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Dr. Jitendra Patel (MBBS, MD, ACME, Ph.D…)

Medical Educator & Researcher

Associate Professor, Department of Physiology

Email: dr.jrpatel84@gmail.com Web: www.esphys.weebly.com

Competency

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No. PY6.2 & PY6.7 (Respiratory Physiology)

CompetencyDescribe the lung volume and capacities (6.2). Describe and discuss lung function tests & their clinical significance. (6.7)

D/L/Core K/KH/Y

AM Written/Viva voce

Integration No

Imp. Concept Lung volume and capacities

Phy. Trivia OLD Vs RLD

OUTLINE

Static Lung volume and capacities:

Definition, Value, Measurement, Physiological

& Clinical Importance, Limitations

Dynamic Lung Volume & Capacities

Differences between obstructive & restrictive

diseasea

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Restrictive-

i) P. fibrosis

ii) D. of pleura (P. effusion)

iii) Polio

iv) Myasthenia gravis

v) Kypho-scoliosis

Obstructive-

i) Emphysema

ii) Chronic bronchitis

iii) Asthma

OBSTRUCTIVE & RESTRICTIVE LUNG DISEASE

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Static lung volumes (5)

1) Tidal Volume (TV)

2) Inspiratory Reserve Volume (IRV)

3) Expiratory Reserve Volume (ERV)

4) Residual Volume (RV)

5) Closing Volume (CV)

TV- is amount of air breath in or breath out of lungs

during normal quiet respiration. (500ml)

IRV- is maximum amount of air that can be inspired over

& above normal tidal inspiration. (3200ml)

ERV- is maximum amount of air that can be expired

forcefully after normal tidal expiration. (1100ml)

RV- is amount of air remains in both the lungs even after

forceful expiration. (1200ml)

Static lung capacities (6)

1) Inspiratory Capacity (IC)

2) Expiratory capacity (EC)

3) Functional Residual Capacity(FRC)

4) Vital Capacity (VC)

5) Total Lung Capacity (TLC)

6) Closing capacity (CC)

IC- is the maximum volume of air that can be inspired

after normal tidal expiration (IRV + TV).

EC- is the maximum volume of air that can be expired

after normal tidal inspiration (ERV + TV).

VC- It is the maximum amount of air that can be expired

forcefully after maximum inspiration (IRV + ERV + TV).

FRC- is the volume of air remains in both the lungs after

normal tidal expiration. (RV + ERV).

TLC- is the amount of air present in both the lungs after

deep inspiration. (TV + ERV + IRV + RV).

Static lung volumes and capacities

1) Tidal Volume (TV) (500ml)

2) Inspiratory Reserve Volume (IRV) (3200ml)

3) Expiratory Reserve Volume (ERV) (1100ml)

4) Residual Volume (RV) (1200ml)

5) Inspiratory Capacity (IC) (3500ml) = TV + IRV

6) Expiratory capacity (EC) (1600ml) = TV + ERV

7) Functional Residual Capacity(FRC) (2300ml) = ERV + RV

8) Vital Capacity (VC) (4800ml) = IRV + TV + ERV

9) Total Lung Capacity (TLC) (6100ml) = VC + RV

Closing Volume (CV)

The volume of gas in the lungs in excess of the

residual volume at the time when

small airways in the dependent portions of the lungs

close during maximal exhalation, as measured by

the single breath nitrogen washout test.

CV = > RV

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Closing Capacity (CC)

The closing capacity (CC) is the volume in

the lungs at which its smallest airways, the

respiratory bronchioles, collapse. It is defined

mathematically as the sum of the closing volume

and the residual volume.

CC = CV + RV

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Measurement

RV, FRC & TLC are measured by He-dilution method and N2

wash-out method all other by simple/ computerized spirometer.

computerized spirometry

Measurement

TV/ERV/IRV/VC-

Measured by simple spirometer.

RV, FRC, TLC-

Measured by He dilution & N2 wash-out method

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FRC (ERV + RV)

Definition-,

Normal Value-,

Measurement-

Significance

Physio., Medico-legal & Clinical Importance of

FRC & RV

1) FRC & RV provide sufficient amount of gasses for

continuous exchange between lungs & p. capillaries (even

between breaths and during expiration),

2) FRC & RV keep almost normal PO2 & PCO2 in alveolar

air and blood.

