Exam 3, L2 Flashcards
(27 cards)
What does a flow-volume loop graphically represent?
It shows flow rate (y-axis) vs. lung volume (x-axis) during forced inspiration and expiration.
What does the top curve of a flow-volume loop represent?
Forced expiration from total lung capacity to residual volume.
What does the bottom curve represent?
Forced inspiration from residual volume to total lung capacity.
What is the significance of peak expiratory flow rate (PEFR)?
It reflects airway patency and is decreased in obstructive and restrictive diseases.
What provides the driving force for passive expiration?
Elastic recoil of the lungs and pleural pressure.
Why do small airways collapse more easily during forced expiration?
Because they lack cartilage, and surrounding pleural pressure may exceed intraluminal pressure.
What is airway traction and what role does it play?
Elastic fibers tether small airways open — loss of these fibers (e.g., in emphysema) increases collapse risk.
How does loss of elastic recoil affect expiratory flow?
Reduces alveolar pressure, narrowing the pressure gradient, and impairs expiration.
What is a fixed obstruction on a flow-volume loop?
A lesion affecting both inspiration and expiration, flattening both limbs of the loop (e.g., endotracheal tube).
What is a variable intrathoracic obstruction?
Obstructs expiration only due to positive intrathoracic pressure collapsing airways (e.g., COPD).
What is a variable extrathoracic obstruction?
Obstructs inspiration only due to negative pressure pulling weak upper airway structures inward (e.g., vocal cord paralysis).
What does FEV1 measure?
The amount of air exhaled during the first second of a forced expiratory maneuver.
What does FVC (Forced Vital Capacity) measure?
Total amount of air exhaled forcefully after full inspiration.
What is the normal FEV1/FVC ratio?
≈80% (≥70% is often used as the lower limit of normal)
What pattern does an obstructive disease show on PFTs?
↓FEV1, ↓FVC, and FEV1/FVC <70%
What pattern does a restrictive disease show on PFTs?
↓FEV1 and ↓FVC but normal or ↑FEV1/FVC ratio
What does the nitrogen washout test evaluate?
Ventilation distribution and small airway collapse using exhaled nitrogen after a 100% O₂ breath.
What are the four phases of the nitrogen washout curve?
Phase I: Dead space (0% N₂)
Phase II: Transitional zone (mix of dead space & alveolar gas)
Phase III: Alveolar plateau (mostly from base, then apex)
Phase IV: Abrupt rise in N₂ indicating small airway closure
What is closing volume?
The volume expired after small airways begin to collapse.
What is closing capacity?
Closing volume + residual volume; the point at which airway closure begins during expiration.
How does aging affect elastic recoil and small airway stability?
Loss of elastic tissue → decreased recoil and traction → increased small airway collapse.
At what age does small airway collapse begin during normal breathing in healthy individuals?
Around age 55, closing capacity surpasses functional residual capacity (FRC).
Why do elderly patients have an increased work of breathing?
Because they experience small airway collapse on every breath, requiring effort to reopen them.
What does a “scooped out” expiratory curve on flow-volume loop indicate?
Obstructive disease, especially emphysema or COPD.
