respiratory physio 4

Question 1

what is the equation for the pressure of air that has been inspired and saturated with water vapor?

Answer 1

Px = Fx (Pb - PH2O)
x = species of breathing gas
F = fractional conc -can be altered by oxygen given (ex 20% to 100%)
Pb = barometric pressure
PH2O = water vapor pressure

Question 2

how do you calculate the pressure that is exerted by a dissolved gas on a surface like a membrane in a solution?

Answer 2

-similar to a gas in gas phase

Partial pressure (atm) = 
concentration of DISSOLVED gas/solubility 

• KNOW THAT THE GAS MUST BE DISSOLVED- NO CONJUGATED FORMS LIKE HGB.
• ALSO NOTE THAT CO2 HAS THE HIGHEST SOLUBILITY SO EXERTS A LOT LESS PRESSURE- DONT NEED THAT MUCH TO DIFFUSE IT ACROSS THE TISSUES

Question 3

ideal gas law and what we can infer from it

Answer 3

pv=nrt also P1V1=P2V2
n = number of moles
r = gas constant
-infer that if temp is kept constant, pressure and volume will be equal
-therefore, if a change in p or v occurs, something else in the equation must change
-IN RESPIRATORY PHYSIO- if p1 > p2 gas exchange will continue until equilib is achieved (P1V1=P2V2)
-IN CLINICAL ANESTHESIA- anesthetic gases administered via lungs diffuse into blood until partial pressure in alveoli and blood are equal (P1V1=P2V2)

Question 4

how do gases in fluids and tissues diffuse?

Answer 4

• it moves in accordance to the partial pressure difference (high to low)
• the amount of gas that moves across a tissue sheet is PROPORTIONAL TO AREA BUT INVERSELY PROPORTIONAL TO THICKNESS

Question 5

How do you calculate the rate of diffusion of fluids (like for diffusion across a pulmonary membrane)

Answer 5

D = [delta P x A x S]/ d x sqrt of MW (see equation slide 75)

• S = solubility of gas in the solution
• A = cross-sectional area of the fluid
• d = distance thru which gas will diffuse
• MW =molecular weight of the gas
• temp of the fluid: stable in body

Question 6

diffusion vs perfusion

PAO2 vs PaO2 and oxygen and carbon dioxide in conc at alveoli vs venous blood

Answer 6

• diffusion- oxygen to blood
• perfusion- into tissues
• capital A for alveolar and a for arterial
• alveoli has more oxygen conc with less CO2 and opposite for venous

Question 7

what can occur that alters the rate of diffusion across the alveolar membrane

Answer 7

D = [delta P x A x S]/ d x sqrt of MW (see equation slide 75)

1) atelectasis decreases s and increases d
2) pneumonia increases d (thickness)
3) pulmonary edema - increases P
4) pulmonary fibrosis - increases d

Question 8

how is blood diffused and perfused down the alveoli to the left heart?

Answer 8

• large partial pressure of oxygen in the alveoli is diffused into the arterial (PA) end of the pulmonary system and that oxygen is then perfused down to the venous end where it enters the left heart

Question 9

what is tissue oxygenation dependent on?

Answer 9

• rate of blood flow

- rate of tissue metabolism

Question 10

if your metabolism is up such as in exercise, what must occur to get it to normal value

Answer 10

-increase blood flow to deliver more oxygen to tissues

Question 11

flow of oxygen

Answer 11

alveoli to capillary and capillary to interstitium, interstitium to cells

Question 12

flow of CO2

Answer 12

• opposite to oxygen
• tissue cells to interstitium to capillaries to alveoli
• smaller change in pressure required as CO2 is much more soluble

Question 13

what is diffusing capacity?

Answer 13

• a common measurement of the lungs ability to transfer gases
• depends on both the diffusion of the gas and its interaction with Hb
• carbon monoxide

Question 14

Diffusing capacity

Answer 14

• the measurement of the lungs ability to transfer gas
• depends on diffusion of the gas and its interaction with Hgb
• carbon monoxide is used because oxygen is used up in the system and conjugated to Hgb so you don’t get an accurate count on the other side
• CO is not used in the system so put in known CO in and measure the PACO (alveolar) after:
  DLCO = Jco/PACO
  DLCO = diffusion capacity for CO
  Jco= known CO2 given

PACO- CO measured at alveoli
** THEN MUST MULTIPLY IT BY 1.23 FOR OXYGEN DIFFUSION
DLCO X 1.23 = DLO2

Question 15

what could be occurring if you get a decrease in diffusion capacity of CO

Answer 15

• anemia- decrease in Hgb could not be holding on to CO
  -thickened or damaged respiratory membrane due to emphysema (air trapped in alveoli)
  pulmonary fibrosis (increase in distance)
  pulmonary htn (increase pressure and distance
  chronic pulmonary thromboembolism- increase in pressure

Question 16

what can increase diffusion capacity of CO

Answer 16

polycythemia -increase in Hgb is increase in bonding to CO