Gas Exchange

Question 1

how is airflow through the bronchioles controlled

Answer 1

when air flows through a tube the airway resistance makes the airflow more difficult

if airway resistance is high airflow slows down and takes more muscle effort to produce

if airway resistance is low airflow is fast and easy

R = 8nL/r4

Question 2

why do we want to change the airway resistance

Answer 2

to send the air in my lungs to the right places, that means alveoli with a good blood supply

Question 3

what are some consequences of too much airway resistance

Answer 3

Asthma

COPD

Airway obstruction

Cronchiectasis

hypoxemia caused by ventilation/perfusion mismatch

Question 4

what is alveolar Ventilation

Answer 4

Volume of air reaching the alveoli

if per minute VA(dot) = VA x F

4L/min

Question 5

what is perfusion

Answer 5

from the right ventricle

5 L blood/min

wil not be calculated

it is the cardiac output

Question 6

what is the diffusion rate equation?

Answer 6

J = SA x D x (P1-P2) all over distance

J = diffusion rate in ml/min
D= diffusion coefficient (different for CO2, and O2)
P1-P2 = Pressure gradient across alveolar membrane
SA = Surface area available for diffusion
Distance = diffusion distnce (thickness of alveolar barrier)

Question 7

what is J for oxygen and CO2 under normal conditions

Answer 7

250 ml O2 are exchanged every minute

200 ml CO2 are exchanged every minute

Question 8

is the diffusion of each gas independent of each other?

Answer 8

yes!!

Question 9

what does the SA correspond to in the diffusion equation?

Answer 9

the surface area avaliable for diffusion

corresponds to the number of alveoli in the lungs

also depends on number of open pulmonary capillaries
(70 -200) ml of blood in pulmonary capillaries

if SA increases, J increases

Question 10

how does emphysema affect the diffusion equation

Answer 10

emphysema (COPD) have a hard time getting sufficient oxygen into their system due to the loss of lots of Alveolar tissue and Surface area

patients need to compensate lack of SA by increasing oxygen concentration

Question 11

what does distance represent in the diffusion equation

Answer 11

the distance represents the diffusion distance (thickness of alveolar barrier)

includes:
fluid layer, alveolar epithelium, intersitial space, and blood vessel wall (very thin)

as distance increases, J decreases

Question 12

how can the distance of diffusion be increased

Answer 12

CHF
Sarcoidosis

Interstitial lung disease,
-leads to deposition of collagen within the interstitial space and increases the diffusion distance and decreases the diffusion of the gases across the barrier

Question 13

what is the D stand for in the diffusion equation and what does it depend on?

Answer 13

D stands for the diffusion coefficient for the gas

D depends on the:

• Solubility of the gas in water (in your body, O2 less soluble in water than CO2)
• The molecular weight of the gas (CO2 weighs more than O2)

Question 14

which diffusion coefficient is larger, O2 or CO2?

Answer 14

Dco2 is 20 times larger then Do2

ths is because the solubillity of CO2 more than counters the difference in molecular weight

therefore CO2 is much easily dissolves across the membrane

Question 15

what does the P1-P2 number represent in the diffusion equation, and what is it normally for PaO2, and PaCO2

Answer 15

P1-P2 represents the pressure gradient across alveolar membrane

O2 = 104-40 = 60 flowing into capillary

CO2 = 40 - 45 = -5 means flowing out of capillary

Question 16

how much time does an RBC spend in a pulmonary capillary and how much of that time does it take to diffuse the oxygen at rest and during exercise

Answer 16

spends about 0.75 seconds under resting conditions

takes 0.25 seconds for the oxygen to complete the process of diffusiion (large safety margin of 0.5 sec)

takes 0.25 seconds for the oxygen to complete diffusion but the oxygen is only in the pulmonary capillary for 0.25 seconds

this is why people with pulmonary disease notice problems with breathing during exercise first

Question 17

what is the DLo2 for a normal person

Answer 17

DLo2 is the diffusion capacity of the lung for oxygen

• about 21ml O2/min/mmHg at rest
• mmHg is the average gradient along alveolar capillary

Question 18

How do we measure the DLo2 for an individual

Answer 18

use Carbon Monoxide (CO)

• binds Hb so avidly that it doesnt dissolve on the plasma
• Paco is 0 mmHG

DLo2 = 1.23xDLco

Question 19

How long does it take CO2 to dissolve across the membrane as the RBC travels along during normal conditions?

Answer 19

almost immediately, therefore huge safety margain and an individual will have to have extensive lung disease before they have problems with CO2 retention

DLco2»»>DLo2

Question 20

why does surface tension matter?

Answer 20

LaPlaces Law: Pressure = 2T/r
T=tension
r=radius

surfactant decreases the surface tension in the alveolar

Question 21

in small alveolus what is the pressure?
in large alveolus what is the pressure?

what is the problem caused by this and how is it solved?

Answer 21

small: high pressure
large: low pressure

air wants to move to the low pressure but the surfactant especially in the small alveolus decreases the pressure (by decreasing the surface tension) to make an equal pressure among large and small alveoli

therefore the alveoli wont collapse

pressure = 2T/r

Question 22

how does surfactant affect the surface tension in regards to the radius

Answer 22

as the radius gets smaller the surfactant will decrease the surface tension more

surfactant decreases T in proportion to the decrease in radius

Question 23

What is surfactant composed of?

Answer 23

• phospholipids
• Dipalmitoylphosphatidylcholine

-Surfactant proteins (SPA,SPB,SPC,SPD)
(SPB, SPD really imporant in function)

Question 24

where is surfactant stored and who produces it?

Answer 24

produced by the type II pneumocytes

stored in the intracellular lamellar bodies

secreted into alveolus