Week 3 Pulmonary & Bronchial Circulations Flashcards
What equals the right ventricular ejection fraction?
LV cardiac output
*left cardiac output = right cardiac output
What does the pulmonary vessels divide into?
Alveolar
- big capillary bed where gas exchange occurs
- high pressure during lung expansion collapses alveolar vessels
Extra-alveolar
- area the arteries and veins that covey blood to any front the conducting airways (tissues that don’t participate in gas exchange.
- larger vessels
- not affected by pressures in the lung
- surrounding lung tissue pulls vessels open during large volume increases
What happens to pulmonary vascular resistance when you inhale?
It increases
What vessels provide longitudinal resistance to flow?
*alveolar vessels
- not regulated by autonomic or hormone control
- alveolar capillary walls contribute to 40% of total resistance
- alveolar arterioles contribute to 50% of resistance
What reduces capillary resistance?
- low lung volumes
- high blood flow rates
What increases capillary resistance?
-low BP or less vascular distending pressures
What is capillary resistance dependent on?
Lung conditions
How does CO affect blood flow through capillaries?
Passive regulation of blood flow through capillaries occurs in response to changes in CO
- increased blood flow accommodated by recruitment and distinction
- prevent rise in pulmonary driving pressure with increase in blood flow
How does BP affect pulmonary vascular resistance?
As you increase vascular pressure, pulmonary vascular resistance will decrease.
*Bc of recruitment and distinction. Increased flow opens other channels that are closed and distended open channels
What is pulmonary wedge pressure a good indicator of what?
Preload on left side of heart
Pulmonary artery diastolic pressure is usually close to wedge pressure. An estimable of the filling pressure of the left side of the heart
Capillary volume closely equals what?
Stroke volume.
Usually 70mL at rest or 1mL/kg of body weight
-with each heartbeat will replace all blood in capillary bed
What is the total blood volume from main pulmonary arter to left atrium?
500mL
What is the blood distribution between artery and vein in pulmonary circulation?
It’s equally distributed between arteries and veins
What is function of the capacitance reservoir for the left atrium?
Pulmonary vasculature acts as a reservoir and cal alter its volume from 50% to 200% of resting volume.
- prevents changes in blood return to left ventricle from affecting left ventricular diastolic filling over 2-3 cardiac cycles.
- a buffer. Helps your body compensate for any abrupt changes in position
What are ways that capillary volume can be increased?
- Recruitment
- Distention
What is the main process that causes pulmonary vascular resistance to go down?
*Recruitment
- increases capillary volume by opening closed vessels
- increased CO raises pulmonary vascular pressure, but decreases pulmonary vascular resistance
- occurs during periods of stress and increased tissue oxygen demand
- chief mechanism for fall in PVR
What is distention?
-Internal vessel pressure raise and open capillary beds
- If goes on too long a can lead to…..
- elevated left atrial pressure distends capillary beds (mitral regurgitation, LV failure)
- lead to lung congestion and heart failure
- mechanism seen at high vascular pressures
How does inspiration affect pulmonary blood flow?
- pleural pressure more negative
- pressure gradient for blood flow in thorax is increased
- RV receives greater blood volume during diastole
- increase in venous return into thorax
- LV ejects less blood secondary to increased pressure gradient between LV and systemic pressures
How does exhalation affect pulmonary blood flow?
- pleural pressure less negative
- more positive thoracic pressure decreases venous blood return
- decreases pressure gradient, prevents venous return to RV
- less RV ejection pressure
- the reduced gradient between LV and systemic arteries allows increased stroke volume
don’t worry too much about
What happens to PVR when lung volume is close to FRC?
PVR is minimal
What happens to PVR with higher and lower lung volumes?
PVR is increased
What happens to extra-alveolar vessels during inspiration?
- They dilate and reduce flow resistance
- They receive increased lung volume as higher alveolar pressure compresses alveolar vessels
What happens to alveolar vessels during inspiration?
