Respiratory and Lung Volumes

What is the Respiratory System?

The Respiratory system is one of the important physiological processes of life. The human respiratory system comprises a pair of lungs, trachea, bronchi and bronchioles, alveoli, pharynx, larynx and the nose. The major roles of the respiratory system are breathing, exchange of gases between the external environment and the body fluids, and respiration. Now, there are several parameters based on which we can classify our respiratory system. One such parameter is: respiration and lung volumes.

Respiratory Volumes and Capacities

Respiratory Volumes

Respiratory volume simply connotes the amount of air that our lungs can inhale, absorb or exhale under certain conditions. It can also be regarded as the lung volume definition.

There is an apparatus for the calculation of volumes of air present in the lungs. This apparatus is recognized as a ‘Spirometer’. It also enables us to check other criteria associated with the lungs.

The respiratory volume can be further categorized into:-

  1. Tidal Volume (TV) -> Tidal volume can be best explained as the quantity of air that we breathe in and out of the body at the time of normal breathing. It stands roughly around 500 ml. A normal person takes 12-16 breaths each minute. So, if we calculate the tidal volume in a minute, it stands around 6000-8000 ml per minute.

  2. Inspiratory Reserve Volume (IRV) -> Whenever we inhale air beyond the normal capacity by exerting maximum force, that extra amount of inhaled air is termed as inspiratory reserve volume. It is calculated that the approximate value comes somewhat between 2500 ml to 3000 ml.

  3. Expiratory Reserve Volume (ERV) -> Whenever we exhale air beyond the normal capacity by exerting maximum force, that extra amount of exhaled air is explained as expiratory reserve volume. It is calculated that the overall value comes around 1000 ml-1100 ml.

  4. Residual Volume (RV) -> After releasing the air from the body, some amount of air still remains in the lungs. Thus, the amount of air still remaining in the lungs, subsequent to vigorous/energetic expiration is quoted as Residual volume. The approximate data ranges between 1100 ml-1200 ml.

Human Lung Capacity

From the above discussion, it is clear that there are certain lung volumes and capacities associated with the human respiratory system. Now, what is lung capacity? When two or more respiratory volumes/ lung volumes are combined, the result we get is lung capacity or to be more precise respiratory capacity. 

The respiratory capacity can be further categorized into:-

  1. Inspiratory Capacity (IC): Whenever a person inhales air immediately followed by releasing it under usual condition (i.e. not forcibly), the air that is received by the body is designated as inspiratory capacity. Thus, inspiratory capacity is found to be a summation of tidal volume and inspiratory reserve volume.

  2. Expiratory Capacity (EC): Just in an opposite manner, when a person exhales air immediately followed by inhalation under usual condition (i.e. not forcibly), the air that is released out of the body is designated as expiratory capacity. Thus, expiratory capacity is found to be a summation of tidal volume and expiratory reserve volume.

  3. Functional Residual Capacity (FRC): As mentioned earlier, some amount of air still stays in the lungs, even after exhalation of air under ordinary conditions. This amount of air can be mentioned as functional residual capacity. It is basically a combination of expiratory reserve volume and residual volume.

  4. Vital Capacity (VC): The maximum amount of air taken in or released out by someone immediately followed by exhalation and inhalation of air respectively is defined as vital capacity. It is an aggregation of tidal volume, inspiratory reserve volume and expiratory reserve volume.

  5. Total Lung Capacity: Total lung capacity is interpreted as the absolute amount of air remaining in the lungs prior to vigorous inhalation of air. This is a sum total of residual volume, expiratory reserve volume, inspiratory reserve volume and tidal volume. The total lung capacity formula is RV+ERV+TV+IRV. Total lung capacity in ml is around 5800 ml.

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Lung Volumes and Capacities Values

We can express lung volumes and capacities normal values as under:-

  1. Inspiratory capacity = 3000 ml- 3500 ml

  2. Expiratory capacity = 1500 ml- 1600 ml

  3. Functional residual capacity = 2500 ml

  4. Vital capacity = 3500 ml- 4500 ml

  5. Total lung capacity = 5800 ml

Lung Volume vs Lung Capacity

There is a vast difference between Lung volume and lung capacity. The amount of air that the human lung can inhale, perceive or exhale is determined as Lung volume. On the other hand, the assimilation of two or more lung volumes gives us lung capacity.

FAQ (Frequently Asked Questions)

1. What is Vital Capacity?

Ans: The greatest possible amount of air a person inhales after expiration or exhales after inhalation is quoted as vital capacity. We can assign it as an aggregation of inspiratory reserve volume, tidal volume or expiratory reserve volume. In other words, it can also be concluded as the sum of inspiratory capacity and expiratory reserve volume. Mathematically, it can also be expressed as VC= IRV+TV+ERV or VC= IC+ERV (as IC=TV+IRV). The normal value of vital capacity is calculated around 3500 ml – 4500 ml. There are certain factors on which vital capacity depends. These are stature, maturity and gender of the person. 

2. How Much Air can a Person Hold in the Lungs?

Ans: Under normal or absolutely usual circumstances, the amount of air being held by lungs or in other words the tidal volume is somewhat around 500ml. But if we take the case of maximum inspiration, the entire amount of air perceived by the lungs or in other words, the total lung capacity is around 5800 ml. Therefore, the answer to how to calculate lung capacity is as follows: The lung capacity of the human body is calculated by the summation of respiratory volumes of the two lungs. However, we must also remember that these values are usually represented as standards and may differ from person to person based on their body structure and medical conditions.