pulmonary circulation Flashcards
RV ejection fraction should equal Lv cardiac output.. why?
even though the pressures are different, you’re dealing with the same volumes
the resistance to flow in pulmonary system compared to systemic
resistance to flow in pulmonary system is one tenth of systemic circulation
what is the structure of the pulmonary artery like>
this walled (1/3) thickness of aorta) and very compliant
RV pressure #
25/0-4
RA pressure #
0-4
LA pressure #
8-10
pulm artery pressure #
25/10
pulmonary vessels are divided into
alveolar and extra alveolar
what do alveolar vessels do
alveolocapillary network involved in gas exchange. the big capillary bed where gas exchange occurs
what collapses alveolar vessels during lung expansion
high positive pressure
what do extra-alveolar vessels do?
they are the arteries and veins which convey blood to and from the resp units. think: similar to conducting airways that do not participate in gas exchange
are extra-alveolar vessels affected by pressures in lung
no
do extra-alveolar vessels compress with positive pressure
no
bronchial vessels
oxygenated blood from systemic circulation, 1-2% of cardiac output, empty into left atrium
when you take a breath in, what do the alveoli do?
squeeze and push on the capillaries and increase resistance
???at low lung volumes, vascular resistance is
high. because extra-alveolar vessels become narrow
???at high lung volumes, resistance is
low. because the capillaries are stretched
alveolar capillary walls contribute to what % of total resistance
40
alveolar arterioles contribute what percentage of resistance
5
in the body, major resistance vessels?
arterioles (75%)
pulmonary resistance of capillary vessels is reduced by ___ lung volumes. high or low?
LOW lung volumes. (and high blood flow rates)
resistance of capillary vessels is greater when
lower BP or less vascular distending pressures
passive regulation of blood flow through capillaries occurs in response to changes in
cardiac output
increases in blood flow are accommodated by
recruitment and distention
when arterial ad venous pressure increases, PVR is
decreased
recruitment is simply
the opening of previously closed vessels
distension is simply
increase in caliber of vessels
explain recruitment
when you increase pressure or flow in the venous or arterial side, all the sudden you recruit some of these small capillary channels that were closed, you recruit them and ope the,. so the increase flow, you get decreased resistance. because now you’ve opened other chapels that hd been closed so you have a bigger surface area.
explain distension
areas that are already open distend, leading to less resistance.
increased blood flow in lungs, decreased
pulm vascular resistance
the two mechanisms for the decrease in PVR that occurs as vascular pressures are raised
recruitment and distension
pulm arter wedge pressure tells you
preload of left side, filling pressure of the left side of the heart
functional capillary volume
70ml. 1ml/kg body weight
the average distance an RBC travels through the network is 600 to 800 um
600 to 800 um which is a very short ditance
pulmonary capillary network blood volume is equal to
RV stroke volume
RBC remain in alveolocapillary network for
one cardiac cycle ( .75sec)
RBC require how much time for gas exchange
less than .25s (third of cardiac cycle)
in diseased lungs, the curve for gas exchange shifts to the
right
total blood volume from main pulm artery to left atrium
500ml
how is the pulm vasculature a capacitance reservoir for the LA
pulm vasculature can alter its volume from 50% to 200% of resting volume
why is the pulm vasculature altering its volume from 50% to 200% a good thing?
its like a buffer so you wont pass out. it prevents changes in blood return to the RV from affecting LV diastolic filling pressures over 2-3 cardiac cycles
capillary bed contains 70ml of blood at rest, and max volume is?
