because the air is coming from different anatomical locations within the airways
Why does the gas composition of air change?
it is coming from the mouth and upper airways. It did not exchange with blood. It has the same composition as outside air. high in O2 and low is CO2.
The first air to leave is composed of what partial pressure?
O2 = 40mmHG and CO2=46mmHG. i.e. high in CO2, but low in O2.
What is the partial pressure of O2 and CO2 in blood that approaches the lung? i.e. venous blood/ pulmonary artery blood?
it aquries oxygen from alveolar air and releases carbon dioxide into the alveolar air.
What occurs as pulmonary artery blood passes through the lungs?
it is high in oxygen and low in CO2
what is the composition of blood leaving the lungs? the composition of pulmonary venous blood?
it is the amount of gas in the air decided by the tool pressure of all the gases, which is 760 mmHg.
What is the partial pressure of a gas?
O2 = 21% of 760 or 160mmHg and CO2 = O
What is the partial pressure of O2 and CO2 that enters the lungs? i.e. in inspired air?
1. O2 = 100 mmHg, CO2 = 40 mmHg, air entering lungs mixes with air already in the lungs the is low in O2 and high in CO2, lowering both values.
2. H2O=47 mmHG - air get humidified so water vapor is present.
What is the partial pressure of O2, CO2 and H2O in alveoli air?
O2 = 95mmHg and CO2 = 40mmHg. the gas that leaves the lungs and enters the are tiers has a similar composition to gas composition of the alveoli. expect there is a slight decrease in O2.
What is the partial pressure of O2 and CO2 in ateries?
O2 = -40mmHg and CO2 = +46. As blood moves through the tissues , O2 levels decrease as tissue consume O2 and its CO2 levels increase as CO2 is added. this blood leaves the tissue and enters the venous system.
How much O2 does the capillaries take and how much CO2 do the capillaries give back the blood?
A small amount of deoxygenated blood gets shunted around the lungs and enters arterial circulation without being oxygenated and this slightly lowers the amount of oxygen in the arterial blood.
Why is the partial pressure of O2 in the arterial blood slightly lower than in the alveoli air?
the greatest drop is in the systemic capillaries and there is also a drop of 5mmHG in the arterial blood. it rises in the pulmonary capillaries. The walls of the arteries and veins are too thick to allow O2 to diffuse across.
There are three places in the circulation where O2 levels change. Where does the oxygen levels in blood drop? Where does it rise?
1. Venous blood returning from bronchial tissue goes directly into the LA
2. venous blood from the thesbian circulation (provides blood to ventricle muscle) drains into the LV
Where is the blood "shunted" past the lungs and therefore not deoxygenated before being mixed with arterial blood?
the alveolar-arterial oxygen gradient (PAO2-PaO2)
what is the difference in PO2 of alveolar gas and arterial blood called?
inc PAO2 and dec. PACO2, b/c large volumes of alveolar air are being replaced with inspired air, so alveolar gas composition approaches that of inspired air O2=160 and CO2=0. It usually can only get to 130 because of RV.
What is the effect of increasing alveolar ventilation (hyperventilation)on gas composition in the alveolar air? A=alveolar, a=arterial
dec. PAO2 and inc. PACO2, b/c small volumes of alveolar air are being replaced with inspired air, so alveolar gas composition approaches that of venous blood.
what is the effect of decreasing alveolar ventilation (hypoventilation) on gas composition in the alveolar air? A=alveolar, a=arterial
Any change in alveolar air will cause a similar change in arterial blood. So an increase in ventilation will cause an increase in PaO2 and a decrease in PaC02.
How will an increase in ventilation (hyperventilation) affect gas composition in arterial blood? A=alveolar, a=arterial
Any change in alveolar air will cause a similar change in arterial blood. So a decrease in ventilation will cause a decrease in PaO2 and an increase in PaC02.
How will an increase in ventilation (hypoventialation) affect gas composition in arterial blood?
at Apex (top). Pulmonary arterial pressure low (b/c of low hydrostatic pressure) near alveolar pressure ( 0mmHg). The pulmonary capillaries will be compressed by the higher alveolar pressure,dec. blood flow. Usually arterial pressure is high enough to prevent closure, so blood flow is just slow. But sometimes when arterial pressure is decreased (hemorrhage) or if alveolar pressure is increased (hyperventilation) BV will compress and area will just be ventilated not perfused. No gas exchange is no perfusion/blood flow so considered Dead space.
In the lungs where is blood flow the lowest?
At Base. blood pressure is higher (due to high hydrostatic pressure), both venous and arterial, than alveolar pressure. Blood flow is driven by the pressure difference between venous and arterial pressure. Here the greatest number of capillaries is open and blood flow is highest.
Where is the lungs is blood flow the greatest?
But sometimes when arterial pressure is decreased (hemorrhage) or if alveolar pressure is increased (hyperventilation) BV will compress and area will just be ventilated not perfused. No gas exchange is no perfusion/blood flow so considered Dead space.
Can alveolar pressure PA ever be greater than arterial pressure Pa?
Due to hydrostatic pressure increasing the blood pressure at the bottom to the lungs compared to the top, The bottom of the lungs are pursued more than the apex of the lungs.
Where are alveoli pursued more? At the apex or bottom of the lungs?
ventiallation is better and perfusion (blood flow) is better.
What does everything is better at the bottom of the lungs refer to?
Apex. 1. The intrapleural pressure at top of lungs is more negative because of gravity pulling the lungs downward in a closed space. This creates a more positive transmural pressure pulling the lungs open 2. The weight of the lungs pulling down on the alveoli at the top also increases their volume.
