Lecture 18: FEV₁/FVC Tests (Exam III) Flashcards by Grayson Young

Q

What is the Bohr Equation?

A

V_DCO₂ / V_T = (P_ACO₂ - P_ĒCO₂) ÷ P_ACO₂

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Q

What is the Bohr equation used to find?

A

Total Dead Space

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Q

Give an example of a Bohr equation with numbers.

A

V_TotalDS / V_T = (40mmHg - 28mmHg) ÷ 40mmHg

0.3 = V_TotalDS ÷ 500mL

V_TotalDS = 150mL

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Q

How would one find alveolar dead space?

A

V_AlveolarDS = V_TotalDS - V_AnatomicDS

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Q

How can anatomical dead space be estimated?

A

1mL of deadspace per 1lb of body weight

(Ex. 200lbs = 200mL anatomic deadspace)

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Q

A 100kg patient presents with a P_ĒCO₂ of 25mmHg, a V_T of 600mls, and a PaCO₂ of 42mmHg. What would the estimated alveolar dead space of this patient be?

A

V_A = ?
V_T = 600mls
V_Anatomic = 220mls (100kg x 2.2 = 220lbs)

V_D ÷ 600mls = (42 - 25) ÷ 42
V_D = 242.86mls

V_A = 22.86mls (242.86mls - 220mls)

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Q

If there is no shunting present then P_ACO₂ should = ____________.

A

PaCO₂

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Q

If ĒCO₂ (mixed expired CO₂) is lower than expected, what conclusion could one likely draw?

A

There is increased dead space.

likely V_AlveolarD

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Q

What would you expect from the flow-volume loop depicted below?

A

Normal

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Q

What would you expect from the flow-volume loop depicted below?

A

Restrictive Disease

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Q

What would you expect from the flow-volume loop depicted below?

A

Obstructive Disease

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Q

What would you expect from the flow-volume loop depicted below?

A

Fixed Obstruction (Ex. ETT)

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Q

What would you expect from the flow-volume loop depicted below?

A

Variable Extrathoracic Obstruction

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Q

What would you expect from the flow-volume loop depicted below?

A

Variable Intrathoracic Obstruction

Peaked beginning likely due to emphysema

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Q

What is FEV₁ ?

A

% of VC expired in 1 second

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Q

What is an ideal FEV₁ assuming VC = 4.5L?

A

FEV₁ = 3.6L

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Q

What is FEF_25-75% ?

A

Slope of line from once 25% of air has been expired to 75% of air expired.

Q

What would a gradually sloped FEF_25-75% (such as the one below) indicate?

A

Obstructive disease

Q

What would a steep sloped FEF_25-75% (such as the one below) indicate?

A

Normal

Q

FEV₁ could largely be considered an indicator of _____ airway health, whereas FEF_25-75% would be more indicative of ______ airway health.

A

large; small

FEV₁ = large airways
FEF_25-75% = small airways.

Q

What is the Vital Capacity of the patient from the graph below?

A

VC = 3.75L (ish)

Q

What is the FEV₁ of the patient from the graph below?

A

FEV₁ ≈ 1.5L

Q

What is the FEV₁/FVC of the patient from the graph below?

A

FEV₁ = 1.5
FVC = 3.75

1.5 ÷ 3.75 = 40%

Q

What is a normal FEV₁/FVC ?

A

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?

- C_RS = Total Compliance of the Respiratory System - C_L = Compliance of the tissue. - C_CW = Compliance of the chest wall (i.e. ribs).

What is the formula for Total Respiratory System Compliance?

- C_RS = Total Compliance of the Respiratory System - C_L = Compliance of the tissue. - C_CW = Compliance of the chest wall (i.e. ribs).

What two factors oppose negative pressure exerted by P_IP ?

- P_ER (Tissues resistance to stretching) - C_CW (ribcage resistance to expansion)

What is the compliance of the respiratory system at FRC?

0.1 L/cmH₂O

Solve for Respiratory System Compliance.

- C_L = 0.2 - C_CW = 0.2 - x = C_RS (1÷x) = (1÷0.2) + (1÷0.2) ↓ (1÷**0.1**) = (1÷0.2) + (1÷0.2) ↓ C_{TotalCompliance(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.***