWER portions of the lung are ventilated BETTER than the apical regions