Pulmonary Circulation-Khundmiri Flashcards
systemic high pressure
pulm low pressure travel smaller distance
?????
Pulmonary system has very low resistance compared to systemic. Why?
less smooth muscles cells in the arteries and capillaries compared to systemic which is rich in smooth muscle
Why is there high compliance in pulmonary system and low compliance in the systemic system?
pulmonary system accommodates for shifts in the blood more quickly than systemic
lung can be divided in to 3 zones;shifting from zone 1-3 you get shifts in blood circulation which needs high compliance
How do you measure pulmonary circulation? Do you need to measure?
you do an US driven catheter through RV going through pulmonary artery and pressure exerted on the balloon will give the pressure in the pulmonary arteries and capillaries
What is the net driving pressure of systemic and pulmonary system?
93 mmHg for systemic circulation:
- At rest the systemic capillaries are closed: Aorta = ~95 mmHg
- At the opposite end of the circuit at the RA = ~2 mmHg
7 mmHg for pulmonary circulation:
- In the pulmonary artery = ~15 mm Hg
- At the other end of the circuit at the LA
The pulmonary artery subdivides into terminal branches with internal wall bigger due to less smooth muscles. The walls are highly distensible compared to vein as they can accommodate cardiac output because of?
because of the tone of the pulmonary smooth muscles the have effect on resistance
transmural pressure difference across the walls will determine pulmonary vascular resistance
can be calculated
Pulmonary vascular resistance
can be calculated by?
PVR = (MPAP-MLAP)/PBF
Mean pulmonary artery pressure (MPAP), mean left atrial pressure (MLAP), pulmonary blood flow (PBF)
normal is 1 mmHg/L/min
Increase in blood flow causes?
decrease in transmural vascular resistance because:
- pulmonary blood vessels are shorter and wider than those in the systemic circulation
- arterioles are alos present in much higher numbers
- pulmonary arterioles are less muscular than those in the systemic circulation
- therefore, their resting tone is low
During exercise you increase your blood flow causing a decrease in pulmonary circulation vascular resistance to increase your oxygenation of the blood
Pulmonary vascular resistance: the extravascular events or the passive factors may have much greater importance in pulmonary vascular circulation resistance compared to the systemic vascular circulation. Why?
Gravity, body position, lung volume,
alveolar and intrapleural pressures, intravascular pressures, and right ventricular output
all can have profound effects on PVR without any alteration in the tone of the pulmonary
vascular smooth muscle.
What is the transmural pressure difference?
As transmural pressure increases, the vessel diameter increases and resistance falls;
as the transmural pressure difference decreases, the vessel diameter decreases and
the resistance increases. Negative transmural pressure differences lead to compression
or even collapse of the vessel.
vessel diameter increase resistance decreases
opposite eventually arteries will collapse
Intrapleural pressure taken during your inspiration does?
this pulls the extravascular vessels to increase blood
when the alveoli fill up they will cause pressure on the capillaries surrounding the alveoli
negative intrapleural pressure in the interstitium around the capillaries will cause expansion of the extra alveolar BV (capillaries surrounding the alveoli are lengthening) whereas alveoli capillaries will extend
What happens to your pulmonary vascular resistance at RV?
the highest due to the extraalveolar BV which have higher pulmonary resistance and alveolar BV would have lower pulmonary resistance
What happens to your pulmonary vascular resistance at TLC? would be
alveolar BV would have higher pulmonary resistance compared than extraalveolar pulmonary resistance
Total resistance would be lowest at FRC and highest at RV and TLC. Why?
resistance would be biphasic (highest at RV and TLC and lowest at FRC )
As lung volume increase, the alveolar walls become more stretched out.
The AV is stretched along their longitudinal axis but crush when viewed in cross section.
Increasing lung volume from RV to TLC which is biphasic, the alveolar wall would be stretched along the longitudinal axis.
Because of their location, the extraAV BV are not going to be influenced directly under alveolar pressure but are controlled by?
intrapleural pressures
Pulmonary blood flow in lungs is similar to ventilation as it is?
gravity dependent
lowest at apex and highest at bottom in standing position
When lying down down, how is pulmonary blood flow?
the lowest would be highest and the bottom would be lower
BF can shift very easily to one position to another because of the high compliance of the vessels
Variation in ventilation in parts of the lung are due to mechanical factors and environmental stress. Why?
the zone are not anatomical but are PHYSIOLOGICAL
What causes the uneven distribution of blood flow in the lung in the different zones?
Zone I: alveolar pressure is higher than arterial pressure than venous pressure (the arteries and capillaries would be crush)
Zone II: arterial pressure higher than alveolar
Zone III: arterial pressure is the highest, venous pressure next, and the lowest pressure would be the alveolar lowest
How does the changing of zones in lungs occur?
two things:
recruitment and distension
During exercise our cardiac output increases several fold without corresponding increase in mean arterial blood pressure however?
drop in pressure will be proportional to decrease in CO–it is passive meaning it is not the result of change in tone of the muscle cells or humoral changes
At resting states not all of the capillaries and arteries are conducting blood. some are open and conducting blood or not conducting blood others are crushed and not conducting blood
with the increasing pressure all of your capillaries will start conducting blood
controlling blood flow to the regions
What comes first recruitment or distension?
research wise we don’t know what happens first so the answer is the decreased PVR seen with elevated perfusion pressure is probably both (stating that they happen at the same time).
recruitment has higher pressure increasing surface area???
distension is due to low ventricular output or high alveolar pressure
Decrease in PACO2, increase in PAO2 will cause what movement of pulmonary arteries?
dilation
Increase in PACO2, decrease in PAO2 will cause what movement of pulmonary arteries?
constriction
What happens in hypoxic pulmonary vasoconstriction?
decrease flow of blood to keep V/Q ratios normal
What occurs when you constrict the alveoli?
decrease the PACO2 and increase in pH????
i’m not getting enough O2 out of the alveoli so stop flowing blood
changing the flow of blood to keep V/Q normal
What occurs when you constrict the artery?
happen because of low O2 causing flow to go to the other lung to maintain the V/Q ratio
body under best scenario
shift blood flow to the other lung to maintain V/Q
What is the difference of the alveolar shunt and capillary shunt ?
alveolar shunt: increased CO2 and decreased O@ as there is no flow of O2 coming from outside (the arteries are still conducting); alveoli?? will shrink because of hypoxia
capillary shunt:
will not get filled up with water due to
Starling forces: keeping the lungs dry
What do the starling forces do?
they cause the flow of fluid into the lymphatic system which is very important in keeping the lungs dry
Which factors in the starling equation will result in acute respiratory distress syndrome oxygen toxicity?
increased capillary permeability
tumor–breast cancer
insufficient lymphatic drainage resulting in pulmonary edema
What are the features of bronchial blood flow?
supplies blood to trachea and airways up to the level of terminal bronchioles and BVs
they supply new ???? oxygen to lung tissue
A second, separate circulatory system in the lung with oxygenated blood from the systemic circulation.
Bronchial blood flow comprises only 1% to 3% of the output of the left ventricle.
The return of venous blood from the capillaries of the bronchial circulation to the heart occurs either through true bronchial veins or through bronchopulmonary veins.
Where do the bronchial veins drain?
azygos and hemiazygos vein
