Pulmonary and bronchial circulation Flashcards
Flash cards comprise Kam power/Deranged physiology and Wests. Only the first 3 pages of Nunns chapter included
Mean pulmonary artery pressure? Pulmonary trunk diametre?
15mmHg or 20cmH20 (25/10) = 1/6 of mean systemic arterial pressure
30mm
Mean pulmonary arteriole pressure
12
Mean pulmonary vein pressure
8
RV pressure
25/0
RA pressure
2
LV pressure
120/0
LA pressure
5
Mean systemic arterial pressure
100 120/80
Mean systemic veinous pressure
5-10
Mean systemic arteriole pressure
30
Mean systemic capillary pressure
20
Mean systemic venule pressure
10
Why is there a more pronounced pressure drop in the systemic circululation than in the pulmonary circulation?
- Muscular arteriole mediated blood flow regulation at entrance to organs leading to profound pressure drop across capillary system in systemic circulation
- Pulmonary artery shorter, thinner walled more distensible than the aorta ith less smooth muscle
Define vascular resistance
Flow = pressure / resistance
Resistance = flow/pressure
How are the pulmonary and systemic arterial systems different? Show this mathematiucally?
Identical flow
Pressure drop across pulmonary circulation (mean values) 15 - 5 = 10mmHg
In systemic circulation drop is 100-5 = 95mmHg
Therefore MUCH higher systemic vascular resistance
What pressures are the capillaries exposed to in the pulmonary system?
- Alveolar pressure - if alveolar pressure is higher than capillary pressure then the capillaries collapse
What is the difference in thw walls of the BV system between the pulmonary and systemic?
Pulmonary blood vessels markedly thinner
How to tell the difference on a microscope between a vein and an artery in the lung?
Veins are not accompanied by airways, whereas arteries are accompanied by arteries especially more distally; arteries and airways travel down the centre of lobules whereas veins travel down the peripheries of lobules
There is however not much difference in their thickness, but generaly veins are fewer in numbre, thinner walls, less muscular, less elastic and more collagenous. Interestingly pulmonary veins drain seamlessley into the LA with no fold/border. At their largest half the width of pulmonary arteries
How is the path different between a vein and an artery in the lung?
Veins are not accompanied by airways, whereas arteries are accompanied by arteries
There is however not much difference in their thickness
How is the pressure different between arteries/veins and capillaries in the lung?
Alveolar capillaries - these are compressed between alveoli by alveolar pressure
Pulmonary vein and arteries - extra-alveolar vessels therefore the alveoli/lung parenchyma pull on the veins and arteries as they expand
Alveolar vs extra-alveolar vessels? Whats the difference? How do their calibres change with inspiration and expiration?
Inspiration/expansion of lung volume - increased alveolar resistance, however reduced pulmonary vein/artery resistance
The inverse with expiration
What is the resistance equation
Resisatnce = input pressure - output pressure/flow
What is the difference between vascular and electrical resistance?
Resistance does not change depending on upstream and downstream pressure in electrical systems; HOWEVER physiologically the pressure changes do change the resistance in the lung
Draw a diagram equating pulmonary vascular resistance with arterial or veinous pressure? Give units? Why does this relationship occur? (2) HOw elastic is the pulmonary capillary?
Now draw another diagram describing the relationship between PVR and lung volume? Explain the trends? Explain the different effects on vessels in different areas that explain this? Where is the normal scope of breathing on these diagrams?
- Recruitment of capillaries with increasing flow
- Distension of existing capillaries with increasing flow reducing their resistance
Baseline flow is not enough to distend to maximal diametre as partial collapse; highly elastic thinner walled vessels with less muscle
What is the Fick principles
VO2 = CO (CaO2 - CvO2)
Volume of oxygen going into the lung, is equal to the amount removed by pulmonary blood flow which is equal to Ca O2 - CvO2
Rearranging the Fick principle for CO =
CO = VO2 / (CaO2 - CvO2)
How do you measure the cardiac output in order to calculate VO2?
Catheter in pulmonary artery
Arterial blood sample
Mixed veinous blood sample
Other methods - dye dilution, thermal dilution
Distribution of blood when upright? Draw a diagram describing this relationship for sitting up, supine and seated? Why is supine not straight?
How was this relationship derived? What i blood flow at the apex of the lung when upright? On exercise how does this change? What effect does reduced pulmonary arterial pressure have on standing curve? What point corresponds to no blood flow? What point corresponds to a change in gradient?
