11-vital Capacity

( Lab. no. 11 )

Estimation of vital capacity

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Vital capacity (V.C): Is the maximal volume of air which can be expelled from the lungs by forceful effort following maximal inspiration. Components of vital Capacity:

 Tidal volume.  Expiratory reserve volume.  Inspiratory reserve volume. [email protected]

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Tidal volume (VT):

The volume of air moved in or out of the lungs with each breath during normal comfortable respiration (=500ml).

Inspiratory reserve volume (IRV):

The maximal volume of air which can be inspired after completing a normal tidal inspiration (2000–3100 ml).

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Expiratory reserve volume (ERV):

The maximal volume of air which can be expired after a normal tidal expiration (750 – 1200ml).

Residual volume (RV):

The volume of air which remains in the lungs after a maximal expiration (1200ml).

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Vital Capacity = VT + IRV

=500 + 3100 = 4800 ml

+ ERV

+ 1200

= 4.8 Liter. -Normal value: Males = 4.8 L. Females = 3.2 L.

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-V.C is related to the size and development of the subject. -It is increased in athletes (runners, swimmers, divers….etc). -It is decreased in older people and in diseases of the respiratory system.

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Volume (L)

54321-

FEV1= about 80% of FVC

1

2

3

4

T (sec)

- A normal spirometric trace of forced vital capacity (FVC), showing forced expiratory volume in the 1st sec.(FEV1) which is equal to 80% of (FVC). [email protected]

-Spirometric traces of FVC for two patients one with an obstructive defect and one with a restrictive defect. [email protected]

-In obstructive lung disease VC is normal, while FEV1 is reduced (30–40 % of FVC). -In restrictive lung disease VC is reduced, while FEV1 does not change as the FVC is already low.

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