Waters III Flashcards
T or F. All O2 delivered from the lungs is delivered to tissue. (or in other words, no O2 is seen in venous circulation)
F. Only about 250ml/min of O2 is delivered out of 1000mL/min in arterial circulation
T or F. There is more CO2 in arterial circulation that O2 at any given time
T. Counter-intuitive but there is way more Co2 in the blood (arterial and venous) than O2.
NOTE: There is more Co2 in venous circulation than arterial
What is respiratory quotient (RQ)?
The ratio of CO2 produced to O2 consumed by tissue
What is a normal RQ?
0.8 (200ml/min produced to 250ml/min used)
RQ for carbs? fat? protein?
carbs=1
fat=0.7
protein=0.8
so for fat and protein, t takes more O2 to produce 1 co2
Gas exchange between alveolar gas and blood and between blood and tissue is entirely by ____.
diffusion
What is the eqn. for Po2?
atmospheric pressure x fraction of O2 molecules in DRY air
or 159 mm Hg usually
What happens when air is inspired?
it is warmed to 37C and humidified (aka water vapor is formed)
What happens to Po2 when air is inspired?
lowers to 150 mm Hg
(760-47 (for water vapor))*0.21
Eqn for conc. of a gas in solution (Henry’s law)
equals a*Px where a=solubility of the gas in solution
thus, two different gases at the same partial pressure can have different concentrations (i.e. CO2 is way more concentrated in water than O2)
What is Fick’s Law of Diffusion?
gas flow (volume/time)= (A/thickness)Diffusion constant(P1-P2)
where P1-P2 = conc. gradient
What variables of Fick’s eqn. does emphysema affect?
decreased A
What variables of Fick’s eqn. does fibrosis affect?
increased thickness
T or F. Co2 diffuses up to 20x faster than O2
T.
What is the Po2 in alveoli? Why isn’t it the same as the atmosphere?
About 105mm Hg because there is mixing with deoxygenated air
alveolar Co2 (PAco2) is around 40 mm Hg
What is the PO2 in arterial (PaO2) blood?
100 mm Hg
What is the Pco2 in arterial (Paco2) blood?
40 mm Hg
What is the PO2 in venous blood?
40 mm Hg
What is the PCO2 in venous blood?
46 mm Hg
Eqn for PAco2
k*(CO2 production rate/alveolar ventilation)
where k= 863 mm Hg at BTPS
What is ‘hypoventilation’?
increase in PAco2 due to alveolar ventilation not keeping up with Co2 production
What factors determine PAo2?
- Pio2 of inspired air (less at high altitude)
- Alveolar ventilation (lower increases PAco2 and decreases PAO2)
- cellular oxygen consumption (higher consumption = higher)
Eqn for PAo2
= Pio2- (PAco2/R), where R takes into account Co2 production/O2 consumption
What is hypoxemia?
lower than normal Po2 (100 mm Hg)
What is the A-a gradient?
PAO2- PaO2 (alveolar- arterial)- used toe examine causes of hypoxemia
What is hypoxia?
decrease in O2 delivery to, or utilization by, tissue. Due to decreased blood flow or decreased O2 binding to hemoglobin
What is hypercapnia?
higher than normal arterial Pco2. Most often due to hypoventilation
Normally oxygen is perfusion limited in the sense that all blood leaving pulmonary capillaries are saturated with O2 due to the short amount of time/distance needed to bind O2 (about 0.3 seconds compared to the 0.75s blood spends in the capillary). What conditions promote diffusion-limited transfer of O2?
- fibrosis
- emphysema
- high altitude
- intense exercise
T or F. Pulmonary vascular resistance (PVR) is very low compared to systemic resistance
T. So you can change the resistance easily is needed
Eqn for PVR
(pulmonary artery pressure-left atrial pressure (aka pulmonary wedge pressure)) / Cardiac output
What is pulmonary HTN defined as?
above 25 mm Hg at rest
What causes primary pulmonary HTN?
inactivating mutation in the BMPR2 gene which promotes vascular smooth muscle cell proliferation
How is pulmonary blood flow regulated?
hypoxia-induced pulmonary vaso-CONSTRICTION
Why would pulmonary vessels constrict with low oxygen?
want to re-route oxygen to low areas
Which parts of the lungs receive the most blood flow?
the base due to gravity
Where are pulmonary capillaries most susceptible to collapse in the vertical lung upon standing?
at the apex because PA is greater than Pa (which is greater than Pv)
Pressures in zone 2 (middle) of the lung
Pa greater than PA greater than Pv
Pressures in zone 3 (base) of the lung
Pa greater than Pv greater than PA
How does alveolar ventilation change in the vertical lung?
the apical pleural pressure is more sub atmospheric than the base, so the alveoli tend to be more open (even in relaxed states) and thus not as compliant (already distended). Therefore alveoli at the BASE can inflate more and ventilate better