Why is there a greater lung volume at the top of the lung compared to at the bottom?
higher on the curve, at higher lung volumes, and where compliance is low. think of a slinky.
Alveoli from different lung location are at different volumes and therefore different location on the compliance curve. Where are alveoli located at the top of lung of the lung compliance curve?
lower on the curve, at a lower lung volume, where compliance is high. Think of a slinky.
Alveoli from different lung location are at different volumes and therefore different location on the compliance curve. Where are alveoli located at the bottom of lung of the lung compliance curve?
When intrapleural pressure falls during inhalation alveoli at the top of lung inflate less than those at the bottom of the lung. Therefore alveolar ventilation, changes in alveolar volume at the top of lung is less than that at the bottom of the lung.
Where is ventilation the highest?
the change in blood flow.
What is greater the change in blood flow (perfusion) or the change in ventilation (change in alveolar volume) as you move bottom to apex of the lung?
the ratio should be one. The point where they are most closely matched is with a V/Q of 0.8 occurs around the 3rd rib from the top (zone 3).
What ration between ventilation (V) to perfusion (Q, blood flow) would give the best exchange btw blood and alveolar air?
alveoli are over perfused and under ventilated, low V/Q, ratio is less than 1
At all places in the lung except one the ratio of ventilation and blood flow is mismatched. What is this ratio at the base?
alveoli are over ventilated and under perfused, high V/Q, ratio is greater than 1
At all places in the lung except one, the ratio of ventilation and blood flow is mismatched. What is this ratio at the apex?
In dead space no gas exchange is possible here. This ventilation is wasted, b/c no blood flow to receive O2 or add CO2. therefore alveolar gas is the same as inspired gas.
What will occur to alveolar gas composition when ventilated lung regions are not pursued (Infinite V/Q).
A shunt is due to airway obstruction, there is perfusion of the lung area but no ventilation to deliver O2 and remove CO2 from blood. gas composition of the alveolus will be the same as the venous blood, high in CO2 and low in O2 since it does not get fresh air.
What will occur to alveolar gas composition when you get perfusion of a lung area that is not ventilated (zero V/Q).
High ventilation relative to perfusion, b/c blood flow is decreased. Because ventilation is high, there is a high O2 added to the blood, and lots of CO2 taken away from the blood. So the alveolar/arteriole PCO2 is low. Blood is almost completely saturated at normal V, so increasing the V does not increase the PO2 in arteriole blood.
What will occur to alveolar/areteriole gas composition in areas of high ventilation compared to perfusion (high V/Q).
unlike shunt which has no ventilation, this has some/little ventilation. PO2 of alveolar air/arterial blood is low. Alveolar CO2 is high. This blood mixes with blood with a normal V/Q ratio decreasing the overall arterial O2 blood and inc the CO2. this dramatically changes arterial gas.
What will occur to alveolar/areteriole gas composition in areas of low ventilation compared to perfusion (low V/Q).
low V/Q dramatically alter arterial gases.
What has a greater effect on gas composition? Low V/Q or high V/Q?
hypoxemia, air has low O2 concentration, and therefore little O2 is inhaled into the alveoli and little O2 is diffused into the arteriole. Both Alveolar air and arterial blood have low O2 conc so the A-a gradient is normal. But there is a decrease in PaO2 causing hypoxemia.
Does high altitude cause hypoxemia or hypoxia?
Hypoxemia, the intake of O2 is less, PO2 in alveolar air is low which decreases the PO2 of blood leaving these alveoli. so there is less arteriole O2 and less alveolar O2. They both decrease in proportion so the ration between arteriole and alveolar PO2 does not change/remains normal. equilibration of O2 across the alveolar/pulmonary capillaries is normal, and systemic
Does hypoventialtion (holding breath) cause hypoxemia or hypoxia?
hypoxemia, decrease arteriole PO2 because O2 can't diffuse into blood. Less oxygen in areteriol blood then in alveoli. PaO2 decreases relative to PAO2 and the A-a gradient is inc.
Does diffusion defect cause e.g. fibrosis cause Hypoxemia or hypoxia?
hypoxemia, Some alveoli are under ventilated, meaning some don't get fresh O2 and remove CO2. When this underventillated blood mixes with blood passing by normal alveoli, the blood has lower PaO2. Since the alveoli are not well ventilated they do not influence overall PAO2. PaO2 falls relative to PAO2 and the gradient increases.
Does V/Q defect cause hypoxemia or hypoxia?
hypoxemia, Some shunts do not bring blood passed ventilated alveoli, so the shunted blood does not get free PO2 and the alveoli has a similar PO2 to inspired air. PAO2 is higher than PaO2, so there is an increase in A-a gradient.
Does shunt cause Hypoxemia of Hypoxia?
by having the patient breath in 100% O2, the A-a gradient will not improve if due to a shunt. , this is because in shunts some blood flow does not have access to alveoli so raising O2 has no effect.
How can you differentiate between hyopemia due to a V/Q defect or diffusion impairment from a shunt?
O2 delivery is the product of CO, dec. CO causes dec. O2.
What happens to Cardiac out put in hypoxia?
Since hyperemia is the dec. in O2 in the blood, hyperemia will cause less O2 to reach the tissue. But hypoxia does not affect hyperemia.
Can Hypoxemia cause hypoxia? and vise versa?
anemia is a decrease hemoglobin concentration, since hb carries O2 to tissue, with less Hb, there will be less O2 going to tissue. therefore is dec. O2 content of blood.
how does anemia cause hypoxia?
CO occupies binding sites on Hb that normally are occupied by O2, thus CO decreases O2 content.
How does carbon monoxide poisoning cause hypoxia?