Exam 3 - Lecture 5 Flashcards
What is PEFR? When does this typically occur?
Peak expiratory flow rate
Early in expiration while elastic recoil is still strong, before significant airway collapse occurs.
During obstruction, when are flow rates diminished? How does this appear on flow/volume loops?
Later parts of expiration when small airway collapse dominates. Concave/scooped descending expiratory limb (stanky leg)
On flow volume loops, how does restrictive pattern appear?
tall and narrow loop, reduced lung volumes but preserved shape
On flow volume loops, how does fixed obstruction pattern appear?
flatted inspiratory AND expiratory limbs
On flow volume loops, how does variable extrathoracic obstruction pattern appear?
flattened INSPIRATORY limb
e.g. vocal cord paralysis
On flow volume loops, how does variable intrathoracic pattern appear?
flattened expiratory limb
e.g. tracheomalacia
a normal FEV1/FVC ratio is
80% or 0.8
What is a decreased FEV1/FVC ratio in adults? What does it suggest?
<70%, which would suggest obstructive lung disease
What FEV1/FVC ratio did he say would be a “headache” to get out of the OR, and why?
<70% ratio
High airway resistance makes ventilation and extubation more risky and unpredictable
What does FEF25-75% measure? Is this mostly effort independent or dependent?
The average flow rate of airflow in middle half of FVC maneuver between 25 and 75% total expired volume
Mostly independent
What is special about FEF25-75%?
Its very sensitive to small airway disease and is a marker of airway reactivity.
Can detect early obstructive changes before FEV1/FVC ratio appears abnormal and is useful for identifying asthma, early COPD, and airway reactivity.
The biggest change in FRC when changing positions is driven by
ERV
What must compensate for the drop in ERV when laying down to keep TLC the same?
IRV
End-tidal CO2 (PETCO2) should roughly equal
Arterial CO2 (PaCO2) ~40mmHg
What is the small difference between PETCO2 and PaCO2 due to?
contribution of deadspace gas
What is phase I of the capnograph?
Baseline, has 0 CO2 as it is just anatomical dead space air coming out
What is phase II of the capnograph?
Transitional phase as it is air from dead space but also alveolar gas.. it has a steep rise
What is phase III of the capnograph?
This is the alveolar plateau, and the line slowly has an upward slope due to continous alveolar emptying
It goes up slightly as there is more time passed since inhalation, so there is more CO2 buildup in the blood.
ETCO2 is highest at
end of expiration
What does a downward slope on end-tidal indicate?
Severe emphysema. Alveolar collapse causes early cutoff
Has uneven emptying, and only the better ventilated apices (apex) contribute to end-expiration.
In emphysema, more gas comes from ___. What does this do to V/Q?
Apex, which worsens ET-PaCO2 mismatch
what is the lag in ETCO2 readings?
Delayed due to tubing dead space and slow sampling.
What does alveolar dead space do to ETCO2 readings?
Falsely lowers PETCO2.
If there is a larger gap between PaCO2 and End tidal, that reflects a larger amount of dead space. You can use this as a trend for acute changes.
What is CO2 content in lungs at FRC?
FRC = 3L
Average PCO2 is 40mmHg
40/760 = 5.263%
3L x .05263 = 158mL CO2
Beginning vs end of expiration
PCO2 at beginning:
PCO2 at end:
Beginning: Low, due to dead space
End: higher, from alveoli
VA= ?
VT - VDS
Quantity of CO2 can be figured out by taking FACO2 and multiplying it by
VA
FECO2 x VT = ?
FACO2 x (VA)
compliance equation
Compliance (C) = ΔV / ΔP
What does compliance “measure” in the lungs?
How easily the lungs expand in response to pressure changes
What is a normal compliance?
Well, a normal delta P is 2.5 (-5cmH2O –> -7.5cmH2O)
A normal Tidal volume is 0.5L
Compliance is measured in L/cmH2O
So its 0.5L/2.5cmH2O
therefore normal compliance is 0.2L/cmH2O
The lungs and chest wall act as a ______ system.
Series system.
When you’re inhaling, the lungs want to ___ and the chest wall wants to ____
collapse; expand
Even though the lungs want to collapse and the chest wall wants to expand, Each of these has its own _______. When you ventilate a person, you’re inflating both together and this behaves as a ______.
compliance of 0.2L/cmH2O
series system
When components are in series, the total compliance is
less than either component
(0.1L/cmH2O)
Whats the formula for series systems?
1/CTOTAL = 1/CLUNG + 1/CCHEST WALL
1/0.2 + 1/0.2 = 5 + 5 = 10 –> CTOTAL = 1/10 –> = 0.1L/cmH2O
What if the lung compliance is 0.7?
1/0.7 + 1/0.7 = 2.86 –> 1/2.86 –> = 0.35L/cmH2O
What is the interpretation of series system?
You need twice as much pressure to get the same volume change as if you were inflating just the lungs or just the chest wall by themselves.
The combination of the two is stiffer than either part alone.
Restrictive disease has ____ compliance and small changes in pressure yields ____ changes. They are _____ to ventilate and _____ work of breathing.
decreased; small; harder; increased
Obstructive disease has ____ compliance and _____ elastic recoil. The lungs inflate _____ but don’t ______.
increased; decreased; easily; return to baseline.
