Pulmonary Blood Flow And VQ Lecture 4 Flashcards
1
Q
Compare and contrast bronchial blood flow and pulmonary blood flow?
A
Bronchial blood flow
- Constitutes a very small portion (1-2%) of the left ventricular output
- Provides the tracheobronchial tree with arterial blood
Pulmonary blood flow
- Constitutes the entire output of the right ventricle
- Supplies the lung with mixed venous blood draining from the systemic veins to oxygenate
- This volume is spread all along the alveolar capillary membrane (50-100 m2 surface area)
2
Q
Identify the blood supply to the tracheobronchial tree down to the terminal bronchioles.
A
- Origin
- Aorta
- Intercostal arteries
- Supplies blood to the tracheobronchial tree down to the level of the terminal bronchioles
- Lung distal to terminal bronchioles (Generations 22, 23) receive blood flow from capillaries directly via diffusion.
3
Q
Identify the blood supply to terminal bronchioles
A
- Terminal bronchioles (generations 22, 23) receive blood flow from capillaries directly via diffusion.
4
Q
Describe the role of the lungs as a reservoir for blood
A
- 450 ml (9%) of total blood volume is in the pulmonary circuit
- Lung act as a reservoir for excessive blood volume, especially in heart failure (20-30% increase)
- Increased intrathoracic pressures decrease pulmonary blood volume
- Blood volume in each region depends on ventilation to each lung region as well.
5
Q
Compare the pulmonary vascular resistance to systemic vascular resistance.
A
- Mean systemic pressure is 100 mmHg
- Mean pulmonary pressure is 15 mmHg
- SVR is (10 x PVR)
- The walls of the pulmonary vessels are very thin
- Higher compliance
- Allows diversion of blood from one region to another, as with recruitment, distension, and HPV
6
Q
Compare the effect of afterload on the right ventricle compared to the left ventricle
A
- Characteristics for right ventricle
- Thin walled, low compliance chamber unless chronic pulmonary hypertension
- Septum and LV function may impair performance
- Very sensitive to afterload changes (fails with acute pulmonary hypertension)
7
Q
Describe the effect of airway pressure on zero order capillaries
A
- Pulmonary capillaries form a dense network around the alveoli, much as a parking garage with scattered post
- Branching is asymmetrical
- Order “0” capillaries collapse or distend, depending on the pressure surrounding them
- Alveolar expansion or collapse plays a major role in pulmonary vascular resistance.
8
Q
Discuss the role of alveolar collapse in pulmonary vascular resistance
A
- The high resistance of the systemic circulation is caused by the very muscular arterioles
- The pulmonary circulation has no such vessels and ordinarily has a very low resistance (< 10mmHg pressure drop from pulmonary artery to left atrium)
- PVR may drop even further as the pressure within it rises due to recruitment and distension
- AS PRESSURE INCREASES, capillaries are distended and recruited.
9
Q
Identify the number of “1” order pulmonary capillaries and their volume
A
- Approximately 3,000,000,000
- Volume is 151 mL
10
Q
Define recruitment and distension as they relate to perfusion
A
- Recruitment refers to perfusion of previously closed capillaries when a critical opening pressure or blood volume is achieved
- Distension refers to widening of individual capillaries.
11
Q
Compare and contrast alveolar and extra-alveolar effects on capillary size
A
- PVR is increased when lung volume is low
- Alveolar vessels expand up to FRC then constrict but remain more patent
- Extra-alveolar vessels are pulled open as the lung expands.