Radioactive xenon with breath hold and emission
Apex of upright lung under normal conditions has barely any blood flow
It is affected by change of posture
Exercise both basal and apical increase, fractional differences between areas of the lung becomes less
Reducing pulmonary artery pressure exacerbates this difference, and flow stops at the top where arterial = alveolar pressure. Much more flow at the bottom.
Raising pulmonary veinous pressure increases flow in the middle zone where veinous > alveolar, but in the middle zone it still drops to zero once arterial < alveolar
What is the 3 zone description of blood flow? Which are present under normal conditions? When do they become apparant?
The pulmonary arterial pressure is just sufficient for zone 1 not to exist - if you had a haemorrhage and decreased pulmonary arterial pressure then you may have zone 1; or if positive pressure ventilation you may induced zone 1.
What does the flow depend on in West Zone 2? What model is used to explain this? Why does blood flow increase as you progress down/descend?
Zone 2 = Pa > Palveolar > P veinous
Blood flow dependent on arterial - alveolar pressure (not veinous). Acting as a starling resistor where capillaries collapse
Blood flow increases due to gravity increasing Pa and Pv above Palveolar which is constant throughout the lung
Non gravitational causes of uneven blood flow in the lung (3)
Random variation sin resistance of vessels
Proximal acinus receive more blood flow than distal regions
Some regions have intrinsically higher resistance
What factors determine pulmonary blood flow?
- Lung volume
- Gravitational forces
- Cardiac output
- FiO2
- PaCO2
- pH
What effect does FiO2 have on pulmonary artery pressure? Draw a diagram of blood flow vs alveolar PaO2? Over what range does it mostly change?
Reduced Fio2 increases mean pulmonary artery pressure, reducing flow. This is hypoxic mediated pulmonary vasoconstriction
Maximum change between PaO2 50 - 150; steepest gradient below 50mmHg
Where does the response to alveolar PaO2 and blood flow get controlled? How does alveolar gas affect this because pulmonary blood has not yet exchanged? What channel is important? What can inhibit this mechanism? Pulmonary blood flow in the foetus is what proportion of cardiac output? What is PVR so high?
Pulmonary artery - as the artery is next to the airway and alveoli, via diffusion alveolar gas moves across into pulmonary artery. Vascular smooth muscle - voltage gated pottasium channels; and nitric oxide inhibits this process.
15%
PVR is so high because the lung has no oxygen coming through it
Metabolic functions of the lung?
- Activation of (1)
- Inactivation of (4)
- Metabolism of and released (2)
- Secretion of (1)
AT2 activation
Inactivation - bradykinin, serotonin, PGE1/2, F2, NA
Adrenaline, AT2 and vasopressin NOT affected
Metabolism of and released - LT and PG (AA metabolism)
Secretion of - IgA in bronchial mucous
PART 2
(already answered) Draw a diagram equating pulmonary vascular resistance with arterial or veinous pressure? Give units? Why does this relationship occur? (2) HOw elastic is the pulmonary capillary?
Now draw another diagram describing the relationship between PVR and lung volume? Explain the trends? Explain the different effects on vessels in different areas that explain this? Where is the normal scope of breathing on these diagrams?
Low lung volumes = loss of extraalveolar vessel radial traction causing partial collapse and vascular resistance rises
At high lung volumes it also causes increasing resistance likely due to high tension from extralaveolar vessel assymetric application of distension causing distortion of the vessel in a way that increases resistance
Draw a diagram describing pulmonary blood flows relationship to posture for sitting up, supine and seated? Why is supine not straight?
Apical blood flow higher when lying down because of the orientation of the lung is not horizontal it is instead slightly head down when lying flat. Blood flow is more uniform however
What is the effect of increased pulmonary veinous pressure on blood flow in relation to vertical distance in the lung in a seated patient - draw a diagram to reflect this
Why does blood flow increase as you descend in the lung within zone 3? Gravitational forces should be equal in their effect on Arterial and Veinous should they not?
Gravitational forces are equal but because the raw pressures are higher recruitment and distension is maximised leading to lower resistance and higher flow
Dividing pulmonary arteries into 3 subdivisions which are
Elastic large
Muscular small - vasoreactive
Non muscular smallest - intra-acinar affected by alveolar pressure
What is in a bronchovascular bundle?
