lecture 18 - O2 and CO2 exchange

Question 1

What is the equation for respiratory minute volume?

Answer 1

VE = VT x f (VT=tidal volume, f=respiratory rate)

Question 2

What is the symbol and unit for respiratory minute volume?

Answer 2

VE, L/min

Question 3

What is the symbol and unit for tidal volume?

Answer 3

VT, L/breath

Question 4

What is the symbol and unit for respiratory rate?

Answer 4

f, breaths/min

Question 5

What is the ‘dead space’ of the lungs?

Answer 5

The air that does not reach the alveoli for gas exchange during a breath and fills the upper airways .

Question 6

What is the approx. volume of dead space in the lungs?

Answer 6

150mL

Question 7

What is the measure of how much air reaches the alveoli for gas exchange?

Answer 7

Alveolar ventilation, VA in L/min

Question 8

What is the symbol and unit for alveolar ventilation?

Answer 8

VA, L/min

Question 9

What is the equation for alveolar ventilation?

Answer 9

VA=(VT-VD)*f (VT=tidal volume, VD=dead space, f=respiratory rate)

Question 10

What is the symbol and unit for dead space?

Answer 10

VD, L/breath

Question 11

What is the difference between tidal volume (VT), dead space (VD) and alveolar ventilation (VA)?

Answer 11

VT is the total volume that enters the lungs in each breath, VD is the volume that sits in the upper airways and does not reach the lungs, and VA is the total volume that reaches the alveoli. The difference between VT and VA is VD

Question 12

What does gas diffusion depend on?

Answer 12

The partial pressures of gases in the airway and exchange pathway

Question 13

What is Dalton’s Law?

Answer 13

States that in a gas mixture, i.e. air, each gas exerts its own individual partial pressure (P). The pressure of the mixed gas is the sum total of the partial pressures of each individual gas.

Question 14

What is atmospheric pressure, in mmHg?

Answer 14

760mmHg

Question 15

What is the goal of the blood air barrier?

Answer 15

To facilitate the transport of inhaled oxygen into the capillaries and transport carbon dioxide into the alveoli to be exhaled

Question 16

What is the principle of Fick’s Law of Diffusion?

Answer 16

Gases move across membrane between alveoli and capillaries by diffusion, which depends on surface area and thickness of the membrane, as well as the pressure difference of gases

Question 17

What is the equation for Flux (amount of gas flowing) according to Fick’s Law of diffusion?

Answer 17

F=A/T * D(P1-P2), (A=surface area, T=thickness, D=diffusion constant, P1-P2 = pressure difference)

Question 18

What is the symbol for the diffusion constant?

Answer 18

D

Question 19

What is the diffusion constant, according to Fick’s LAw of Diffusion?

Answer 19

A constant (D) that depends of the gas solubility and molecular weight of a gas, such as O2 or CO2

Question 20

Why does CO2 diffuse around 20x faste than O2?

Answer 20

CO2 is more soluble so has a greater diffusion constant, D

Question 21

What is emphysema, and how does it influence gas exchange?

Answer 21

Disease characterised by dilation of alveolar walls, reducing the surface area for gas exchange

Question 22

What is pulmonary fibrosis, and how does it influence gas exchange?

Answer 22

Thickening and scarring of the thin alveolar membranes, which increases the thickness that gases must diffuse through, limiting exchange

Question 23

What is the main factor that drives movement of gases across the alveolar and capillary membranes?

Answer 23

Difference between the partial pressures of O2 and CO2 in the alveoli and arteries (PAO2 vs PaO2 and PACO2 and PaCO2)

Question 24

What is the symbol for alveolar partial pressure of O2?

Answer 24

PAO2

Question 25

What is the symbol for alveolar partial pressure of CO2?

Answer 25

PACO2

Question 26

What does the gas pressure difference between alveoli and capillaries depend?

Answer 26

1.) partial pressure of gas in inspired air (though this is relatively constant, and negligible for CO2)
2.) alveolar ventilation (amount of air)
3.) blood gas level (oxygen consumption or carbon dioxide production)

Question 27

How does exercise or rest influence partial pressure of oxygen in the blood?

Answer 27

Exercise increases oxygen consumption so lowers pressure, while rest does the opposite

Question 28

How do gases move along a pressure gradient?

Answer 28

Move down a pressure gradient, from high partial pressure to low partial pressure