Floreani: Alveolar Gas Exchange

Question 1

3 things that gas exchange depends upon

Answer 1

1. Ventilation
2. Perfusion
3. Barriers: tissue, blood cell and air-liquid interface across which gases diffuse

Question 2

In the lung, at what level does gas exchange begin?

Answer 2

At the level of the respiratory bronchiole

Question 3

What is the thickness of the blood-gas barrier in microns?

Answer 3

0.5 microns

Question 4

What is the area of the blood-gas barrier?

Answer 4

Very large! About 50-100 square meters

Question 5

Is ventilation per unit volume greater at the apex or the base?

Answer 5

Greatest at the base!

Question 6

Is intrapleural pressure more negative at top or bottom of the lung?

Answer 6

More negative at the top or apex

Question 7

Is there a larger pressure at the base or the apex?

Answer 7

At the base, to balance downward acting weight

Question 8

Is the resting volume of alveoli less at lung apex or base?

Answer 8

Less at lung base

Question 9

Which part of lung gets greater blood flow?

Answer 9

The base

Question 10

What is the result of a mismatch in V/Q?

Answer 10

Decrease in partial pressure of arterial oxygen (PaO2)

Question 11

What do these variables stand for:

PAO2 = PIO2 or FiO2 (PB - PH2O) – PCO2/R

Answer 11

Where PB = barometric pressure
PH2O = 47 mm at 37 o
FiO2 is fraction of inspired Oxygen ( .21 to 1.0)
Where R = the Respiratory quotient
( VCO2 / VO2 ) with a usual resting value of 0.8 to 1.0

Question 12

What is the normal range for PaO2?

Answer 12

70 to 100mm

Question 13

Decreased PaO2

Answer 13

hypoxemia

Question 14

Basic causes of hypoxemia

Answer 14

Lack of O2 in alveoli or decreased PAO2

Abnormalities in lung structure and function

Question 15

Hypoxemia can be caused by hyperventilation. What are some things that can cause this?

Answer 15

Sedation
Neuromuscular diseases
Muscle disorders
Pharmacologic blockade
High spinal cord lesions
Brainstem infarction

Question 16

What is the most common cause of hypoxemia in clinical disease states?

Answer 16

Mismatch in V/Q ratio or ventilation-perfusion mismatch

Question 17

What does a high V/Q ratio indicate?

Answer 17

Increased dead space, or ventilation to non-perfused units

Question 18

Another cause for hypoxemia could be diffusion defects. Discuss this.

Answer 18

Alveolar-capillary membrane compromised. Diffusion of gas across those membranes impaired, resulting in hypoxemia.

Question 19

Hypoxemia can be caused by a shunt. Intra-cardiac shunts and extra-cardiac shunts. What are some intra-cardiac shunts?

Answer 19

Patent foramen
Atrial septal defects
Ventricular septal defects
Congenital heart disease

Question 20

What are some extra-cardiac shunts?

Answer 20

Pulmonary AVMs

A-V fistulas

Question 21

V/Q that approaches 0

Answer 21

No ventilation as blood bypasses

Question 22

Does right to left shunt effect PaCO2 or PaO2?

Answer 22

Dramatic effect of PaO2, but minimal effect on PaCO2