Alveolar Ventilation, Blood Flow

Question 1

Atmospheric pressure is 760mmHg. In the airways the air is humidified by water vapor. How much does the water vapor contribute to this pressure within the airways?

Answer 1

about 47mmHg

this number is subtracted from 760mmHg before calculating partial pressures of gases in the airways

Question 2

What is the average alveolar pressure of O2?

Answer 2

100mmHg

Question 3

What is minute ventilation?

Answer 3

Tidal Volume x # of breaths/min.

Question 4

What is anatomic dead space?

Answer 4

Areas with ventilation that do not participate in gas exchange because there is no respiratory membrane.

Question 5

What is alveolar dead space?

Answer 5

Areas with no gas exchange because of lack perfusion or thickened respiratory membrane that does not allow diffusion of gas (COPD).

Question 6

What is physiologic dead space?

Answer 6

Anatomical DS + Alveolar DS

Question 7

How is alveolar ventilation calculated?

Answer 7

(Tidal Volume - Physiologic DS) x breaths/min

Question 8

Is increasing respiratory rate or Tidal volume more effective at increasing alveolar ventilation?

Answer 8

Tidal Volume

Question 9

What effect does hyperventilation have on alveolar pressure of CO2?

Answer 9

Decreases the amount of CO2 in the alveoli.
(hypoventilation increases CO2)
-this is for CO2 concentrations that are constant meaning a constant level of diffusion across the respiratory membrane

Question 10

What respiratory quotient do each of the three major energy sources produce in the lungs?

Answer 10

Carbs: 1.0
Protein: 0.8
Lipids: 0.7

Question 11

What 4 factors are involved in determining the ability of a gas to diffuse across a membrane?

Answer 11

1. Pressure gradient
2. Surface Area
3. Solubility
4. Membrane thickness

Question 12

What is the difference between a diffusion limitation and perfusion limitation regarding gases in the lungs?

Answer 12

Diffusion Limitation: means that a gas binds hemoglobin very well and that the alveolar pressure and partial pressure in the blood never really equilibrate. (CO)

Perfusion Limitation: means that a gas does not bind Hb as readily and the pressures between the alveoli and blood of the gas equilibrate quickly. (N2O, O2, CO2)

Question 13

Why is pressure low in the pulmonary circulation compared to systemic circulation?

Answer 13

Very low resistance

• higher compliant vessels
• very little smooth muscle

Question 14

How are alveolar vessels and extra-alveolar vessels influence by lung volume?

Answer 14

High Volume

• alveolar vessels compressed b/c they are exposed to alveolar pressure (increased resistance)
• extra alveolar vessels distend b/c they are exposed to intrapleural pressure (decreased R)

Low Volume
-opposite for both types

Question 15

Describe the 3 zones of the lungs.

Answer 15

Zone 1: only occurs in diseased states
-alveolar pressure is greater than venous and arterial pressure meaning ventilation occurs but no perfusion

Zone 2:
-arterial pressure is greater than alveolar allowing blood flow only during times are increased cardiac output (exercise)

Zone 3:
-both arterial and venous pressure are greater than alveolar meaning these vessels are open all the time and using gas exchange.