Pulmonary Blood Flow And VQ Lecture 4 Flashcards
Compare and contrast bronchial blood flow and pulmonary blood flow?
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)
Identify the blood supply to the tracheobronchial tree down to the terminal bronchioles.
- 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.
Identify the blood supply to terminal bronchioles
- Terminal bronchioles (generations 22, 23) receive blood flow from capillaries directly via diffusion.
Describe the role of the lungs as a reservoir for blood
- 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.
Compare the pulmonary vascular resistance to systemic vascular resistance.
- 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
Compare the effect of afterload on the right ventricle compared to the left ventricle
- 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)
Describe the effect of airway pressure on zero order capillaries
- 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.
Discuss the role of alveolar collapse in pulmonary vascular resistance
- 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.
Identify the number of “1” order pulmonary capillaries and their volume
- Approximately 3,000,000,000
- Volume is 151 mL
Define recruitment and distension as they relate to perfusion
- 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.
Compare and contrast alveolar and extra-alveolar effects on capillary size
- 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.
Describe the effect of increased blood flow on pulmonary vascular resistance (PVR)
- 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
Describe the effect of increasing lung volume (above FRC) on PVR
- 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
List five factors that increase PVR
- Atelectasis
- Hypoxia
- Hypercapnia
- Acedemia
- Catecholamines
- Histamine
- Serotonin
- Prostaglandins (D, E2,F, H)
- Lung inflation or deflation from FRC changes
- Increase perivascular pressure
List five factors that decrease PVR
- Isoproterenol
- Milrinone
- Flolan
- Acetylcholine
- Bradykinin
- Prostaglandins (E, I, PGI)
- Theophylline
- Nitric oxide
- Increased CO
- Increased pulmonary blood volume
Describe the effect of alpha-1 agonist, beta-2 agonist, and V-1 agonist on PVR
- Alpha 1
- Noradrenaline - Constriction
- Beta 2 agonist
- Adrenaline - Dilation
- V-1 agonist
- Vasopressin - Dilation
Define hypoxia pulmonary vasoconstriction (HPV)
- 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
Identify the triggering action for HPV
The triggering effect of HPV is in response to low ALVEOLAR PO2 (<70mmHg)
Describe the effect of HPV on PVR and blood flow
- Increased PVR
- Decreases blood flow
List four drugs that decrease HPV
- Beta 2 agonist
- Calcium channel blockers
- Inhalation anesthetics
- Minoxidil
- Nitrovasodilators
- Theophylline
- Increases Qs/Qt (Shunt) by increasing perfusion to areas with low ventilation
List four drugs that increase HPV
- Almitrine
- Cycloxygenate inhibitors
- Beta blockers
Describe why lower regions of the lung receive more blood volume
- 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)
What is the main MOA of Zone 1?
- Pulmonary arterial pressure falls below alveolar pressure
- Ventilation is greater than perfusion
- V/Q is high
MOA of Zone 2
- Pulmonary arterial pressure increases due to hydrostatic pressure (gravity)
- Better ventilation
- Perfusion matching occurs
MOA of Zone 3
- Pulmonary arterial pressure increases and exceeds alveolar pressure
- More perfusion than ventilation
- V/Q ratio is low
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.
List eight factors contributing to pulmonary edema.
- Increased pulmonary permeability
- Increased capillary hydrostatic pressure
- Increased capillary permeability
- Decreased interstitial hydrostatic pressure
- Decreased colloid osmotic pressure
- Decreased interstitial hydrostatic pressure
- Decreased colloid osmotic pressure.
- Insufficient lymphatic drainage
List four causes of negative pressure pulmonary edema
- Post extubation laryngospasm
- Epiglotittis, Croup
- Choking/ foreign body
- Strangulation/ Hanging
- ET tube obstruction
- Tumor/ Goiter
- Near drowning
- Direct suctioning of ET tube adapter
List four causes of hypoxemia
- Hypoventilation (Drugs, inadequate MV)
- Diffusion issue (CHF, ARDS)
- Shunt (anatomic, atelectasis)
- Ventilation perfusion mismatch (COPD)
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
Identify the most common cause of hypoxemia during anesthesia
- Hypoxemia (drugs, inadequate MV)
- Diffusion issue (CHF, ARDS)
- Shunt (anatomic, atelectasis)
- Ventilation perfusion mismatch (COPD)
Describe the typical distribution of perfusion
- V/Q is typically matched almost 1:1 despite zones
- Three factors affects V/Q matching
- Gravity
- Alveolar/ Capillary collapse in non ventilated areas
- Hypoxic pulmonary vasoconstriction
- Blood flow and ventilation are matched very evenly
- Almost no blood flow to unventilated regions
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
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.
Describe the effect of anesthesia on FRC, lung compliance and airway resistance
- Decreases FRC
- Decreases lung compliance
- Increases right airways resistance
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
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
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
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
- Hypoventialion
- Hypoxemia
- Hypercarbia
- Ventilation/perfusion inequality is the most common cause of hypoxemia.
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
