116 Questions
What is the primary function of the human respiratory system?
To facilitate the exchange of oxygen and carbon dioxide
What is created to facilitate the transport of air to the alveoli and alveolar gas to the environment?
A pressure gradient
What characterizes the lung's complex branching network of airway segments and viscoelastic tissues?
Tremendous variations in gas velocities and flow regimens
What three forces must be overcome to move gas into and out of the lungs?
Resistive, elastic, and inertial forces
What is the equation that describes the mechanical behavior of the total respiratory system?
P = PR + PE + PI
What is the term used do describe airway pressure relative to atmosphere ?
Transrespiratory pressure
What is the term used do describe airway pressure relative to pleural pressure ?
transpulmonary pressure
What is assumed to be linearly related to flow in the context of respiratory mechanics?
Resistive pressure losses
Which of the following is a source of resistive properties in the respiratory system described in the text?
all of the above
What happens to resistive pressure losses with more rapid flow rates in the respiratory system?
They vary nonlinearly
What do the coefficients R, E, and I represent when P refers to transrespiratory pressure for the respiratory system mechanics?
Total respiratory system
What components contribute to the resistive properties of the respiratory system mentioned in the text?
Parenchymal and chest wall tissues
airway resistance may reflect
airway caliber
What is the relationship between tissue resistive losses and breathing frequency according to the text?
Inversely proportional
In adult patients, what percentage of subglottal total lung resistance is attributed to lung tissue resistance at typical breathing rates?
80%
What is the collective name given to losses that are proportional to flow in the context of respiratory mechanics?
Resistive losses
What does the difference between Ppeak and Pplat represent in volume-cycled ventilation?
The resistive pressure loss
What is the purpose of estimating resistance during volume-cycled ventilation with an end-inspiratory pause?
To detect airway caliber changes during an intraoperative asthma exacerbation , or obstruction within the ETT
What can cause alterations in the resistive pressure loss (PR) during volume-cycled ventilation?
All of the above
What is the formula to estimate the resistance (R) during volume-cycled ventilation?
R = Ppeak - Pplat / VI
which of the following represent increased resistance?
middle diagram
What is elastance defined as in the context of respiratory mechanics?
Pressure change per unit volume
In the total respiratory system elastance calculation, what do EL and Ecw represent?
Lung elastances and chest wall elastances
Which type of elastance refers to the change in elastic distending pressure per unit volume during breathing or ventilation?
Dynamic elastance
What causes elastic pressures in the respiratory system?
recoil of the lungs and chest wall
What is the mathematical relationship between the total respiratory system elastance, lung elastance, and chest wall elastance in the form of compliance ?
1/Crs = 1/CL + 1/CW
What is the effect of emphysema on lung?
It increases lung compliance
What is a factor that reduces chest wall compliance?
Abdominal distension
What is the term used to describe the reciprocal of elastance?
Compliance
What is a factor that increases total respiratory or lung elastance?
Consolidation
which of the following represent increased elastance?
right diagram
What can be determined by dividing the difference between Pplat and PEEP by VT during volume-cycled ventilation?
Total respiratory system elastance
when the respiratory system elastance should be determined during ventilation?
during periods of high-flow
Which factor is used to determine respiratory system elastance during the end-inspiratory pause in volume-cycled ventilation?
PEEP
What parameter is calculated by the difference between Pplat and PEEP in the context of respiratory mechanics?
Elastic pressure
what is the formula provided for determining elastance ?
Ers = Pplat − PEEP / VT
What is the typical range of static respiratory system compliance in normal mechanically ventilated lungs?
50-100 mL/cm H2O
What is the effect of a recruitment maneuver on Ers?
It decreases Ers
Why may Ers increase due to strain stiffening of lung tissues?
Because collagen fibers become load-bearing elements
What is the goal of titrating PEEP to achieve an optimal balance between intratidal recruitment and parenchymal overdistention?
