A&P Respiratory Diffusion
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1. What is diffusion and it relation to pulm physiology?
2. What is the driving force for Alveolar capillary diffusion?
- 1. Movement of gas molecules by random motion from areas of high concentrations (PP) to areas of low concentrations (PP)
- 2. The different PP of O2 and CO2
1. Pulm artery PaCO2 vs PACO2? What does this cause?
2. Normal Pulm artery PaO2 and PAO2? What does this cause?
- 1. ~ 45 vs. 40 - drive CO2 out of the blood
- 2. ~ 40 vs. 104 - Drives O2 into the blood
1. Is diffusion a slow process? What physical property assist in the speed and ease of diffusion?
- 1. Very FAST ~0.25 seconds to equilibrate
- 2. CO2 and O2 are lipid soluble
1. What does Dalton's law state?
2. PP of a molecule is directly proportional to its concentration.
3. the PP of a gas is directly proportional to its rate of?
- 1. the Total (Ptotal) = sum of the individual PP
- 2. T
- 3. Diffusion
1. Does the PP of a gas change if its in liquid?
– Does not matter if it is mixed with another gas (e.g., O2 mixed with N2, as is the case for air) or dissolved in an aqueous solution (e.g., O2 dissolved in water or blood)
1. What is the relationship bt Temperature and Solubility?
2. IF temp is constant, how does the PP of a gas above a liquid related to the amt of dissolved gas?
3. What law describes these relationships?
- 1. Solubility of a gas is inversely related to
- 2. Partial pressure of the gas above the liquid is = to the Partial pressure of the SAME gas ABOVE the liquid
- 3. Henry's Law
1. A hyperthermic pt will need more or less anesthetic gas based on who's law?
- 1. More anesthetic gas
- 2. Henry's
1. The amt of dissolved gas is directly proportional to the PP above the gas. At constant temp, What other factor influences the amt of dissolved gas?
2. How is this computed?
3. What are the solubility constants of O2 and CO2?
- 1. Solubility coefficient of the gas. Ex. CO2 is 20x more soluble in blood than O2
- 2. – Quantity of gas = Solubility coefficient X gas partial pressure.
- 3. O2 = 0.003ml/dl/mmHg
- CO2 = 0.067ml/dl/mmHg
1. With a PP of 100 mmHg, how much O2 will be dissolved in 1dl (100mls) of plasma?
1. 0.003 x 100 = 0.3ml/dL of plasma
1. What is "overpressurizing" volitale anesthetics?
- 1. – Significant increase in the concentration (i.e. partial pressure) delivered to patient to increase the alveolar concentration
- • Results in increased concentration dissolved in blood that is ultimately delivered to tissue
1. Both of these laws deal with TRANSPORT
PROCESSES and relate to Diffusion of
1. Graham's law and Fick's Law
Graham's Law states
– Rate of effusion of a gas (gas moving thru a small orifice) inversely proportional to square root of its MW.
1. Diffusion Constant determined by two factors:
- 1. – Solubility of the gas
- – Molecular weight of the gas
- • Specifically the square root of the molecular weight
1. what is the solubility constant of O2, CO2, and Nitrogen
- 1. 2.26 ml/dL
- 57.03 ml/dL
- 1.30 ml/dL least soluble
1. Using Graham's law how do you calculate the amt of O2 dissolved in the Blood?
- – Quantity of gas = Solubility coefficient X (gas
- partial pressure ÷ total barometric pressure)
- - ex. So, the amount of oxygen dissolved in 1 dL ofarterial blood (PO2 = 100mmHg) at sea level (760 mmHg) is:
- – Quantity of gas = 2.26 mL/dL X (100 ÷ 760) = 0.3 mL/dL of blood
1. Diffusion constant or Coefficient is determined by what 2 things?
1. Solubility constant and √MW
1. Which law describes the rate of diffusion of gases thru tissues? ie pulmonary capillary interface
1. Fick's Law - vol/min
1. N20 is 35x more soluble than nitrogen in the blood?
2. What does this cause?
- 1. T
- 2. accounts for rapid movement of N2O from alveoli into blood and SLOW replacement of N2 from blood to alveoli causing "shrinking". This concentrates other gases and ⇑ induction rate.
1. If using N2O at the end of Sx, What must you do to prevent hypoxia at RA 21%?
1. Allow time for nitrous to be replaced with O2 in the alveoli. It takes longer to diffuse out and will dilute PP of O2 in the alveoli
1. What is Perfusion Limitation?
1. • Under normal conditions, gas transfer in the lung is perfusion limited. O2 tension equilibrates rapidly. as blood flows by, this re-increase the gradient between alveoli and blood. Therefore, it is perfusion limited.
1. How long does RBC spend in the pulm capillary?
2. How fast does equilibration take place?
3. Therefore, O2 uptake is usually perfusion limited?
- 1. 0.75 sec
- 2. 0.25 sec
- 3. T
1. What is diffusion limited gas exchange?
1. Occurs when equilibration does not occur dt alveolar and pulm gas tensions. NOT blood flow issue
1. CO, cabon monoxide, is diffusion limited or perfusion limited?
1. When there is a low PAO2 or Alveolar wall thickening, gas exchange is Diffusion or Perfusion limited?
1. Diffusion limited. Gas tension does not equilibrate by the time RBC leaves the pulm capillary.
1. During exercise, pulm capillary flow increases. Time is reduced by?
1. by ~ 1/3 or 0.25 sec.
1. Alveolar O2 capillary uptake is also influence by decrease O2 PP... such as high altitude.
2. If exercising at high altitude and equilibrating cannot occur, is this diffusion or perfusion limited?
3. Lung dz effects this?
- 1. T - equlibration may not take place
- 2. diffusion limited
- 3. makes even worse
1. What are three example of diffusion limiting situations?
- 1. Thickening of Alveolar capillary membrain - Classic example - Pulmonary Fibrosis
- 2. High altitude or low FIO2
- 3. Increase pulm blood flow - exercise - diffusion is not fast enough to keep up with flow
- - worsened with lung dz
1. What gradient is the driving force that moves gas from one point to the another?
2. Especially since this is an active or passive process?
- 1. Partial pressure gradient
- 2. Passive
1. If pulm capillary membrain is thick, what might you do to increase diffusion?
2. Diffusion-limited gas exchange is one cause of arterial hypoxia
- 1. Increase partial pressure gradient - ie increase FIO2
- 2. T
1. Anesthetic gases are diffusion limited or perfusion limited?
2. So, even in a dz lung state, drug gas uptake is not effected?
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