Question

Study the following equations w.r.t. pulmonary volumes and capacities. The (-) indicates a minus sign.
(a)TLC-(ERV+IRV+RV)
(b)EC-ERV
(c)VC-(ERV+IRV)
(d)FRC-RV
(e)IC-RV
How many of the above equations represent tidal volume?
(1)Two
(2)Three
(3)Four
(4)Five

Answer 1

Hint: Pulmonary volumes and capacities are used for the clinical assessment of the respiratory system. This is because these volumes and capacities are almost the same for everyone and if someone has a different value then it might be indicative of an underlying respiratory illness.

Complete answer:
Tidal volume(TV) is defined as the amount of air that is inspired or expired during normal respiration and its value lies around 500 mL.
 Let us look at the individual equations given to us and solve them to conclude whether they represent tidal volume or not.
-TLC-(ERV+IRV+RV)
Total Lung Capacity (TLC): Total volume of air accommodated in the lungs at the end of forced inspiration. This includes RV, ERV, TV, and IRV.
Thus, TLC-(ERV+IRV+RV) = TV
-EC-ERV
Expiratory Capacity (EC): Total volume of air an individual can expire after a traditional inspiration. This consists of tidal volume and expiratory reserve volume (TV+ERV).
Thus, EC-ERV = TV
-VC-(ERV+IRV)
 Vital Capacity (VC): The utmost volume of air an individual can inhale in after forced expiration. This includes ERV, TV, and IRV or the utmost volume of air an individual can breathe out after a forced inspiration.
Thus, VC-(ERV+IRV) = TV
-FRC-RV
 Functional Residual Capacity (FRC): Volume of air that will remain within the lungs after a traditional expiration. This includes ERV+RV.
Thus, FRC-RV = ERV and not TV
-IC-RV
Inspiratory Capacity (IC): Total volume of air an individual can inspire after a traditional expiration. This consists of tidal volume and inspiratory reserve volume ( TV+IRV).
Thus, IC-RV is not equal to TV
So, the correct option is ‘Three’.

Note: -Inspiratory Reserve Volume (IRV): Additional volume of air, an individual can inspire by a forcible inspiration. This averages 2500 mL to 3000 mL.
-Expiratory Reserve Volume (ERV): The extra amount of air an individual can expire through forcible expiration. Its value is around 1000 mL- 1100 mL.
-Residual Volume (RV): Volume of air remaining within the lungs even after a forcible expiration. This averages 1100 mL to 1200 mL.