Pulmonary Circulation Flashcards
What is the only vascular bed to receive the entire cardiac output?
pulmonary circulation
Is the series circulation in parallel or series with the pulmonary circulation?
series
Why is ischemic damage rare in the lung?
multiple supplies of O2
Why is the pulmonary blood pressure lower than the systemic blood pressure?
vascular resistance is less than TPR
Is the afterload lower in the left ventricle or right ventricle?
right ventricle
What is the normal anatomic shunt and what percentage of CO does it carry?
Left to left shunt
1-2% of cardiac output
Where does the lymphatic system drain into ?
caudal mediastinal lymph node and thoracic duct
How are the valves of the lymphatic system regulated?
- By mechanical pumping during breathing
- by sympathetic activity
Are there arterioles in the pulmonary circulation?
No
Why does pulsatile pressure still exist in the pulmonary circulation?
Since resistance is so low
What is the mean Ppa?
What Ppa indicates pulmonary hypertension?
What Ppa indicates pulmonary edema?
Mean = 11 mmHg
If Mean Ppa>20 - pulm hypertension
If mean Ppa>25 - pulmonary edema
Diastolic P in pulmonary artery is nearly equal to what?
Left ventricular P
What occurs during exercise in the pulmonary circulation?
- radius of the vessels increases and resistance therefore decreases passively
- Compliance of the vessels is high so P doesn’t increase much
(There is not autoregulation, this all occurs passively)
Vessels in the alveoli are exposed to what type of P? Extraalveolar vessels are exposed to what type of P?
Alveolar vessels - alveolar P
extralveolar vessels - intrapleural P
What occurs to the alveolar blood vessels during inflation?
- they are stretched and become narrower
- radius decreases and so resistance increases
- This reduces their pressure
What happens to extraalveolar blood vessels in response to inflation?
- There is a more negative intrapleural P as the lung inflates
- their transmural P increases
What is the relationship btwn alveolar and extra-alveolar vessels? How does this affect total resistance?
They are in series, so resistance is additive
When is PVR at a minimum?
FRC
PVR increases at any other value
During normal breathing what is the normal alveolar pressure, and what effect does this have on the alveolar vessels?
alveolar P fluctuates around zero and so all the vessels remain open
During mechanical ventilation what happens to alveolar pressure? What does this mean for you as a physician?
It becomes slightly positive
- capillaries can collapse and inc their R
- must ventilate at lowest possible P near the FRC
Name some vasodilators that affect pulmonary vascular resistance? (4)
- prostacycline
- histamine (bronchoconstrictor)
- calcium channel blockers
- Nitric oxide
What happens in the lung when a certain area is not able to be ventilated and becomes hypoxic?
blood is shunted to a better ventilated region of the lung by hypoxic vasoconstriction
Name some vasoconstrictors that affect pulmonary vascular resistance? (3)
- inc PCO2, low pH
- norepinephrine - weak effect
- angiotensin II
In what part of the lung is blood flow greatest? Why?
at the base of the lung
-due to gravity and passive distension
What happens to the pressure inside the capillaries as you distend down the lung?
it gradually increases
-due to the pressure from intrapleural fluid under the influence of gravity
When a person is standing upright what is their apex pressure? What is their base pressure?
Apex= Ppa -10 Base= Ppa + 10
What zone does this describe and what occurs:
PA>Pa>Pv
Zone 1
- not normally present
- capillaries will collapse and flow stops-no perfusion
- can occur during blood loss or cardiac output decrease
What zone does this describe and what occurs here:
Pa>Pv> PA
zone 3
- flow inc due to gravity and passive distension
- capillaries are wide open
How is flow determined in zone 3?
by the difference btwn PA-Pv
What zone does this describe and what occurs here:
Pa>PA>Pv
Zone 2
-partial collapse of capillaries on low pressure side but with maintenance of flow
How would you determine the flow in zone 2?
Difference btwn Pa and PA
-Pv has no effect - it is downstream
Describe what changes in the four starling filtration pressures cause pulmonary edema?
- inc capillary permeability
- inc in capillary hydrostatic pressure
- mitral valve stenosis - dec interstitial hydrostatic P
- dec colloid osmotic P
Does high or low protein in the blood cause pulmonary edema?
low protein —hypo
In the equation: QS/QT = (C”c”O2-CaO2)/ (C”c”O2-CvO2), what occurs if QS =0?
normal condition of no shunt
CaO2 = C”c”O2
In the equation: QS/QT = (C”c”O2-CaO2)/ (C”c”O2-CvO2), what occurs if QS =QT?
all blood is shunted - no oxygenation
CaO2 = CvO2
In the equation: QS/QT = (C”c”O2-CaO2)/ (C”c”O2-CvO2), what occurs if QS =QT/2?
50% Shunt- aterial oxygen content is average of shunt and functional capillary content
-CaO2 = (C”c”O2+ CvO2)/2
Does shunting give more hypoxemia or hypercapnea?
more hypoxemia due to the O2 dissociation curve
-CO2 curve is linear
Can breathing O2 rich gas help people with abnormal shunts?
NO - they physically cannot be oxygenated so this is just a waste