To maximize Crs
which of the following can alter lung or chest wall elastance during a specified tidal volume ventilation and lead to Alterations in pressure elastance (PE) ?
all of the above
Why is dynamic Ers higher than static elastance?
Due to viscoelasticity and gas redistribution
What is the cause of increasing strain and load-bearing elements within the lung tissues?
Collagen fibers become more dominant
What is the purpose of titrating PEEP to achieve an optimal balance?
To minimize Ers and maximize Crs
What is the effect of strain stiffening on lung tissues?
Ers increases
What is the relationship between elastin and collagen fibers at low levels of tissue strain?
Elastin fibers are the dominant
What is typically associated with the kinetic energy of accelerating the gas column in the central airways?
Inertial pressures
In which situations is inertia a significant contributor to the apparent airway pressure or the work of breathing?
During sudden changes in air flow
What is inertial pressure typically expressed as the product of?
A lumped "inertia" parameter and volume acceleration
What is the primary contributor to the inertial pressure during respiratory motion?
Gas column acceleration
Why can't Rrs and Ers be estimated without an end-inspiratory pause in the ventilator waveform?
The resistive and elastic pressures cannot be separated visually.
During pressure-controlled ventilation, what determines airway flow and VT?
Gradient between airway and alveolar pressures
When are dynamic estimates of total respiratory Rrs and Ers valid?
During controlled modes of ventilation with a relaxed chest wall
In which situations can the mechanics of the chest wall be accounted for when estimating transpulmonary pressure?
With the use of esophageal manometry
What method is suggested for more robust estimates of respiratory Rrs and Ers without an end-inspiratory pause?
Multiple linear regression analysis
How is elastance (compliance) most easily measured according to the text?
during periods of zero flow
When can quasi-static PV curves be constructed according to the text?
during very slow inflations/deflations
the expiratory limb of PV curve can be constructed by ?
inflating the lungs to TLC
What defines compliance according to the text?
The slope of pressure-volume curve
What does the lower inflection point (LIP) reflect when using sigmoidal functions to describe curves in the context?
Maximum alveolar recruitment
Why is it crucial to apply enough PEEP during protective ventilation?
to avoid lower inflection point
What phenomenon occurs in PV curves due to lung volume being dependent on the direction of distending pressure during inspiration or expiration?
Hysteresis
During protective ventilation, why is it advised to avoid the upper inflection point (UIP)?
To prevent alveolar overdistention
What should be done in protective ventilation to avoid the lower inflection point (LIP)?
Apply Enough PEEP levels
What should be done in protective ventilation ?
apply Enough PEEP and low tidal volume
What is a limitation of managing ventilation based on quasi-static PV curves?
PV curves do not reflect lung mechanics during dynamic breathing processes
What is the work of breathing represented as?
The product of the applied distending pressure and resulting volume change
Why is the work of breathing assessed during inspiration only?
Because the respiratory musculature must overcome both elastic and resistive pressures to bring air into the lungs
What is the frequency at which energy expenditure is minimized?
The energetically optimum breathing frequency
What is mechanical power an index of?
The rate of energy dissipation
Why is mechanical power used to assess the risk of developing ventilator-induced lung injury?
Because it is an index of the rate of energy dissipation
What is the purpose of assessing the work of breathing?
To assess the risk of developing ventilator-induced lung injury
monitoring of respiratory pressure can be measured in?
all of the above
Why is airway pressure during controlled mechanical ventilation not the actual pressure at the airway opening?
Due to the resistive and compliant properties of the breathing circuit and face mask/ETT
What is often improperly used as a surrogate for lung distension?
Airway pressure
Where can pressure be measured in order to monitor respiratory pressures?
All of the above
What does the pressure measured in the trachea or at the airway opening represent?
The pressure transduced at the anesthesia machine or ventilator
What is transrespiratory pressure determined by?
