Respiratory III Flashcards
why is PO2 in the pulmonary capillaries after gas exchange 95mmHg
because of bronchial circulation
what is the partial pressure of a gas
the pressure of one gas in a mix of gases
what is the formula for partial pressure of a gas
Patm x fractional concentration of a gas
what is atmospheric gas partial pressures
600mmHg nitrogen and 160 mmHg oxygen
what is the partial pressure of water in the lungs
47mmHg
what is the result of the generation of a partial pressure of water in the lungs
air is humidified and decreases the partial pressure of the other gases
what is the partial pressure of O2 in the lungs
149 mmHg
at normal alveolar ventilation and O2 absorption rates what is PAO2
100mmHg
what does increasing alveolar ventilation do to PAO2
increase it
what is the solubility coefficient
attractability of molecules to water
what does the solubility coefficient tell you if it is high
the gases diffuse quickly
what is henrys law
partial pressure = concentration of dissolved gases/solubility coefficient
which is more soluble: CO2 or O2
CO2
what is the formula for concentration of dissolved gas
= solubility coefficient x partial pressure
what does gas exchange at the respiratory membrane depend on
-transport rate through the respiratory membrane
-the rate of alveolar ventilation
what does an increase in alveolar ventilation do to PAO2 and gas exchange
increases both with an upper limit of 150 mmHg
what does transport through the respiratory membrane depend on
-difference in partial pressures across the membrane
- solubility of gas in fluid
-cross sectional area of membrane
- distance of diffusion
-molecular weight of gas
what is the formula for volume of gas diffusing through the tissue barrier per unit time
V = change in pressure x A x S/ (d X square root of MW)
what will be the PO2 of a tissue with high metabolic activity
lower PO2
which diffuses more rapidly: O2 or CO2
CO2
if more pulmonary capillaries are recruited what happens to surface area for diffusion
it increases such as converting from zone 2 to zone 3
what does an increase in thickness of the diffusion barrier do to diffusion
decreases it
what are the components of the respiratory membrane
-surfactant
-alveolar epithelium
-alveolar basement membrane
-interstitial space
- endothelial basement membrane
- capillary endothelium
under normal conditions, O2 transport into pulmonary capillaries is _____
perfusion limited
under fibrosis, emphysema, strenuous exercise O2 transport into pulmonary capillaries is
diffusion limited
what does the diffusion capacity of the lung measure
respiratory membranes functional integrity.
- if lung impairment is perfusion limitation or diffusion limitation
what is the diffusion capacity of the lung measured by
amount of a gas entering pulmonary blood per unit of time
what do you need to know in order to calculate diffusion capacity of the lung
gas’s alveolar pressure, pulmonary capillary pressure, and rate of uptake by the blood
why cant DLCO2 be calculated
because of its rapid diffusion
why is DLO2 difficult to calculate
most of O2 binds to hemoglobin
why is carbon monoxide idea for DL
because it is diffusion limited
what would an abnormally low DLCO test indicate
-thickening of the barrier (increased d)
- decreased surface area (low A)
-decreased uptake
what would cause thickening of the barrier
interstitial edema or fibrosis
what would cause decreased surface area
-emphysema
- low CO
- tumors
-ventilation perfusion mismatch
what would cause decreased uptake
anemia and decreased blood volume in pulmonary capillaries
what is the normal A-a gradient in a young non smoker
5-10mmHg
how much does the A-a gradient increase with with age
increases by 1 mmHg for each decade
what is the formula for normal A-a gradient
age/4 +4
what is PAO2 predicted based on
-partial pressure of O2 inspired
- the PaCO2
-ratio of CO2 produced/O2 consumed - the respiratory quotient
what does a large difference in PAO2 and PaO2 tell you
diffusion problem
what is PvO2 (veins
40 mmHg
what is PAO2 (alveoli)
100 mmHg
what is PaO2 (arteries)
95 mmHg
what is FiO2 (definitiion and number)
percentage of inspired O2 - 21%
what is PH2O
47 mmHg
what is PaCO2 (arterial CO2)
40 mmHg
what is the respiratory quotient and number
CO2 produced (200 ml/min) divided by the O2 consumed (250 ml/min) = 0.8