12
Q
Describe the effect of increased blood flow on pulmonary vascular resistance (PVR)
A
- PVR is increased when the lung volume is low
- Increased PVR
- Atelectasis, hypoxia, hypercapnia, acedemia, catecholamines, histamine, serotonin, prostaglandins, lung inflation, increase perivascular pressure
- Decreased PVR
- Isoproterenol, milrinone, flolan, acetylcholine, bradykinin, prostaglandins, theophylline, nitric oxide, increase CO, increased pulmonary blood volume
13
Q
Describe the effect of increasing lung volume (above FRC) on PVR
A
- Under normal conditions some capillaries are either closed or open with no flow
- Other vessels are open but not fully distended
- PVR becomes less when pressure and flow increases due to distension and recruitment
- ALVEOLAR vessels expand up to FRC then constrict
14
Q
List five factors that increase PVR
A
- Atelectasis
- Hypoxia
- Hypercapnia
- Acedemia
- Catecholamines
- Histamine
- Serotonin
- Prostaglandins (D, E2,F, H)
- Lung inflation or deflation from FRC changes
- Increase perivascular pressure
15
Q
List five factors that decrease PVR
A
- Isoproterenol
- Milrinone
- Flolan
- Acetylcholine
- Bradykinin
- Prostaglandins (E, I, PGI)
- Theophylline
- Nitric oxide
- Increased CO
- Increased pulmonary blood volume
16
Q
Describe the effect of alpha-1 agonist, beta-2 agonist, and V-1 agonist on PVR
A
- Alpha 1
- Noradrenaline - Constriction
- Beta 2 agonist
- Adrenaline - Dilation
- V-1 agonist
- Vasopressin - Dilation
17
Q
Define hypoxia pulmonary vasoconstriction (HPV)
A
- Contraction of smooth muscles in the walls of small arterioles in hypoxic region
- Occurs in response to low alveolar PO2 (<70 mmHg), not pulmonary artery PO2
- Directs blood flow away from hypoxic regions of the lung
18
Q
Identify the triggering action for HPV
A
The triggering effect of HPV is in response to low ALVEOLAR PO2 (<70mmHg)
19
Q
Describe the effect of HPV on PVR and blood flow
A
- Increased PVR
- Decreases blood flow
20
Q
List four drugs that decrease HPV
A
- Beta 2 agonist
- Calcium channel blockers
- Inhalation anesthetics
- Minoxidil
- Nitrovasodilators
- Theophylline
- Increases Qs/Qt (Shunt) by increasing perfusion to areas with low ventilation
21
Q
List four drugs that increase HPV
A
- Almitrine
- Cycloxygenate inhibitors
- Beta blockers
22
Q
Describe why lower regions of the lung receive more blood volume
A
- Pulmonary arterial pressure increase and exceeds alveolar pressure
- More perfusion than ventilation (V/Q ratio is low)
- Lower regions fo the lung receive greater blood flow than upper (non dependent) regions
- Gravity is the principle reason blood flow is greater to dependent portions of the lung (base)
23
Q
What is the main MOA of Zone 1?
A
- Pulmonary arterial pressure falls below alveolar pressure
- Ventilation is greater than perfusion
- V/Q is high
24
Q
MOA of Zone 2
A
- Pulmonary arterial pressure increases due to hydrostatic pressure (gravity)
- Better ventilation
- Perfusion matching occurs
25
MOA of Zone 3
* Pulmonary arterial pressure increases and exceeds alveolar pressure
* More perfusion than ventilation
* V/Q ratio is low
26
Describe Zone 4 and its significance
* Some fluid is forced out of the capillary and into the perivascular space (ISF exceeds PA)
* This zone is usually very small as alveolar vessels are closed by increased PVR from collapse alveolus
* May be larger in pathological states.
27
List eight factors contributing to pulmonary edema.
