Respiratory and Lung Volumes

Introduction

The respiratory system is one of the major biological systems which helps in the breathing process. The respiratory system helps in gaseous exchange along with the removal of waste from the blood. To check the condition of the respiratory system we should understand some parameters related to the lungs. These parameters are nothing but respiratory capacity and lung volumes.

What is Respiratory System ?

A respiratory system is a group of organs involved in breathing by exchanging oxygen and carbon dioxide. The respiratory system involves many parts of the body including the nose, mouth, throat, trachea, bronchi, lungs, and many other parts.

The mouth and nose help in the inhalation of air into the body from the outer environment. The sinuses maintain sufficient moisture levels in the inhaled air and filter out unwanted particles. The throat passes the air to the trachea which delivers it to the lungs via bronchial tubes.

The lung is the main organ of the respiratory system which resides in the chest covered by the rib cage and surrounded by the pleural membrane. Bronchi are split into tiny branches called bronchioles and end in alveoli. The exchange of gases such as oxygen and carbon dioxide takes place within the lungs thanks to alveoli.

As blood passes through capillaries, it enters through the pulmonary artery and exit through the pulmonary vein. A capillary wall allows blood to release carbon dioxide into alveoli, while a capillary wall allows air to get to the alveoli and oxygen to be captured.

Diaphragm is a strong muscle wall that separate chest cavities from abdominal cavities. Whenever the diaphragm moves downward, force is created in the chest, which draws in and expands the lungs. It is the ribs that protect your chest cavity and help your lungs expand and contract by moving slightly.

Respiratory Volumes and Capacities

Respiratory volume is the amount of gas exchanged in the respiratory system during the respiratory cycle. Respiratory volume is classified as follows −

• Tidal Volume (TV) − This refers to the amount of air that is entered or expelled via the respiratory system with each breath. The normal value of the tidal volume is around 500 ml. If the tidal values increase or decrease it can cause various symptoms.

• Inspiratory Reserve Volume (IRV) − IRV refers to the extra volume of gas we inhale by exerting maximum force.

• Expiratory Reserve Volume (ERV) − ERV refers to the extra volume of gas we exhale by exerting maximum force.

• Residual Volume (RV) − RV refers to the quantity of gas that remains in the lung after exhalation.

Respiratory capacity is defined as the sum of various respiratory volumes. Respiratory capacity is further categorized as follows −

• Inspiratory Capacity (IC) − IC refers to the maximum volume of gas that one can inspire after expiring normally.

• Expiratory Capacity (EC) − EC refers to the maximum volume of gas that one can expire after inspiring normally.

• Total Lung Capacity (TLC) − TLC refers to the maximum volume of gas accumulated in the respiratory system after forced inspiration.

• Vital Capacity (VC) − The amount of gas exhaled after the highest inspiration is called vital capacity.

• Functional Residual Capacity (FRC) − It's the amount of gas remaining in the respiratory system after a normal expiration.

Human Lung Capacity

Humans have a total lung capacity of around 6 liters. Total lung capacity can be calculated by adding residual volume, expiratory reserve volume, tidal volume, and inspiratory reserve volume together. Lung capacity can be tested with the help of spirometry.

Spirometry can be used to measure −

• Forced Expiratory Volume (FEV1) −FEV1 refers to the volume of gas one can breathe out during forced expiration at one second.

• Forced Vital Capacity (FVC) − FVC refers to the quantity of oxygen an individual can exhale when he or she blows out rapidly.

Lung Volumes and Capacity Values

Let us look into the normal values of lung volume and capacity in the case of both male and female.

Respiratory Volumes	Values(ml)
	Male	Female
Tidal volume (TV)	500	500
Inspiratory reserve volume (IRV)	3300	1900
Expiratory reserve volume (ERV)	1100	700
Residual volume (RV)	1200	1100

Respiratory volumes and their normal values

Respiratory Volumes	Values(ml)
	Male	Female
Total lung capacity (TLC)	6000	4200
Vital capacity (VC)	4800	3100
Functional residual capacity (FRC)	2400	1800
Inspiratory capacity (IC)	3800	2400

Respiratory capacities and their normal values

Methods to Measure Lung Volume and Capacity

• Plethysmography can be used to identify the capacity of the lung by placing the patient under a plethysmograph.

• The helium dilution method is used to identify the functional residual capacity of the lung by using a mixture of oxygen and helium.

• Nitrogen washout method Using a nitrogen washout method, the functional residual capacity can be determined by monitoring the nitrogen content of exhaled gases.

Conclusion

This tutorial gives a better understanding of the respiratory system. Respiratory volume and lung capacities have been described in this tutorial. Lung capacity and volume values are tabulated in this tutorial. In conclusion, this tutorial is useful to understand the basic concepts of respiratory and lung volumes.

FAQs

Q1. What is minute ventilation? Write down the normal value of minute ventilation.

Ans. Minute ventilation is the volume of gas inspired and expired over 1 minute. The normal value of minute ventilation is 4000 to 6000 ml per minute.

Q2. How do you measure tidal volumes?

Ans. Tidal volumes can be measured with the help of a spirometer. The patient should breathe into a tube that is attached to a spirometer. The spirometer detects the volume of gas that is exhaled and inhaled and records the tidal volume.

Q3. What are the two instances of variation in tidal volume?

Ans. The tidal volume can be increased by hyperventilation and tidal volume can be decreased by hypoventilation.

Q4. Write down the difference between respiratory capacity and respiratory volume.

Ans. Respiratory volume is the amount of gas exchange in the respiratory system during the respiratory cycle, which is less and respiratory capacity is the sum of various respiratory volumes, which is more.

Q5. What are the functions of bronchi?

Ans. The functions of bronchioles are as follows; bronchi deliver the air to the lungs and filter out the waste materials from the air. Because of its moist nature, it traps the microbes and prevents them from reaching the lungs.