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160 Cards in this Set
- Front
- Back
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What is compliance
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how readily the lung accepts a change in volume
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Formula for compliance
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change in volume (L) / change in pressure (cc H20)
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Compliance example: negative intrathoracic pressure of 5 cm H20 on inspiration, and the lungs accepted 0.75 L of air - what is the compliance
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0.15L/cmH20 or 150ml/cmH20
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What is total lung compliance in normal adult
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200ml, so for every 1cm H20 pressure change - the lung volume increases or decreases 200ml
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Is compliance better or worse with natural ventilation vs ventilator
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Neither - they are the same
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Compliance of lung is divided into two parts
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1. elastic forces on the lung tissue
2. elastic forces caused by surface tension of the fluid that lines the alveoli |
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Elastic forces are determined by what
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elastin and collagen fibers between the lung parenchyma
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When the lung is deflated
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the fibers are in a kinked (spring) state
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When the lung expands
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the fibers stretch
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For every 1cmH20 of transpulmonary pressure change
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the lung will expand 100-200ml over 10-20 sec
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As lung compliance increases
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more volume is accepted
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As lung compliance decreases
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less volume is accepted
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Will a compliant lung receive more volume than a non-compliant lung if the pressure stays the same
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not sure how to answer this one
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Explain surface tension
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The thin layer of fluid (that interfaces with the air) and creates a skin that is difficult to break
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The larger the surface area
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the larger the surface tension
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Surface tension explains why
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a meniscus can form, a raindrop doesn't fall apart and why a bug can walk on water
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Water coating the inside a balloon
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makes the balloon more difficult to expand because of the attractive forces of the water
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Alveoli filled with saline is ___________ than water coated with surfactant
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more compliant
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What reduces the compliance of the lung
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the air:water interface
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Surface tension accounts for ______ total lung compliance
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2/3
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What is opening pressure
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if an alveoli collapses - the force needed to expand the alveoli and overcome the attractive force of the fluid
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Explain Law of Laplace
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describes that the distending pressure of a liquid bubble (not alveoli) is influenced by the surface tension and the radius
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Law of Laplace equation
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pressure = (2)(surface tension)/radius
distending (inflating) or collapsing (recoil) pressure is directly related to surface tension of the air:fluid interface and inversely related to the radius of the sphere |
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Distending pressure in a sphere is
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directly proportional to the surface tension - P=2T/
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Which means... as surface tension increases - the pressure required to hold it open
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increases
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Law of Laplace - explain relationship between pressure and radius
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distending pressure is indirectly related to the radius of a sphere
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Which means... as size of the bubble increases, the pressure required to hold it open
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decreases
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Law of Laplace does not come into play until
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critical opening pressure has been reached because a great deal of pressure may be required to break the fluid interface and begin alveolar expansion
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What phenomenon occurs
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distending pressure in small alveoli > than distending pressure in large alveoli - so air will travel from small to large alveoli (and small will collapse)
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What prevents the small alveoli from collapsing
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surfactant
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How does surfactant work
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reduces surface tension by breaking up the H2O molecule's attraction to each other
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Where is surfactant secreted
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epithelial cells called type II alveolar epithelial cells
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What does surfactant contain
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phospholipids, protein, and ions
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Primary phospholipid in surfactant
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DPPC - diplamitoyl phosphatidylcholine
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DPPC
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has a hydrophobic and hydrophilic end
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Where and how are hydrophobic and hydrophilic ends postioned
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DPPC molecule positions itself at the alveolar gas liquid interface with hydrophobic end towards the gas phase and the hydrophilic end towards the liquid potion
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How does surfactant prevent the small alveoli phenomenon
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as alveoli reduces in size - the proportion of surfactant to surface increases and improves the effectiveness of the surfactant
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Interesting point
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although the effect of surfactant is greatly reduced in large radius alveoli - LaPlace's Law comes into play when the distending pressure is reduced
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If recoil force of alveoli outweighs the distending pressure/force
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atelectasis - alveolar collapse
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Critical pressure is the same as
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opening pressure
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Once alveoli closed - why is it hard to re-expand
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attractive water bonds
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Surfactant deficiency - general causes
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acidosis, hypoxia, hyperoxia, atelectasis, pulmonary congestion
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Specific causes of surfactant deficiency include
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ARDS, RDS (peds), pulmonary edema, PE, PNA, excessive lavage, drowning, extracoporeal oxygenation (ECMO)
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Compliance problems other than alveoli
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lung tissue and chest wall compliance
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Causes for chest wall compliance issues
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obesity, narcotics
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Where and how are hydrophobic and hydrophilic ends postioned
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DPPC molecule positions itself at the alveolar gas liquid interface with hydrophobic end towards the gas phase and the hydrophilic end towards the liquid potion
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How does surfactant prevent the small alveoli phenomenon
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as alveoli reduces in size - the proportion of surfactant to surface increases and improves the effectiveness of the surfactant
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Interesting point
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although the effect of surfactant is greatly reduced in large radius alveoli - LaPlace's Law comes into play when the distending pressure is reduced
