Alveolar Ventilation and Perfusion Flashcards
what is the leading cause of low blood oxygen
-V/Q inequality
PaO2 level that is hypoxemia
- <80 mmHg
the total pressure of a mixture of gasses is the sum of
- the partial pressures exerted by each gas
what is conditioning?
- warming, cleansing, and humidifying inspired air
what is the partial pressure of water vapor
- 47 mmHg
what happens when you introduce water vapor into a mixture of dry gases
- dry gas partial pressure falls accordingly
what does the blood deliver to the lungs
- CO2
what do the lungs give to the blood
- O2
what is alveolar ventilation
- volume of air reaching alveoli to participate in gas exchange x respiratory rate
the first 150 mL of air that is inspired is
- expired air from the previous breath
amount of CO2 produced by the body’s metabolism per minute compared to the amount of CO2 eliminated by alveolar ventilation - during steady state
- equal
relationship between alveolar ventilation and PACO2
- inverse
increased PaCO2 will result in at change in pH
- fall in blood pH
can doubling ventilation double PAO2
- no
- cannot rise higher than PO2 of humidified air (150)
regulation of ventilation by the CNS is driven primarily by
- arterial PCO2
hyperpnea
- increase in rate and depth of alveolar ventilation caused by a rise in metabolism
tachypnea
- rapid, shallow breathing to maintain sufficient gas exchange
apnea
- cessation of breathing
hypoapnea
- slow, shallow breathing
PaCO2 of hyperventilation
- less than 35 mmHg
PaCO2 of hypoventilation
- greater than 45 mmHg
if the lung is functioning perfectly, what will be the partial pressures of gas in the pulmonary blood versus alveolar gas
- equal
what does the A-a difference compare
- calculated PAO2 and PaO2
partial pressure of CO2 in alveolar gas versus that in the arterial blood
- equal
in a subject standing or sitting upright, where is ventilation greatest
why?
- base of the lung
- gravity pulls lung downward and creates more negative interpleural pressure at the apex that holds alveoli more open
at end expiration, which alveoli are held more open
- alveoli at top of lung
alveoli at the base
- more compliant
- greater increase in volume for a given increase in pressure.
pressure, volume of the pulmonary circulation
- low pressure, high volume
what does the low pressure of pulmonary circulation help prevent
- fluid extravasation (pulmonary edema)
pulmonary arterioles shape, size
- numerous, short, thin walled
auto regulation of pulmonary arterioles
- lack autoregulation
compliance of pulmonary arterioles
- high compliance
pulmonary capillary compliance to arterial pressure
- high compliance
capillaries are also uniquely susceptible to
- alveolar air pressure
where are extra-alveolar vessels located
- not adjacent to alveoli
extra-alveolar vessels when lung volume increases
- increase in caliber and decrease in resistance
extra-alveolar vessels when lung volume decreases
- decrease in caliber and increase in resistance
alveolar vessels are located
- adjacent to alveoli
alveolar vessels when lung volume increases
- decrease caliber and increase resistance
alveolar vessels when lung volume decreases
- increase caliber and decrease resistance
negative alveolar pressure during inspiration will do what to alveolar vessels
- dilate and decrease resistance
positive alveolar pressure during expiration what do what to alveolar vessels
- collapse alveolar vessels and increase resistance
high alveolar pressures at high lung volumes create
- lung zones with high vascular resistance and low blood flow
high intravascular pressure will do what to alveolar vessels
- increase caliber of compliant ones
- lower resistance
increases arterial or venous pressure leads to what in pulmonary vascular resistance
- a decrease in pulmonary vascular resistance
what can increased intravascular pressures also do
- recruit previously non-perfused pulmonary capillaries
capillaries because the lung is a very low pressure hemodynamic system
- many capillaries may be minimally perfused
many capillaries may be minimally perfusion during
- periods of low activity and quiet breathing
perfusion pressure and vascular resistance in upper zones of lung
- low perfusion pressure
- higher vascular resistance
capillaries in upper lung respiratory units
- susceptible to collapse under influence of alveolar air pressure
perfusion pressure and vascular resistance in lower zones of lung
- higher perfusion pressure
- low resistance
vascular resistance in zone 1
why
- high. vasculature is snapped close.
- alveolar pressure higher than pulmonary arterial and pulmonary venous pressure
result of collapse of alveolar capillaries and expansion of zone 1
- increase physiologic dead space
pressures in zone 3
- pulmonary venous and arterial pressure higher than alveolar pressure
lung perfusion is highest where
- zone 3
why is there a dip in blood flow at the very bottom of the lung
- extra alveolar vessels are compressed at low lung volumes
pressure in zone 2
- alveolar pressure intermediate to arterial and venous pressure
arterial pressure in zone 2
- high enough to keep capillary open
- closer to the bottom
arterial pressure in zone 2 at you go up up the lung
- decreases as you go up the lung
- artery will collapse and pinch off blood flow
blood flow in zone 2 dependent on
- difference between arterial and alveolar pressures
V/Q is highest at
- apex
V/Q is lowest at
- base
alveoli in apex of lung
- low compliance
- low ventilation
- low blood flow
- high PAO2
alveoli in base of lung
- high compliance
- high ventilation
- high blood flow
- low PAO2
hypoxia (low areas of O2 tension) will have what effect on the vasculature
result
- vasoconstriction
- directs blood away and toward more well ventilated areas to preserve V/Q
consequence of hypoxic pulmonary vasoconstriction
- increases pulmonary artery pressure
result of long standing pulmonary hypertension
- cor pulmonale (right ventricular hypertrophy)