Extensinos fo the visceral pleura
Bronchi, nerves, lymphatics, pulmonary arteries and bronchial artery +/- pulmonary vein (proximal are separate, closer to the airway are part of the bundle but the vein is somewhat apart in the interlobular septa)
Where do pulmonary capillaries start with reference to airway anatomy>
terminal bronchioles forming a vascuar sheet interrupted by intercapillary posts
Bronchial circulation arises from?
Systemic circulation
Right bronchial artery from an intercostal artery
Left bronchial artery usually two arties with separate origins from the aorta
How much of the venous bronchial blood drains back into systemic circulation?
1/3 –> via azygous and hemiazygous veins
The rest forms a physiological shunt
3 sources of blood the pulmonary artery receives
Deoxygenated systemic blood
Deoxygenated bronchial blood - 1/3 of bronchial circulation
Oxygenated arterial blood from bronchial circulation via Sperr arteries
4 sources of pulmonary veinous blood
Oxygenated venous blood from pulmonary capillaries
Deoxygenated blood from intrapulmonary shunting
Deoxygenated blood from bronchial circulation 2/3 of bronchial drainage
Deoxygenated venous blood from Thebesian circulation 0.5mm in diametre
Innervation of pulmonary vessels
SNS > PSNS
4 Function of the pulmonary circulation
- Gas exchange
- Blood filter
- Blood reservoir - 500ml as a high capacitance
- Metabolic - metabolism of noradrenaline, PG, bradykinin, seratonin; activation of angiotensin; production of LT and PG
Describe the distribution of blood stored in the pulmonary circulation
150ml in arteries
80ml in capillaries
250ml in veinous
Surface area for gas exchange
50-70m^2
What % of circulation goes to the bronchial circulation
1%
Which ventricle has slightly higher cardiac output?
LV due to bronchial physiological shunt of blood
Mean pulmonary capillary pressure
10
What difference in hydrostatic pressure do you find between the apex and the base of the lung when upright?
Base 10mmHg more than pulmonary artery mean (25mmHg mean); and apex vice versa
Explain what pressures the circulation is subjected to in the apex of a normal uprgiht lung?
Pulmonary blood - 5mmHg mean (15/5 to 10/0)
Alveolar pressure 0 +/- 1 cmH20 but can be much higher in PPV
Where does zone 2 start in the upright lung relative to the heart?
Apex down to 10cm above the level of the heart
Where does zone 3 start and end in the normal heart?
10 above the level of the heart to the base
What is zone 4
Interstitial pressure > alveolar and veinous pressure
Reduced blood flow in most dependent regions
What passive factors affect pulmonary vascular resistance?
- Distension and recruitment - resistance decreases as flow increases (mostly passive distension)
- Lung volume - vascular resistance lowest at FRC
- Gravity
How is pulmonary capillary flow different to systemic blood flow
Pulsatile as minimal dampening of pressure waveform
What is normal pulmonary vascular resistance?
150-200 dynes/sec/cm^5 (1/10 of systemic vascular resistance)
Pulmonary vascular resistance primarily comes from arteries, veins or capillaries?
Evenly spread
Unlike systemic vascular resistance which primarily comes from arterioles
What active factors regulate pulmonary vascular resistance
- Autonomic control - SNS (density of receptors less than systemic vessels); vagal muscurinic supply
- Hypoxic pulmonary vasocontriction - mainly at arterial pre-capillary vessels close to alveoli and with prolonged hypoxia is biphasic with rapid change in first 5 minutes, with second phase of activity 40 minutes later with maximal response at 2-4 hours. This is augmented by acidosis
- Alveolar hypercapnoea causes vasoconstriction
- Humeral - catecholamines, thromboxane and LT vasoconstrict, PGI2 vasodilates, seratonin vasoconstricts
- Drugs - nitric oxide vasodilates, nebulised prostacyclin vasodilates, phosphodiesterase inhibits inhibit cGMP breakdown and cAMP causing vasodilation. As does milrinone, levosimendan, sildanafil and volatile anaesthetics
Describe the phases of pulmonary hypoxic vasoconstriction?
mainly at arterial pre-capillary vessels close to alveoli and with prolonged hypoxia is biphasic with rapid change in first 5 minutes, with second phase of activity 40 minutes later with maximal response at 2-4 hours
Mediators of hypoxic pulmonary vasoconstriciton?
Low alveolar PO2 nd less extent mixed veinous PO2
How does hypoxic pulmonary vasoconstriction occur?
