10. Gas Exchange

Question 1

Anatomic dead space are airways that do not partake in gas exchange and funtion in humidifying air breathed in and airflow to airways. What is incharge of airway resistance?

Answer 1

the diameter of the bronchiole

Question 2

What happens when airway resistance is high vs when airway resistance is low?

Answer 2

When resistance is high, airflow slows down and takes more muscle effort, while when low, airflow is fast and easy

Question 3

What is the equation used to calculate R (resistance)

Answer 3

R= (8 x n(viscosity) x L (length tube) ) / (r^4 (radius tube))

Question 4

What is the main control of bronchiole diameter (also know as airway resistance)?

Answer 4

Smooth muscle of the airway walls, the radius of the airway has greatest impact on airflow, contraction/relaxation of smooth muscle can be used to direct air to alveoli with BLOOD

Question 5

What is the equation for minute alveolar ventilation?

Answer 5

VA(dot)= VA (tidal volume-dead space) x Frequency of breath (4L/min is average value)

Question 6

What is perfusion of the lungs (Q)? (always given)

Answer 6

blood that reaches the aveoli via the capillaries from the right ventricle, 5Lblood/min

Question 7

What is the equation to calculate diffusion rate in mL/min (J), an equation used to determine the diffusion of gases during alveolar gas exchange?

Answer 7

J = (S.A. x D x (P1-P2)) / Distance
KEY
SA= surface area availible for diffusion
D= Diffusion coefficient for each gas
P1-P2= pressure gradient across alveolar membrane
Distance= difussion distance (thickness of alveolar barrier)

Question 8

Under normal resting conditions, what is J in mL/min of both O2 and CO2 (calculated independently)?

Answer 8

250 mL O2 are exchanged every minute

200 mL CO2 are exchanged every minute

Question 9

What factor of the J equation depends on number of alveoli in the lungs, as well as the number of open pulmonary capillaries?

Answer 9

Surface Area (SA)
At rest: 70ml blood in capillaries, 200ml during exercise!

Question 10

How can a disease, such as emphysema or COPD, affect the diffusion of gases (J)?

Answer 10

People with COPD have a hard time getting oxygen into their system (dec in SA) causes a decrease in J

Question 11

For the distance factor of the diffusion equation, the average distance is 0.6 microns and commonly includes? (4)

Answer 11

Fluid layer
alveolar epithelium
interstitial space
blood vessel wall

Question 12

What is a case where the thickness of the alveolar barrier increases, leading to an increase in distance, causing an decrease in diffusion of gas (J)?

Answer 12

Deposition of collagen within the interstitial spaces caused by a disease

Question 13

The D in the equation is for diffusion coefficient which is determined by? (2)

Answer 13

1. the solubility of the gas in water (O2 is less soluble in water than CO2)
2. The molecular weight of the gas (CO2 weighs more than O2)

Question 14

What is important to remember about the solubility of CO2?

Answer 14

solubility counters the fact that it is larger, the diffusion coefficient is 20x higher for CO2 than the diffusion coeficient for O2

Question 15

For P1-P2, what are the Ps? and how do they differ? and what is important to remember?

Answer 15

P1 is the pressure on the inside of the alveoli and P2 is the pressure on the outside of the alveoli (venous blood).

Remember!: O2 and CO2 must be calculated seperately

Question 16

What is the normal gradient for O2 between the venous blood and alveoli? What does that number mean

Answer 16

PvO2=40mmHg while PAO2=100mmHg
100-40=60mmHg
This means O2 likes to diffuse d/t gradient, this makes up for lack of solubilty and diffusion coefficient

Question 17

What is the normal gradient for CO2 between venous blood and alveoli? Why?

Answer 17

PACO2= 40mmHg PvCO2= 45mmHg: 40-45= -5mmHg

This means CO2 does not use gradient to diffuse, since diffusion coefficient is so large!

Question 18

How much time does a RBC spend in the pulmonary capillary under resting conditions and how long does it take O2 to reach equilibrium?

Answer 18

RBC under resting spends about 0.75s and takes 0.25 seconds for O2 to reach equilibrium. So that means you have 0.50s as a safety margin

Question 19

What occurs during exercise/ RBCs time spent in the pulmonary capillaries?

Answer 19

RBCs only spend 0.25s in the capillary, meaning they need to bring O2 to equilibrium in that exact time. This is when someone with a lung disease notices problems

Question 20

DLO2 stands for diffusion capacity of the lung for oxygen, what is it at rest?

Answer 20

About 21mL O2/min/mm Hg, this is different from the estimated 60mmhg early because it takes into account the entire alveoli. As time goes on, diffusion becomes less and less desireable

Question 21

How would one measure DLO2 with carbon monoxide (CO)?

Answer 21

Since CO binds to hemoglobin, so none is dissolved in the artery (PaCO=0). have patient breath in a small percentage of CO

DLO2= 1.23 x DLco

Breath in and out, difference is what is diffused

Question 22

RBCs spend about 0.75s in capillaries for CO2 exchange, equilibrium is made with CO2 almost instantly! what does this mean for the DLco2 at rest?

Answer 22

DLco2 at rest is estimated at 400mLCO2/min/mmHg

Question 23

Why is the lung last to mature in babies and what occurs if a baby is born prematurely?

Answer 23

Lungs are developed last because they are not needed until month 9. If a baby is born prematurely, it does not have type II pneumocytes which produce surfactant, which decrease surface tension so the lungs do not collapse

Question 24

Surface tension does what in alveoli in the lungs?

Answer 24

minimizes the amount of water touching air, makes the alveoli want to shrink

Question 25

What is LaPlace’s Law?

Answer 25

Pressure = 2T(surface tension)/ r (radius)

Question 26

How does LaPlace’s law related to the different sizes of alveoli?

Answer 26

In a large alveoli, radius increases, so the pressure is low.
In small alveoli, radius decreases, so the pressure is high

Question 27

Since all alveoli are connected, when there are small alveoli with high pressure, the pressure is released into ?

Answer 27

Large aveoli with low pressure, causing collapsed alveoli and lack of air into the area, decreasing surface area

Question 28

Surfactant changes surface tension (T) and reduces it in mainly ________?

Answer 28

smaller aveoli compare to larger

Question 29

Surfactant is made by type II pneumocytes and consists of?

Answer 29

Phospholipids, sufactant proteins (SP) SPA/B/C/D

SPB is most important, stored in intracellular lamellar bodies and secreted into alveolus

Question 30

Due to the lowering of pressure d/t lowering of tension by surfactant, what does this mean for the small and large aveoli that share the same airway?

Answer 30

there is no gradient and the small is not transfered to the large, both have small pressure now = no collapse

Question 31

What does collapsing of small into large alveoli d/t no surfactant or d/t increased surface tension cause?

Answer 31

Decrease in surface area availible for diffusion