3) Provide distending pressure to keep alveoli open

ensure continuous exchange of gasses,

4) Medico-legal-

-To find death was before or after drowning (if death is due

to drowning piece of lung will not float in water) -

- death of infant before or after birth (in still birth

collapsed lung will not float in water),

5) Clinical-

N/↑ - Obstructive disease, ↓ - Restrictive

(while ↓↓ TLC used to confirm diagnosis of RLD)

Vital Capacity (VC)

VC = TV + ERV + IRV

Definition-,

Normal Value-,

Measurement-

Factors affecting

Significance

Factors affecting the VC-

1) Sex- less in females (25% less in females), ,

2) Body built- V.C. specially more in long & thin individuals,

3) Posture- V.C. highest in standing position (due to

relatively high position of diaphragm),

4) Life Style- more in active & athletes while less in

sedentary persons,

5)Occupation- Specially more in artists who play flute etc,

6) Pregnancy- less as diaphragm is pushed up

Significance of VC-

Physiological

Indicated respiratory efficiency

(Index of pulmonary function).

Clinical

V.C. is reduced in both obstructive and restrictive

diseases V.C. used to diagnose, to asses severity and

prognosis of respiratory diseases

Limitations of VC-

i) Less sensitive test to ∆ early stages of respiratory

diseases

ii) Can’t use to differentiate obstructive and restrictive

diseases.

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Dynamic lung volumes and capacities

1) Timed / Forced vital capacity (TVC, FEV)

2) FEV1/FVC ratio-

3) Peak expiratory flow rate (PEFR)- It is the maximum rate

at which air can be expired after deep inspiration.

Value:400-600 L/min. measured by Wright’s peak flow meter.

4) Maximum Mid Expiratory Flow Rate (MMEFR)

FEF 25-75% → Patency of small airways

FEF 200-1200ml → Patency of large airways

5) Respiratory Minute Volume (RMV/PV) =

TV x R. Rate = (500 x 12-14) 6L/mt.-

The amount of air breathed in or out of lungs every minute

is called RMV

6) Alveolar Ventilation =

(TV – dead space volume) x R.R = (500 – 150) x 15

= 4.2 L/mt.-

The amount of air in lungs that participate in gaseous

exchange every minute is called AV

7) Maximum Voluntary Ventilation (MVV) or

Maximum Breathing Capacity (MBC)

= 125-170 L/mt.-

The maximum amount of air that can be breathed in and

out of lungs by forceful respiration per minute is called

MBC or MVV. Douglas bag is used for collection of air.

8) Breathing Reserve = MVV – RMV

9) Dyspneic index = MVV – RMV x 100/MVV

(90% is Normal, if <60% = Dyspnea at rest)

Forced or Timed Vital Capacity (FVC)

1) Definition-

When VC is recorded in respect to time (means performed

as soon as possible). It has 3 parts-

-FEV1 (is fraction of FVC expired in 1st sec) is 83% of FVC,

-FEV2 (forced expiratory volume at the end of 2 sec.) is 93%

-FEV3 (forced expiratory volume at the end of 3 sec.) is

97% .

It is dynamic lung test.

2) Physiological Significance –

indicate the status of airway resistance and patency of

Airways (Index of air flow rate)

3) Clinical Significance-

(i) Used to ∆ early obstructive lung diseases (FEV1 ↓ed, VC

may be normal)

(ii) Differentiate between obstructive and restrictive

diseases (FEV1 ↓ in obstructive while ↑ or N in

restrictive)

(iii)To calculate FEV1/FVC ratio (specially less in

obstructive diseases)

Normal RLD OLD

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Differences b/t obstructive & restrictive D

Lung function test Obstructive Restrictive

Vital Capacity (VC)N or ↓ N or ↓

Residual Volume (RV) ↑ ↑ ↓

Functional Residual Capacity (FRC) ↑ ↓

Total Lung Capacity (∆ of RLD) ↑ ↓↓

FEV1 (severity of OLD) ↓↓ N. or ↑

FEV1 / FVC (∆ of OLD)↓↓

N. or ↑

PEFR ↓↓ N. or ↑

FEF25-75% (small airway obstruction) ↓↓ N. or ↑

FEF200-1200 (large airway obstruction)↓↓ N. or ↑

Lung function tests (PFT) can be grouped as follows:

i) To test the efficiency of ventilation or mechanical

aspects of respiration: Static & dynamic lung tests

ii) To test efficiency of gas exchange at alveolar

level : Diffusing capacity of O2/CO2

iii) To test efficiency of R.S. in relation to exercise: 1) Dyspneic index, 2) Max. O2 uptake (VO2 max).

iv) Blood analysis: 1) PaCO2, 2) PaO2, 3) Blood pH.

(Haldane’s apparatus)

v) Gas analysis of expired air (collected by Douglas

bag) & alveolar air (collected by Haldance priestly

method)

vi) V/P studies (by N2 wash-out & radio-active xenon

method)

vii) X-ray (Chest), CT, MRI, Biopsy

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Noting is permanent even problem also…..

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