First phase - voltage gated K channels (outward K current)
Second phase 0 endothelin with reduction in endothelial nitric oxide synthesis when PO2 below 70mmHg
What factors augment hypoxic pulmonary vasoconstriction
Metabolic and respiratory acidosis
What is the diametre of a pulmonary capillary
7-10microm
Blood gas interface thickness
0.2 - 0.3micrometre
How much time does each RBC spend in the acpillary network?
0.75 seconds
Is recruitment or distension more important to reduction in vascular resistance with increased pressure or flow
At low vascular pressures recruitment is more important
At high vascular pressures distension is more important
Units of resistance
cmH20 / L /min
mmHg/L/min
Dynes.sec/cm^5
Give 4 pulmonary vasoconstricotrs
Endothelin
Noradrenaline/adrenaline
Seratonin
Thromboxane
Histamine
Give 5 pulmonary vasodialtors
Nitric oxide
PGI2
Phosphodiesterase inhibitors
ACh
CaB
What is the relationship of blood flow to distance above and below the heart in the upright lung
linear
Colloid osmotic pressure in pulmonary vessels
25-28mmHg
Colloid osmotic pressure in lung interstitium?
17-20mmHg
What is the normal lymph flow in the lung per hour?
20ml/hr
Where is ACE found in the lung
capillary endothelial cells in smalll pits
What % of overall bradykinin is metabolised i the lung
80%
What is an example of an amine?
seratonin, norepinephrine, hsitamine, dopamine
What are peptides processed in the lung
angiotensin 1 and bradykinine
How is the pulmonary blood volume affected by going from supine to erect
Decreases pulmonary blood volume by a third
What is the difference between intravascular pressure, transmural pressure and driving pressure
Intravascular pressure - is the pressure at any one point relative to the atmosphere
Transmural pressure - difference in pressure between inside of a vessel and tissue surrounding the vessel
Driving pressure is the difference between one poin tin the circulation and another point downstream
Intrathoracic pressure is related to alveolar pressure how
Intrathoracic pressure = alveolar pressure - alveolar transmural pressure
How is the anatomical location of early pulmonary oedema explained
- Pulmonary arteries and veins travel with bronchi, nerves and lymphatics in bronchovascular bundles, which are extensions of the visceral pleura
◦ The clinical relevance of these structures is the tendency of oedema fluid to accumulate in them, creating “peribronchial cuffing”
What % of the pulmonary capillary bed is filled at baseline
◦ 75% of the capillary bed is filled at baseline with gravity dependent variation
Give the pressures within the pulmonary circulation
◦ PA systolic pressure = 18-25 mmHg
◦ PA diastolic pressure = 8-15 mmHg
◦ Mean pulmonary arterial pressure = 9-16 mmHg
◦ Pulmonary capillary pressure = 8-10mmHg
◦ Pulmonary venous pressure = 6-12 mm Hg
What physiological factors affect pulmonary arterial pressure
Flow = pressure/resistance
Pressure = flow x resistance
Flow is cardiac output therefore can describe the factors determining this
Resistance hagen poiseulle
Radius is afected by
◦ Blood flow
◦ Lung volume
◦ Hypoxic pulmonary vasoconstriction - most effected by alveoalr hypoxia, PaO2 <70mmHg causes closure of hypoxa sensitive pottasium channel –> depolarisation and opening of voltage gated calcium channels –> vasoconstriction
◦ Humoural and hormonal mediators (eg. eicosanoids, amines, adrenaline)
◦ Drugs (eg. nitric oxide and sildenafil)
◦ Neural
How si the pulmonary resistance changed
◦ Blood flow
◦ Lung volume
◦ Hypoxic pulmonary vasoconstriction - most effected by alveoalr hypoxia, PaO2 <70mmHg causes closure of hypoxa sensitive pottasium channel –> depolarisation and opening of voltage gated calcium channels –> vasoconstriction
◦ Humoural and hormonal mediators (eg. eicosanoids, amines, adrenaline)
◦ Drugs (eg. nitric oxide and sildenafil)
◦ Neural
What is the volume of blood in the pulmonary system? How much modulation is there in this? Why can it act as a reservoir
450mls
During straining drops to 250mls
Recruitment and distension
Volume of blood in the pulmonary capillaries
80mls
Central blood volume
450mls in the lung
350mls int he heart durnig diastole
800mls total
15% of blood volume in errect position
What is the equation of pulmonary vascular resistance with a Swanz Ganz catheter
PVR = (mean PAP - PCWP) / CO
Dynes.sec/Cm/5
Normal 100dyanes.sec/cm^5
1/10 of systemic vascular resistance
