Lung volumes

ObjectivesTo know about different lung volumes and capacities

To know how to measure them And their significance in diagnosing lung diseases

4 volumes and 4 capacities

Tidal volumeInspiratory

reserve volumeExpiratory

reserve volumeResidual volume

Vital capacityInspiration

capacityFunctional

residual capacityTotal lung

capacity

THESE ARE MEASURED USING A TECHNIQUE CALLED SPIROMETRY

INDIRECT SPIROMETRY USING HELIUM DILUTION TECHNIQUE IS USED TO MEASURE FRC THOUGH WHICH RV AND TLC ARE DERIVED

DIRECT SPIROMETRY CAN MEASURE ALL THE REMAINING LUNG VOLUMES AND USED TO DERIVE OTHER LUNG CAPACITIES

Tidal volume“The tidal volume (TV) is the volume

of air that is drawn into the lungs during inspiration from the end-expiratory position (and also leaves the lungs passively during expiration) in the course of quiet breathing.”

Normal value = 6-8 ml/kg

Inspiratory reserve volumeThe maximum amount of air

that can be inhaled after a normal tidal volume inspiration

Normal value 1900-3300ml

Expiratory reserve volume“The expiratory reserve volume (ERV) is the maximum volume of air that can be forcibly exhaled after a quiet expiration has “been completed (i.e., from the end-expiratory position).”

Normal value is 700 -1000 ml

Residual volume “The residual volume (RV) is the volume of air

that remains in the lungs after a maximal expiratory effort.

Set by balance b/w actions of expiratory muscle & recoil forces of lung which act to decrease lung volume & outward recoil forces of chest wall devouring lung expansion

Normal value is

Vital capacityVolume of air that can be exhaled from lungs after

maximum inspirationVital capacity =IRV + TV + ERVNormal value is 60-70ml /kg

Inspiratory capacityMaximum amount of air that can be inhaled from end of tidal volume i.e from a normal expiratory position

INSPIRATORY CAPACITY= IRV + TV

Functional residual capacity“The functional residual capacity

(FRC) is the volume of air that remains in the lungs at the end of a normal expiration.”

FRC = ERV+ RV

Total lung capacity“The total lung capacity (TLC) is the total volume of air

contained in the lungs at the end of a maximum inspiration.”

TOTAL LUNG CAPACITY = IRV + TV + ERV + RV It “is determined by the balance between the force-generating capacity of

the inspiratory muscles and the opposing elastic recoil forces of the lung and chest wall.

Weakness of the muscles of inspiration or increased stiffness of the lung reduces TLC.

Loss of retractive forces exerted by the lung, as in emphysema, enlarges TLC.”

Normal values at a glance (for a 20yr old healthy seated make)

Tidal volume=0.6L Residual

volume=1.4L E.R.V= 1.9L I.R.V= 3.0L

I.C=3.0LF.R.C=3.2LT.L.C= 6.3 LV.C= 4.8 L

Thank you