They compress
- capillary resistance increased during elevated alveolar pressures
- pulmonary capillaries are vessels of major vascular resistance
What are the effects of mechanical ventilation on pulmonary venous pressure?
- alveolar pressure artificially increased
- increases the amount of ZONE 2 lung volume relative to pulmonary venous pressure
- the rise in alveolar pressure increases resistance to blood flow in ZONE 2
- can decrease CO or increase V/Q imbalance or mismatch
Oxygenated blood from the aorta nourishes what lung structures?
- conducting airways to terminal bronchioles
- parenchyma supporting structures
- pleura, interlobar septal tissues, pulmonary arteries and veins
What is the pressure of bronchial blood flow?
Systemic pressure
How much of bronchial circulation returns to the right atrium via the azygos vein?
50%
What are some of the functions fo the pulmonary lymphatic system?
- critical to keep alveoli free of fluid moving from capillaries
- hydrostatic starling forces tent to move fluid out at 20mL/hr
- Numerous lymphatic drain fluid from interstitium which is kept at a slight negative pressure
- alveolar edema interferes with pulmonary gas exchange
What is the Fick Principle?
One method of determining CO, blood flow through lungs/min
What is the indicator dilution principle?
Dye injected into venous circulation
Diluted concentration measured on arterial side
What is gravity’s effects on systemic blood pressure?
- degree of pressure change from level of the heart
- pressure gradient of 0.74mmhg/cm
- in supine position, arterial pressure higher in feet than head
What is the effects of gravity of pulmonary circulation?
- Greater alterations in flow occur bc pulmonary circulation pressures much lower
- distribution of blood flow in the lungs affected by gravity (in upright lung)
- changes in pulmonary arterial pressure affect distribution of blood flow over the height of the lung
What is hydrostatic pressure?
- the pressure effect gravity has on a column of fluid
- alters the potential energy of fluid in a column.
- gravity affects the perfusion of blood in the different zones of the lung.
What is considered the zero reference point for hydrostatic pressure
Right atrium level and middle of lung
What portion of the lung receives more blood flow?
The lung base receives a greater portion of RV ejection fraction than apex of the lung
What is PA?
Alveolar pressure
Arteriole sac
Highest at apex of the lung. Will close off small capillaries in ZONE 1, no gas exchange taking place
What is Pa?
Pulmonary Artery pressure
De-oxygenated blood coming into the lung
What is Pv?
Pulmonary Venous pressure
-oxygenated blood going out to tissues
Describe the difference zones of the lung
- ZONE 1
- does not receive blood flow. (PA>Pa)
- pulmonary capillaries collapse by higher PA
- high V/Q mismatch
- ZONE 2
- intermittent blood flow. Blood flow with systole bc at that point Pa>PA
- some gas exchange occurring
- ZONE 3
- most ideal
- Pa>Pv>PA
- blood vessel stays open entire time
- ZONE 4
- an abnormal condition of reduced blood flow
**ventilation increases as you go down the lungs and increased blood flow
The perfusion of the lung zones depends on what?
-the relationship between alveoli and blood pressure in pulmonary arteries and veins
What affects the perfusion distribution in the lung?
- gravity affects the regional distribution of blood flow in different lung zones
- transmutation distending pressure of vessels at bottom of lung > apex
- alveoli pressure affects blood flow
- pulmonary, arterial, venous, and alveolar pressure difference create lung zones
What factors expand ZONE 1?
- decreased pulmonary artery pressure
- shock, hypovolemia
- increased alveolar pressure
- PEEP
- occlusion of blood vessels
- PE
What factors reduce ZONE 1?
- increased pulmonary artery pressure
- infusion of fluid or blood
- reduced hydrostatic effect
- change pt position
- standing to supine
What is the pulmonary-hemodynamic curve?
-assessment of driving pressures across the pulmonary vasculature as CO varies
How does pulmonary vascular resistance change blood flow?
