Gas Exchange Flashcards
What does effective respiration mean?
enough oxygen intake to meet metabolic demands
In respiratory physio, solution refers to what?
Water vapor, body fluid, interstitial fluid, and cytosol
What is Dalton’s law of partial gas pressure?
Each gas exerts a portion of the total pressure in an environment. Thus:
Ptotal = (P1+P2+Pn)
What happens to the air we inhale? What is the consequence of this for Dalton’s law?
Water vapor added, so this much be subtracted to find partial pressure
What is the equation for a particular species of gas, once in the lungs and saturated with water vapor?
Px= Fx(Pb-Ph20)
What is Henry’s law? Equation?
The partial pressure exerted by a gas when dissolved
Partial pressure = [C] of dissolved gas / solubility coefficient
Does conjugated oxygen or CO2 exert any pressure?
No, it is the dissolved form of gas that exerts a partial pressure
Is CO2 more or less soluble than oxygen? What is the effect of this?
Much more, thus it exerts much less partial pressure than oxygen, and it much more easily uptaken in the tissues
What is the ideal gas law? What are the variables in human tissues?
PV=nRT
PV and n
Is respiratory physio, gas will continue to flow down its gradient until what point?
P1V1 = P2V2
i.e. until partial pressures in alveoli and blood are equal
What is Fick’s law of diffusion?
The amount of gas that moves across across a tissue sheet is proportional to the area, but inversely proportional to the thickness
What is the equation of Fick’s law?
diffusion = dP(A)(S) / D(MW^.5)
What are the two variable that need consideration with gas exchange through capillaries?
Diffusion
Perfusion
What does A mean in respiratory physio? a?
A = alveolar a= arterial
What is the location of gas exchange?
The respiratory unit
What are the components of the respiratory unit?
Bronchiole
Alveolar ducts
Atria
Alveoli
How does atelectasis change the Fick’s equation?
∆P and A are decreased
How does pneumonia change the Fick’s equation?
Interstitial tissues and alveoli are inflamed, with increased fluid thickness, so the
distance through which gases must diffuse increases, and diffusion rate decreases
How does pulmonary edema change the Fick’s equation?
Increases D (thickness)
How does pulmonary fibrosis change the Fick’s equation?
Increases D (thickness)
Where does the blood comes from in hemoptysis?
From the respiratory membrane
What happens to the slope of the blood pO2 pressure curve during exercise? Why?
Lowers the slope
Higher perfusion (HR up), meaning less time for diffusion to happen
What are the two factors that determine the tissue PO2?
Rate of blood flow
Rate of tissue metabolism
Why is there a drop in the PO2 when it arrives at the left side of the heart?
Shunt of the pulmonary circulation from the bronchial arteries
Why is only a small pressure difference needed to exchange CO2? (~5 mmHg)
High solubility coefficient
What are the two variables that determine [PCO2] in tissues?
- Rate of tissue metabolism
2. Rate of blood flow
What happens to the slope of the PCO2 in alveolar capillaries during exercise? Why?
Lowers slope (absolute value)
Increased HR
What is used to measure the lungs ability to transfer gases? Why?
CO because it is taken up, stays in, and is not used by tissues
What is the equation for the diffusion capacity of the lung?
DLCO = Jco / PAco
A decrease in DlCO means what?
Lower rate of diffusion of oxygen
e.g. in thickened or damage respiratory membrane or anemia
What does COPD do to DlCO?
Decreases it
What does pulmonary fibrosis do to DLCO?
Decreases it
What does interstitial lung disease do to DLCO?
Decreases it
What does pulmonary HTN do to DLCO? Why?
Decreases it
Increase in capillary wall thickness
What does chronic pulmonary thromboembolism do to DLCO?
Decreases it
What does anemia do to DLCO?
Decreases it
What does polycythemia do to DLCO?
Increases it
IS DLCO sensitive? Specific?
Sensitive, but NOT specific
What happens to the partial pressure of CO2 as you move from tissues to lungs?
Decreases
What is the atmospheric pressure at sea level in mmHg?
760 mmHg
What is the solubility coefficient of oxygen? CO2? What does this mean?
Oxygen = 0.024 CO2= 0.57
Thus CO2 is much more soluble in water
What are the two variables we can change in the partial pressure equation Px = Fx(Pb-Ph2o)? How?
Fx (with oxygen)
Pb (with hyperbaric chamber)
According to Fick’s law, the larger the surface area of a tissue, the (higher/lower) the rate of diffusion
Higher
According to Fick’s law, the thicker a tissue is, the (higher/lower) the rate of diffusion
Lower
What is the partial pressure of oxygen in the pulmonary capillaries at the arterial end? Venous end?
Arterial end = 40 mmHg
Venous end = 104 mmHg
True or false: under normal. resting conditions, the entire capillary/alveolar surface area is needed to diffuse oxygen.
What is the consequence of this?
False–it’s more like a third.
This allows a buffer for times during increased oxygen demand (such as exercise)
(Summarizing the O2 diffusion graph): If there is an increase in tissue metabolism, how is the higher demand for oxygen met? How does increase oxygen demand change the curve?
Increasing blood flow
The curve shifts downward (more blood flow is needed to attain each PO2 mmHg)
What does the graph of the blood flow to mmHg PO2 look like?
Square root
What does the graph of the blood flow to PCO2 mmHg look like?
1/x
What happens to the curve of CO2 diffusion with increased metabolism?
Shifts rightward (meaning that a higher blood flow is needed to achieve the same mmHg pCO2)
In determining the diffusing capacity of the lungs, why is it that the partial pressure of CO can be used directly in the equation, rather than the amount that is dissolved in blood like the other gases?
Hb picks it up so readily, that the partial pressure = the dissolved pressure
How do you convert the DLCO (diffusion rate of CO) to the diffusion rate of O2?
Multiply by the diffusion factor coefficient for oxygen (1.23)
Why is there a lower diffusion rate of O2 in pulmonary HTN?
Increases in capillary wall d/t higher pressures
What does the alveolar gas equation tell you?
What fraction of oxygen the patient is taking in
