Blood supply, gas exchange, ventilation & perfusion Flashcards
because of differences in compliance between the base an apex, any given change in intrapleural pressure will bring what volumic change?
large volume change at base and small volume change at apex
what is the point of bronchial circulation? what purpose does it serve?
supplies oxygenated blood to airway smooth muscle, nerves and lung tissue, has a nutritive function
which circulation does the bronchial circulation come from?
systemic circulation
where does the pulmonary circulation come from?
right ventricle
what percentage of cardiac output do both the pulmonary arteries carry?
100%
where does the pulmonary vein return to?
left atrium
why is this considered a high flow low pressure system? what is the average systolic pressure? diastolic? (of the pulmonary circuit) what is the systolic average of the systemic circulation?
high flow because the time it takes 5L of blood to move around the body is the same as the systemic circulation
25mmHg, 8mmHg; low pressure compared to systemic: 120 mmHg
air diffuses across membranes down which gradient?
partial pressure gradient
what are the partial pressures of O2 and CO2 in the alveoli?
100 mmHg, 40 mmHg (13,3 kPa, 5,3 kPa)
what are the partial pressures of O2 and CO2 in the arteries?
100 mmHg, 40 mmHg (13,3 kPa, 5,3 kPa)
what are the partial pressures of O2 and CO2 in the veins?
40 mmHg, 46 mmHg (5,3 kPa, 6,2 kPa)
what is the rate of diffusion across the membrane directly proportional to?
partial pressure gradient, gas solubility, available surface area
what is the rate of diffusion across the membrane indirectly proportional to?
thickness of the membrane
where is the rate of diffusion across the membrane most rapid?
short distances
do pathologies affect gas exchange?
yes
what does an alveoli’s thin membrane allow?
short diffusion distance
what does emphysema do?
destruction of alveoli reduces surface area for gas exchange. PO2 (alveoli) normal or low, PO2 (blood) low
what does fibrotic lung disease do?
thickens alveolar membrane which slowing gas exchange. Loss of lung compliance may decrease alveolar ventilation. PO2 (alveolar) normal or low, PO2 (blood) low
what does pulmonary edema do?
fluid in interstitial space increase diffusion distance. Arterial PCO2 may be normal due to higher CO2 solubility in water. exchange surface normal. PO2 (alveoli) normal, increased diffusion distance, PO2 (blood) low
what is ventilation?
air getting to alveoli L/min
what is perfusion?
local blood flow L/min
where are ventilation and perfusion matched?
pulmonary capillaries
how are ventilation and perfusion matched in pulmonary capillaries?
influenced by both hydrostatic (blood) pressure (Pa) and alveolar pressure
what is lung blood flow like at the base of lungs?
lung blood flow is high because arterial pressure exceeds alveolar pressure and vascular resistance is therefore low
what is lung blood flow like at the apex of lungs?
lung blood flow is low because arterial pressure is less than alveolar pressure. This compresses the arterioles and vascular resistance is increased
where does the majority of the mismatch take place?
in the apex
when ventilation < blood flow, what happens?
if ventilation decreases in a group of alveoli, PCO2 increases and PO2 decreases, blood flowing past those alveoli does not get oxygenated (goes too fast? not enough gradient?), then dilution of oxygenated blood from better ventilated areas. “shunt”
how does the body compensate?
constriction of blood vessels with low PO2 (because increased PCO2 causes mild bronchodilation) diverting blood to better-ventilated alveoli
this method of compensation is specific to which circulation?
pulmonary circulation (systemic vessels have an opposite reaction, they dilate)
when ventilation > blood flow, what happens?
increase in alveolar PO2 and decrease in alveolar PCO2 “alveolar dead space”
how does the body compensate?
increase in alveolar PO2 induces pulmonary vasodilatation (increases perfusion), decrease in alveolar PCO2 induces bronchial constriction (decreasing ventilation)
what does alveolar dead space refer to?
refers to alveoli that are ventilated but not perfused
what does physiological dead space refer to?
alveolar dead space + anatomical dead space
Who IS the real slim shady?
Kitty
NEW arterial blood sample should reflect lung/ tissue partial pressure values?
lung
veinous blood sample should reflect lung/ tissue partial pressure values?
tissue
how come the volume of CO2 transferred in a minute is not 10 times less than the volume of O2 transferred in a minute (because concentration gradient is 10 times less)?
because CO2 is more soluble in water and diffusion is directly proportional to solubility
what does emphysema do to compliance and elasticity? to number of alveoli?
more compliance, less elasticity
less groups of more alveoli
ideally, what is the ventilation/perfusion ratio?
1
do we have a uniform ventilation rate/ perfusion rate?
no (permanent change)
is blood flow greater/less than ventilation at the base?
greater
is blood flow greater/less than ventilation at the apex?
lesser
where is ventilation equal to blood flow?
rib 3, the only place where the ventilation/ perfusion ratio is of 1
what is the ventilation/perfusion ratio at the base of the lung?
almost 1
where do we find mismatch?
the apex of the lung
what is “shunt”?
when blood is not getting rid of CO2, picks up no oxygen, when it looks like it was just transferred from the right side to the left
how does the pulmonary circulation react to hypoxia?
it contracts
how does the systemic circulation react to hypoxia?
it dilates (better oxygenation)
by which dead space is physiological dead space dominated?
anatomical dead space- alveolar dead space is minimal
when is alveolar dead space significant?
in pathology
alveolar dead space is when alveoli are ventilated not perfuses/ perfused not ventilated?
ventilated not perfuses (think of anatomical dead space, which is ventilated, but where no gas exchange happens)