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If recoil force of alveoli outweighs the distending pressure/force
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atelectasis - alveolar collapse
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Critical pressure is the same as
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opening pressure
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Once alveoli closed - why is it hard to re-expand
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attractive water bonds
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Surfactant deficiency - general causes
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acidosis, hypoxia, hyperoxia, atelectasis, pulmonary congestion
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Surfactant deficiency - specific causes
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ARDS. RDS (peds), pulmonary edema, PE, PNA, excessive lavage, drowning, extracoporeal oxygenation (ECMO)
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Compliance problems other than alveoli
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lung tissue and chest wall compliance
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Causes for chest wall compliance issues
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obesity, narcotics
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What is effect of narcotic chest wall rigidity
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ancillary muscle contraction
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PMR
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to fix? - need help with this one
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Hook's law describes
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elastance
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Elastance is
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1. the opposite of compliance
2. ability to return to the pre-existing shape after deformity |
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What is the formula for Hook's Law
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elastance = change in pressure/change in volume
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Which is more elastic - rubber or steel
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steel
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Blowing holes in alveoli at high ventilatory pressures is an example of
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when the elastic limits are reached - they break
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In alveoli, as the pressure increases - the volume
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increases (up to the point when it ruptures)
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During normal inspiration, the intrapleural pressure decreases from it's normal baseline which causes
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bronchial airways to lengthen and increase in diameter
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Is this a passive or active process?
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passive - not driven by ANS
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During expiration
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intrapleural pressure increases which causes bronchial airways to shorten and decrease in diameter (change is unremarkable)
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However, in respiratory disorders such as emphysema or chronic bronchitis
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bronchial gas flow and intrapleural pressure may change significantly - especially during expiration when passive exhalation and passive bronchial constriction occurs
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Formula for Poiseuille's Law
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flow = Pr^4
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Poiseuille's Law can be arranged for
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flow, pressure, or airway portions such as length and radius
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Turbulent flow can be created at
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high pressures and high flow rates
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The time constant is the time in seconds it takes to inflate a particular lung region to
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60% of its potential filling capacity
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Time constants are a product of
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resistance and compliance
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If everything remains constant and the only factor that changes is airway resistance, then as resistance doubles - time to inflate
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doubles
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If resistance remains constant and compliance doubles - the time constant
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is halved
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Time constant
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can go either direction
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During normal restful breathing, inspiration requires ____ work but expiration is a _____ process
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some, passive
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The work of inspiration involves overcoming 3 forces
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1. expand the chest wall against the resistance or elastic force of the chest wall
2. expand the lungs and overcome the viscosity of the tissues (lung to chest wall and alveoli to itself) 3. overcome the resistance of the airways to air movement |
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During normal quiet breathing, how much energy is utilized
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3-5%
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Heavy exercise or any increase in airway resistance (narrowing bronchioles) increases the WOB by as much as
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50x
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Which explains
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why people are limited on the amount of work they can do - lack of available energy to the respiratory muscles results in fatigue
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Three components of the normal ventilatory pattern
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1. TV
2. RR 3 I:E ratio |
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Tidal volume is
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volume of air normally moved into the lungs in a quiet breath
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Normal TV
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7-9ml/kg of ideal body weight
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Normal RR
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12-15 breaths per minute
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Normal I:E ratio
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1:2
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The normal pause that occurs at the end of exhalation is included in the
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exhalation phase
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What is dead space
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inspired air that does not reach the alveoli
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Three types of dead space
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1. anatomic
2. alveolar 3. physiologic |
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What is anatomic dead space
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amount of air in conducting airways
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What is formula for anatomic dead space
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2ml/kg
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Keep in mind that during inspiration
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fresh gas mixes with non-fresh gas
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Minute alveolar ventilation calculation
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MV = (TV-deadspace) x RR
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What two things have profound effect on minute alveolar ventilation
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depth of volume and RR
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In increasing total alveolar ventilation, what has more effect - increased in depth of breathing or increase in RR
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increase in depth of respiration is far more effective
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Which has more dead space - LMA, ETT
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LMA
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From where is dead airspace measured (in reality)
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circuit - trachea - terminal bronchioles
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Therefore, what other value would be higher for a LMA
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PaCO2
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Apnea
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no spontaneous ventilation
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Eupnea
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normal spontaneous breathing
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Hyperpnea
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increased volume but unchanged rate
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Biots
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short episodes of rapid uniform deep inspiration followed by 10-30 seconds of apnea
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Hyperventilation
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increased alveolar ventilation - either rate, volume or both causing PaCO2 to decrease
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Hypoventilation
