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24 Cards in this Set

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ventilation
the flow of gas in and out of the lungs
perfusion
the filling of the capillaries with blood
what may alters perfusion
pulmunary artery pressure

alveolar pressure

gravity
what may alter ventilation
airway blockages,
local changes in compliance,
gravity
what causes a ventilation-perfusion(V/Q) imbalance
inadequate ventilation
inadequate perfusion
or both
four possible V/Q states in the lungs
normal V/Q ratio
low V/Q ratio(shunt)
high V/Q ratio(dead space)
absence of V/Q(silent unit)
normal V/Q ratio (1:1)

ventilation matches perfusion
in a healthy lung, a given amount of blood passes an alveolus and is matched with an equal amount of gas
low V/Q ratio (shunts)

perfusion exceeds ventilation
blood bypasses the alveoli w/out gas exchange occurring;
this is seen with obstruction of distal airways, such as:

pneumonia
atelectasis
tumor
mucus plug
high V/Q ratio (dead space)

ventilation exceeds perfusion
the alveoli do not have adequate blood supply for gas exchange to occur;
this is characteristic of a variety of disorders, including

pulmonary emboli
pulmonary infarction
cardiogenic shock
absence of V/Q (silent unit)

absence or limited ventilation and perfusion
this is seen with
pneumothorax &
severe acute respiratory distress syndrome
average normal PaO2=

average normal PaCO2=

*partial pressure varies in different lung areas
100mmHg

40mmHg

`

`
under normal conditions and in upright positions,
ventilation is greater than perfusion in the lung apices
under normal conditions and in upright positions,
perfusion and ventilation are greater in the lung bases
where is the nervous system control of breathing initiated
w/in the medulla oblongata and pons of the brain stem
medulla oblongata
controls inspiration, expiration, and breathing pattern
pons
controls rate and depth of respiration
sensory input to brainstem
impulses that influences breathing and respiration are transmitted to the brainstem from:

chemoreceptors,
stretch receptors,
proprioceptors,
baroceptors, and
the external environment.
central chemoreceptors in medulla
> PCO2 and/or
< blood pH
causes:
> alveolar ventilation as a compensatory mechanism to maintain PCO2 and pH at normal levels
Peripheral chemorecptors in the aortic arch and carotid bodies
< pH, and/or
> PCO2 and/or
< PaO2
causes:
> alveolar ventilation
what prevents overdistention of the lungswhen they are inflated
-stretch receptors in the alveolar septa

-bronchi

-bronchioles
proprioceptors in muscles and tendons of moveable joints
stimulate ventilation w/exercise to increase O2 supply during increased O2 demand
Baroreceptors alter respiration relative to changes in artial B/P
elevated artial B/P lowers respiration

B/P below 80 mmHg increases respiration
external environment factors that ALTER respiration
cold
physical stress
air pollution
smoking
pain
external environment factors that INCREASE O2 demand
infection
fever