1. Increased pulmonary permeability
2. Increased capillary hydrostatic pressure
3. Increased capillary permeability
4. Decreased interstitial hydrostatic pressure
5. Decreased colloid osmotic pressure
6. Decreased interstitial hydrostatic pressure
7. Decreased colloid osmotic pressure.
8. Insufficient lymphatic drainage
28
List four causes of negative pressure pulmonary edema
1. Post extubation laryngospasm
2. Epiglotittis, Croup
3. Choking/ foreign body
4. Strangulation/ Hanging
5. ET tube obstruction
6. Tumor/ Goiter
7. Near drowning
8. Direct suctioning of ET tube adapter
29
List four causes of hypoxemia
1. Hypoventilation (Drugs, inadequate MV)
2. Diffusion issue (CHF, ARDS)
3. Shunt (anatomic, atelectasis)
4. Ventilation perfusion mismatch (COPD)
30
Describe the clinical result of V/Q mismatch
* Ventilatory obstruction decreases V/Q to abnormally low levels (shunt)
* Low perfusion states may also adversely affect V/Q by increasing V/Q to abnormally high levels (dead space)
* V/Q = 0 is a SHUNT
* V/Q = infinity means, no perfusion/ DEADSPACE
31
Identify the most common cause of hypoxemia during anesthesia
* Hypoxemia (drugs, inadequate MV)
* Diffusion issue (CHF, ARDS)
* Shunt (anatomic, atelectasis)
* Ventilation perfusion mismatch (COPD)
32
Describe the typical distribution of perfusion
* V/Q is typically matched almost 1:1 despite zones
* Three factors affects V/Q matching
1. Gravity
2. Alveolar/ Capillary collapse in non ventilated areas
3. Hypoxic pulmonary vasoconstriction
* Blood flow and ventilation are matched very evenly
* Almost no blood flow to unventilated regions
33
Compare the distribution of blood flow and ventilation
* Blood flow and ventilation decrease almost linearly from bottom to top
* Ventilation decreases less, such that V/Q ratio is abnormally high in the apex
* Distribution of both is affected by posture exercise and position
34
Identify the effect of moving from the top to the bottom of the lung on V/Q ratio, perfusion, alveolar PO2, and alveolar PCO2
* Zone 1
* Ventilation is greater than perfusion -PA \>Pa \>Pv -
* Pulmonary arterial pressure falls below alveolar pressure
* Zone 2
* Better ventilation perfusion matching occurs
* Pa\>PA \>Pv
* Pulmonary arterial pressure increases due to hydrostatic pressure (gravity)
* Zone 3
* V/Q ratio is low
* Pa \> Pv \> PA
* Pulmonary arterial pressure increases and exceeds alveolar pressure.
35
Describe the effect of anesthesia on FRC, lung compliance and airway resistance
* Decreases FRC
* Decreases lung compliance
* Increases right airways resistance
36
Discuss anatomic and physiologic shunt as they relate to ventilation and bronchial/Thebesian circulations
* Shunt refers to blood that enters the arterial system without entering ventilated areas of the lung
* Bronchial and thebesian circulations constitute constitute ANATOMIC shunt while blood passing though poorly ventilated lung represents PHYSIOLOGIC shunt
37
Describe the effect of shunt on increasing inspired oxygen concentrations and PaO2
* The shunt flow creates PaO2
* PaO2 gradient of 500 mmHg
* Addition of shunted blood with low O2 concentration greatly reduces the PO2 of arterial blood
38
Discuss expected V/Q ratios in healthy patients
* In a healthy patient almost all ventilation and blood flow (95%( go to compartments to a V/Q ratio of about 1.0
* Blood flow and ventilation are matched very evenly
* Almost no blood flow to unventilated regions
39
Describe the effects of lung disease on V/Q ratios
* In a patient with lung disease, V/Q distributions is not equally distributed
* Considerable blood flow goes to compartment with V/Q 0.03-0.3. This blood will be poorly oxygenated and will depress PO2
* Considerable ventilation will go to units without perfusion and so CO2 will not be eliminated.
* Optimal matching of ventilation and perfusion allows for optimal gas exchange
* Varying degrees of mismatching of ventilation and perfusion leads to varying degrees of
1. Hypoventialion
2. Hypoxemia
3. Hypercarbia
4. Ventilation/perfusion inequality is the most common cause of hypoxemia.
40
Describe compensation for V/Q abnormalities in patients with lung disease.
* Increased minute ventilation via central and peripheral chemoreceptors
* Dissociation curve for CO2 is linear (favors elimination) and dissociation curve for O2 is flat (favors loading of oxygen)
* Hypoxic pulmonary vasoconstriction and pulmonary bronchoconstriction assign in matching perfusion and ventilation
