111114 diffusion

Question 1

what is in the diffusion rate formula?

Answer 1

pressure difference
area
solubility

distance
square root of molecular weight

Question 2

clinically, which factors might contribute to diffusion impairment in the lung?

Answer 2

SA
distance (thickness)
pressure gradient

Question 3

what do the chemoreceptors sense?

Answer 3

the DISSOLVED gases, like oxygen. so if placed bag over head vs give oxygen/CO, both cases the person would die but the placed bag case would cause a more traumatic condition b/c you’re not getting the normal diffusion of oxygen.

Question 4

role of hemoglobin in the pulmonary capillary?

Answer 4

it takes up the O2, so it creates that pressure gradient for O2 to dissolve in the blood. so much more volume of O2 crosses the respiratory membrane.

Question 5

why is O2 more susceptible to diffusion impairment than CO2?

Answer 5

solubility-CO2 is 20x more soluble

Question 6

solubility of O2

Answer 6

0.03 ml/L/mm Hg

Question 7

normal stroke volume

Answer 7

70 mL

Question 8

what is the normal oxygen requirement in a normal adult at rest?

Answer 8

250 mL O2/min (this is diffusion rate)

this is how much diffuses across to the capillary per minute

Question 9

how many mL of O2 are removed on average from 100mL of blood passing through systemic capillaries?

Answer 9

5 mL

Question 10

what is diffusing capacity-the eqn?

Answer 10

diffusion rate/(alveolar partial pres-mean capillary partial pressure)

Question 11

why is CO used to calculate DL (diffusion capacity)?

Answer 11

there isn’t any CO dissolved in blood b/c of high affinity for hemoglobin, so you don’t have to measure the mean capillary pressure

there is always a gradient for CO to pass since barely any of it is dissolved in blood

Question 12

methods of diffusion capacity?

Answer 12

steady state

single breath

Question 13

steady state method for measuring DL-advantages/disadvantages?

Answer 13

more natural
easier for pts with lung disease
can be used during exercise
sometimes more invasive

Question 14

what is the single breath methods for measuring diffusion capacity?

Answer 14

exhale to residual volume, full vital capacity inspiration of trace CO and reference gas, 10 second breath hold, then maximal expiration

the reference gas is not taken into the blood

Question 15

what are advantages/disadvantages of single breath method?

Answer 15

rapid testing and immediate results
more difficult to perform–pts with lung disease may find it hard to take a deep breath and hold of 10 sec

values are higher than steady state DL

Question 16

normal diffusion capacity values for males

Answer 16

low 30s in ml/min/mm Hg

normals will be different for different age, height, gender

Question 17

how does exercise affect DL?

Answer 17

increases by factor of 3

Question 18

in abnormal lung that takes 0.75 seconds for the PO2 to increase from 40 to 100mm Hg, what happens to DL?

Answer 18

decreases

you don’t get hypoxemic at rest. HOWEVER, there’s no reserve for exercise

Question 19

why is CO2 not vulnerable as much to diffusion impairment?

Answer 19

more soluble
more carefully controlled (by central chemoreceptors vs peripheral chemoreceptors for O2). central chemoreceptors are very sensitive for CO2

Question 20

diffusion capacity is affected by

Answer 20

membrane diffusing capacity
perfusion problems
ventilatory problems

Question 21

in restrictive lung disease, what is DL/VA

Answer 21

normal (DL is decreased and VA is also decreased)

Question 22

obstructive lung disease–what is DL/VA?

Answer 22

low (DL is decreased, VA is normal of even greater than normal)

Question 23

emphysema

Answer 23

loss of elastic recoil-won’t deflate as well
so now need to use chest to compress. however, when you compress alveoli will compress airways at the same time. so as you’re pushing air out, you’re also squeezing the airway shut. so then you try and try–balloon pops

emphysema is a problem mainly during expiration

Question 24

V/Q mismatch

Answer 24

shunt
or
dead space

Question 25

if there’s adequate ventilation, how can you have respiratory insufficiency?

Answer 25

can be in lungs–
diffusion impairment
or
V/Q mismatch

can be in blood--
abnormal hemoglobin (CO poisoning, etc)
reduced volume (hemorrhage)