Statics: Lung Ventilation and Compliance Flashcards
role of pulmonary surfactant
- lower surface tension in the lung
- imparts mechanical stability to alveoli
- prevents collapse at low lung volumes
definition of minute ventilation
- volume of gas moving in and out of the lungs per minute
minute ventilation calculation
inspired volume = expired volume = (tidal volume x respiratory frequency)
typical tidal volume of a person
- 500 mL
anatomic dead space
- conducting airways that do not participate in gas exchange
how much anatomic dead space exists in 500 mL tidal volume
- 150 mL
alveolar ventilation
- the total volume of inspired air that enters the alveoli per minute as is available for gas exchange
another source of dead space
- alveoli who ventilation exceeds capacity of the blood flowing to those alveoli to exchange gases
what is physiologic dead space
- combination of anatomic and alveolar dead space
physiologic dead space in normal healthy individuals
- close to the anatomic dead space
- 25-30% of ventilation
elastance
- property to resist being stretched
- and return to original state when released
elastic recoil of the lung opposes
- inflation
elastic recoil of the lung assists
- deflation
why is the slope of inspiration lower than that of expiration on the pressure-volume loop?
- higher distending pressures are needed during inspiration to achieve a given lung volume
what is the name for the process in which the inflation and deflation limbs follow different paths
- hysteresis
forces due to surface tension exist at
- alveolar air-liquid interface
compliance of air filled lung determined by
- tissue forces
- surface forces
what occurs due to the imbalance of cohesive interactions
- force
what happens in a liquid filled lung in regard to compliance
- air-liquid interface and surface tension forces eliminated
- compliance determined by tissue forces only
why is the surface tension of water high
- polar water molecule interacts poorly with hydrophobic gas phase
pressure of small bubble radius
- higher pressure needed to support surface tension
what happens to the radius of alveolar walls at end expiration
- radius shortens
result of high surface tension on thin alveoli at low lung volumes
- cause them to collapse
result of higher pressures within smaller alveoli
- force them to empty into larger alveoli
pulmonary surfactant secreted by type II alveolar cells from
- lamellar bodies
composition of lung lining
- 90% lipid
- 10% protein
lipid fraction of lung lining composed of
- DPPC
which surfactant proteins are critical for formation of the surface layer
- SP-B and SP-C
which surfactant proteins participate in lung defense
- SP-A and SP-D
surfactant surface tension properties
- dynamic
- vary as a result of compression or expansion of alveolar surface area
density of surfactant as alveolar surface area decreases during expiration
- density increases
density of surfactant as alveolar surface area increases during inspiration
- density decreases
surface tension at high lung volumes
- dynamically increases
surfactant maximally reduces alveolar surface tension at ________ when tendency for alveolar collapse is greatest
- end expiration
best explanation for hysteresis in air-filled lung pressure volume curve
- surfactant layer breaks up during lung expansion and increases surface tension
- during deflation surfactant layer becomes more compressed and decreases surface tension
premature infants have a great difficulty doing what
and are susceptible to
- initiated and maintaining lung inflation
- susceptible to neonatal respiratory distress syndrome
low compliance and the need to develop higher pressures to repeatedly expand collapsed lungs
- increases work of breathing
- can lead to respiratory failure
result of alveolar interdependence
- interconnecting walls of neighboring alveoli support one another
what happens when alveolar pressure falls to zero relative to atmosphere during each pause in spirometer testing
- transmural pressure gradient is equal to the pleural pressure as measured by the esophageal balloon
what is used to construct static lung compliance curves
- volume of air exhaled
- intrapleural pressure
elastic recoil and compliance in emphysema
- elastic recoil decreased
- compliance increased
lungs with emphysema in terms of inflating and deflating
- inflate easily
- no elastance to deflate properly
elastic recoil and compliance in pulmonary fibrosis
- elastic recoil increased
- compliance decreased
lungs with fibrosis in terms of inflating and deflating
- difficult to inflate
- deflate more forcefully
system compliance
- algebraic sum of lung and chest wall acting together
- coupled by negative pressure in pleural space
residual volume mainly set by
- force of contracting expiratory muscles being opposed by the chest wall and ribs that resist further compression
what sets the functional residual capacity
- tendency of chest to spring outwards balanced by tendency of lungs to collapse
at approximately 60% of vital capacity
- chest wall at natural resting point
- recoil pressure mainly due to lung itself
at lung volumes greater than 60% of vital capacity
- both lung and chest wall must be distended by positive pressure
- both actively contribute recoil
at positive pressures greater than 30 cm H2O
- lung reaches tensile limit
- further increases may rupture visceral pleura
what is a pneumothorax
- air entering the intrapleural space
what happens if pleural pressure becomes equal to atmospheric pressure
- lung may collapse
what is a simple pneumothorax
- one time leak
- air enters and leaves pleural space equally with each breath
what is a tension pneumothorax
- air that enters the pleural space, can’t leave, and builds up positive pressure
how do we treat pneumothorax
- relieve positive pressure with chest tube
- apply suction to intrapleural space
- re-expands lung and re-compresses rib cage to re-establish normal mechanical coupling
the cycle of energy gain and loss for the lung is opposite that of
- the chest wall
the work of breathing is proportional to
- product of changes in volume and pressure
cost of tidal breathing
- 5% of total body O2 consumption
cost during exercise
- about 30% during exercise
work of breathing elevated in
- obesity
- pulmonary fibrosis
- respiratory distress syndrome
- pulmonary interstitial edema
- obstructive lung disease
why is work of breathing increased in obesity
- chest wall load is increased
- chest wall compliance is reduced
why is work of breathing increased in pulmonary fibrosis
- compliance of the lung is reduced
why is work of breathing increased in respiratory distress syndrome
- lack of pulmonary surfactant decreases lung compliance and causes recurrent collapse
why is work of breathing increased in pulmonary interstitial edema
- stiff lung
why is work of breathing increased in obstructive lung diseases
- airway resistance increased
- elastic recoil reduced
FRC in emphysema
why?
- FRC increases
- harder to get air out of lungs so more would stay in there after expiration
