Respiratory Anatomy & Physiology: A Review

Question 1

Define Compliance

Answer 1

The change in volume of the lung when exposed to a pressure

Question 2

Define Hypercapnia

Answer 2

Increased CO2
May result from hypoventilation or an increase in dead space with no increase in MV

Question 3

Define elastic recoil

Answer 3

The force by which the lung pasively deflates at end inspiration

Question 4

Define the A-a gradient

Answer 4

A measure of the lung’s ability to transfer O2 to pulmonary capillaries
The larger the gradient, the poorer the O2 transfer
Measured as (age in years/4) + 4
Normal = 5-10mmHg

Question 5

What does alveolar stability primarily rely on?

Answer 5

Surfactant

Question 6

What is the function of the upper airway?

Answer 6

Gas conditioning
Filters, heats & humidifies air

Question 7

What is expiratory reserve volume (ERV) + residual volume (RV)?

Answer 7

ERV + RV = functional residual capacity (FRC)

Question 8

What is expiratory reserve volume (ERV) + tidal volume (Vt) + inspiratory reserve volume (IRV)?

Answer 8

ERV + Vt + IRV = vital capacity (VC)

Question 9

Define functional residual capacity (FRC)

Answer 9

FRC = teh volume of air remaining in the lungs after passive exhalation of tidal volume

Question 10

Define airway resistance

Answer 10

When a gas passes through a tube the molecules strike the sides creating resistance; the smaller the tube the more resistance is created

It’s calculated using the radius & length of a tube, and viscosity of the inhaled gas:
Resistance (R) = 8nl/TTr4, where n = viscosity of gas, l = length of tube and r = radius

Question 11

Define Boyle’s Law

Answer 11

At a constant temperature volume varies inversely with pressure

Question 12

Define trans-respiratory pressure (Prs), also known as trans-airway pressure

Answer 12

Pressure gradient from mouth to alveoli

Question 13

Define trans-pulmonary pressure (PL), also known as trans-pleural pressure

Answer 13

Pressure gradient from alveoli to the pleural space

Question 14

Define trans-thoracic pressure (Pw)

Answer 14

The pressure gradient from the pleural space to the external chest wall/body surface

Question 15

Calculate the A-a gradient and PAO2 with the following values:
PaO2: 65mmHg
PaCO2: 50mmHg
FiO2: 0.40
pH: 7.33
HCO3: 25
Barometric pressure: 765mmHg

Answer 15

PAO2: [(atmosphere - 47mmHg) x FiO2] - (PaCO2 / 0.8 RQ)
= [(765mmHg-47mmHg) x 0.4] - (50mmHg/0.8) = 224.7mmHg

A-a gradient: PAO2 (224.7mmHg) - PaO2 (65mmHg) = 159.7

Question 16

Answer the following on the oxyhemoglobin dissociation curve with a LEFT SHIFT:

a) What 4 conditions cause it to shift left?
b) What is the name of the effect?
c) How does it effect O2/Hgb affinity?
d) Where does it occur?

Answer 16

Oxyhemoglobin dissociation curve shifts LEFT:

a) Decrease in: CO2, H+ ions (pH rises), temperature, 2,3 DPG
b) Haldane effect
c) Increases Hgb’s affinity for O2
d) Occurs at alveolar capillaries

Question 17

Answer the following on the oxyhemoglobin dissociation curve with a LEFT RIGHT:

a) What 4 conditions cause it to shift right?
b) What is the name of the effect?
c) How does it effect O2/Hgb affinity?
d) Where does it occur?

Answer 17

Oxyhemoglobin dissociation curve shifts RIGHT:

a) Increase in: CO2, H+ ions (pH lowers), temperature, 2,3 DPG
b) Bohr effect
c) Decreases Hgb’s affinity for O2
d) Occurs at systemic capillaries

Question 18

List the layers O2 moves through when moving from alveolar gas to Hgb

Answer 18

In order:
Surfactant
Epithelial cell
Interstitium
Endothelial cell
Plasma
Red cell membrane

Question 19

Calculate lung compliance if a pt has the following values:
Vt: 450 mL
Pplat: 20 cmH2O
PEEP: 5 cmH2O

Answer 19

Formula:
CL = ΔV (mL) (tidal volume)
ΔP (cmH2O) (plateau pressure - PEEP)

CL = 450mL / (20cmH2O - 5cmH20) = 30 cmH2O