Lecture 18: FEV₁/FVC Tests (Exam III) Flashcards
What is the Bohr Equation?
VDCO₂ / VT = (PACO₂ - PĒCO₂) ÷ PACO₂
What is the Bohr equation used to find?
Total Dead Space
Give an example of a Bohr equation with numbers.
VTotalDS / VT = (40mmHg - 28mmHg) ÷ 40mmHg
0.3 = VTotalDS ÷ 500mL
VTotalDS = 150mL
How would one find alveolar dead space?
VAlveolarDS = VTotalDS - VAnatomicDS
How can anatomical dead space be estimated?
1mL of deadspace per 1lb of body weight
(Ex. 200lbs = 200mL anatomic deadspace)
A 100kg patient presents with a PĒCO₂ of 25mmHg, a VT of 600mls, and a PaCO₂ of 42mmHg. What would the estimated alveolar dead space of this patient be?
VA = ?
VT = 600mls
VAnatomic = 220mls (100kg x 2.2 = 220lbs)
VD ÷ 600mls = (42 - 25) ÷ 42
VD = 242.86mls
VA = 22.86mls (242.86mls - 220mls)
If there is no shunting present then PACO₂ should = ____________.
PaCO₂
If ĒCO₂ (mixed expired CO₂) is lower than expected, what conclusion could one likely draw?
There is increased dead space.
likely VAlveolarD
What would you expect from the flow-volume loop depicted below?
Normal
What would you expect from the flow-volume loop depicted below?
Restrictive Disease
What would you expect from the flow-volume loop depicted below?
Obstructive Disease
What would you expect from the flow-volume loop depicted below?
Fixed Obstruction (Ex. ETT)
What would you expect from the flow-volume loop depicted below?
Variable Extrathoracic Obstruction
What would you expect from the flow-volume loop depicted below?
Variable Intrathoracic Obstruction
Peaked beginning likely due to emphysema
What is FEV₁ ?
% of VC expired in 1 second
What is an ideal FEV₁ assuming VC = 4.5L?
FEV₁ = 3.6L
What is FEF25-75% ?
Slope of line from once 25% of air has been expired to 75% of air expired.
What would a gradually sloped FEF25-75% (such as the one below) indicate?
Obstructive disease
What would a steep sloped FEF25-75% (such as the one below) indicate?
Normal
FEV₁ could largely be considered an indicator of _____ airway health, whereas FEF25-75% would be more indicative of ______ airway health.
large; small
FEV₁ = large airways
FEF25-75% = small airways.
What is the Vital Capacity of the patient from the graph below?
VC = 3.75L (ish)
What is the FEV₁ of the patient from the graph below?
FEV₁ ≈ 1.5L
What is the FEV₁/FVC of the patient from the graph below?
FEV₁ = 1.5
FVC = 3.75
1.5 ÷ 3.75 = 40%
What is a normal FEV₁/FVC ?
80%
What is the FEV₁ of the black line below?
3.6L
What is the FEV₁ of the blue line below?
1.5L
The two graphs below would be indicative of what?
FEV₁ / FVC = 3.8 ÷ 5 = 76%
Normal Physiology
The two graphs below would be indicative of what?
FEV₁ / FVC = 2.5 ÷ 3 = 83%
Restrictive Disease
The two graphs below would be indicative of what?
FEV₁ / FVC = 1.5 ÷ 3.5 = 43%
Obstructive Disease
What FEV₁ / FVC would be considered pathologic?
< 70%
Calculate the FEV₁ / FVC of the green line below.
What is this indicative of?
VC = 5 - 1.5 = 3.5
FEV₁ = 3
FEV₁ / FVC = 3÷3.5 ≈ 86%
Normal or Restrictive disease
Calculate the FEV₁ / FVC of the red line below.
What is this indicative of?
VC = 5 - 0 = 5L
FEV₁ = 4L
FEV₁ / FVC = 4÷5 ≈ 80%
Normal
What is abnormal about the flow-volume loop below?
Normal breathing should be closer to FRC
What is the formula for Total Respiratory System Compliance?
- CRS = Total Compliance of the Respiratory System
- CL = Compliance of the tissue.
- CCW = Compliance of the chest wall (i.e. ribs).
What is the formula for Total Respiratory System Compliance?
- CRS = Total Compliance of the Respiratory System
- CL = Compliance of the tissue.
- CCW = Compliance of the chest wall (i.e. ribs).
What two factors oppose negative pressure exerted by PIP ?
- PER (Tissues resistance to stretching)
- CCW (ribcage resistance to expansion)
What is the compliance of the respiratory system at FRC?
0.1 L/cmH₂O
Solve for Respiratory System Compliance.
- CL = 0.2
- CCW = 0.2
- x = CRS
(1÷x) = (1÷0.2) + (1÷0.2)
↓
(1÷0.1) = (1÷0.2) + (1÷0.2)
↓
CTotalCompliance(RS) = 0.1L / cmH₂O
How will body positioning affect ventilation at FRC?
- Upright: ribs assist ventilation
- Supine: ribs impede ventilation.
If a lung was completely blocked off, what would occur to compliance?
Compliance would be cut in ½.
Note: If you’re using my cards, I won’t be making new notecards over concepts we already discussed. I’ll be studying my notecards from the previous test. Just a heads up.
