Lung Volumes and Capacities

Question 1

Lung volumes

Answer 1

1. Static lung volumes & capacities
   unit: ml or L

2) Dynamic lung volumes & capacities
unit: ml/min or L/min

Question 2

Tidal volume (TV) *

Answer 2

the volume of air that moves into and out of the lung in each breath.
AVR: 500ml. (range:- 500 -750ml)

Question 3

Expiratory reserve volume (ERV)

Answer 3

The volume that can be expired after expiration of a tidal volume
(ERV; ∼1 L),
AVR:1.5 L.

Question 4

Inspiratory reserve volume (IRV)

Answer 4

the volume that can be inspired over and above tidal volume
(IRV; ∼2 L).
IRV is 2–3 L.

Question 5

Residual volume (RV)- ( PREVENTS LUNG COLLAPSE)*

Answer 5

air left in the lungs after a maximal expiratory effort is the residual volume
RV;∼1.3 L.
cannot be measured from a simple spirometer

Question 6

Inspiratory capacity(IC)

Answer 6

The maximum volume of air that can be inspired after reaching the end of a quiet expiration.
✓ (IC = TV+ IRV).
Normal value :3500 mL

Question 7

Functional residual capacity (FRC)

Answer 7

The volume of the air remaining inside the lungs after normal expiration
(FRC = ERV +RV).
Normal value :2300- 2500 mL

Question 8

Vital capacity (VC)- Important for diagnosis*

Answer 8

It is the maximum volume of air that can be expired
after a maximal inspiration.
(VC = ERV + TV + IRV)/ can use IC formula
Normal Value: ∼4.5 L

Question 9

Total lung capacity (TLC)*

Answer 9

It is the volume of air in the lung system after a maximal inspiration
(TLC = RV + ERV + TV + IRV)
Normal value: ∼5 L.
- may reach 6L for athletes

Question 10

Forced vital capacity (FVC):

Answer 10

VC and FVC same in normal person

-The largest amount of air that can be expired after a maximal inspiratory effort, is frequently measured clinically as an index of pulmonary function.

Question 11

Timed Vital Capacity (TVC) or Forced expiratory volumes (FEV):

Answer 11

The fraction of the vital capacity expired during the first second of a forced expiration

Accordingly, volume expired each unit time is measured and expressed as % of TVC; as –
*FEV1–80 to 85% (1st second)
*FEV2–90 to 95% (2nd second)
*FEV3–>97% (3rd second)

Question 12

FEV1% (Tieffeneau’s index):

Answer 12

FEV1 expressed as the ratio in percentage terms
FEV1% = (FEV1 / VC) x 100 %
normal value: 80 %
less than 75%= obstructive lung disease

Question 13

Minute lung ventilation

Answer 13

8 l : volume of air expired during 1 minute of quiet breathing

Question 14

Respiratory minute volume(RMV)/(MV)

Answer 14

Volume of air entering or leaving the respiratory system per minute
= Rate of respiration(RR) X tidal volume(TV)
= 12 X 500
= 6000mL/min

Question 15

Minute alveolar ventilation

Answer 15

minute ventilation minus minute ventilation of the death space

Question 16

Peak Expiratory flow rate (PEFR):

Answer 16

Maximum velocity of flow in liters / min with which air is forced out of the lungs
✓ Recorded by peak – flowmeter
✓Normal value: 400-600L/min
✓ Index of patency of airways

Question 17

Significance of FRC.

Answer 17

i. Buffering of alveoli gas -Continuous exchange of gases is possible due to presence of some air always in the lungs, and thereby concentration of O2 and CO2 in blood are maintained constant.
ii. Breath holding .
iii. Dilution of toxic inhaled gases occurs due to the reserve of 2500 ml of air in the lungs (FRC) most of the times.

Question 18

Significance of vital capacity (VC)

Answer 18

Estimation of VC allows the assessment of maximum inspiratory and expiratory efforts and, thus, gives useful information about the strength of respiratory muscles.

Question 19

Factors affecting vital capacity

Answer 19

i. Size of the thoracic cavity: VC is more in males because of large chest size and more muscle power than females.
ii. Age: In old age, VC decreases due to the decrease in the elasticity of the lungs.
iii. Strength of respiratory muscles: In swimmers & divers, VC is more because of increased strength of the respiratory muscles.
iv. Gravity: In standing position, VC is more than in sitting and lying position because of the gravity.

Question 20

Significance of FEV1 and FVC*

Answer 20

✓ for the identification of obstructive and restrictive lung disease.
➢ Restrictive disorders –VC decrease, FEV1normal (Pulmonary fibrosis; Kyphoscoliosis; Ankyosisspondylitis)
-restriction in trachea, lungs cant inflate properly
-* FEV1 reduced (<80%)
* FVC reduced (<80%)
* FEV1/FVC normal (>0.7)

➢ Obstructive diseases –VC normal & FEV1 decrease (Bronchial asthma; Emphysema)
-obstruction in respi part, (blockage in expiration)
* FEV1 reduced (<80%)
* FVC reduced to a lesser extent
than FEV1
* FEV1/FVC reduced (<0.7)

Question 21

Flow Volume Loops ( identify flow loop graph)

Answer 21

• Identify inspiratory and expiratory components – opposite from ventilator waveforms!
  -Reveals a pattern typical for certain diseases
  kink- Obs.L.D