200 ml during exercise
increased CO does what to pulm vascular pressures
raises
increased CO does what to PVR?
decreases
when does recruitment occur
during periods of stress and increased tissue 02 demand
when does distention occur
high vascular pressures
what can distention lead to
lung congestion and heart failure
capillary volume during exercise
doubles to give time for adequate gas exchange during increased blood flow
pleural pressure - inspiration
greater sub atmospheric (more negative then -5mm H2o)
pleural pressure - exhalation
lower pleural pressure gradient (less negative than -5mm h2o)
when lung volume is close to FRC (end of exhalation), PVR is
minimal
PVR is increased with
higher and lower lung volumes
what do extra-alveolar vessels do during inspiration
dilate
what do alveolar vessels do during inspiration
compress. pressure drops with each breath
what does mech vent do to alveolar pressure
artificially increases
effect of positive pressure ventilation on CO
can decrease
effect of positive pressure ventilation on v/q imbalance
can increase
bronchial circulation runs from
conducting airways to terminal bronchioles
bronchial blood flow is what % of cardiac output
1-2%. flows at systemic pressures
50% of bronchial blood circulation returns to
RA via azygos vein
what does the pulmonary lymphatic system do
keeps alveoli free of fluid moving from capillaries
pressure of interstitium
slightly negative
hydrostatic starling forces move fluid out at
20ml/hr
there is a net pressure of +1 out of the vessel so what occurs?
theres a net leakage of fluid out of the capillary into the interstitum and the lymphatic pump pulls that fluid out and keeps the interstitum free of fluid, allowing gas exchange to occur.
two measurement techniques for pulm blood flow
fick principle and indicator dilution principle
fick principle
measurement of arterial and mixed venous blood and determination of 02 consumption
V02 at rest is
300ml/min
indicator dilution principle
inject dye into venous circulation, diluted concentration measured on arterial side
thermodilution is also used to measure
CO
in the supine position, arterial pressure is highest where
feet
the effect of gravity on pulm circulation is
greater than systemic. because pulm circulation pressures are much lower.
zero reference points
RA level and middle of lung
supine or prone does what to hydrostatic pressure?
minimizes
what is hydrostatic pressure
the pressure effect gravity has on a column of fluid
what part of the lung receives more blood? base or apex
base
in zone 1, where is pressure the highest
alveolar > arterial > venous
in zone 1 where is pressure the lowest
venous
in zone 2 where is pressure the highest
arterial > alveolar > venous
in zone 3 where is pressure the highest
arterial >venous > alveolar
whats gas exchange like in zone 1
none
zone 1 has a higher or lower v/q ?
higher
you ventilate which parts of your lung more?
lower
from the top of the lungs down, you have
increased blood flow and increased ventilation
the perfusion zones in the lung depend on the relationship between
alveoli and BP in pulm arteries and veins
blood flow in zone 2
intermittent “waterfall affect”. with systole, you intermittently have a higher pressure
zone 3 blood flow
ideal!
zone 4
abnormal condition of reduced blood flow… high pulm venous pressures.. pulm edema. increased vascular resistance
alveoli pressure is higher in the apex of the lung, so
less blood flow
blood vessels are more distended in which part of the lung
base
what will shock and hypovolemia do to zone 1perfusion?
expand zone 1. because PA pressure is decreased
what will PE do to zone 1 perfusion
expand zone 1 because blood vessels are occluded
what does peep do to zone 1
increases
how to reduce zone 1
increase PA pressure (give blood or fluids), reduce hydrostatic effect by changing position from standing to supine.
pulmonary vascular resistance
active regulation of blood flow
how does PVR regulate
active regulation occurs by altering vascular smooth muscle tone in pulm vessels (arterioles)
most active regulation of pulmonary vessels is mediated by
local metabolic influences
motor innervation of pulm vasculature comes from
sympathetic branch of ANS. causes vasoconstriction of pulm vessel walls
reduced PA02 causes
vasoconstriction
increased PAO2 causes
vasodilation
increased PCO2 causes
vasoconstriction
histamine causes
vasoconstriction
nitric oxide causes
vasodilation
thromboxane A2
potent vasoconstrictor
what does thromboxane A2 work on ?
constricts pulm arterial and venous smooth muscle. produced during acute lung tissue damage
prostaglandin I2 (prostacyclin)
potent vasodilator and inhibitor of platelet activation
nitric oxide - vasoconstrictor or vasodilator?
