"Medical Physiology Diffusion of Oxygen and Carbon Dioxide Huaiyu Hu" GABY Flashcards Preview

Unit 6 > "Medical Physiology Diffusion of Oxygen and Carbon Dioxide Huaiyu Hu" GABY > Flashcards

Flashcards in "Medical Physiology Diffusion of Oxygen and Carbon Dioxide Huaiyu Hu" GABY Deck (25)
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1
Q

Henry’s law states that when a liquid and gas phase are in __1__ at a given temperature, the concentration of gas in solution is __2__ proportional to the partial pressure of the gas

A
  1. equilibrium

2. directly

2
Q

At equilibrium, the ___ of the gas is identical in the gas and liquid phases

A

partial pressure

3
Q

Henry’s law

A

Describes the equilibrium between gaseous and liquid phases

4
Q

What does the following equation represent?

[C]=aP

A

Henry’s law

[C] –> gas concentration in solution
a –> solubility coefficient
P –> partial pressure of gas

5
Q

The values of the solubility coefficient depend on:
(1)
(2)
(3)

A

(1) the specific gas
(2) the liquid in which the gas is dissolved
(3) temperature

6
Q

The concentration of a gas dissolved in blood is expressed in ___, or as ___ that would be in equilibrium with the solution in accordance with Henry’s law if a gas phase were present

A

vol% (or molar); the partial pressure in mm Hg of gas

7
Q

Since the partial pressure of oxygen in alveolar gas (PA02) is __1__ than in pulmonary artery blood (PVO2), and since PAC02 is __2__ than PVCO2, these gases are transferred by __3__ across the alveolar-capillary membrane

A
  1. greater
  2. less
  3. diffusion
8
Q

Fick’s law

A

Describes the rate of movement of gas between two compartments containing gases of differing partial pressures

9
Q

In solutions chemical potentials are determined by the __1__; in gases chemical potentials are determined by __2__

A
  1. concentration of molecules

2. partial pressures

10
Q

In the lung, diffusion occurs across the ___ membrane

A

alveolar-capillary

11
Q

The ___ barrier separates the alveolar gas from the liquid blood

A

alveolar-capillary membrane

12
Q

What does the following equation represent?

V=(A/T)•D•(PA -PC)

A

Fick’s law

V –> the flow (ml/min) of a gas
A –> the alveolar surface area available for diffusion (about 50 - 100 m2)
T –> the thickness of the alveolar membrane (< 0.5 micron)
(PA - PC) –> the difference in partial pressure (mm Hg) of the gas between the alveoli
and the pulmonary capillary blood
D –> the diffusion coefficient (cm2/min/mm Hg) of the gas

13
Q

The diffusion coefficient of a gas (D) is proportional to its __1__ and inversely proportional to the square root of its __2__

A

(1) solubility

(2) molecular weight

14
Q

Why do patients develop hypoxemia before arterial hypercapnia when impairment to diffusion occurs?

A

Because carbon dioxide diffuses about 20 times more rapidly than oxygen across the alveolar-capillary membrane

15
Q

Red blood cells in their plasma spend about ___ sec in the pulmonary capillaries at resting cardiac outputs

A

0.75 - 1.2

16
Q

At time zero, the partial pressure is that of __1__; at 0.75 sec the partial pressure is that of __2__

A

(1) mixed venous blood

(2) end- capillary blood

17
Q

Alveolar partial pressure is different for each gas and depends on:
(1)
(2)
(3)

A

(1) the inspired gas composition
(2) the rates of inspiration and expiration
(3) the rate of removal of the gas by capillary blood

18
Q

Perfusion-limited uptake

illustrated by N20

A
  • rapid equilibration
  • uptake from lung can be increased by increasing cardiac output –> reduces amount of time the blood stays in the capillary after equilibration of alveolar partial pressure with its capillaries
19
Q

Diffusion-limited uptake

illustrated by CO

A

*higher affinity for Hb –> prevents equilibration of partial pressure between alveolar gas and capillary plasma

20
Q

Uptake of oxygen from the lung by the blood is ___ limited

A

perfusion

21
Q

Why would an individual with a diffusion problem would have exercise-induced hypoxemia?

A

Because transit time in the pulmonary capillaries is reduced by 2/3 to 0.25.

22
Q

Why would an individual with a diffusion problem (compared to a healthy person) will be even more hypoxemic?

A

At high altitude, the partial pressure of inspired oxygen is reduced –> decreasing the partial pressure of oxygen in the alveolar gas

A normal individual will equilibrate their end-capillary blood with alveolar gas

In an individual with a diffusion problem the end- capillary partial pressure of oxygen will be even lower than the alveolar partial pressure of oxygen

23
Q

Why is DLCO rather than DLO2 measured at steady state?

A

Because binding of CO to hemoglobin maintains a virtually zero PCO in pulmonary capillaries when a nonlethal alveolar PCO is used, thus maintaining the partial pressure gradient between alveoli and capillaries

24
Q

What equation relates DL02 and DLCO?

A

DLO2=1.23DLCO

25
Q

Factors that influence DLCO

A

Body position
-DLCO greater when supine than upright

Exercise
-increases DLCO

Lung diseases and dysfunction that decrease DLCO

  • loss of lung tissue from surgery
  • mismatch of ventilation to perfusion
  • pulmonary hypertension with edema

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