Resp 1 - West Ch 3 Diffusion

Front 1

Fick's law:
Rate of trasnfer of a gas through a sheet of tissue is proportional to the tissue ____ and the difference in gas ____ ____ between the two sides. Inversely proportional to the tissue ______.

Back 1

area
partial pressure

thickness

Front 2

___ diffuses about 20x faster than ___ because of a much higher solubility but around the same molecular weight

Back 2

CO2
O2

Front 3

Carbon monoxide gas tightly bonds to hemoglobin in the cell, so large amounts of CO can be taken up without large partial pressure changes.
Therefore, the transfer of CO is _____ limited

Back 3

diffusion - the amount of CO that gets into the blood is limited by the diffusion properties of the blood-gas barrier and not by the amount of blood available

Front 4

Nitrous oxide does not combine with hemoglobin, and therefore the partial pressure rises rapidly.
Therefore, N2O is ______ limited

Back 4

perfusion - the amount of N2O taken up by the blood depends entirely on the amount of available blood flow and not at all the diffusion properties of the blood-gas barrier

Front 5

O2 combines with hemoglobin but with a lower avidity than CO. Under normal resting conditions, the first 1/3 of capillary O2 transfer is _____ limited and equilibrium is reached.
In abnormal conditions (diffusion somehow impaired), PO2 doesn't reach alveolar value by the end of the capillary and there is some ______ limitation as well.

Back 5

perfusion

diffusion

Front 6

Oxygen floods down a large pressure gradient:
PO2 of RBC entering capillary = __mmHg
Alveolar PO2 = __mmHg
RBC reaches PO2 of Alveolar gas by the time it is __ its way along the capillary => diffusion reserves are enormous

Back 6

40
100

1/3

Front 7

Blood spends about __ sec in the capillary at rest and reduced to __ sec during exercise (yet there is no fall in end-capillary PO2)

Back 7

3/4
1/4

Front 8

Severe exercise at high altitude is one of the few situation where diffusion impairment of O2 can be convincing. Why?

Back 8

Exercise decreases capillary travel time to 1/4 sec and the high altitude has lower alveolar PO2 so O2 moves across more slowly

Front 9

The diffusion process is challeged by _____, alveolar _____, and _____ of the blood-gas barrier

Back 9

exercise
hypoxia
thickening

Front 10

Measurement of diffusing capacity:
Use __ because it is diffusion limited
Diffusing capacity _____ on exercise
Normal diffusing capacity is about __ml/minmmHg

Back 10

CO
increases
25

Front 11

What does this equation mean:
DL = VCO/PAco

Back 11

This is the diffusing capacity of the lung.
It is the volume of CO transferred in ml/min/mmHg of alveolar partial pressure. The partial pressure of CO in capillary blood is extremely low and so dropped
(DL = VCO/P1-P2)

Front 12

The uptake of O2 should be considered in 2 stages:
____ of O2 through blood-gas barrier
reaction of the O2 with _______
Sum of resistance: 1/DL = 1/DM + 1/constant x Vc

Back 12

diffusion
hemoglobin

1/diffusion capacity of the lung = 1/diffusion of membrane + 1/rate of rxn of O2 with Hb x volume of capillary blood

Front 13

Using Fick’s law of diffusion of gases through a tissue slice, if gas X is 4 times as soluble and 4 times as dense as gas Y, what is the ratio of the diffusion rates of X to Y?
A. 0.25
B. 0.5
C. 2
D. 4
E. 8

Back 13

C
density = molecular weight for this question.
Vgas = DA/deltaX
D = solubility/sqrt(molecular wt)

Front 14

An exercising subject breathes a low concentration of CO in a steady state. If the alveolar PCO is 0.5 mmHg and the CO uptake is 30 ml min-1, what is the diffusing capacity of the lung for CO in ml min-1 mmHg-1?
A. 20
B. 30
C. 40
D. 50
E. 60

Back 14

E
DL = Vco/PAco
DL = 30/0.5 = 60

Front 15

In a normal person, doubling the diffusing capacity of the lung would be expected to:
A.Decrease arterial PCO2 during resting breathing.
B.Increase resting oxygen uptake when the subject breathes 10% oxygen.
C.Increase the uptake of nitrous oxide during anesthesia.
D.Increase the arterial PO2 during resting breathing.
E.Increase maximal oxygen uptake at extreme altitude.

Back 15

E. Any gas molecule that is under the stated conditions is perfusion limited and not diffusion limited and will not be affected by increasing the diffusing capacity other than equilibration may occur earlier in the capillary. This would eliminate answers A, B, C, and D. If the alveolar O2 is reduced to very low levels (50 mmHg or less), then transport will become diffusion limited and increasing the diffusing capacity will augment transport.

Front 16

If a subject inhales several breaths of a gas mixture containing low concentrations of carbon monoxide and nitrous oxide:
A.The partial pressures of carbon monoxide in alveolar gas and end-capillary blood will be virtually the same.
B.The partial pressures of nitrous oxide in alveolar gas and end-capillary blood will be very different.
C.Carbon monoxide is transferred into the blood along the whole length of the capillary.
D.Little of the nitrous oxide will be taken up in the early part of the capillary.
E.The uptake of nitrous oxide can be used to measure the diffusing capacity of the lung.

Back 16

C. The partial pressure of carbon monoxide in the end-capillary blood is zero due to the strong binding of CO with the hemoglobin molecule. With respect to answers B, Dand E nitrous oxide is perfusion limited, therefore it will be in equilibrium with end-capillary blood, taken up early in the capillary and cannot be used to measure diffusing capacity.

Front 17

Concerning the diffusing capacity of the lung:
A.It is best measured with carbon monoxide because this gas diffuses very slowly across the blood-gas barrier.
B.Diffusion-limitation of oxygen transfer during exercise is more likely to occur at sea level than at high altitude.
C.Breathing oxygen reduces the measured diffusing capacity for carbon monoxide compared with air breathing.
D.It is decreased by exercise.
E.It is increased in pulmonary fibrosis which thickens the blood-gas barrier.

Back 17

C. Breathing oxygen reduces the θ for CO due to its competition with CO for binding sites. capacity because it is diffusion limited and the PCO in the blood is zero. Answer B is is incorrect due to a reversed order. Answer Answer D and E are the opposite of true

Front 18

The diffusing capacity of the lung for carbon monoxide is increased by:
A.Emphysema which causes loss of pulmonary capillaries.
B.Asbestosis which causes thickening of the blood-gas barrier.
C.Pulmonary embolism which cuts off the blood supply to part of the lung.
D.Exercise in a normal subject.
E.Severe anemia.

Back 18

D
Increased pulmonary blood flow (cardiac output) results in increased area for diffusion due to recruitment of new vessels. This will also increase the blood volume in the lung. Answers A and C decrease in area available for diffusion. Answer B increases the diffusion distance. Answer E decreases the Vc term which is part of DL.