Trachte: Blood Flow and Metabolism Flashcards
What does the pulmonary artery contain?
Mixed venous blood
What’s the PO2 in the pulmonary artery? PCO2?
PO2- 40
PCO2- 46
Describe the path of the pulmonary artery?
Branches w/ the airways down to the TERMINAL BRONCHIOLES.
Breaks into the PULMONARY CAPILLARIES for gas exchange.
What are pressures in the pulmonary capillaries normally?
Usually LOW–little resistance so the heart doesn’t have to work hard to perfuse lungs
25/8 mmHg
What conditions significantly alter pressures in the pulmonary capillaries?
CHF
Mitral Valve stenosis
Blood isn’t being pumped adequately so pressure in pulmonary systems begin to rise–> pulmonary edema
What is the mean pressure in the pulmonary capillaries?
15 mmHg
What is CO?
5 L/min
What is Left atrial pressure?
5 mmHg
What’s the pulmonary resistance? How does this compare with systemic resistance?
***2 ml/mmHg
systemic is 98/5 which is about 10x higher
What pressures surround the pulmonary capillaries?
Alveolar pressure (surrounded by alveoli)
How does pressure around the pulmonary capillaries differ during exhalation and inhalation?
exhalation- couple mmHg
Inspiration- subatmospheric
What happens to pulmonary vessels during inspiration?
They’re PULLED OPEN
Are there any conditions that radically change the pressure surrounding the vessel?
- Tension pneumothorax–can shut down blood flow if pressure gets high enough
- Positive pressure ventilation–> above atm pressure
- Tension pneumothorax–can shut down blood flow if pressure gets high enough
Why does pulmonary a. resistance DECREASE w/ an INCREASE in pulmonary a. pressure?
- RECRUITMENT of additional capillaries in conducting blood flow
- DISTENSION of capillaries conducting blood to allow for more blood flow
- EXPANSION of lungs reduces resistance
How can alveolar pressure increase resistance?
Alveolar pressure can COMPRESS vessels to INCREASE RESISTANCE if it is greater than capillary pressure
How NTs contract vessels to increase resistance?
NE
5HT
Histamine
What NTs relax pulmonary vessels to REDUCE resistance?
Ach
isoproterenol
prostacyclin–> PGI2 (inhibits platelet agg and causes dilation) prevents MI
What is the fick principle?
O2 consumption = CO (CAO2 – CVO2)
What is the equation for pulmonary blood flow?
Pulmonary blood flow= VO2/(CAO2 – CVO2)
How can you measure concentration of O2 in the arterial blood?
Inject a dye
Why is there more blood flow to the base of the lung usually than the apex?
gravity
What are the 3 potential zones of perfusion?
- Zone 1 : PA > Part > Pvenous
- Zone 2: Part > PA > Pvenous
- Zone 3: Part > Pvenous > PA
What are the characteristics of Zone 1?
PA > Part > Pvenous
- NO FLOW occurs in this region
- This does not occur naturally but can occur in HEMORRHAGE OR POSITIVE BREATHING PRESSURE
- NO GAS EXCHANGE
What is zone one referred to as? Where is it most likely to occur?
alveolar dead space
APEX of the lung
What does zone 2 represent?
What determines blood flow in this region?
Does venous pressure influence flow?
Part > PA > Pvenous
PRESSURE DIFFERENTIAL between arteries and Alveoli
Venous pressure DOES NOT influence flow
Where is zone 2 most likely to occur?
APICAL REGION of lung where pressures are the lowest
What does zone 3 represent?
Part > Pvenous > PA
What is flow in zone 3 dependent on? Where does it occur?
Arterial/venous pressure difference (normal for the circulatory system)
MIDREGIONS or BASE of lugns
What happens during alveolar hpyoxia? What is this mechanism independent of?
alveolar hypoxia CONSTRICTS blood vessels perfusing the hypoxic region of the lung
NERVES
What is the mechanism for alveolar hypoxia leading to constriction? What does this do to the membrane potential?
INHIBITION of voltage gated K channels–>
more K stays inside cell>
DEPOLARIZES cell/DECREASE MEMBRANE POTENTIAL>
INCREASE in Ca leading to vasoconstriction
What controls fluid movement out of the pulmonary vasculature?
Starling foces
What is the formula for fluid escape?
Fluid escape = Kf (Pcap – P int) – ∂ (πcap – πint)
What are the constant values for fluid escape?
Capillary pressure is 15- interstitial pressure can vary
Osmotic pressure is normally 25–> this should keep your lungs dry
Why is there a slight leak of fluid out of the lungs? How does this differ from systemic circulations?
Lymphatic drainage (20 ml/hr)
MUCH LOWER in systemic circulations b/c of LOWER hydrostatic pressure
What are situations when fluid movement is increased?
Heart failure–> back up of fluid from heart into lung–> increased fluid in lungs–> SOB
Not enough protein
What happens if too much fluid escapes from the lungs?
alveolar edema>
SOB
What are other functions of the pulmonary circulation?
- RESERVOIR for blood (we lay down blood drains from legs to lungs)
- FILTER blood (thrombi in legs/periphery can’t get to the brain)
What does the lung do to ang I?
Activates it to Ang II (mediated by ACE)
What does the lung do to bradykinin?
Inactivates it (mediated by ACE)
What affect does the lung have on 5HT levels?
Accumulates it and removes it from circulation–> 5HT is a vasoconstrictor
What does the lung synthesize?
both PGs and leukotrienes
It can also REMOVE leukotrienes from circulation
What are PGS and leukotrienes?
Bronchoconstrictors
What is an important role of PGE in pulmonary/systemic circulation?
Keeps DA open in fetal circulation.
How do ACE inhibitors cause cough?
Prolong bradykinin actions–> COUGH
If you wished to treat a patent ductus arteriosus pharmacologically what would you use?
Indomethacin (COX inhibitor)
