Respiratory Quiz #4 Flashcards
Identify factors that determine exchange rates of gases across membranes
Fick’s Law combined with the diffusion rate determined from Graham’s Law (solubility) provides the means for calculating the exchange rates of gasses
Define Fick’s Law
the net diffusion rate of a gas across a fluid membrane is proportional to
• the difference in PARTIAL PRESSURE, the AREA of the membrane, inversely proportional to the THICKNESS of the membrane
• =>summarizes all the laws, if incr fio2 you will have more diffusion, area of membrane is important, if only 1 lung will have lower diffusion rates, inversely related to thickness of membrane bc more to cross, diffusion is limited
• => Fick’s law isn’t about giving you specific numbers, it tells you who you will have a hard time oxygenating
Identify two factors which determine the concentration of a gas in a solution using Henry’s Law
- partial pressure X solubility coefficient = concentration of gas
- both are directly proportional
- concentration can be incr by incr pp or solubility
Compare solubility coefficients for oxygen, carbon dioxide, carbon monoxide and nitrogen
- o2 - 0.024, carbon dioxide - 0.57(most soluble), carbon monoxide - 0.018, nitrogen - 0.012, helium - 0.008 (least soluble)
- =>if a bubble of carbon dioxide is trapped during open heart surgery it won’t embolize, it gets absorbed, not much of embolic effect at all
Using Henry’s Law, calculate the amount of oxygen dissolved in blood for PO2 of 50, 100,and 600 mmHg 10, CGAS = K X PGAS K=0.003
- 0.003x50=0.15, 0.003x100=0.3, 0.003x600=1.8 mL O2/100mL blood
- =>Ex: so for every 100mL of blood you would have 0.3mL of o2
Identify the mechanism responsible for most carriage of oxygen in the plasma
most oxygen is carried by hemoglobin, some is dissolved and carried in plasma
Describe the effect of increasing FiO2 from 100 to 600 mmHg on oxygen carrying capacity
increases o2 carrying capacity very little
Identify the average capillary exposure/transit time
- 0.7 seconds average, normal is 0.3
* =>0.4 sec grace period
Identify the normal time period required for diffusion to occur
normal oxygenation occurs in 0.3 seconds
Describe the effect of lower alveolar PO2 on diffusion and arterial PO
will decrease diffusion, lower po2=lower endpoint, less of a partial pressure gradient means slower diffusion and lower endpoint
Compare arterial and tissue PO2 and the effect on diffusion
arterial =95mmHg, tissue=40mmHg, oxygen diffuses (loads) into the cell (by concentration gradient)
Discuss the mechanism of diffusion of carbon dioxide across alveolar space
venous pco2= 46mmHg, alveolar pco2= 40mmHg, carbon dioxide crosses the alveolar septa by simple diffusion (by concentration gradient), much lower pp gradient, crosses readily bc of high solubility
Discuss the mechanism of diffusion of oxygen across the alveolar septa
=>simple diffusion based on partial pressure gradient and concentration gradient
Define Graham’s Law
- when gases are dissolved in liquids the relative rate of diffusion of a given gas is proportional to its solubility and inversely proportional to the square root of its molecular mass
- ex: process that occurs in the alveoli of the lungs
- =>larger the molecule the slower the diffusion
Compare the diffusion capacity of oxygen relative to carbon dioxide, nitrous oxide, carbon monoxide and nitrogen
- Nitrous oxide 14.0, oxygen is 1, co2 is 20.5
* hypoxic mixture, diffusion hypoxia if not on a 100% o2 after nitrous use
Describe the two major elements of diffusion capacity and their components
- membrane capacity - affected by factors involving movement of gas between alveoli and blood
- =>membrane affected by vq mismatch also
- reaction time with hemoglobin - affected by factors involving movement into capillary and uptake by RBC
- =>if low hct, that would decrease diffusion
List four conditions that decrease diffusing capacity
• thickening of the barrier, decreased surface area, decreased uptake by erythrocytes, VQ mismatch
