Exam 3 - PFTs continued Flashcards
(35 cards)
Why do restrictive lung diseases have an increased airway resistance?
Because they have lower lung volumes
Lower lung volumes = smaller airway diameter = increased resistance
Why do obstructive diseases have an abnormal effort dependent line?
The have lost elastic recoil tissue
On forced exhalation the more compressable airways collapse
What 2 things allow for passive expiration?
- A change in pleural pressure
- An increased elastic recoil pressure
Describe alveolar pressures during passive expiration?
- Alveolar pressures are positive at the beginning of expiration causing air to flow out of the lungs due to a ▵P (Alveolar pressure > atmospheric pressure)
- The pressure in the airways gradually decreases as you move closer to the trachea
What prevents small airway collapse during a normal-passive expiration?
- The positive internal airway presssure (pushes airways open from inside)
- The negative PIP (pulls airways open externally)
During a forced expiration, what happens to the airway pressures?
- PIP becomes more positive
- PER remains the same
- PA becomes more positive
Why don’t small airways collapse during a normal forced expiration?
When do they collapse in a normal lung?
- Because at the “choke point” (small airways without cartilage), the internal airway pressure = the PIP, so there is no ▵P and no airway collapse
- The airways will collapse at low lung volumes because there is not enough internal airway pressure to keep them open
Describe why patients with obstructive dx have difficulty exhaling air completely?
- They have a loss of elastic recoil pressure, which decreases alveolar pressure
- The loss of alveolar pressure decreases the ▵P of the small airways causing them to collapse at the choke point (PIP > Pairway)
Why are lungs at low volume more prone to collapse?
- The internal pressure is lower
- The airway walls are already closer together
What prevents small airway collapse in normal lungs?
- ER in the alveolar tissue
- ER in small airway tissue and ER in tissue connected to other airways causing traction, holding them open from the outside (traction)
In what areas of the lung can airway pressures be lower than PIP and remain open?
The upper airways, cartilage prevents them from collapsing
Define a fixed extra and intra thoracic obstruction?
What is an example of a fixed intra/extra-thoracic obstuction?
How is the flow volume loop effected?
- Extra-thoracic would be an obstuction above the chest, intra-thoracic would be an obstruction inside the airways inside the chest cavity (see black dashes in picture) - they cannot be distinguesd on FV loops
- Endotracheal tube (is both in the chest cavity, and above the chest cavity)
- The ETT lumen is smaller than the tracheal diameter causing increased resistance on inspiration and expiration
- This flow volume loop would show a decreased peak inspiratory AND peak expiratory flow
What is a variable intrathoracic obstruction?
Causes?
- A collapse of the airways only during a forced expiration (variable)
- During inspiration the more negative intrapleural pressure pulls the obstruction out of the way
- Causes: Due to a loss of ER tissue; occurs in obstuctive dx (COPD, emphysema, asthma)
How is the flow volume loop effected by a variable intrathoracic obstruction?
The peak expiratory flow is cutoff only on expiration
What is a variable extrathoracic obstruction?
Causes?
Treatment?
- Collapse of the upper airways/trachea ONLY during inpsiration
- Airways with weakened or missing cartilage will collapse during inspiration due to the negative internal airway pressure
- During expiration the positive airway pressure pushes open the obstruction
- Causes: Paralyzed vocal cords and weakened/removed tracheal cartilage
- Treatment: PPV, removes negative pressure during inspiration
How is the flow volume loop effected by a variable extrathoracic obstruction?
- The peak inspiratory flow is decreased
What does FEV1 stand for?
What is normal FEV1/FVC?
- Forced Expiratory Volume in 1 second
- Normal is 80% (should be able to expire 80% of our vital capacity in 1 second)
What is the VC and FEV1/FVC in the figure?
VC: 4.5 L (graph does not include RV)
FEV1/FVC: 4.5-.75 =3.75, 3.75/4.5=0.833, 83%
What does a decreased FEV1/FVC mean?
- It means the patient cannot forcefully expire normally - less volume is being expired (usually from an already lowered TLC)
- A decreased FEV1/FVC is indicative of obstructive lung disease
Does this patient have normal lungs?
If not, why?
- No
- Even though the FEV1/FVC is normal, the VC is much lower than normal as is the peak expiratory flow rate
This is indicative of restrictive lung dx
Is this flow volume loop normal?
If not, why?
- No
- The FEV1/FVC is very low, and the expiration is very long
- This is indicative of obstructive lung dx
What considerations do you need to make for patients with obstructive lung dx on a ventilator?
- They require a increased expiratory time due to the loss of elastic recoil
- Will need an increased expiratory to inspiratory ratio
When determining obstructive dx, what are the reversibilities of the different dx with a bronchodilator?
Emphysema/COPD - not reversible (ER issue, not SM contraction issue)
Chronic bronchitis - partially reversible
Asthma - reversible
What is the FEV1/FVC of both lines?
What do these indicate?
X: FEV1 = 4L, FVC = 5L, 4/5=0.8- normal
Z: FEV1 = 3L, FVC = 3.5L, 3/3.5=0.857 normal FEV1/FVC but low FVC = restrictive dx
