Spirometry Procedure, Side Effects and Uses

Introduction:

• Spirometry is a pulmonary function test.
• It helps to assess the volume of air inhaled and exhaled
• A spirometer is the instrument used to estimate the volume of air involved in breathing movements which helps in the clinical assessment of pulmonary functions.

Topics covered:

• Pulmonary Volumes
• Pulmonary Capacities

Definition:

Pulmonary volume/ Respiratory volume is the quantity of air which human lungs can hold or expel under different conditions.

Detailed Explanation:

i. Tidal Volume (TV)
- The volume of air inspired or expired during normal respiration.
- TV - 500 ml approx.

ii. Inspiratory Reserve Volume (IRV)
- The additional volume of air, a person can inspire above TV, by a forcible inspiration.
- IRV - 2500 - 3000 ml

iii. Expiratory Reserve Volume (ERV)
- The additional volume of air, a person can expire above TV, by a forcible expiration.
- ERV - 1000 - 1100 ml

iv. Residual Volume (RV)
- The volume of air remaining in the lungs even after a forcible expiration
- RV - 1100 - 1200 ml

v. Minute Respiratory Volume (MRV)
- The volume of air entering the respiratory tract in a minute.
- It is TV × Respiratory rate
=500 ml × (12 to 16/min)
=6000 - 8000 ml/min

vi. Dead Space Volume (DSV)
- The volume of inhaled air that remains in the conducting airways and does not take part in gaseous exchange.
- It is 1/3rd the value of tidal volume
- 150 ml approx.

vii. Minute Alveolar Ventilation
- The volume of air reaching alveoli for exchange in a minute.
- It is (TV - DSV) × Respiratory rate
= (500ml - 150ml) × (12 to 16/min)
= 350 ml × (12 to 16/min)
= 4200 - 5600 ml/min
 

Respiratory Capacities

Definition:

Respiratory Capacities are Sum of two or more respiratory volumes

Detailed Explanation:

• Following Respiratory capacities are used in clinical diagnosis:

i. Inspiratory Capacity (IC)

• Total volume of air a person can inspire after a normal expiration.
• It includes tidal volume and inspiratory reserve volume
• IC = TV + IRV

ii. Expiratory Capacity (EC)

• Total volume of air a person can expire after a normal inspiration.
• It includes tidal volume and expiratory reserve volume
• EC = TV + ERV

iii. Functional Residual Capacity (FRC)

• Volume of air that will remain in the lungs after a normal expiration.
• It includes expiratory reserve volume and residual volume
• FRC = ERV + RV

iv. Vital Capacity (VC)

• The maximum volume of air a person can breathe in after forced expiration.
• It is the maximum volume of air a person can breathe out after a forced inspiration.
• It includes inspiratory reserve volume, expiratory reserve volume and tidal volume
• VC = IRV + ERV + TV

v. Total Lung Capacity (TLC)

• Total volume of air accommodated in the lungs at the end of forced inspiration.
• It includes reserve volume, inspiratory reserve volume, expiratory reserve volume and tidal volume
• TLC = RV + IRV + ERV + TV
• Or it can be: TLC = RV + VC
   

Frequently Asked Questions - FAQs

Q1. Why do athletes have more vital capacity?
Ans.
- Athletes have more vital capacity because their oxygen requirement is more as they do strenuous activities.
- Due to strenuous exercise, muscle development occurs which helps in lungs extension, thus vital capacity increases.

Q2. Why is residual volume important?
Ans.
 - Residual volume is volume of air remaining in the lungs even after a forcible expiration
 - Residual volume is important because the air that remains in the lungs after forceful exhalation prevents lungs from collapsing.

Q3. What is the difference between residual volume and functional residual capacity?
Ans.
- Residual volume (RV) is the volume of air remaining in the lungs even after a forcible expiration
- Functional residual volume (FRC) is the volume of air that remains in the lungs after a normal expiration.
- It includes expiratory reserve volume and residual volume
- FRC = ERV + RV

Q4. What causes dead space?
Ans.
The volume of inhaled air that remains in the conducting airways and does not take part in gaseous exchange leads to dead space formation.

Q5. What is the significance of vital capacity?
Ans. 
- Vital capacity is the maximum volume of air a person can breathe in and out after forced expiration and inspiration respectively.
- This helps to remove deoxygenated blood from the body and allows to inhale fresh air.