potent endothelium-derived endogenous vasodilator
does NO have a systemic or localized effect?
strictly localized effect
NO is formed by L-arginine and leads to
smooth muscle relaxation through synthesis of cyclic GMP
how does NO (and also sodium nitroprusside) work?
guanylyl cyclase, which is responsible for the synthesis of cGMP,
what is inhaled NO used for
selective pulmonary vasodilation
comparison of NO and O2 binding to hemoglobin
NO binds to hemoglobin 200,000x > oxygen.
is NO better at low concentrations or high
low! it is very toxic at high concentrations
global reduction in alveolar oxygen tension does what to PVR?
increases total PVR by constriction of arterioles and small arteries
as alveolar oxygen tension decreases, surrounding arterioles
constrict
oxygen diffusing into pulm arteriole walls causes smooth muscle
dilation
alveolar hypoxia produces
hypoxic pulmonary vasoconstriction
what enhances HPV
hypercapnia and acidosis
HPV is a localized or systemic response?
localized
when the systemic circulation is hypoxic, causes ____ but when the pulmonary circulation is hypoxic, causes ____
vasodilation, vasoconstriction
HPV is an important mechanism of balancing v/q. explain.
there is a shift of blood flow to ventilated pulmonary regions. results from decreased formation and release of nitric oxide by pulmonary endothelium in hypoxic region
increase PAO2,
increase blood flow
pulmonary hypertension
increased resistance to blood flow in the lung.
pulm hypertension causes increased work of breathing for which part of the heart?
right ventricle. causing hypertrophy, tricuspid regurgitation, and right heart failure
what causes pulm hypertension - high PVR - elevated PA pressures
generalized alveolar hypoxia, lung disease, COPD, low inspired PO2, increased PCO2, pain, patient too light, histamine release
why is primary pulm hypertension so serious?
small muscular pulm arteries narrow, pulm artery pressure increases, RV pressures rise to compensate until occurrence of RV failure, lung transplant only effective treatment
tidal volume is distributed evenly or unevenly
unevenly!! ventilate base way more than apex in upright lung.
what part of the lung are alveoli more expanded?
top
what part of the lung is compliance greater
base
what part of the lung is FRC higher
top
increased resistance and/or decreased compliance indicates
longer alveolar filling time
why are the PO2 values higher in the top of the lung as opposed to the base?
because no gas exchange is occurring so no oxygen is being extracted
goal for systemic oxygen partial pressure range
85-100mmHg
normal A-a P02 differences are
10-15mmHg
what to larger A-a PO2 gradients indicate?
intrinsic pulm disease, shunting.
hypoxemia with normal (A-a) PO2 gradient indicates
hypoventilation
shunt =
perfused but not ventilated
right to left heart shunt
a portion of CO flowing through pulm circulation that doesnt participate in gas exchange. fraction of blood flow bypasses the lung to enter the systemic arteries without becoming oxygenated leading to venous admixtures
venous admixture is
the blood flow equivalent of wasted ventilation
true anatomical shunts
bronco pulmonary venous anastomoses, intracardiac thebesian veins, mediastinal veins, pleural veins
right to left heart shunt is also known as
pulmonary venous admixture
left to right heart shunt is also known as
pulmonary venous recirculation
L to R shunt
a portion of the CO returns to the right heart without flowing thru the body. does not affect systemic arterial oxygen tension.
L to R shunt
a portion of the CO returns to the right heart without flowing thru the body. does not affect systemic arterial oxygen tension.
**know recruitment and distension
.
*** from apex to base, blood flow and ventilation
increase
***pulmonary vasculature is very
distensible and thin
*** unique to the lungs - with increased pressure and increased flow you get what effect on resistance
decreased resistance
** also unique to the lungs, low O2 causes
vasoconstriction . hypoxic PV constriction.
LV pressure
120/10
aortic pressure
120/80
resistance of capillary vessels is reduced by ___ blood flow rates. high or low?
high blood flow rates (and low lung volumes)
