29 - Lung Volumes

Question 1

o Tidal Volume (Vt):

Answer 1

500 ml during quiet breathing
 Volume of air leaving/entering nose/mouth per breath
 Determined by mechanics of chest wall, lungs, and activity of respiratory control centers in brain (b/c control center affects respiratory muscles)

Question 2

o Residual Volume (RV):

Answer 2

1.5 L (emphysema ↑ this)
 Volume of gas left in lungs after max. forced expiration
 Determined by force generated by expiration muscles, inward elastic recoil of lungs…airway collapse occurs allowing for trapped gas in alveoli
 Prevents lung from collapsing at low lung volumes

Question 3

o Expiratory Reserve Volume (ERV):

Answer 3

1.5 L
 Volume of gas expelled from lungs during maximum forced expiration (starts @ end of normal tidal expiration)
 Determined by the difference between functional residual capacity (FRC) and Residual volume (RV)

Question 4

o Inspiratory Reserve Volume (IRV):

Answer 4

2.5 L
 Volume of gas inhaled into lungs during maximum forced inspiration (starts @ end of normal tidal inspiration)
 Determined by strength of contraction of inspiratory muscles, inward elastic recoil of lung and chest wall and starting point

Question 5

o Functional Residual Capacity (FRC):

Answer 5

3L
 Volume of gas remaining in lungs at end of normal tidal expiration
 Represents the balance of inward/outward elastic recoil

Question 6

o Inspiratory Capacity (IC):

Answer 6

3L

 Volume of air inhaled into lungs during maximum inspiratory effort beginning at FRC

Question 7

o Total Lung Capacity (TLC):

Answer 7

6L
 Volume of air in lungs after maximum inspiratory effort
 Determined by strength of contraction of inspiratory muscles, inward elastic recoil of lung and chest wall

Question 8

o Vital Capacity (VC):

Answer 8

4.5 L

 Volume of air expelled from lungs during maximum forces exhalation starting after a maximum forced inspiration

Question 9

• Not measured by spirometry:

Answer 9

o Residual volume
o Functional reserve capacity
o Total lung capacity
o Everything else can be measured by spirometry

Question 10

• Forced Vital Capacity (FVC)

Answer 10

o Total volume of air that can be forcibly expired after max. inspiration (same thing as VC)

Question 11

• Forced Expiratory volume in 1st second of exhalation (FEV1)

Answer 11

o Cumulative volume can be measure for the 2nd and 3rd seconds, too.

Question 12

• FEV1/FVC ratio

Answer 12

o Fraction of total forced vital capacity that can be expelled in the 1st second
o 80% is typical
o Ratio reflects resistance to airflow***

Question 13

• Forced Expiratory Flow in the middle of expiration (FEV25-75)

Answer 13

o Parameter obtained from flow-volume curve
o It is the flow rate at 25-75% of exhaled vital capacity
o Parameters useful in assessment of obstructive/restrictive lung diseases

Question 14

o Obstructive LD (Ex. Asthma):

Answer 14

 ↓ in FVC and FEV1, but FEV1 is reduced more. So, would create a decreased ratio

Question 15

o Restrictive LD (Ex. alveolar fibrosis):

Answer 15

↓ in compliance, ↓ FVC and FEV1, but FVC is reduced more. So, would create an increased ratio

Question 16

4) Recognize different patterns of flow volume curve in typical cases of obstructive lung disease, restrictive lung disease, and upper airway obstruction

Answer 16

Asthma (obstructive) - has a steep decline between 25-75

Upper airway obstruction has decreased total volume and does not reach any peaks, simply plateaus

Restrictive lung disease also has a decreased volume and it is shifted far to the right… the flow must be high for the volume to increase at all and when it does increase, it has a similar shape, but smaller size

Question 17

• Dead Space

Answer 17

o Volume of airways and lungs that don’t participate in gas exchange

Question 18

• Anatomic Dead Space (~150 mL)

Answer 18

o Volume of the conducting airways (nose, trachea, bronchi, bronchioles).
o At the end of expiration, conducting airways are filled with alveolar air.

Question 19

• Functional Dead Space

Answer 19

o Alveoli that do not participate in gas exchange due to mismatch in ventilation/perfusion.
o Typically ~0 mL in normal people.

Question 20

• Physiologic Dead Space (VD)

Answer 20

o Total volume of the lungs that does not participate in gas exchange.

VD = Anatomical Dead Space + Functional Dead Space

  So, b/c Functional DS in healthy people ~ 0…Anatomical Dead Space = VD •	If physiological is larger than anatomical = suggests ventilation/perfusion defect •	Vd/Vt determines estimate of wasted ventilation

Question 21

6) Calculate minute ventilation

Answer 21

• Minute Ventilation: total rate of air movement into and out of lungs
 MV = tidal volume x Respiration Rate

Question 22

Calculate alveolar ventilation

Answer 22

• Alveolar Ventilation (VA): rate at which new air reaches gas-exchange areas of lung (takes into account physiologic dead space)
 VA = (tidal volume – dead space) x Respiration Rate

Question 23

• Alveolar Ventilation Equation:

Answer 23

describes the inverse relationship between alveolar ventilation and alveolar pressure of CO2

VA = (VCO2 x K) / PACO2

Question 24

7) Describe alveolar ventilation equation and its meanings with respect to the relationship between tissue CO2 production, alveolar ventilation, and alveolar partial pressure of CO2

Answer 24

• Alveolar Ventilation Equation: describes the inverse relationship between alveolar ventilation and alveolar pressure of CO2
• CO2 production rate can be determined by knowing alveolar ventilation and alveolar pressure of CO2
• If you breath out air faster (alveolar ventilation ↑) then it would make sense that the pressure of CO2 in the alveolar would ↓ b/c you’re getting rid of it faster.