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Lung volume and capacity are important metrics to differentiate a normal lung from a diseased lung. But, we often get confused between lung volume and lung capacities. If you are the one who gets all volume and capacities mixed up, this article will help you clear the concept. In this article we will discuss:

• The normal range of volume and capacities.
• Lung volume and capacities in obstructive pulmonary disease.
• Lung volume and capacities in restrictive pulmonary disease.
• How actually lung volume is a part of lung capacities.

By the end of this article, you will be somewhat better than you were before.

Table Of Contents

1. Lung volume and capacity
2. Lung volume explained
3. Lung capacities explained
4. Lung volume and capacity graph
5. Normal lung volumes and capacities chart
6. The difference between obstructive and restrictive pulmonary disease
7. Factors affecting lung volume and capacities
   • Effect of age on lung volume/capacities
8. Final word

Lung Volume and Capacities Explained in Hindi

Lung volume and capacity

Lung volume and capacities are the measures of the amount of air in the lungs when we breathe normally and forcefully. During respiration, there occurs the movement of air in and out of the pulmonary system. When respiration is normal, the lesser amount of air moves in and out which increases when we rate of respiration increases during running, etc.

So, lung volume is the measure of the volume of gas/air that moves in and out during normal respiration and forceful respiration. The amount of air in the lungs can be subdivided into four (4) volumes and four (4) capacities.

Lung volume explained

Lung volume is the volume of gas that moves in and out during our inspiration and expiration. It is measured in Litres. So, let us discuss how inspiration and expiration are measured in their different forms.

Four lung volumes are:

1. Tidal volume.
2. Inspiratory reserve volume.
3. Expiratory reserve volume.
4. Residual volume.

#1 Tidal volume (TV): To understand tidal volume, just sit relaxed on a chair and close your eyes. Now, try to feel your inspiration and expiration (air expelled) with closed eyes. The volume of air inhaled or exhaled during this rest breathing is the tidal volume. So, tidal volume is defined as "The volume of gas inhaled or exhaled during the resting breath is called the tidal volume".

#2 Inspiratory Reserve Volume (IRV): Inspiratory reserve volume is the maximum volume of air that can be inhaled during a forceful inspiration. Actually, it is the additional air to the tidal volume that can be inspired during the forceful inspiration.

To understand it, again sit relaxed on a chair with your eyes closed. Now, take a deep breath to your maximum capacity and expel it out. This, additional air you inhaled in addition to the tidal volume mentioned above,  is the IRV.

#3 Expiratory Reserve Volume (ERV): Expiratory Reserve Volume is defined as the amount of air that can be expelled during forceful expiration. Now, close your eyes and after taking normal inspiration, try to exhale the maximum amount of air possible. This extra amount of air in addition to normal expiration is ERV.

#4 Residual Volume (RV): Even after forceful expiration, there is some volume of air still left inside the lung. That is, the lung doesn't get fully emptied even after forceful expiration. The amount of air that remains in the lungs after maximum exhalation is the residual volume.

So, it can be defined as the volume of air remaining in the lung after ERV has been done.

Lung capacities explained

The four lung capacities are:

1. Inspiratory capacity.
2. Vital capacity.
3. Functional residual capacity.
4. Total lung capacity.

#1 Inspiratory capacity (IC): Inspiratory capacity is the volume of air that can be inspired from the end of the tidal expiration or the volume of air that can be inspired forcibly after a normal inspiration.

So, it is the sum of Tidal Volume (TV) + Inspiratory Reserve Volume (IRV).

#2 Vital Capacity (VC): Vital Capacity (VC) is defined as a change in volume of the lung after maximal inspiration followed by maximal expiration is called Vital Capacity of lungs. It is the sum of tidal volume, inspiratory reserve volume and expiratory reserve volume. The vital capacity of normal adults ranges between 3 to 5 litres.

It is the total volume of air within the lung that is under volitional control. It is the sum of IRV + TV + ERV.

VC is actually Forced Vital Capacity. To measure it, first, achieve maximum inspiration then forcibly expel all the air as fast as possible into a measuring device.

#3 Functional residual capacity (FRC): It is the volume of air that remains after the tidal expiration. So, it is the combination of RV + ERV.

#4 Total Lung Capacity (TLC): It is the total volume of air that remains in the lungs/thorax after a maximum inspiration.

It is the sum of IRV + TV + ERV.

Lung volume and capacity graph

We can represent all these four lung volumes and four capacities in a graph. Once again carefully read the descriptions on volume and capacities and then try to interpret it through this graph.

Normal lung volumes and capacities chart

VOLUME		CAPACITY
TV	500	IC	3000
IRV	2500	VC	4000
ERV	1000	FRC	2500
RV	1500	TLC	5500
All numbers in: ml (mili leter)

The difference between obstructive and restrictive pulmonary disease

Obstructive and Restrictive pulmonary disease shows different lung volumes and capacities. In restrictive pulmonary disease, all the capacities of the lung reduce and in obstructive pulmonary disease it all increases. Let us try to understand it through this graph.

Factors affecting lung volume and capacities

There are many factors that affect static lung volumes/capacities. The factors like age, gender, weight, height and ethnicity are the main physiological determinants of the static lung volumes/capacities. However, there are other factors which should be considered. Like, level of physical activity, regular exercise, especially swimming and endurance training. Alternatively, ascending to a high altitude may decrease lung volumes probably due to increased pulmonary blood flow, pulmonary edema or premature small airway closure (1).

Let's try to find out how age affects lung volume and capacities.

Effect of age on lung volume/capacities

The respiratory system undergoes various anatomical, physiological and immunological changes with age. The structural changes include chest wall and thoracic spine deformities which impairs the total respiratory system compliance leading to increase work of breathing. Respiratory muscle strength decreases with age and can impair effective cough, which is important for airway clearance (2). All these factors affect the lung volume and capacities, this is why we recommend breathing exercises which are important for the health of the respiratory system. If the excess sputum is collected inside the lungs it also affects breathing, we can get rid of this naturally by following the postural drainage position technique at home.

The lung matures by age 20–25 years, and thereafter aging is associated with progressive decline in lung function. The alveolar dead space increases with age, affecting arterial oxygen without impairing the carbon dioxide elimination. The airways receptors undergo functional changes with age and are less likely to respond to drugs used in younger counterparts to treat the same disorders. Older adults have decreased sensation of dyspnea and diminished ventilatory response to hypoxia and hypercapnia, making them more vulnerable to ventilatory failure during high demand states (ie, heart failure, pneumonia, etc) and possible poor outcomes (2).

Final word

There are a number of factors that affect lung volume and capacities. All these volumes are measured by techniques which we will discuss later.

Further reading: What is Bucket Handle Movement of Ribs, it's Anatomy

Reference:

1. Lutfi, M.F. The physiological basis and clinical significance of lung volume measurements.Multidiscip Respir Med12,3 (2017). https://doi.org/10.1186/s40248-017-0084-5
2. Sharma, G., & Goodwin, J. (2006). Effect of aging on respiratory system physiology and immunology.Clinical interventions in aging,1(3), 253–260. https://doi.org/10.2147/ciia.2006.1.3.253

Dr Sunit Sanjay Ekka (PT)

Dr Sunit Sanjay Ekka (PT) is a Physical Therapist in practice for the last 15 years. He has done BPT from SVNIRTAR, a premium Government institution. His patients are his best teacher, whatever he gets to learn from them he loves to share it through the blog. He also shares content through his popular YouTube channel "Sunit Physiotherapist".

jonesmorant.blogspot.com

Source: https://physiosunit.com/lung-volume-and-capacity-2/

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