- active regulation occurs by altering vascular smooth muscle tone in pulmonary vessels (arterioles)
- pulmonary capillary smooth muscle alters PVR
- vasomotor tone of pulmonary vessels is affected by may factors
What is the most active regulator of pulmonary vessels?
Regulation is primary regulated by local metabolic influences
What causes vasoconstriction of pulmonary vessels?
- reduced PAO2*
- increased PCO2*
- histamine*
What causes vasodilation of pulmonary vessels?
-increased PAO2*
-nitric oxide*
-
What is Thromboxane A2
- a potent vasoconstrictor
- constrictor of pulmonary arterial and venous smooth muscle
- will send blood elsewhere other than damaged area of lung where gas exchange can occur
What is Prostacyclin (Prostaglandin 12)?
- potent vasodilator
- produced by endothelial cells
What does nitric oxide do to epithelium?
- potent endothelium-derived endogenous vasodilator
- strictly localized effect
- leads to smooth muscle relaxation through synthesis of cyclic GMP
- can be toxic in high concentrations and binds irreversibly to heme iron in hemoglobin
What are the effects of alveolar oxygen tension on pulmonary blood flow?
- partial pressure of oxygen (PAO2) in alveoli is a critical governing pulmonary circulation
- PO2 in alveoli more important than oxygen tension in mixed venous blood
- oxygen diffusion into pulmonary arteriole walls causes smooth muscle dilation
- as alveolar oxygen tension decreases, surrounding arterioles constrict.
- will shunt areas of blood award from places getting not ventilation well (like mucous plug). Sense low O2 and shunt blood to areas venting better
- global reduction in alveolar oxygen tension increases total PVR by constricting arterioles and small arteries
What does alveolar hypoxia produce?
Hypoxic pulmonary vasoconstriction(HPV)
- localized response
- response enhanced if high CO2
- opposite reaction than systemic circulation hypoxia
- systemic blood vessels dilate in response to hypoxia
- HPV is an important mechanism of balancing V/Q ratio.
- shift of flow to better ventilated pulmonary regions
What is pulmonary HTN?
-increased resistance to blood flow in the lung
-high pulmonary vascular resistance, elevated pulmonary artery pressures.
Can be seen with:
-generalized alveolar hypoxia (COPD)
-hypoventilation
-low inspired PO2
-increased PCO2
-pain
-histamine release
*can increase work of right ventricle
What is primary pulmonary HTN?
*serious pulmonary vascular condition
- small muscular pulmonary arteries narrow
- very high pulmonary artery pressures
- RV pressure increases to compensate until RV failure
- lung transplant is only effective treatment
Is ventilation evenly distributed throughout lung?
No
Lower portion of lung tends to be ventilated > than apex
Is compliance greater at base or apex of the lung?
Greater at the base
Why does the apex of the lung have a higher PO2?
Because it’s not getting perfused and oxygen isn’t being extracted
What. Is a normal A-a gradient?
Alveolar to arterial parietal pressure gradient is normally 10-15 mmHg
Looks at how well O2 gets from alveolar space into the artery
-larger gradients indicate intrinsic pulmonary disease—>shunting
What is a right to left shunt?
De-oxygenated Blood coming from right area of the heart and not participating in gas exchange
Will decrease partial pressure of O2
There are some small, normal shunts
What is left to right heart shunt?
Pulmonary venous recirculation
- portion of OC returns to right heart without flowing through the body
- does not affect systemic arterial oxygen tension
- oxygen tension in right heart is increased
CaO2
Oxygen carry capacity
How much O2 is carried in the arterial blood
20mL/dL
DO2
Oxygen delivery
How much oxygen is carried in the blood and how fast it is being delivered to the tissues
1000mL/min
EO2
Oxygen extraction ratio
Hoe much O2 is extracted by the tissues
25% for whole body (individual tissue beds will vary)
VO2
Oxygen consumption
How much oxygen is consumed by the tissues
250mL/min (at rest)
CvO2
Venous oxygen content
How much O2 is carried in the venous blood
15mL/dL
