Lung Volumes & Capacities

Question 1

Tidal Volume (VT)

Answer 1

is the amount of air inspired / expired in a single breath.
•Varies under circumstances -for instance, increases
during aerobic exercise
•Normal resting = 500 ml

Question 2

Residual Volume (RV)

Answer 2

volume of air that cannot be forced out, no matter how hard one tries.
•Getting the ‘wind knocked out of you’ – you were
forced into RV
•Cannot be determined by spirometry

Question 3

Inspiratory Reserve Volume (IRV)

Answer 3

additional volume that can be inhaled greater than tidal volume.
•The gap between inspiration during tidal volume and
maximal inspiration.

Question 4

Expiratory Reserve Volume (ERV)

Answer 4

additional volume that can be exhaled greater than tidal volume.
•This does not include residual volume.
•Requires activation of expiratory muscles (i.e., active
respiration).

Question 5

Total Lung Capacity (TLC)

Answer 5

maximal volume to which lungs can be expanded with greatest effort

TLC = IC + FRC
= VC + RV
= ERV + RV + IRV + VT

Cannot be measured by spirometry

Question 6

Functional residual capacity (FRC)

Answer 6

amount of air that remains in the lungs following a normal expiration.

FRC = ERV + RV

Cannot be determined by spirometry
Helps prevent collapse of lungs, reduces workload, dilutes toxic inhaled gases

Question 7

Vital capacity (VC)

Answer 7

amount of air that can be maximally inspired following a maximal expiration.

VC = IRV + VT + ERV

VC influenced by posture, ability of diaphragm to contract/relax, strength of respiratory muscles, thoracic wall expansibility, resistance to air flow, lung elasticity, disease

Question 8

Inspiratory capacity (IC)

Answer 8

capacity of air that can be maximally inspired following a normal exhale

IC = VT + IRV

Question 9

As One Ages:
•TLC?
•RV?
•VC?

• Extra detail:
• ERV?
• RV?
• So FRC?
• IC?

Answer 9

As One Ages:
•TLC stays similar
•RV increases
•VC goes down

• Extra detail:
• ERV decreases
• But RV increases to a greater extent
• So FRC increases
• IC decreases

Question 10

Seated vs. Supine body position:
•TLC seated vs supine
•RV seated vs supine
•VC seated vs supine

Extra detail:
•FRC seated vs supine
•ERV seated vs supine
•IC seated vs supine (slightly)

Answer 10

Seated vs. Supine body position:
•TLC seated > supine
•RV seated = supine
•VC seated > supine

Extra detail:
•FRC seated > supine
•ERV seated > supine
•IC seated < supine (slightly)

Question 11

Obesity:
•TLC and VC?
•RV?
•Seated vs. supine become very ______to one another

Extra detail:
•ERV?
•IC?
•FRC?

Answer 11

Obesity:
•Reduces TLC and VC
•RV stays similar
•Seated vs. supine become very similar to one another

Extra detail:
•ERV largely reduces
•IC less largely impacted
•FRC is lower

Question 12

Define Emphysema

Answer 12

“obstructive lung disease (OLD)”
•Characterized by limitations of airflow due to partial or complete obstruction, hard to “push” air out often
•TLC and RV increases
•VC decreases

Question 13

Define Fibrosis

Answer 13

“restrictive lung disease (RLD)”
•Characterized by reduced expansion of lungs, hard to inflate or fill the lungs
•RV, TC, VC decreased

Question 14

What is a Helium (He) dilution & describe how it works:

Answer 14

Inhalation of a known concentration (C1) of helium [insoluble in blood] from a known volume (V1)

Change in concentration (C2) allows for determination of V2 = FRC

• RV = FRC – ERV
• TLC = FRC + IC

Question 15

What is Body plethysmography:

Answer 15

Enclosed rigid box -> Breath against shutter
•Pressure in lungs change
•Pressure in box changes proportionally in opposite direction

-Boyle’s Law (P1V1 = P2V2)

Question 16

Explain the Nitrogen-Washout Technique for determining residual volume:

Answer 16

Determines dead space.

Individual breaths 100% O2 through one-way valve, all expired gas is collected, monitored until N2 reaches zero.
Total volume of all gas expired is determined, and multiplied by % of N2 in mixed expired air (80%).

Question 17

Pulmonary Dead Space Basic model =

Answer 17

VT = VA + VD

• VA = volume that participates in gas exchange (alveolar)
• VD = volume that does not participate in gas exchange (conducting airways)
• Traditionally: VD/VT = (FACO2- FECO2)/FACO2
• Underestimates VD in diseased individuals

Question 18

Define Physiological dead space:

Answer 18

VD/VT = (PaCO2 - PECO2)/PaCO2

• Physiological dead space is Anatomical Dead Space + Alveolar Dead Space
• Sensitive to pathophysiological conditions
• Anatomical dead space = 1 mL per lb BW (150 lbs = 150 mL)