spirometry is the process of recording the Changes in the volume of air into and out of lungs during breathing. the instrument used for it is called spirometer or Respirometer. the graph showing the changes in pulmonary air volumes and pulmonary air Capacities Under different Conditions of breathing is called spirogram.
The pulmonary air volumes are :
i. Tidal volume (TV): The volume of air inspired or expired during a
normal breathing. it is about 500 ml for a healthy person.
out of 500 ml air only 350 ml air can reach up to alveolie while 150 ml air
remain in respiratory tract from nasal
Chamber to terminal bronchioles (conducting zone) and this air is Called dead
space air.
ii. Inspiratory reserve volume (IRV): The additional volume of air
that Can be inspired over tidal volume during a forceful inspiration. It is
about 2500 ml to 3000 ml.
iii. Expiratory reserve volume (ERV): The additional volume of air
that Can be expired over tidal volume during a forceful expiration. It is about
1000 ml to 1100 ml.
iv. Residual volume: The volume of air that remain in lungs even after forceful expiration. it is about 1100 ml to 1200 ml.
By adding up a few respiratory air volumes , various respiratory Capacities
Can be derived.
i. Inspiratory Capacity (IC): The total volume of air a person Can
inspire after a normal expiration. IC = TV + IRV
ii. Expiratory Capacity (EC): The total volume of air a person Can
expire after a normal inspiration. EC = TV + ERV
iii. Functional Residual Capacity(FRC): The total volume of air
that will remain in lungs after normal expiration. FRC = ERV + RV
iv. Vital Capacity(VC): The maximum volume of air a person can breath
in after a forced expiration. This includes ERV, TV and IRV. The maximum volume
of air a person can breath out after a forced inspiration. VC = TV + IRV + ERV
v. Total lung Capacity(TLC): The total volume of air that can be
accommodated in the lungs at the end of forceful inspiration. TLC = VC + RV
or TLC = TV + IRV + ERV + RV