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decreased alveolar ventilation - either rate, volume or both causing PaCO2 to increase
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Tachypnea
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rapid rate
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Cheyne Stokes
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10-30 seconds of apnea - then very fast volume and rates - then gradual decline to apnea
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Kussmaul
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increased depth and rate (DKA)
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Orthopnea
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inability to breathe unless in the upright position
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Dyspnea
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difficulty breathing (conscious aware of)
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Tidal volume
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volume of air inspired or expired in each normal breath
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Normal TV
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500ml
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Inspiratory reserve volume
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extra volume of air that can be inspired over and above normal tidal volume
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Normal IRV
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3000ml
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Expiratory reserve volume
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extra volume of air that can be forcefully expired after a normal exhaled tidal volume
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Normal ERV
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1100ml
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Spirometry
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means to measure various volumes in the lungs
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Alveolar dead space
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occurs when lung is being ventilated and not perfused
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Alveolar dead space calculation
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can't be calculated
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Physiologic dead space
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sum of anatomical and alveolar dead space
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Which is effective in terms of oxygen exchange - anatomical or alveolar dead space
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neither
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Where is the best measurement for ETCO2 monitoring
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look at picture
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What is the normal discrepancy between ETCO2 and PaCO2
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PaCO2 is usually 5 torr higher
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Why?
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because of mixing
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What population has a higher discrepancy
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smokers
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Residual volume
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amount of air that remains after a forceful expiration
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normal RV
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1200ml
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Capacity measurements are
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combinations of volumes
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Vital capacity is
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the amount of volume that can be expelled fromthe lungs after taking a very deep breath
IRV + TV + ERV |
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Normal VC
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4800ml
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Another name for vital capacity
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Forced vital capacity - FVC
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One pulmonary function test
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amount of forced expired volume (FEV) in one second/FVC
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Normal FEV-1/FVC value
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80%
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What disease population has problems with this test
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COPD - exhalation problem
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Functional residual capacity
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amount of volume left in lungs after normal expiration
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Why important to anesthesia
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amount of volume (located in area of lungs) where much of the air exchange is occuring
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What can decrease the FRC
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supine position, trendelenburg, compression of abdomen, belly insufflation (all push abdominal contents upward - displacing diaphragm upward)
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Volumes compared to young men - women are
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20% less
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Functional residual capacity
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amount of volume left in lungs after normal expiration *important to anesthesia
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FRC equals
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ERV + RV
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Several factors that impact FRC
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1. body habitus
2. sex 3. posture 4. lung disease 5. diaphragmatic tone |
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Body habitus
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FRC proportional to height - obesity greatly decreases FRC (loss of chest compliance)
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Sex
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FRC > males than females
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Posture
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FRC decreases as pts are moved from an upright to supine or prone position as a result of less chest compliance due to abdominal contents pushing against diaphragm - greatest change 0-60 degrees, no change in head down position up to 30 degrees
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Lung disease decreases
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compliance of lung, compliance of chest or both resulting in lower FRC
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Diaphragmatic tone
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diaphragmatic tone
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Know chart
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IRV - 3000
TV - 500 ERV - 1100 RV - 1200 |
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Spirometry measures basic lung volumes but does not measure
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FRC or RV
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What test measures FRC and RV
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Plethysmography
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Plethysmography uses what law
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boyle's law
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Describe plethysmography
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sealed chamber with mouthpiece - at end of normal expiration, the mouthpiece is closed - pt then asked to make an inspiratory effort - as the pt tries to inhale the lungs expand decreasing pressure within the lungs increasing lung volume - in turn increases the pressure within the box since it is a closed system and the volume of the body compartment has increased - temp and pressure remain constant volume changes
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Small airways lack ____ so they depend on _____ and ____ to keep them open
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cartilage, adjacent structures, volume
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The volume at which the airways close is called
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closing capacity
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Alveoli in dependent areas with low volumes have what problem
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continue to be perfused (Q) - but not ventilated (V)
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How is closing capacity measured
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with a tracer such as xenon gas
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Closing capacity is usually well below the FRC but steadily rises with
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age
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This explains what
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why there is a decline in arterial oxygen tension as we age
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By what age does FRC = closing capacity in supine position
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44
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By what age does FRC = closing capacity in upright position
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66
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FRC is affected by
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position
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Closing capacity is only affected by
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age (not position)
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Lung anatomy review
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segmental bronchus
large subsegmental bronchi - about 5 gen small bronchi - about 15 gen terminal bronchioles respiratory bronchioles - 3 orders alveolar ducts and sacs |
