Lung volumes & Lung Capacities

By Dr. Mudassar Ali Roomi (MBBS, M.Phil.)

Assist. Prof. Physiology

LUNG VOLUMES AND CAPACITIES

SPIROMETER

4 Lung Volumes• TV (Tidal Volume) = 500 ml

• I.R.V (Inspiratory Reserve Volume) = 3000 ml = 3 L

• E.R.V (Expiratory Reserve Volume) = 1100 ml

• R.V (Residual Volume) = 1200 ml

Tidal Volume (VT)• Volume of air inspired or expired with each normal

quiet breath.• Value = 500 ml in adult male.

Inspiratory Reserve Volume (IRV)

• Extra volume of air that can be inspired over & above normal tidal volume, when person inspires with full force.

• Value = 3000 ml.

Expiratory Reserve Volume (ERV)• Maximum extra volume

of air, that can be expired by forceful expiration after the end of normal tidal expiration.

• Value = 1100 ml.

Residual Volume (RV)

• Volume of air remaining in the lungs after most forceful expiration.

• Value = 1200 ml

LUNG CAPACITIES(sum of 2 or more lung volumes)

• T.V = 500 ml• I.R.V = 3000 ml = 3 L

I.C (Inspiratory Capacity)= 3500 ml = 3.5 L

E.R.V = 1100 mlR.V = 1200 ml

F.R.C (Functional Residual Capacity) = 2300 ml

V.C (Vital Capacity)= TV + IRV + ERV= 500 + 3000+ 1100= 4600 ml

T.L.

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Inspiratory Capacity (IC)

• TV + IRV• Amount of air a person

can breathe in beginning at normal expiratory level & distending the lungs to maximum amount.

• Value= 3500 ml.

Functional residual capacity (FRC)

• ERV+ RV• Amount of the air that

remains in the lungs at the end of normal expiration.

• Value: 2300 ml.

Vital capacity (VC)

• VC = IRV + TV + ERV• Maximum amount of air a

person can expel from the lungs after 1st filling the lungs to their max. extent & then expiring to max. extent.

• value= 4600 ml• Calculations based on height • Females:(27.63 - (0.112 x age) x

(height in cm) • Males: (21.78 - (0.101 x age) x

(height in cm)

Total lung capacity (TLC)

• Max. volume to which the lungs can be expanded with greatest possible effort.

• VC + RV = TLC• Value= 5800 ml

FACTORS AFFECTING LUNG VOLUMES & CAPACITIES

• Sex: 20 -25 % less in women than in men.

• Height & built: Greater in larger people.

• Athletes: larger

• Small & Asthenic people: Smaller

• The Forced vital capacity (FVC) of the lung is the volume of air that can be forcibly expelled from the lung from the maximum inspiration to the maximum expiration.

• Forced expiratory volume in 1 second (FEV1) is the volume of air that can be expelled from maximum inspiration in the first second.

• Restrictive pattern• Due to conditions in which the lung volume is

reduced e.g fibrosing alveolitis, scoliosis. The FEV1 and FVC are reduced proportionately.

• Obstructive pattern• Due to conditions in which the airways are

obstructed e.g. asthma or COPD. The FEV1 and FVC are reduced disproportionately.

• Grading or Severity of COPD on the basis of FEV1%

FEV1%

<80% = mild <60% = moderate <40% = severe

Forced expiratory ratio (FEV1/FVC ratio)

• The FEV1/FVC ratio is the FEV1 expressed as a percentage of the FVC (or VC if that is greater) i.e the proportion of the vital capacity inhaled in the first second.

• It distinguishes between restrictive and obstructive lung diseases.

• Obstruction is defined as an FEV1/FVC ratio of <70%

• Restrictive ventilatory pattern

• FVC reduced <80%FEV1 reducedFEV1/FVC ratio normal

• Obstructive ventilatory pattern

• FVC normal or reducedFEV1 reduced <80%FEV1/FVC ratio reduced

Flow volume loops

• This is the same forced expiration converted electronically to illustrate flow rate as the lung empties.

• The x axis represents volume - from full inspiration to full expiration.

• The y axis represents the flow rate.

• Obstructive disease: ?• Restrictive disease:?