The difference between airway pressure and atmospheric pressure
Which of the following may contribute to high airway opening pressures?
Obesity, abdominal insufflation, and steep Trendelenburg position
What does increased transrespiratory pressure not necessarily indicate?
Parenchymal overdistention
What is transrespiratory pressure a measure of?
The pressure difference between the lungs and chest wall
What is transpulmonary pressure a measure of?
The distending pressure across the lungs alone
How can transpulmonary pressure be obtained non-invasively?
Using an esophageal balloon catheter
Why is the esophageal balloon catheter several centimeters long?
To provide an average estimate of the pressure field surrounding the lungs
What is a limitation of esophageal manometry?
All of the above
In which situations is the use of esophageal manometry valuable?
All of the above
How is the esophageal balloon catheter typically positioned?
Through the mouth or nose and into the middle-to-distal third of the esophagus
transpulmonary pressure measurements are valuable in ?
adjustment of appropriate levels of PEEP
What is required to measure transpulmonary pressure?
Measurement of airway opening pressure and estimates of the pressure within the pleural space
Where is the pressure measured to estimate intrapleural pressure?
In the esophagus
What is recommended to limit in order to minimize alveolar overdistension?
Plateau pressures
Which respiratory variable is considered one of the most important when stratifying mortality risk during ARDS?
Driving pressure
What does the driving pressure involve in its computation?
Pplat and PEEP
the same plateau pressure could correspond to ?
very different transpulmonary pressures
to minimize alveolar overdistension, recommendations suggest limiting plateau pressures to ?
26-30 cm H2O
What is auto-PEEP that is typically observed in ventilated patients with COPD caused by?
positive pressure present within the alveoli at end-exhalation
How can the amount of auto-PEEP be estimated in mechanically ventilated patients?
By occluding the airway at end exhalation
Consequences of of auto-PEEP?
significant respiratory and hemodynamic compromise
How is auto-PEEP can be assess in spontaneously breathing patients ?
by esophageal balloon
What is a primary cause of auto-PEEP in patients with ARDS, sepsis, and respiratory muscle weakness?
Combination of increased airway resistance and reduced lung elastic recoil
factors that can contribute to Auto-PEEP/intrinsic-PEEP ?
all the answers are correct
Where should the flow-measuring device be placed for accurate measurement?
Between the circuit Y-connector and the proximal end of the ETT/LMA
What is a clinical use of flow monitoring?
Detection of nonzero end-expiratory flows
What can occur if auto-PEEP is not addressed?
Increased risk of lung hyperinflation and reduction of venous return
where most ventilators and anesthesia machines measure flow?
close to machine
What can be done to eliminate auto-PEEP?
Increase expiratory time and reduce the tidal volume and respiratory rate
What is a limitation of measuring flow close to the ventilator?
Flow rates may differ from those at the patient's lungs
What is the most common method to infer airway flow during ventilation?
Measurement of a differential pressure decrease across a fluid resistive element
Why are pneumotachographs not used routinely?
They are sensitive to temperature and humidity, and difficult to clean and sterilize
What is an advantage of orifice flowmeters?
They have a large internal diameter that limits the formation of condensation and minimizes obstruction
What is used in most anesthesia machines for flow measurement?
Hot wire anemometers
What is required for sensing bidirectional flow in a single conduit using hot wire anemometers?
Two wires in series
Why do hot wire anemometers require calibration?
To account for variations in gas density or humidity
What is an advantage of hot wire anemometers compared to pneumotachographs and orifice flowmeters?
They have a better dynamic response
how most anesthesia machines and ventilators determine volume ?
electrically/numerically integrating the corresponding flow signal.
Why is accurate measurement of volume essential in anesthesia machines and ventilators?
To accurately account for gas quantity
Learn about the convective and diffusive gas transport processes involved in the human respiratory system, as well as the pressure gradients and volume changes necessary for air exchange in the alveoli. Explore the complex branching network of the lung's airways.
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