Question

The total volume of air accommodated in the lungs at the end of forced inspiration is known as total capacity (TLC). TLC is equal to
(where, TV = Tidal volume, IRV= Inspiratory reserve volume, ERV = Expiratory reserve volume, RV= Residual volume)
A)TLC= ERV+ IRV+TV
B)TLC=TV+RV+ERV
C)TLC=ERV+RV
D)TLC=ERV+IRV+TV+RV

Answer 1

Hint: Upon the maximum effort of inspiration, the volume of air in the lungs is known as a lung capacity or total lung capacity (TLC). The average lung capacity is 6 liters among healthy adults. The different factors that affect the different changes in lung capacity among individuals are age, gender, body composition, and ethnicity.

Complete answer
-From a summation of different angles, the lung capacity is derived. About 6 liters of the air is the average total lung capacity of an adult human male.
-At the end of the forced inspiration the total volume of air accommodated in the lungs is called Total Capacity(TLC).
-Total lung capacity is equal to the vital capacity and the residual volume.
-Total exchangeable air in the system is known as vital capacity.
-Total lung capacity is calculated by adding tidal volume, inspiratory reserve volume, and expiratory reserve volume.
-Therefore, the sum of Expiratory Reserve Volume (ERV), Inspiratory reserve volume (IRV), Tidal volume (TV), and Residual volume (RV) is the total lung capacity.

Additional information
Tidal Volume(TV) - during the respiratory cycle it is the amount of air that can be inhaled or exhaled and the function of the respiratory center’s respiratory muscles and the mechanics of the lungs and chest walls are depicted by it.
Inspiratory Reserve Volume(IRV)- when the amount of air forcibly inhaled after normal tidal volume is known as inspiratory reserve volume. It is usually kept in reserve but used during deep breathing. 1900-3300ml is the normal adult value.
Expiratory Reserve Volume(ERV) - when the amount of air forcibly exhaled after the normal tidal volume is known as expiratory reserve volume. 700-1200ml is the normal adult value and can be reduced by obesity, ascites, or after upper abdominal surgery.
Residual Volume(RV) - after maximal exhalation, it is a volume of air that remains in the lungs. 1200ml(20‐25 ml/kg) is the normal adult value and indirectly measured from the summation of FRC and ERV.
-It cannot be measured by spirometry.

So, the correct answer is, "TLC=ERV+IRV+TV+RV".

Note:
-The volume of air in the lungs upon the maximum effort of inspiration is known as lung capacity or total lung capacity
-From TLC = RV+IVC, or from TLC = FRC+IC it is calculated and the most preferred method for calculation is the body plethysmography. It can also be measured by the radiologic technique.