SpirometerBy: khulood Hussein

The most important function of the lungs is to maintain tension of oxygen and carbon dioxide of the arterial blood within the normal range.

The term lung volumes refers to the non-overlapping subdivisions , or fractions of the total lung air.

The term lung capacities refers to combination of two or more lung volumes.

Lung Volumes Tidal Volume (TV): the volume of air

inspired or expired during quiet breathing. Average value 500 mL .

Inspiratory reserve volume (IRV): the volume of air inspired with effort in excess to the TV.

Avg. value 2500 mL.

Lung VolumesExpiratory reserve volume (ERV):

the volume of air expired with effort in excess to the TV. Avg. value 1000 mL.

Residual Volume (RV): the volume of air left

in the lungs after a maximum expiration Avg. value 1200 mL.

Lung VolumesMinute ventilation (MV): the

amount of air inspired or expired per minute when the person is at rest.

MV=TV x respiratory rate per min .

Alveolar ventilation (AV): the volume of air subjected to gas exchange.

AV=(TV-dead space) x respiratory rate.

Lung Capacities

Inspiratory capacity (IC): the max. amount of air that can be inspired with max. effort starting from the resting expiratory point . Normal value 3L.

IC= IRV+TVFunctional residual capacity (FRC): the amt. of air remaining in the lungs at the end of a normal (quiet) expiration .Normal value 2200 mL.

FRC=ERV+RV

Lung Capacities

• Vital capacity (VC): the tot. volume of air expired forcefully after a maximal inspiration. Average value 4.5L.

• VC=IRV+TV+ERV

• Total lung capacity (TLC): the volume of air present in the lungs at the end of a deepest inspiration. Average value 6L.

TLC=VC+RV

SPIROMETER

A spirometer measures air breathed in and out and produces graphs. From the graphs you can measure different lung capacities which can be useful guides to health.

Obstructive lung diseasesThe main feature is a decrease in expiratory

flow rate throughout expiration.TLC is increased , RV is elevated. over many years more and more air tends to remain in the lungs which increase TLC and RV.

AsthmaCOLD-COPD

Restrictive Lung diseasesThe main feature is reduced lung volume

mainly TLC and RV, which may be due to interstitial lung disease or chest wall deformity that reduce the air in the lungs.

Elderly peopleLung FibrosisObesity