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59 Cards in this Set
- Front
- Back
Diffusion of gases characteristics (2)
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1. Random (Brownian) movement of gas molecules due to kinetic energy
2. Collisions - intermolecular and with boundaries of system (gas cyclinder, capillary membrane, alveolar membrane) |
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What is the definition of pressure?
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force/area
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What are the units of gas pressure?
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mmHg (torr), cm H20, psi, Pa, atm
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SI unit?
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Pa
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Total gas pressure is proportional to?
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the total concentration of gas molecules
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In a mixture of gases, each gas exerts a partial pressure; the partial pressure of the gas is proportional to?
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its fractional concentration in the mixture, ie, Pgas = F gas x Pt
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Dissolved gas molecules have (3)?
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kinetic energy, diffuse in solution, and exert pressure (tension)
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The pressure of a gas in a solution is proportional to its?
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concentration (Henry's Law)
Cgas = alpha x Pgas |
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Net diffusion of a gas occurs in response?
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to a difference in gas partial pressure
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What law does this involve?
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Fick's Law
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What is the diffusivity of oxygen, co2, co, n2, helium?
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oxygen: 1.0
co2: 20.3 CO: 0.81 N2: 0.53 Helium: 0.95 |
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Composition of alveolar gas is _______ from that of atmospheric air.
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different
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What is are 4 reasons alveolar gas is different than atmospheric air?
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1. Alveolar gas is only partially replaced by atmospheric air with each breath
2. Oxygen is absorbed from alveolar gas 3. Carbon dioxide is added to alveolar gas 4. atmospheric air is humidified as it enters the resp. system |
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FRC is 2300 mL, how much new air is delivered to the alveoli with each normal breath? This amount of alveolar gas is also removed.
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350 mL
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Thus, with each breath only _____ of the total alveolar gas is replaced by new air, this is important in?
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1/7, preventing sudden changes in blood gas concentrations
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What is absorbed from alveolar gas?
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Oxygen
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How is the alveolar partial pressure of oxygen (PA02) determined?
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by the balance between oxygen delivery (via alveolar ventilation) and oxygen absorption
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For a normal person breathing normal atmospheric air at sea level, PAO2 cannot exceed?
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150mmHg, even with a marked increase in alveolar ventilation
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Breathing gas with a higher PO2, however can increase?
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PA02
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What is ADDED to alveolar gas?
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carbon dioxide
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What is the CO2 production/excretion rate? Alveolar ventilation rate?
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200mL/min, 4.2L/min
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With those rates what is the alveolar PCO2?
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40mmHg
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PACO2 is inversely related to?
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alveolar ventilation
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Atmospheric air is _______ as it enters the respiratory system.
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humidified
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What is the SVP of water at body temp?
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47mmHg
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The partial pressure of H20 of alveolar gas is?
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47mmHg
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Humidification does what to the partial pressures of inspired oxygen and nitrogen?
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lowers
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Composition of expired gas, is a combo of?
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dead space gas and alveolar gas
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What changes progressively during the course of expiration?
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P02 and PC02
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The alveolar wall contains an extensive?
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network of interconnecting capillaries that form a "sheet" of blood around the alveolus itself
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The structures separating alveolar gas from blood in the alveolar capillaries are collectively called?
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the respiratory membrane (blood-gas barrier)
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What is the average total thickness of the respiratory membrane?
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0.6 micrometers
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The structures separating alveolar gas from blood in the alveolar capillaries include?
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1. Fluid lining of the alveolus, including surfactant
2. Very thin Type I epithelial cells 3. Epithelial basement membrane 4. Interstitial space 5. Capillary basement membrane 6. Capillary endothelium |
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What is the total surface area of the respiratory membrane?
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is estimated to be 50-100 meters squared
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What is the total amount of blood in the pulmonary capillaries at any time?
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60-140 mL
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What factors affect the rate of gas diffusion across the respiratory membrane? (4)
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1. Thickness of the respiratory membrane (d)
2. Surface area of the respiratory membrane (A) 3. Diffusivity of the gas in the respiratory membrane (S/MW0.5) 4. Difference in gas partial pressure across the respiratory membrane (deltaPgas) |
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Rate of diffusion is inversely related to?
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thickness
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What can increase the thickness of the respiratory membrane and impair gas exchange?
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pulmonary interstitial edema and fibrosis
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Rate of diffusion is directly related to?
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surface area
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What can reduce surface area?
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surgical removal of lung tissue and in certain pulmonary diseases (emphysema is associated with coalescence of alveoli)
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Diffusivity is directly related to? and inversely related to?
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gas solubility in the membrane and inversely related to molecular weight of the gas
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What diffuses 20 times faster through the membrane than oxygen?
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Carbon dioxide
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Carbon dioxide diffuses how many times faster than nitrogen?
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40
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What is the definition of diffusion capacity of the respiratory membrane?
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volume of gas that diffuses across the membrane per minute in response to a partial pressure difference of 1 mmHg
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What is oxygen's diffusion capacity at rest?
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20ml/min(mmHg)
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What is the maximum diffusion capacity of o2?
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65ml/min(mmHg)
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Why can there be an increase in diffusion capacity of oxygen? (2)
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1. Opening of "dormant" capillaries
2. Better ventilation-perfusion matching |
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What is carbon dioxides diffusion capacity?
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technical difficulties preclude direct measurement
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What is the estimated carbon dioxide diffusion capacity?
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400-450ml/min(mmHg) at rest and maximum of 1200-1300mL/min (mmHg)
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At rest, the transit time of the RBC in the pulmonary capillary is about?
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0.75 seconds
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P02 of blood entering the capillary is? PAO2 is?
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40mmHg (mixed venous P02), 100mmHg
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Describe oxygen uptake
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Oxygen diffuses down its large partial pressure gradient; at rest, capillary P02 increases to that of alveolar gas (diffusion equilibrium occurs) by the time blood has moved about 1/3 the length of the capillary (0.25 sec)
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There is said to be a very large "_______ _______"
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diffusion reserve
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Even with strenuous exercise, where blood transit time may be as little as 0.25 sec, diffusion equilibrium.....?
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for oxygen occurs, and end-capillary PO2 is essentially the same as PA02
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Diffusion impairment (disequilibrium) is unusual, but may occur in what certain circumstances?
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1. Patient with thickened respiratory membrane
2. Exercise at high altitude, particularly in patient with thickened respiratory membrane |
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PC02 of blood entering the pulmonary capillary is? PACO2 is?
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45 mmHg (mixed venous PCO2), 40 mmHg
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Describe carbon dioxide removal
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Co2 diffuses down its partial pressure gradient; diffusion equilibrium normally occurs by the time the blood has moved about 1/3 the length of the capillary (0.25)
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Diffusion impairment of C02 may create a?
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difference between end-capillary PCo2 and PACo2, particularly during exercise
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With Fick's Law, what factors is the rate of diffusion directly related to and inversely related to?
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Directly: partial pressure of gas, solubility, and surface area
Inversely: thickness and MW |